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The partial substitution of mineral fertilizers with straw in agricultural soils could help to control soil acidification, reduce the risk of eutrophication from agricultural runoff, and increase the utilization efficiency of straw. However, the effects of such coupled practices on greenhouse gas (GHG) emissions and production yields in vegetable fields are not clear. Therefore, the objectives of this study were to (1) understand methane (CH4) and nitrous oxide (N2O) emissions in response to the same amounts of straw return with varied amounts of mineral fertilizers, and (2) to identify a solution which could better coordinate GHG emissions, vegetable production yield, and the utilization of agricultural straw following disposal. We conducted four-season (lettuce-cabbage-chili-lettuce) vegetable cultivation for 1 year using a control treatment (CT), mineral fertilization only (F), and four mineral fertilization treatments plus maize straw (FS, 0.7FS, 0.6FS, and 0.5FS). We then examined seasonal changes of CH4 and N2O fluxes, CH4 and N2O cumulative emissions, soil organic carbon (SOC), nitrate nitrogen (NO3−-N) and ammonium nitrogen (NH4+-N) content, vegetable yields, global warming potential (GWP), greenhouse gas intensity (GHGI), and N2O emission factors (EF). Compared to the F treatment, the application of maize straw increased the N2O flux significantly in the FS, 0.7FS, 0.6FS, and 0.5FS treatments. In treatments with added straw, the reduced application of mineral fertilizer led to a reduction in the cumulative N2O emission; this was due to the reduced content of NO3−-N content. The lowest CH4 flux and cumulative CH4 emission were observed in the 0.7FS treatment; this may be due to a form of competitive oxidation between CH4 and NH4+-N from urea. Furthermore, the application of maize straw in combination with a full dose of mineral fertilizers led to high GWP and GHGI values, which showed increases of 88.7% and 78.8%, respectively, in comparison with the F treatment. When taking SOC storage variations into account, which were caused by straw decomposition during cultivation, we identified a negative net GHGI (NGHGI) value (− 0.0448 kg CO2-eq kg−1 yield) in the 0.7FS treatment. This indicated that the NGHGI had decreased by 116.2% relative to the F treatment when based on similar vegetable yields. Straw combined with 70% mineral fertilizer led to better GHG emissions and vegetable yield when taking into account the carbon sequestration and decomposition caused by the addition of straw.

Grassland afforestation strongly influences the structure and function of soil microorganisms. Yet the mechanisms of how afforestation could simultaneously alter both the soil fungal and bacterial communities and its implications for ecosystem management are poorly understood, especially in nitrogen-limited ecosystems. Using high-throughput sequencing of 16S rRNA and ITS rRNA genes, the present study investigated the changes in soil properties and soil microorganisms after afforestation of natural grasslands with Chinese pine (Pinus tabuliformis) on the Loess Plateau in China. Results showed that soil bacterial diversity had no significant differences among the grassland (GL), forest-grassland transition zone (TZ), and forestland (FL), while soil fungal diversity in the GL was significantly higher than that in the FL and TZ (P 0.05). The proportion of shared OTUs in the soil bacterial community was higher than that in the soil fungal community among the three land use types. The dominant bacterial phylum shifted from Proteobacteria to Actinobacteria, while the dominant fungal phylum shifted from Ascomycota to Basidiomycota after the GL conversion to the FL. The functional groups of ECM fungi increased significantly while biotrophic fungi decreased significantly after grassland afforestation. Both the soil bacterial and fungal communities in the TZ showed great similarity with those in the FL. In addition, among all examined soil properties, soil nitrogen (N) showed a more significant effect on the soil microbial communities. The reduction of soil N after grassland afforestation resulted in both the structure and function changes in soil microbial communities. Our results demonstrated simultaneously differential changes in the composition and diversity of both soil bacterial and fungal communities after afforestation from grasslands to planted forests.

We examined differences in soil metabolites from the rice root rhizosphere of long-term rice-rice-fallow (RRF) and rice-rice-rape (RRR) rotations, and examined the effects of 1,2-benzenediol on nitrogen-use efficiency (NUE) and rice growth. The metabolite composition of rice rhizospheres was analyzed using the gas chromatography-mass spectrometry (GC-MS). A range of 0.2, 2.0 and 200 μmol L−1 concentrations of external 1,2-benzenediol were applied to examine their effects on rice growth, nitrate reductase (NR) and glutamine synthetase (GS) activities, and physiological nitrogen-use efficiency (PNUE). The metabolite composition of rhizospheres differed significantly between RRR and RRF. Soil total N and 1,2-benzenediol concentrations during the early rice season were significantly lower under RRR than RRF. Rice growth and NUE significantly enhanced at 0.20 μmol 1,2-benzenediol L−1, but inhibited at 2.0 μmol L−1 or higher. Changes in root morphology and uptake associated with 1,2-benzenediol possibly had contributed to a higher NUE of the early season rice under RRR. The NR and GS activities in rice roots were significantly higher with 0.2 μmol L−1 1,2-benzenediol than without 1,2-benzenediol treatment. Crop rotation significantly affected rice rhizosphere metabolites. An optimal soil 1,2-benzenediol concentration under long-term RRR rotation may be associated with an enhanced NUE and root N uptake and assimilation, resulting in an increased rice growth and yield.

Soil tillage, a major agricultural management, could effectively alter soil structure and plant growth, particularly under groundnut plantations. To understand effects of different tillage measures...

Reforestation is widely used to restore degraded infertile soils in the coastal area. Substantial attention has been paid to the functioning of AMF in vegetation restoration because arbuscular mycorrhizal fungi (AMF) are considered beneficial to this process. However, little is known about the effect of AMF product, glomalin-related soil protein (GRSP), on soil organic carbon (SOC) sequestration during the forest restoration. We conducted a study in a tropical region where the native forest has been seriously deforested with only a few grasses and then a series of restoration approaches have been made to restore the forest ecosystem. The study sites include a barren land (BL), a Eucalyptus exserta planted forest (EF), a mixed broadleaved forest (MF) and a secondary natural forest (SF), which represents the un-, early-, middle- and late-restoration stage, respectively. The results showed that the restoration increased EE-GRSP and T-GRSP by 3.9-12.3 times and 1.9-4.6 times compared with the barren land, respectively. The proportion of GRSP in SOC is 1.6-2.0% (EE-GRSP/SOC) and 6.5-15.8% (T-GRSP/SOC), respectively. Also, a significantly positive relationship was found between the proportion of GRSP in SOC and recalcitrant SOC composition percentage (aromatic C), as well as between GRSP and soil aggregate stability. These results together suggest that the restoration of the degraded tropical forest is beneficial to soil C sequestration with the accumulation of GRSP, most likely, through an improvement of the soil aggregate stability and increase of the proportion of recalcitrant soil C chemical composition.

Estimating balanced nutrient requirements for a watermelon plantation is essential to increase its fruit yield and nutrient use efficiency. This is vital for China, which produces 60% of world&rsquo, s watermelons with excessive fertilizer application. Therefore, datasets between 2000 and 2019 from field experiments in major watermelon producing regions across China were collected to assess relationships between fruit yield and nutrient uptake, and to estimate nitrogen (N), phosphorus (P), and potassium (K) requirements for a target yield using a modified Quantitative Evaluation of the Fertility of Tropical Soils (QUEFTS) model. The results showed that the QUEFTS model predicted a linear increase in fruit yield to 60&ndash, 70% of the total potential yield when balanced amounts of N, P, and K nutrients were absorbed. To produce 1000 kg of watermelon, 2.11 kg N, 0.27 kg P, and 2.69 kg K were required in shoot, and the corresponding internal efficiencies (IE) were 475, 3682, and 372 kg fruit per kg of N, P, and K, respectively. The modified QUEFTS model also simulated that a balanced N, P, and K removal by fruit (accounting for 50.9%, 58.2%, and 66.4% of these nutrient accumulations in shoots, respectively). Field validation experiments further verified that the modified QUEFTS model could be used for estimating balanced nutrient requirements. Results from this study can provide practical guidance on fertilizer recommendations for improving fruit yield while preventing excessive or deficient nutrient supplies in China&rsquo, s watermelon plantations.

How to address soil carbon (C) sequestration and crop straw recycling is an intractable challenge for agriculture. The application of various agricultural straws (including fresh straw, decomposed straw, straw-derived biochar) to soil alters the soil C pool. In order to understand soil C dynamics and the potential C sequestration characters after the addition of straw and/or straw-derived biochar, an in-situ mesocosm experiment was conducted under five treatments as (1) no straw and no biochar control (CT), (2) straw addition only (ST), (3) straw with a straw-decay bacterium (STDB), (4) biochar addition only (BC) and (5) a combination of straw with biochar (STBC). Carbon dioxide (CO2) flux from soil, total soil organic C (SOC) and soil labile organic C (LOC), as well as soil aggregate associated organic C have been analyzed within a dryland rape-maize cropping system. The results showed that soil CO2 flux increased with the addition of crop straws (ST, STBC and STDB), but decreased under BC because of a lower LOC under BC, especially microbial biomass C fraction in the LOC. The combined application of STDB increased the percentages of macro-aggregates (>2 mm and 0.25–2 mm). Meanwhile, the decomposition of organic matter was increased, and the CO2 flux was also increased. The 0.053-0.25 mm aggregate under BC had the highest fine intra-aggregate particulate organic C (iPOC), which promoted C sequestration. However, the higher coarse-iPOC in >2 mm and 0.25–2 mm aggregates under ST and STDB promoted SOC decomposition and also CO2 flux. Compared with all three straw treatments (ST, STBC and STDB), the sole biochar addition reduced CO2 flux while increased net C sequestration without significant decreases of crop yields and net primary productivity. The sole biochar addition did improve the physical protections for SOC from soil aggregates. The obtained results showed differential responses of soil C pool and aggregates associated organic C to straw and/or straw-derived biochar addition while providing insights into potential soil C sequestrations or mitigations by using agriculture based organic materials.

We grew rice in phosphorus (P) deficient subtropical paddy soil in a field study and used 13CO2 continuous labelling to investigate photosynthetic carbon (C) partitioning and allocation under FLOOD versus WET/DRY conditions, with and without P fertilization (80 mg P kg−1). The plants and soil were sampled after each of three WET/DRY cycles to determine 13C allocation in above- and belowground plant biomass, microbial biomass, the rhizosphere, and bulk soil. Irrespective of water management, P-fertilized plants had higher biomass and P content and more total 13C in the rice-soil system, especially the 13C incorporation into the shoots (51%–96%), than samples without P fertilization. Root and bulk-soil 13C were largely independent of both P fertilization and water management. However, by the third sampling, P fertilization had increased the amount of 13C and microbial biomass 13C in the rhizosphere soil (RS) by 28% (WET/DRY) and 95% (FLOOD), and by 47% (WET/DRY) and 50% (FLOOD), respectively. The WET/DRY condition had significantly higher microbial biomass and 13C contents than FLOOD condition only in the RS. These results indicate that a well-established aboveground plant biomass following P fertilization is required to increase belowground C allocation. Thus, WET/DRY conditions, like FLOOD conditions, can provide moisture sufficient for unhindered P availability in rice-paddy system.

Canopy gaps are a key component of the disturbance regime and old-growth character in subalpine coniferous forests. Despite the importance of canopy gaps in the dynamics and management of subalpine forests, limited information is available on the temporal dynamics of microbial pools and their roles in the responses of soil organic matter and nutrient flux to canopy gaps. This study tests the hypothesis that gap creation facilitates soil organic carbon (C) retention by soil microbial biomass in the organic horizon. Based on the degree of decomposition, the organic horizon can be divided into fresh litter layer (LL), fragmented litter layer (FL) and humified litter layer (HL) components; these layers represent different stages of litter decomposition. We examined the microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and microbial biomass phosphorus (MBP) from the gap center to closed canopy in a subalpine Minjiang fir (Abies faxoniana) forest during different seasons. Gap creation promoted soil organic C retention by soil microbial biomass in the organic horizon. Storage of total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) accumulated in the HL. Moreover, gap creation accelerated C, nitrogen (N) and phosphorus (P) releases from the LL but inhibited C, N and P outputs from the HL. Microbial biomass in the LL responded rapidly and sensitively to canopy gaps. The most important factors affecting microbial biomass in the organic horizon were soil temperature and snow cover, which are governed by the canopy gap. Microbial pools and their stoichiometry were significantly and positively correlated with TOC. A thorough comprehension of the spatio-temporal traits of microbial biomass pools in the organic horizon under gap creation could aid the regeneration of protected subalpine fir forest on the eastern Tibetan Plateau.

Soil organic carbon (SOC) is at the core of soil fertility. Although fertilization strategies can alter SOC stocks, their effects on SOC chemical composition is less known. Using the solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy, we examined changes in the SOC chemical composition of three soils (0–20 cm depth) from an annual wheat-maize double-cropping system across central to south China. These soils had been subjected to 22 years (1990–2012) long-term fertilization. Compared with no-fertilization control, SOC stocks were significantly increased under chemical fertilization (NPK), NPK plus straw (NPKS), and NPK plus manure (NPKM). The O-alkyl C (labile C), not the alkyl C (persistent C), was consistently increased across the three fertilized treatments. Additionally, all fertilized treatments decreased the ratio of alkyl-C/O-alkyl-C (SOC decomposition index) or aliphatic-C/aromatic-C (SOC complexity index), indicating that the SOC decomposition was delayed, or SOC was converted into a more complicated structure. The soil C of NMR-determined functional groups (alkyl C, O-alkyl C, aromatic C, and carbonyl C) was positively correlated with the cumulative C input ( P 0.05). The conversion rate of functional groups was highest in O-alkyl C, indicating a largest contribution to the increase of SOC accumulation. Soil C:N ratio, pH, and clay were the main factors affecting the functional-group conversion rates, whereas annual precipitation, temperature, and accumulated temperature (>10 °C) played smaller roles. In conclusion, these results can be applied to the improvement of agricultural soil C sequestration capacity through changing SOC chemical structure under long-term fertilizer managements.

The differences of molecular characteristic of humic acid (HA) under long-term application of chemical fertilizer and manure for 34 years were determined by 13 C cross polarization magic angle spinning nuclear magnetic resonance ( 13 C CPMAS NMR) spectroscopy in order to investigate the carbon (C) sequestration in soils. The results showed that the relative content of alkyl C increased in manure treatments, compared to control and chemical fertilizer treatments. There were positive correlations between alkyl C and hydrogen to carbon (H/C) ratio (R 2 = 0.84, P 2 = 0.57, P 2 = 0.55, P 2 = 0.76, P = 0.01), H/C ratio and aromaticity (R 2 = 0.37, P = 0.04), aromaticity and amounts of HA (R 2 = 0.71, P 2 = 0.65, P 2 ) n /Long-chain (CH 2 ) n ratio increased for 0.03–0.37 and 0.03–0.18 in chemical fertilizer treatments and manure treatments, separately. These findings suggest that application of manure favours alkyl C sequestration in HA and tends to be more closely linked to amorphous C than crystalline C, while incorporates less short-chain (CH 2 ) n , compared to chemical fertilizer treatments. Moreover, the E4/E6 ratio of HA increased with more alkyl C.

Introduction: To estimate differential accumulation of soil organic carbon (SOC) and its ecological significance is very important to smallholder farmers in the Tanzania’s semiarid areas. This study investigated the accumulation of SOC and other important soil nutrients under organic and no-fertilizations, and correlated SOC with crop yields. Using data from long-term experimental study sites of semiarid in Tanzania, we estimated SOC accumulation in different soil treatments and depths where a total of 128 soil samples were collected at the depths of 0–20 cm and 20–40 cm from two villages (sites) with organic fertilization and no-fertilization treatments. Sites under organic fertilization were defined as those which have received manure fertilization for more than 5 years on continuum basis. Outcomes: The accumulation of SOC was significantly greater in soils under organic fertilizations (1.15 and 0.80 MgC ha −1 at soil depth and 20–40 cm) and decreased with increasing soil depths. Similarly, TN and P decreased from 0.40 and 2.40 Mg (0–20 cm) to 0.16 and 2.10 Mg (20–40 cm), respectively. Other important soil nutrients such as calcium (Ca 2+ ), potassium (K + ), magnesium (Mg 2+ ), and sodium (Na + ) had similar pattern. In addition, soil bulk density was less under organic fertilization (1.1 g/cm 3 ) than under no-fertilization (1.2 g/cm 3 ) and it increased with soil depths. Correspondingly, the crop yields were significantly higher (1.6 tn ha −1 ) under organic fertilizations than (0.6 tn ha −1 ) under no-fertilizations indicating that crop yields were significantly affected by SOC. Discussion: Organic fertilization i.e., especially cattle manure in the area has considerable fertility potential. To optimize soil fertility potential, we need to consider such kind of fertilization from household to national level. Conclusion: Our results demonstrated that manure application was the best fertilization method for improving soil fertility in most croplands of Tanzania’s semiarid areas, especially in this era of climate change scenarios.

Arbuscular mycorrhizal fungi (AMF) could improve crop yield by nutrient uptake from soil. However, how AMF of topsoil and subsoil respond to long-term differential application of mineral and organic fertilizers and how they are influenced in presence of different crops and growth stages have never been assessed together. Next generation sequencing was applied to profile soil AMF communities in both topsoil and subsoil from a typical arable soil (Eutric Regosol) in the Sichuan Base, southwest China. Soils were collected at anthesis and harvest of winter wheat and maize after 15-years of differential fertilization of an annual maize-wheat rotation (same inputs of nitrogen, N; but different in carbon, C; phosphorus, P; and potassium, K): (i) no-fertilization control (CT), (ii) 100% mineral NPK fertilizer (NPK), (iii) 60% mineral N and 100% mineral PK plus 40% N as crop residues (NPKCR); and (iv) 60% mineral N and 100% mineral PK plus 40% N as pig (organic) manure (NPKOM). Compared to CT, AMF diversity significantly decreased in topsoil, but increased in subsoil for both wheat and maize under NPK, NPKCR and NPKOM. The AMF community composition differed between NPK and CT in both topsoil and subsoil of maize and wheat. Both distance-based redundancy analysis (db-RDA) and structural equation modeling (SEM) suggested that AMF communities in topsoil and subsoil of maize and wheat responded in differences in soil available P, soil organic carbon, fertilization and climate (temperature and/or rainfall). Fertilization and available N, not AMF community, had significantly positive effects on wheat and maize aboveground dry matter and grain yield. Results from the present study shed light on how AMF communities in topsoil and subsoil respond to different soil fertility management over the long-term. Insights of this study are valuable in managing an important part of biological soil fertility.

Energy crops are a basic material in the bioenergy industry, and they can also mitigate carbon emissions and have environmental benefits when planted on marginal lands. The aim of this study was to evaluate the potential productivity of energy crops on marginal lands in China. A mechanistic model, combined with energy crop and land use characteristics, and meteorological and soil parameters, was used to simulate the potential productivity of energy crops. There were three main results. 1) The total marginal land in China was determined to be 104.78 × 106 ha. The 400-mm precipitation boundary line, which is the dividing line between the semi-humid and semi-arid zones in China, also divided the marginal land into shrub land and sparse forest land in the southeast and bare land, bare rock land, and saline alkali land in the northeast. 2) The total area of the marginal land suitable for planting energy crops was determined to be 55.82 × 106 ha, with Xanthoceras sorbifolia and Cerasus humilis mainly grown in the northern China, Jatropha curcas and Cornus wilsoniana mainly grown in the southwest and southeast, and Pistacia chinensis mainly grown in the central area, while also having a northeast-southwest zonal distribution. 3) Taking the highest yield in overlapping areas, the potential productivity of target energy crops was determined to be 32.63 × 106 t/yr. Without considering the overlapping areas, the potential productivity was 6.81 × 106 t/yr from X. sorbifolia, 8.86 × 106 t/yr from C. humilis, 7.18 × 106 t/yr from J. curcas, 9.55 × 106 t/yr from P. chinensis, and 7.78 × 106 t/yr from C. wilsoniana.

The only known sink for nitrous oxide (N2O) is biochemical reduction to dinitrogen (N2) by N2O reductase (N2OR). We hypothesized that the application of N2O-reducing denitrifier-inoculated organic fertilizer could enhance soil N2O consumption while the disruption of nosZ genes could result in inactivation of N2O consumption. To test such hypotheses, a denitrifier-inoculated granular organic fertilizer was applied to both soil microcosms and fields. Of 41 denitrifier strains, 38 generated 30N2 in the end products of denitrification (30N2 and 46N2O) after the addition of Na15NO3 in culture condition, indicating their high N2O reductase activities. Of these 41 strains, 18 were screened in soil microcosms after their inoculation into the organic fertilizer, most of which were affiliated with Azospirillum and Herbaspirillum. These 18 strains were nutritionally starved to improve their survival in soil, and 14 starved and/or non-starved strains significantly decreased N2O emissions in soil microcosms. However, the N2O emission had not been decreased in soil microcosms after inoculating with a nosZ gene-disruptive strain, suggesting that N2O reductase activity might be essential for N2O consumption. Although the decrease of N2O was not significant at field scales, the application of organic fertilizer inoculated with Azospirillum sp. TSH100 and Herbaspirillum sp. UKPF54 had decreased the N2O emissions by 36.7% in Fluvisol and 23.4% in Andosol in 2014, but by 21.6% in Andosol in 2015 (H. sp. UKPF54 only). These results suggest that the application of N2O-reducing denitrifier-inoculated organic fertilizer may enhance N2O consumption or decrease N2O emissions in agricultural soils.

Long-term effects of biochar application on soil carbon mineralization are important to evaluate the potential of biochar in carbon sequestration. Over a one-year period of time, we monitored soil respiration from a wheat-maize rotation cropping system after five years (once a year) of consecutive biochar application. In doing so four treatments with three replications each in a random design were examined: (1) a control plot without biochar and straw addition (CT), (2) 4.5 Mg biochar ha −1 year −1 (B4.5), (3) 9.0 Mg biochar ha −1 year −1 (B9.0) and (4) straw return (SR, ∼15 Mg wheat + maize aboveground biomass ha −1 year −1 ). An equivalent amount of inorganic fertilizers with biochar was broadcasted on the soil surface and then plowed into ∼16 cm soil depth prior to seeding. Both temporal dynamics and cumulative amounts of soil respiration were not significantly changed under the two biochar applications than under CT, but significantly increased under straw return than under CT and two biochar treatments. The annual respiration was 29.42, 29.96, 30.08, and 39.00 Mg CO 2 ha −1 year −1 in CT, B4.5, B9.0 and SR treatments, respectively. Meanwhile, soil respiration positively correlated with soil temperature but negatively with soil moisture. Sensitivity of soil respiration to temperature (Q 10 ) was significantly decreased due to biochar addition. These results indicated the potential of applying biochar to enhance soil carbon sequestration.

The allocation dynamics of newly assimilated carbon (C) and nitrogen (N) and their responses to management practices in dryland cropping systems are poorly understood. We aim to enhance this knowledge with relevance to identifying management practices that may increase soil organic C (SOC) stocks and N use efficiency. Using in-situ 13 CO 2 and urea- 15 N pulse labelling of wheat ( Triticum aestivum L.) at the late heading stage, we investigated allocation of newly assimilated C and N in crop and soil pools as influenced by long-term conventional tillage (CT) and reduced tillage (RT) mixed farming practices. On the first day after labelling, 91–92% of the added 13 C (1.49 g 13 CO 2 -C m −2 ) and 81–82% of the soil applied 15 N (0.1 g urea- 15 N m −2 ) were recovered in the crop and soil pools. Over 50 days ( i.e. at grain maturity), only 4–5% of the 13 CO 2 was allocated belowground, with 60–64% of this belowground 13 C released via soil respiration, and 72–74% of the 15 N was recovered in the soil to 30-cm depth and only 0.5–0.7% was allocated aboveground. The long-term differences in tillage practices did not influence allocation of new C ( 13 C) and N ( 15 N) in the wheat crop–soil pools, including aggregate-size fractions. This may be one of the factors in the lack of effect of the contrasting practices on SOC and N stocks, structural stability, microbial biomass, crop N uptake and wheat productivity. The results suggest soil and agronomic functionality in drylands may not be enhanced through conservation tillage management only.

Permanently flooded rice fields, a special kind of all year-round flooded rice fields in China, where the crop system is summer rice ( Oryza sativa ‘Q You 6′) with winter fallow, contribute to both CH 4 and N 2 O emissions. To investigate their CH 4 and N 2 O emissions over a whole year (November 2009 to October 2010) and responses to long-term tillage-cropping systems, four treatments after the conversion of such rice fields were examined: conventional tillage with a single summer rice and floodwater winter fallow (CTRF) or drained winter rapeseed ( Brassica napus ‘W You 25′) (CTRR), no-tillage narrow- or wide-ridge with a rice and rapeseed rotation (NTNRR or NTWRR). Results showed that CTRF emitted the highest CH 4 owing to permanently flooding water layer and higher soil organic carbon concentrations. Compared to CTRF, CH 4 emissions under other three tillage-cropping systems were decreased not only in the winter season but also in the rice-growing season. In contrast, N 2 O emissions over a whole one-year rice-rapeseed rotation cycle were almost equivalent to each other under these four tillage-cropping systems. Also compared to CTRR, the two no-tillage-cropping systems tended to enhance CH 4 while decrease N 2 O emissions, though with insignificant effects. The annual cumulative emissions of CH 4 and N 2 O were highest under CTRF (1.07 ± 0.20 kg CO 2 -eq ha −1 kg −1 yield) and significantly decreased under CTRR, NTNRR and NTWRR (0.59 ± 0.10, 0.67 ± 0.05 and 0.58 ± 0.09 kg CO 2 -eq ha −1 kg −1 yield, respectively), indicating that the summer rice-winter rapeseed rotation system, irrespective of tillage management, rather than the summer rice-winter fallow system, had achieved the objective of higher yields with less greenhouse gas emissions. These results demonstrate that the no-tillage wide-ridge with a rice and rapeseed rotation (NTWRR) is the most efficient management in terms of decreasing CH 4 and N 2 O emissions in Southwest China.

Studies have shown that biochar amendment could increase soil nutrient availability and crop production, but the contributions of nutrients including nitrogen (N), phosphorus (P), and potassium (K) in the biochar to plant production need to be tested. A pot experiment was conducted to identify the effects of maize straw-based biochar (BC) amendment on spinach fresh yield and dry biomass production, compared with non-biochar non-fertilization control (CT) and non-biochar chemical fertilization (NBF, equivalent amounts of N, P, and K). After 50-day growth, fresh leaf yield was increased by 63.7% or 38.0% under BC or NBF than under CT, and by 18.7% under BC than under NBF. Meanwhile, both leaf dry biomass and total plant (leaves + roots) biomass were similar between BC and NBF, but significantly higher under BC (47.5% in total) and NBF (56.2% in total) than under CT. In addition, root dry biomass was similar between BC and CT, but significantly higher under NBF than under BC or CT. These results indi...

The maintenance and accumulation of soil organic carbon (SOC) in agricultural systems is critical to food security and climate change, but information about the dynamic trend and efficiency of SOC sequestration is still limited, particularly under long‐term fertilizations. In a typical Purpli‐Udic Cambosols soil under subtropical monsoon climate in southwestern China this study thus estimated the dynamic, trend and efficiency of SOC sequestration after 22‐year (1991–2013) long‐term inorganic and/or organic fertilizations. Nine fertilizations under a rice–wheat system were examined: control (no fertilization), N, NP, NK, PK, NPK, NPKM (NPK plus manure), NPKS (NPK plus straw), and 1.5NPKS (150% NPK plus straw). Averagely, after 22‐years SOC contents were significantly increased by 4.2–25.3% and 10.2–32.5% under these fertilizations than under control conditions with the greatest increase under NPKS. The simulation of SOC dynamic change with an exponential growth equation to maximum over the whole fertilization period predicted the SOC level in a steady state as 18.1 g kg⁻¹ for NPKS, 17.4 g kg⁻¹ for 1.5NPKS, and 14.5–14.9 g kg⁻¹ for NK, NP, NPK, and NPKM, respectively. Either inorganic, organic or their combined fertilization significantly increased crop productivity and C inputs that were incorporated into soil ranging from 0.91 to 4.63 t (ha · y)⁻¹. The C sequestration efficiency was lower under NPKM, NPKS, and 1.5NPKS (13.2%, 9.0%, and 10.1%) than under NP and NPK (17.0% and 14.4%). The increase of SOC was asymptotical to a maximum with increasing C inputs that were variedly enhanced by different fertilizations, indicating an existence of SOC saturation and a declined marginal efficiency of SOC sequestration. Taken all these results together, the combined NPK plus straw return is a suitable fertilizer management strategy to simultaneously achieve high crop productivity and soil C sequestration potential particularly in crop rotation systems.

The input of recently photosynthesized C has significant implications on soil organic C sequestration, and in paddy soils, both plants and soil microbes contribute to the overall C input. In the present study, we investigated the fate and priming effect of organic C from different sources by conducting a 300-day incubation study with four different 13C-labelled substrates: rice shoots (shoot-C), rice roots (root-C), rice rhizodeposits (rhizo-C), and microbe-assimilated C (micro-C). The efflux of both 13CO2 and 13CH4 indicated that the mineralization of C in shoot-C-, root-C-, rhizo-C-, and micro-C-treated soils rapidly increased at the beginning of the incubation and decreased gradually afterwards. The highest cumulative C mineralization was observed in root-C-treated soil (45.4 %), followed by shoot-C- (31.9 %), rhizo-C- (7.90 %), and micro-C-treated (7.70 %) soils, which corresponded with mean residence times of 39.5, 50.3, 66.2, and 195 days, respectively. Shoot and root addition increased C emission from native soil organic carbon (SOC), up to 11.4 and 2.3 times higher than that of the control soil by day 20, and decreased thereafter. Throughout the incubation period, the priming effect of shoot-C on CO2 and CH4 emission was strongly positive; however, root-C did not exhibit a significant positive priming effect. Although the total C contents of rhizo-C- (1.89 %) and micro-C-treated soils (1.90 %) were higher than those of untreated soil (1.81 %), no significant differences in cumulative C emissions were observed. Given that about 0.3 and 0.1 % of the cumulative C emission were derived from labelled rhizo-C and micro-C, we concluded that the soil organic C-derived emissions were lower in rhizo-C- and micro-C-treated soils than in untreated soil. This indicates that rhizodeposits and microbe-assimilated C could be used to reduce the mineralization of native SOC and to effectively improve soil C sequestration. The contrasting behaviour of the different photosynthesized C substrates suggests that recycling rice roots in paddies is more beneficial than recycling shoots and demonstrates the importance of increasing rhizodeposits and microbe-assimilated C in paddy soils via nutrient management. National Natural Science Foundation of China/41430860 National Natural Science Foundation of China/41371304 Chinese Academy of Sciences/XDB15020401 Key Laboratory of Agro-ecological Processes in Subtropical Region Chinese Academy of Sciences Institute of Subtropical Agriculture/ISA2015101 State Administration of Foreign Experts Affairs

The profile characteristics of soil carbon reflect the combined effects of vegetation and erosion. However, the quantitative assessment of soil carbon in profile and its dynamics affected by vegetation restoration and erosion is still extremely inadequate. In this study, we synthesized soil and vegetation properties, stable carbon isotopic compositions, and radiocarbon ages to investigate the soil carbon processes in two temperate forests of different successional stages (Populus forest versus Quercus forest) on the Chinese Loess Plateau. The objectives of this study are to (1) examine the dynamics of soil organic carbon (SOC) and soil inorganic carbon (SIC) in the topsoil and subsoil, and (2) evaluate the effect of vegetation restoration and historical erosion on the changes of SOC and SIC in the temperate forests. We found that from Populus to Quercus forests, the SOC stock increased in the topsoil but declined in the subsoil, whereas the SIC stock exhibited a completely opposite variation trend. The significant increase in litter biomass enhanced the SOC in the topsoil, while a stronger historical erosion and priming effect would contribute to the decrease of SOC in the subsoil along succession. Changes in δ13C and Δ14C in the soil profile provided evidence that the turnover rate of SOC increase in the topsoil but decrease in the subsoil along succession. Over the past 10,000 years, due to soil erosion process, the estimated loss of the SOC and SIC was 26.2 and 64.1 Mg ha-1 in Populus forest and 20.2 and 42.6 Mg ha-1 in the Quercus forest. Our results indicated that the litter input and erosion processes make great effect on the carbon dynamics in the topsoil and subsoil of the study region.

Plastic film mulching (FM) is widely applied in agro-ecosystems to improve soil hydrothermal conditions for better crop productivities. However, effects of such FM practices on nitrous oxide (N2O) emissions are not well known in high nitrogen (N) input vegetable fields. Using static chambers under no-mulching (NM) and FM with four N application rates N2O emissions were monitored in a hot pepper (Capsicum annuum)-radish (Raphanus sativus) rotation in southwest China over three years (Cycle 1, 2 and 3) from May 2014 to February 2017. These four N application rates for each vegetable crop were 0, 150, 300 and 450 kg N ha−1 and 0, 100, 200 and 300 kg N ha-1 in the respective hot pepper and radish seasons. Compared to NM, FM insignificantly reduced N2O emissions in the hot pepper season owing to lower soil moisture, while significantly increased N2O emissions in the radish season owing to higher soil NH4++NO3− and temperature. Additionally, FM had no remarkable effects on N2O EFs or crop yields of hot pepper or radish. N application exerted stronger effects on N2O emissions under FM and NM in Cycle 1 than in other two cycles during the hot pepper season owing to higher temperature and rainfall, resulting in very high N2O EFs (2.56 %–7.43 %). The average seasonal EF was 1.52 % (0.15 %–7.43 %), while the average annual EF was 1.74 % (0.16 %–5.32 %), which was comparable to the 2006 IPCC defaulted of 1.00 %. Yield-scaled N2O emissions under FM were significantly increased in the radish season, but not in the hot pepper season. Additionally, N application remarkably increased N2O emissions and crop yields in the hot pepper season, with a bigger effect on N2O emissions than on crop yields, leading to increased yield-scaled N2O emissions with increasing N application between 0 and 450 kg N ha-1. Moreover, the stimulation effect of N application on crop yield was strongest under 150 kg N ha-1 with lower yield-scaled emissions. In addition, N application remarkably increased N2O emissions and crop yields, but were more prominent on crop yields than N2O emissions during the radish season, resulting in insignificant increase of yield-scaled N2O emissions between 0 and 300 kg N ha-1. Our results demonstrated that no-mulching with 150 or 300 kg N ha-1 fertilization in the hot pepper or radish season is a more suitable agronomic practice to simultaneously mitigate N2O emissions while increasing crop yields in subtropical vegetable fields.

Excessive applications of chemical fertilizers (e.g., nitrogen fertilizers) result in soil degradation, while organic manure application can alleviate soil degradation and rebuild a healthy soil. However, the effect of organic manure application on alleviating soil degradation over long-term fertilization remains poorly understood. Using soils (Ferralic Cambisol) that had been collected from a long-term fertilization experiment for 23 years (1990 − 2013) in subtropic South China, we showed that soil organic carbon (SOC) stocks increased by 2.5 times following 23 years of manure fertilizations (pig manure or a combination of manure and chemical fertilizers) or by 1.4 − 1.8 times following non-manure fertilizations, compared to the initial SOC stock in 1990. Strikingly, soil bulk density after 23 years fertilizations decreased in the order: 1.41 g cm−3 (manure) > 1.26 g cm−3 (no fertilizer) > 1.12 g cm−3 (chemical fertilizer), suggesting that long-term manure fertilization increased soil bulk density when compared to the non-manure treatments. The X-ray micro-computed tomography further demonstrated that compared to the non-manure treatments, manure fertilizations decreased the number of pores, throats and paths as well as porosity. In addition, the stock of oxalate-extractable Al and Fe increased by 2 times following 23 years of manure fertilizations, relative to the initial soil. In summary, this study for the first time showed that changes in mineral reactivity impact soil physical properties and the potential of soils to stabilize C, strengthening the possibility in alleviating soil degradation and rebuilding a healthy soil.

Neurotoxicant exposure by the over intake of manganese (Mn) and crop Mn accumulation related with fertilization and other agronomical measures had attracted wide attentions, while information is limited about variations in grain Mn with geographical changes in both soil and precipitation. A total of 438 wheat-grain site samples were therefore collected from two regions that were categorized by soil pH (non-acidic, pH > 7 and acidic, pH

The effect of biochar application on the net ecosystem carbon budget (NECB) and the mechanism controlling methane (CH4) emission in paddy soils under vegetable–rice rotations are poorly understood. A 2-year field experiment was conducted with three treatments: control (no fertilizer or biochar application), chemical fertilizer (BC0) and biochar plus chemical fertilizer application (BC1) to analyze greenhouse gas (GHG) fluxes, soil organic carbon (SOC) content, as well as the abundance and community structure of methanogens and methanotrophs in a vegetable–rice rotation. Biochar addition (BC1) did not affect the yield, or the emission of total CH4 or nitrous oxide (N2O) but significantly increased carbon dioxide (CO2) emission as compared to BC0 in the vegetable season. Rice yield in BC1 was 14.1 % higher than in the control but was lower than in BC0 because of lower available nutrients in BC1 than in BC0. During the rice season, cumulative CH4 emission under BC1 was increased by 2.65 times as compared with BC0 (P

The soil organic carbon (SOC) saturation deficit (Csd) of silt and clay fractions represents the potential for SOC sequestration in a stable form and can influence organic C stabilization efficiency. Little is known, however, about temporal changes of stable soil Csd and how it is affected by soil properties, climate and C inputs. We investigated the temporal changes in the Csd of fine fractions (sd under manure treatments varied from −0.72 to −1.24% yr−1 after 17 years of fertilization, indicating that stable C levels under manure treatments were significantly higher than those under other treatments. Stable soil Csd was controlled by a combination of soil properties, temperature, and C inputs at all sites, and the higher variance of Csd of fine fractions can be explained by the soil properties (up to 50%). Furthermore, the quantity of C inputs was the most influential variable for stable soil Csd. These results revealed key controls on stable C sequestration potential and indicated the need to develop management strategies to promote stable C sequestration under long-term intensive fertilization.

An excess of material input in fruit orchards has brought serious environmental problems, particularly in China. However, studies on the estimation of greenhouse gas (GHG) emissions in peach orchards are limited. In this study, based on questionnaire surveys in major peach-producing regions, including the North China Plain (n = 214), as well as northwest (n = 22) and southwest (n = 33) China, the carbon footprints (CFs) of these orchards were calculated by the life cycle assessment. The potential emission reduction in each region was estimated by combining the GHG emissions and CFs with plantation areas and fruit yields. The results showed that the average GHG emissions in the North China Plain, northwest, and southwest regions were 15,668 kg CO2-eq ha−1, 10,386 kg CO2-eq ha−1, and 5580 kg CO2-eq ha−1, with corresponding CFs of 0.48 kg CO2-eq ha−1, 0.27 kg CO2-eq ha−1, and 0.20 kg CO2-eq kg−1, respectively. The main contribution source of GHG emissions in these three regions was fertilizer (77–95%), followed by electricity, pesticides, and diesel. By adopting advanced farming practices with high yield and a high partial factor productivity of fertilizer, the GHG emissions could be reduced by ~13–35%, with the highest potential reduction in the North China Plain. In conclusion, the GHG emissions and their CFs were impressively high in China’s major peach-producing regions, but these GHG emissions could be substantially decreased by optimizing nutrients and irrigation management, including the rational selection of fertilizer rates and types with water-saving irrigation systems or practices (e.g., mulching) for increasing fertilizer and water use efficiency, and maintaining a sustainable peach production in China or similar countries.

In the present study, soil samples collected from 20-year (1993‒2013) long-term tobacco plantation and perennial fallow were analyzed to study the influence of soil acidification on soil physicochemical and mineralogical properties. Results showed a significant decrease of soil pH, Ca2+, Mg2+, Na+ and total exchangeable cations, except K+, under tobacco plantation than under fallow land. Further X-ray diffraction (XRD) analysis for 1 mm soil size demonstrated an increase of vermiculite and kaolinite, but an obvious decrease of original potassium-bearing mica and potassium feldspar, under tobacco plantation than under fallow. For the

Soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon (MBC) and nitrogen (MBN) are important factors of soil fertility. However, effects of the combined chemical fertilizer and organic manure or straw on these factors and their relationships are less addressed under long-term fertilizations. This study addressed changes in SOC, TN, MBC and MBN at 0-20 cm soil depth under three 17 years (September 1990-September 2007) long-term fertilization croplands along a heat and water gradient in China. Four soil physical fractions (coarse free and fine free particulate organic C, cfPOC and ffPOC; intra-microaggregate POC, iPOC; and mineral associated organic C, MOC) were examined under five fertilizations: unfertilized control, chemical nitrogen (N), phosphorus (P) and potassium (K) (NPK), NPK plus straw (NPKS, hereafter straw return), and NPK plus manure (NPKM and 1.5NPKM, hereafter manure). Compared with Control, manure significantly increased all tested parameters. SOC and TN in fractions distributed as MOCiPOCcfPOCffPOC with the highest increase in cfPOC (329.3%) and cfPTN (431.1%), and the lowest in MOC (40.8%) and MTN (45.4%) under manure. SOC significantly positively correlated with MBC, cfPOC, ffPOC, iPOC and MOC (R(2) = 0.51-0.84, P0.01), while TN with cfPTN, ffPTN, iPTN and MTN (R(2) = 0.45-0.79, P0.01), but not with MBN, respectively. Principal component analyses explained 86.9-91.2% variance of SOC, TN, MBC, MBN, SOC and TN in each fraction. Our results demonstrated that cfPOC was a sensitive SOC indicator and manure addition was the best fertilization for improving soil fertility while straw return should take into account climate factors in Chinese croplands.

The function of indigenous mycorrhizal fungi in improving crop growth is not well addressed because of methodological limitations. In this study, we determined the effects of the indigenous arbuscular mycorrhizal (AM) fungal community on the growth responses and salt tolerance of cotton and maize. Through a 2-year field trial with in-growth microcosms constructed by polyvinylchloride (PVC) tube cores and 30-μm nylon mesh that were buried in different saline soils, two core treatments, static (freely allowed AM fungal colonization) and vibrating (patting the top core edge twice every day to break any extraradical hyphae that intends to access into the core to reduce AM fungal colonization), were applied in field conditions. The results showed that vibration did not affect the growth of the control non-mycorrhizal plant, sugar beet, but significantly affected the growth of the mycorrhizal plants, cotton and maize. These data indicated that such core systems could provide a reliable method to quantify the functions of the AM fungal community in situ. Mycorrhizal colonization of cotton and maize significantly declined in the vibrating treatment compared to the static treatment. Phosphorus (P) uptake and biomass production of cotton and maize were significantly higher in the static than the vibrating. The indigenous AM fungal community promoted leaf proline accumulation in cotton and a higher K+/Na+ ratio via selective preferential uptake of K+ over Na+. These effects and enhanced P uptake derived from AM fungi were related to alleviating salt stress and promoted the growth of cotton and maize in saline soils. Our results demonstrated that indigenous AM fungi play a role in improving crop growth by alleviating the harmful effects of high salinity in intensified cropping systems.

Soil fauna can significantly affect soil CO2 and N2O emissions, but little is known about interactions between faunal groups and their relative contribution to such emissions. Over a 64-day microcosm incubation, we studied the effects of an epigeic earthworm (Eisenia fetida), mesofauna (Collembola plus oribatid mites) and their combinations on soil CO2 and N2O emissions under two faunal densities. Earthworms significantly enhanced soil CO2 and N2O emissions, while mesofauna only increased N2O emissions. Soil CO2 and N2O emissions were significantly affected by earthworm density, but not by mesofauna density. No significant interactive effects between earthworms and mesofauna were found on soil CO2 and N2O emissions. Our results indicate that earthworms probably play the dominant roles in determining soil CO2 and N2O emissions where they coexist with soil mesofauna.

The aim of this study was to investigate influences of six-year past application rates of nitrogen and a catch crop, sweet corn (Zea mays L. ssp. Saccharata Sturt), on soil microbial community and diversity in a greenhouse-based intensive vegetable soil in eastern China. Soil electrical conductivity, pH, mineral nitrogen, phospholipid fatty acids (PLFA) profiles and carbon source utilization patterns under five annually past nitrogen rates (0, 348, 522, 696 and 870 kg nitrogen ha−1) were evaluated after the establishment of sweet corn during 1–1.5-month fallow period over three-year tomato/cucumber/celery rotations. The past nitrogen application rates exerted significant effects on soil electrical conductivity, pH, nitrate-nitrogen, ammonium-nitrogen and carbon source utilization patterns, but not on PLFAs profiles. The sweet corn had a significant effect on soil chemical properties, total and actinobacterial PLFAs, but not on carbon source utilization patterns. Soil electrical conductivity, nitrate-nitro...

Biochar amended to soil may improve soil aggregation and in turn increase soil organic carbon (SOC) stabilization. In an intensive wheat–maize rotation system of the North China Plain, we investigated effects of one-year biochar application on soil aggregate-size distribution and structure stability, and aggregate-associated C concentrations. Three biochar (

According to the economy theory, plants should preferentially allocate photosynthate to acquire below-ground resources under elevated atmospheric carbon dioxide (eCO 2 ) but decrease below-ground C allocation when nitrogen (N) is sufficient for plant growth. Arbuscular mycorrhizae (AM) represent a critical mechanism of below-ground nutrient acquisition for plants. The dynamics of arbuscular mycorrhizal fungi (AMF) could therefore reflect the response of plant C allocation under eCO 2 and N addition. We examined the responses of glomalin-related soil protein (GRSP) to eCO 2 (approximately 700 μmol mol −1 CO 2 ) and/or N addition (100 kg N ha −1 yr −1 as NH 4 NO 3 ) in a modeled subtropical forest to better understand its potential influence on soil C storage. We hypothesized that GRSP would increase under eCO 2 and decrease under N addition. Furthermore, the positive effects of eCO 2 on GRSP would be offset by extra N addition, and GRSP would remain unchanged under combined eCO 2 and N addition. Our results showed that the mean concentrations of easily extractable GRSP (EE-GRSP) and total GRSP (T-GRSP) were 0.35 ± 0.05 and 0.72 ± 0.13 mg C cm −3 , respectively, which accounted for 2.76 ± 0.53% and 5.67 ± 0.92% of soil organic carbon (SOC) in the 0–10 cm soil layer. Elevated CO 2 significantly increased T-GRSP by 35.02% but decreased EE-GRSP by 5.09% in the top 10 cm soil layer. The opposite responses of T-GRSP and EE-GRSP to eCO 2 might result from an unchanged photosynthate investment to AMF with possible changes in their decomposition rates. The effect of N on GRSP was contrary to our hypothesis, i.e., there was a 1.72%–48.49% increase in T-GRSP and a slightly increase in EE-GRSP. Both EE-GRSP and T-GRSP concentrations increased under the combination of eCO 2 and N addition, which was inconsistent with our hypothesis. The significant increase of EE-GRSP under the combination of eCO 2 and N addition was partly caused by more rapid plant growth and reduced microbial diversity, and the marginal increase of T-GRSP indicated that the interaction between eCO 2 and N addition offset their independent effects. In addition, the relatively higher accumulation ratios of GRSP (22.6 ± 13.6%) compared with SOC (15.9 ± 9.4%) indicated that more rapid GRSP deposition in the soil might accelerate SOC accumulation under eCO 2 and N addition. Our results will improve the understanding of the functioning of GRSP in soil C sequestration under global environmental change scenarios.

Studies on glomalin-related soil protein (GRSP) have focused on soil aggregation and fungal physiology, whereas it is not known how exogenous GRSP could positively impact on these processes, soil enzyme activity and plant growth. Easily extractable GRSP [EE-GRSP, 0.022 mg protein/mL citrate buffer (20 mmol, pH 7.0)] from a 26-year-old citrus orchard was exogenously applied into 5-month-old potted trifoliate orange ( Poncirus trifoliata ) for 3 months to evaluate effects on soil water-stable aggregate distribution, relevant soil enzyme activities and plant growth. Depending on the applied concentrations as 1/2, 1/4 or full strength, exogenous EE-GRSP generally significantly increased the distribution of soil water-stable aggregates and mean weight diameter (MWD, an aggregate stability indicator). Values of MWD and plant biomass production curvilinearly positively correlated with exogenous EE-GRSP applications. Exogenous EE-GRSP generally significantly increased the activity of rhizospheric polyphenol oxidase, peroxidase, acid and alkaline phosphatase. Both the 1/2-strength and 1/4-strength, but not the full-strength exogenous EE-GRSP, significantly stimulated plant growth performance. Our results firstly demonstrated the positive contribution of exogenous EE-GRSP to soil aggregation, relevant rhizospheric enzyme activities and/or plant growth, which has important implications for exploring GRSP in enhancing soil structure and/or plant performance.

Root-derived carbon (C) is considered as critical fuel supporting the interaction between plant and rhizosphere microbiome, but knowledge of how plant–microbe association responds to soil fertility changes in the agroecosystem is lacking. We report an integrative methodology in which stable isotope probing (SIP) and high-throughput pyrosequencing are combined to completely characterize the root-feeding bacterial communities in the rhizosphere of wheat grown in historical soils under three long-term (32-year) fertilization regimes. Wheat root-derived 13 C was dominantly assimilated by Actinobacteria and Proteobacteria (notably Burkholderiales), accounting for nearly 70% of root-feeding microbiome. In contrast, rhizosphere bacteria utilizing original soil organic matter (SOM) possessed a higher diversity at phylum level. Some microbes (e.g. Bacteroidetes and Chloroflexi) enhancing in the rhizosphere were not actively recruited through selection by rhizodeposits, indicating a limited range of action of root exudates. Inorganic fertilization decreased the dependence of Actinobacteria on root-derived C, but significantly increased its proportion in SOM-feeding microbiome. Furthermore, significantly lower diversity of the root-feeding microbiome, but not the SOM-feeding microbiome, was observed under both organic and inorganic fertilizations. These results revealed that long-term fertilizations with increasing nutrients availability would decrease the preference of rhizosphere microbiome for root-derived substrates, leading to a simpler crop–microbe association.

Carbon (C) and nitrogen (N) allocation and assimilation are coupled processes, likely influencing C accumulation, N use efficiency and plant productivity in agro-ecosystems. However, dynamics and responses of these processes to management practices in semi-arid agro-ecosystems are poorly understood. A field-based 13CO2 and urea-15N pulse labelling experiment was conducted to track how C and N allocation and assimilation during canola growth from flowering to maturity were affected by short-term (2-year) tillage (T) and no-till (NT) with or without 100 kg urea-N ha−1 (T-0, T-100, NT-0, NT-100) on a Luvisol in an Australian semi-arid region. The T-100 caused greater (P cf. non-fertilized) treatments, followed by a rapid release of microbial immobilized N, thus increasing N availability for plant uptake. In contrast, management practices had insignificant impact on soil C and N stocks, aggregate stability, microbial biomass, and 13C retention in aggregate-size fractions. In conclusion, tillage and N fertilization increased belowground C allocation and crop N uptake and yield, possibly via enhancing root–microbial interactions, with minimal impact on soil properties.

Application of chemical fertilizer or manure can affect soil microorganisms directly by supplying nutrients and indirectly by altering soil pH. However, it remains uncertain which effect mostly shapes microbial community structure. We determined soil bacterial diversity and community structure by 454 pyrosequencing the V1-V3 regions of 16S rRNA genes after 7-years (2007-2014) of applying chemical nitrogen, phosphorus and potassium (NPK) fertilizers, composted manure or their combination to acidic (pH 5.8), near-neutral (pH 6.8) or alkaline (pH 8.4) Eutric Regosol soil in a maize-vegetable rotation in southwest China. In alkaline soil, nutrient sources did not affect bacterial Operational Taxonomic Unit (OTU) richness or Shannon diversity index, despite higher available N, P, K and soil organic carbon in fertilized than in unfertilized soil. In contrast, bacterial OTU richness and Shannon diversity index were significantly lower in acidic and near-neutral soils under NPK than under manure or their combination, which corresponded with changes in soil pH. Permutational multivariate analysis of variance showed that bacterial community structure was significantly affected across these three soils, but the PCoA ordination patterns indicated the effect was less distinct among nutrient sources in alkaline than in acidic and near-neural soils. Distance-based redundancy analysis showed that bacterial community structures were significantly altered by soil pH in acidic and near-neutral soils, but not by any soil chemical properties in alkaline soil. The relative abundance (%) of most bacterial phyla was higher in near-neutral than in acidic or alkaline soils. The most dominant phyla were Proteobacteria (24.6%), Actinobacteria (19.7%), Chloroflexi (15.3%) and Acidobacteria (12.6%); the medium dominant phyla were Bacterioidetes (5.3%), Planctomycetes (4.8%), Gemmatimonadetes (4.5%), Firmicutes (3.4%), Cyanobacteria (2.1%), Nitrospirae (1.8%), and candidate division TM7 (1.0%); the least abundant phyla were Verrucomicrobia (0.7%), Armatimonadetes (0.6%), candidate division WS3 (0.4%) and Fibrobacteres (0.3%). In addition, Cyanobacteria and candidate division TM7 were more abundant in acidic soil, whereas more Gemmatimonadetes, Nitrospirae and candidate division WS3 were more abundant in alkaline soil. We conclude that after 7-years of fertilization, soil bacterial diversity and community structure were shaped more by changes in soil pH rather than the direct effect of nutrient addition.

Purpose Soil acidification from chemical N fertilization has worsened and is a major yield-limiting factor in the red soil (Ferralic Cambisol) of southern China. Assessment of the acidification process under field conditions over a long term is essential to develop strategies for maintaining soil productivity. The objective of this study was to quantify soil acidification rates from chemical fertilizers and determine the amount of manure needed to inhibit the acidification process.

Both arbuscular mycorrhizal (AM) fungi and phosphate solubilizing bacteria (PSB) are involved in phosphorus (P) mobilization and turnover but the influence of their interaction on organic P mineralization in the root free soil (hyphosphere) have been little studied. We investigated the interactive effects of an AM fungus (Rhizophagus irregularis, RI) and/or PSB (Pseudomonas alcaligenes, PA) on phytate mineralization and subsequent transfer to the host plant (Medicago sativa) using a two-compartment microcosm with a central 30 μm nylon mesh barrier. The root growth compartment containing 5 mg inorganic P (Pi, KH2PO4) kg−1 soil was inoculated with RI or uninoculated and the AM fungal hyphal soil containing 75 mg organic P (Po, Na-phytate) plus 0 or 5 mg Pi kg−1 soil was inoculated with PA or uninoculated. Sole inoculation with RI increased shoot P content compared with the uninoculated treatment and dual inoculation with both RI and PA did not increase shoot P compared with sole RI inoculation. Sole PA inoculation significantly increased microbial biomass P (MBP). Compared with sole PA inoculation soil MBP increased under zero-Pi addition but decreased under 5 mg Pi kg−1 soil addition in the dual inoculation RI/PA treatment. The uninoculated microcosms had the lowest acid phosphatase activity and the highest phytate-P remaining in the soil. Inoculation with PA led to higher acid phosphatase activity and lower phytate-P than did RI. Dual RI/PA inoculation had the highest acid phosphatase activity and the lowest phytate-P remaining in the soil. Addition of 5 mg Pi kg−1 soil to the hyphal compartment decreased phytate-P remaining in the RI and/or PA treatments. The phytate-P remaining in the soil was negatively correlated with soil acid phosphatase activity or MBP in the presence of RI but there was no correlation between shoot P and soil phytate-P. In conclusion, our results indicate that the mineralization of soil phytate was promoted by the interaction between the AM fungus and its hyphosphere PSB.

Soil degradation and water pollution could have resulted from inappropriate phosphorus (P) supply. Soil Olsen P is generally a good indicator to estimate bio-availability of P and environmental risk in alkaline soil. The change in Olsen P is always strongly affected by soil organic carbon (SOC) when different forms of inorganic and/or organic P are applied to farmlands with chemical fertilizer and/or manure. We related soil Olsen P to apparent P balance (APB) and SOC in alkaline soils at three 15-year (1991–2005) fertilization sites of northern China. Six treatments were examined: unfertilized control, chemical nitrogen (N), chemical NP, chemical N plus potassium (NK), chemical NPK, and chemical NPK plus animal manure (NPKM, same total N but 20–80% more P). Compared to the initial Olsen P in 1990, after 15 years Olsen P was increased under P fertilization but decreased under no-P fertilization. At the three 15-year fertilization sites, annual mean Olsen P was 4.9–12.3 times higher under NPKM, 1.9–2.8 times higher under NP and NPK, but only 28.3–84.8% under Control, N and NK. Annual mean percentage of Olsen P to total P was higher under NPKM (4.6–8.1%) than under other five fertilizations (0.4–2.9%). Change in Olsen P significantly positively correlated with accumulated APB under all fertilizations (r2 = 0.10–0.31, P

Projected future decreases in snow cover associated with global warming in alpine ecosystems could affect soil biochemical cycling. To address the objectives how an altered snow removal could affect soil microbial biomass and enzyme activity related to soil carbon and nitrogen cycling and pools, plastic film coverage and returning of melt snow water were applied to simulate the absence of snow cover in a Tibetan alpine forest of western China. Soil temperature and moisture, nutrient availability, microbial biomass and enzyme activity were measured at different periods (before snow cover, early snow cover, deep snow cover, snow cover melting and early growing season) over the entire 2009/2010 winter. Snow removal increased the daily variation of soil temperature, frequency of freeze–thaw cycle, soil frost depth, and advanced the dates of soil freezing and melting, and the peak release of inorganic N. Snow removal significantly decreased soil gravimetric water, ammonium and inorganic N, and activity of soil invertase and urease, but increased soil nitrate, dissolve organic C (DOC) and N (DON), and soil microbial biomass C (MBC) and N (MBN). Our results suggest that a decreased snow cover associated with global warming may advance the timing of soil freezing and thawing as well as the peak of releases of nutrients, leading to an enhanced nutrient leaching before plant become active. These results demonstrate that an absence of snow cover under global warming scenarios will alter soil microbial activities and hence element biogeochemical cycling in alpine forest ecosystems.

The aim of this research was to investigate the genetic basis for variation in root penetration ability and associated traits in the mapping population derived from the Australian bread wheat cultivars Halberd and Cranbrook in soil columns containing wax layers grown in controlled conditions and to compare this with performance in the field. Root and shoot traits of the doubled haploid line (DHL) from a cross of Halberd and Cranbrook were evaluated in soil columns containing wax layers. Contrasting DHLs that varied in the ability to penetrate a wax layer in soil columns were then evaluated for maximum root depth in the field on contrasting soils at Merredin, Western Australia. Genetic control was complex, and numerous quantitative trait loci (QTL) (53 in total) were located across most chromosomes that had a small genetic effect (LOD scores of 3.2–9.1). Of these QTL, 29 were associated with root traits, 37 % of which were contributed positively by the Halberd with key traits being located on chromosomes 2D, 4A, 6B, and 7B. Variation in root traits of DHL in soil columns was linked with field performance. Despite the complexity of the traits and a large number of small QTL, the results can be potentially used to explore allelic diversity in root traits for hardpan penetration.

We determined the historical change in soil organic carbon (SOC) stocks from long-term field trials that represent major soil types and climatic conditions of northern China. Soil carbon and general circulation models were validated using these field trial data sets. We then applied these models to predict future change in SOC stocks to 2100 using two net primary production (NPP) scenarios (i.e., current NPP or 1% year−1 NPP increase). The conversion rate of plant residues to SOC was higher in single-cropping sites than in double-cropping sites. The prediction of future SOC sequestration potential indicated that these soils will be a net source of carbon dioxide (CO2) under no fertilizer inputs. Even when inorganic nutrients were applied, the additional carbon input from increased plant residues could not meet the depletion of SOC in parts of northern China. Manure or straw application could however improve the SOC sequestration potential at all sites. The SOC sequestration potential in northern China was estimated to be −4.3 to 18.2 t C ha−1 by 2100. The effect of projected climate change on the annual rate of SOC change did not differ significantly between climate scenarios. The average annual rate of SOC change under current and increased NPP scenarios (at 850 ppm CO2) was approximately 0.136 t C ha−1 yr−1 in northern China. These findings highlight the need to maintain, and where possible increase, organic carbon inputs into these farming systems which are rapidly becoming inorganic fertilizer intensive.

Anti-seasonal drying-wetting cycles since 2010 have substantially altered its soil and vegetation status in the drawdown zone of China&rsquo, s Three Gorges Reservoir (TGR). Such alternations may thus affect the composition and functioning of soil microbial communities, including the beneficial arbuscular mycorrhizal fungi (AMF), which enhance plant performance. Moreover, limited information is available if AMF communities are different in soils and roots, particularly under contrasting land-use changes. By combining the Illumina Miseq sequencing with bioinformatics analyses, AMF communities in both rhizosphere soils and roots of a stoloniferous and rhizomatous C4 perennial of Cynodon dactylon were characterized under three land-use types: (1) crop cultivated, (2) non-cultivated non-disturbed, and (3) disturbed non-cultivated land. A total of 35 and 26 AMF taxa were respectively detected from C. dactylon rhizosphere soils and roots from these three land-use types, which had endured four anti-seasonal drying/summer-wetting/winter cycles. Contrasting differentiations in the AMF community composition and structure were displayed in the C. dactylon rhizosphere soils and roots, and between land-use types. Nonmetric multidimensional scaling analyses revealed that AMF communities significantly correlated to soil organic carbon in the rhizosphere soils and roots of C. dactylon, to land-use types only in rhizosphere soils, whereas to soil moisture only in roots. Our results highlight the effects of soil nutrients and land-use changes on AMF community composition and diversity under the canopy of C. dactylon in TGR. The identified dominant AMF taxa can be employed to vegetation restoration in such degraded habitats globally.

This study addressed if long-term combined application of organic manure and inorganic fertilizers could improve the synchrony between nitrogen (N) supply and crop demand. 15 N-labeled urea was applied to micro-plots within three different fertilized treatments (no fertilizer, No-F soil; inorganic NPK fertilizers, NPK soil; and manure plus inorganic NPK fertilizers, MNPK soil) of a long-term field trial (1990–2009) in a dryland wheat field in the south Loess Plateau, China. After one season of wheat harvest, 15 N use efficiency was 20, 58, and 65 % in the No-F, NPK, and MNPK soil, respectively. During the early wheat growth stage, microbial immobilization of applied 15 N was significantly (P