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Abstract In the realm of forest resource inventory and monitoring, stand-level biomass carbon models are especially crucial. In China, their importance is underscored as they form the bedrock for estimating national and international forest carbon storage. This study, based on the data from 52,700 permanent plots in the 9th National Forest Inventory (NFI) of China, was directed towards developing these models. After computing biomass and carbon storage per hectare using specific tree models for 34 species groups, we devised robust volume-derived biomass and carbon storage models for 20 forest types. The application of these models and historical data reveals notably a decline in China's forest carbon storage to 4.90Pg by the late 1970s due to aggressive forest exploitation. However, subsequent conservation and afforestation campaigns have affected a recovery, culminating in a storage of 8.69Pg by the 9th NFI. Over the past 40 years, China's forest carbon storage has surged by 3.79Pg, split between natural forests (2.25Pg) and planted forests (1.54Pg). In benchmarking against three pre-existing models, we discerned discernible biases, underscoring the need for larger modeling sample sizes. Overall, our models stand as a monumental stride in accurately gauging forest carbon storage fluctuations in China, both regionally and nationally.

Contrasting fertilization modifies soil phosphorus (P) transformation and bioavailability, which impact crop P uptake and P migration in the soil profile. A long-term (25-year) fertilizer experiment was employed to investigate crop yield, P uptake and changes in sequentially extracted P fractions in the soil profile, and their relationships on a calcareous soil derived from loess material under a winter wheat and summer maize double-cropping system. The experiment involved seven nutrient management treatments: control (CK, no nutrient input), N, NK, NP, and NPK, representing various combinations of synthetic nitrogen (N), phosphate (P), and potassium (K) applications, as well as combinations of NPK fertilizers with either crop residues (SNPK, where S refers to maize stalk or wheat straw) or manure (MNPK, where M refers to dairy manure). Wheat and maize yields were significantly higher with P input fertilizer relative to the P-omitted treatments. Long-term application of P-containing fertilizers markedly raised the contents of inorganic (Pi) and organic (Po) P fractions at 0–20 cm depth compared with the P-omitted treatments. Moreover, both Pi and Po fractions were markedly higher under MNPK than under NPK and SNPK treatments. For achieving high yield for wheat and maize, the critical contents of labile P were 54 and 63 mg kg−1, and those of moderately labile P were 48 and 49 mg kg−1, respectively, defined by the linear plateau model. In addition, the change points of labile P and moderately labile P were 99 and 70 mg kg−1, above which CaCl2-P content significantly increased. Moreover, long-term P input significantly accumulated different P fractions in the deeper soil layers up to 100 cm, with large portions of organic P being a composite of labile and moderately labile P, especially in MNPK treatment. Our results suggest that excessive P supply with organic manure resulted in massive P accumulation in the topsoil and promoted soil P fraction transformation and availability in the deep soil layers, especially in an organic P form that has often been neglected.

Basic soil productivity (BSP) is the productive capacity of farmland soils with their own physical and chemical properties during a specific crop season under local field management. Improving BSP as an effective way to increase or maintain crop yield, and researching its changes and potential driving factors under long-term fertilization are crucial for ensuring high and stable crop yields. In this study, the yields of BSP were simulated using the decision support system for agrotechnology transfer (DSSAT) crop model based on three long-term experiments, and its changing characteristics and driving factors were investigated under various fertilization treatments in wheat–maize rotation systems during 1991–2019. Five treatments were included: (1) unfertilized control (CK); (2) balanced mineral fertilization (NPK); (3) NPK plus manure (NPKM); (4) high dose of NPK plus manure (1.5NPKM); and (5) NPK plus crop straw (NPKS). This study found that the BSP of wheat and maize exhibited a fluctuating increase or stable change trend under four fertilization treatments at the Yangling (YL) and Zhengzhou (ZZ) sites, while a fluctuating reduction trend was observed at the Qiyang (QY) site. Compared with CK, NPKM, 1.5NPKM and NPKS significantly (p < 0.05) improved the BSP of wheat and maize at the YL and ZZ sites. The BSP of both maize and wheat under NPKM and 1.5NPKM was significantly (p < 0.05) higher than that under NPK or NPKS, whereas no statistically significant difference was found between NPK and NPKS at the QY site. The contribution rates of basic soil productivity (CBSP) of maize and wheat at the YL (41.5–60.7% and 53.0–64.3%) and ZZ sites (44.4–59.2% and 56.8–66.7%) were overall higher than that at the QY site (25.8–37.6% and 48.3–60.1%). In most cases, the difference in CBSP among different fertilization treatments was consistent with that in BSP. Moreover, a significant positive correlation was recorded between BSP and soil pH (r = 0.73, p < 0.01; r = 0.87, p < 0.01), TN (r = 0.56, p < 0.01; r = 0.62, p < 0.01) and TK content (r = 0.49, p < 0.01; r = 0.58, p < 0.01) in maize and wheat. Soil pH significantly correlated positively with the BSP of maize (R2 = 0.54, p < 0.001) and wheat (R2 = 0.49, p < 0.001) at the QY site, but negative correlation (R2 = 0.20, p < 0.001; R2 = 0.30, p < 0.001) was only found in maize at the YL and ZZ sites. The BSP of maize and wheat showed a significant negative linear correlation with MAP (R2 = 0.49–0.67, p < 0.001) and MAT (R2 = 0.36–0.62, p < 0.001). Random forests (RF) and variance partitioning analysis (VPA) revealed that soil properties and its interaction with the climate showed a higher explanation rate for BSP, indicating that these factors are the key drivers of BSP change. Overall, chemical fertilizers combined with manure can effectively increase BSP, while the effects of fertilizer combined with straw on BSP vary by region. The changes in BSP in wheat–maize cropping were mainly driven by both the soil and its interactions with the climate.

Partial substitution of synthetic nitrogen fertilizer with manure (organic substitution) is highly recommended to minimize environmental risks without compromising crop productivity in intensive agricultural systems. However, our understanding of the effect of organic substitution on soil organic carbon (OC) and total nitrogen (TN) in deep soil and its impact on crop productivity remains limited. Here we investigated OC and TN changes in soil profile down to 100 cm, crop yield, and sustainable yield index under synthetic nitrogen, phosphate, and potassium fertilizers (NPK), NPK plus straw (NPKS), and organic substitution (NPKM) treatments over two decades in four upland fields across different climate zones. Compared with the initial values, two decades of NPKM treatment significantly (p < 0.05) increased OC and TN stocks in either topsoil (by 25.6–103.8 and 15.8–89.8%) or deep soil (by 2.9–71.3 and 5.7–36.9%), respectively, across all sites. The increases in OC and TN stocks in 0–100 cm soil receiving NPKM were significantly higher than those receiving NPK at all sites and NPKS at three high-evaporation sites. Compared with NPKS and NPK treatments, crop yield and N uptake were significantly increased under NPKM treatment only at the Qiyang site. Furthermore, OC sequestration in the entire soil profile down to 100 cm and TN accumulation in topsoil exhibited significant positive correlations with crop N uptake, relative crop yield, and sustainable yield index. In conclusion, long-term partial substitution of synthetic N fertilizer with manure facilitates soil OC and TN sequestration in the entire 100 cm profile and thus maintains high crop productivity in upland areas.

In this work, nitrogen doped carbon dots (N-CDs) were synthesized through one step hydrothermal reaction using ginkgo fruit and ethylenediamine as precursors. The luminescence of the N-CDs was speculated to be related with the electron transition of C=N bonds derived from grafting amines groups onto the the functional groups on the surface. MnO4− could selectively quench the fluorescence of N-CDs due to the formation of N-CDs-MnO4− complex on the surface. The linear relation between quenching efficiency and MnO4− concentration ranged from 1 to 60 µmol/L with a detection limit of 0.64 µmol/L. In the presence of hydrazine (N2H4), MnO4− was reduced to Mn2+ and the fluorescence of carbon dots was recovered. Results indicated that it can act as a secondary fluorescent probe for quantitative analysis of N2H4 in the scope of 0.5 to 14 µmol/L with a detection limit of 0.384 µmol/L. The N-CDs were successfully applied to analyze MnO4− and N2H4 in real samples with satisfactory recoveries (97.34-104.0% and 97.56-104.4%, respectively), implying good applicability in practical analysis.

Seeking food security, contemporary Chinese agriculture has followed a trajectory of overfertilization and associated environmental problems, hence the need for nitrogen-balancing practices that do not compromise yield and quality. Here we present a national meta-analysis using 224 studies with 1972 comparisons to quantify the potential to reduce nitrogen (N) fertilization to improve environmental outcomes while maintaining yield and grain protein. We calculated a nitrogen reduction ratio (NRR), as 100 × ( N _C − N _T )/ N _C ; where N is N fertilizer rate and subscripts indicate farmer practice (C) and reduced N rate treatment (T). Our meta-analysis showed that the NRR that maintained yield and grain protein content at the level of current practice was up to 10% in wheat and up to 30% in maize and rice. Larger yield-neutral NRR could be achieved in more fertile, heavier-textured soils, and with practices including enhanced-efficiency N fertilizer, combined application of organic and inorganic N fertilizer, and incorporated straw. Assuming a reduction in N fertilizer usage by 10% for wheat and by 30% for maize and rice in the current cropping area, there is a potential to save 5.7 Mt N yr ^−1 ; reduce loss of reactive nitrogen by 1.26 Mt N yr ^−1 , equivalent to 63% of annual total Nr losses for rice in China, reduce N-related greenhouse emissions by 75.2 Mt CO _2 -eq yr ^−1 , equivalent to 14.5%–25% of the emissions associated with the N fertilizer chain in China; and improve N use efficiency by 23%. Our results highlight the feasibility of maintaining yield and grain protein, and achieving substantial environmental benefits with reduced fertilization rate, and the environmental and agronomic scenarios where these outcomes are more likely.

Plastic film mulching often increases the yield of winter wheat in the Loess Plateau of China, but the physiological mechanisms are unclear, especially in response to the interaction between mulch and water supply. In this study, we investigated the interactive effects of initial soil water (dry, moderate, and wet), soil cover (plastic mulch, bare soil), and seasonal conditions on the dynamics of dry matter partitioning, water-soluble carbohydrates (WSC), and flag leaf senescence, and their relations with yield and its components. Plastic mulch increased dry matter accumulation at anthesis and maturity relative to bare soil, with no interaction with season or initial soil water. Allocation of dry matter to leaf, stem, and spike did not change with soil cover. Compared with bare soil, mulch increased WSC accumulation by 14% at anthesis and its translocation by 16%. Soil cover did not influence the senescence of flag leaf after anthesis as indicated by similar dynamics of the C:N ratio. Grain yield was higher under plastic mulch than bare soil in two out of three seasons, and was associated with a higher translocation amount of WSC and post-anthesis dry matter that linked grain weight, grain number, and harvest index.

Organic phosphorus (Po) may play a vital role in phosphorus availability via its mineralization by alkaline phosphatase (ALP), being encoded by phoD gene, in calcareous soil. Understanding the effects of long-term fertilization on the community of phoD harboring bacteria and the related alteration of the P availability owing to the changes in ALP secretion may offer a chance to elucidate the Po contribution to soil available P. Based on a long-term experiment, we analyzed the phoD gene harboring microbial diversity, abundance and composition, ALP and Po forms, and their relationship. The treatments involved were control without any fertilizers (CK), synthetic nitrogen and potassium (NK), synthetic nitrogen, phosphorus and potassium (NPK), NPK and crop stalk return (SNPK), and NPK plus organic manure (MNPK). Fertilization increased the abundance and diversity of phoD gene harboring microbial over CK. Those receiving NPK and NPK treatments integrated with organic supplements significantly improved the relative abundance of Proteobacteria but decreased Gemmatimonadetes at the phylum level, while all fertilized treatments appreciably increased the relative abundance of Lysobacter but decreased that of Gemmatirosa and Afipia, at the genus level. SNPK and MNPK treatments noticeably increased the relative abundance of Methylobacter but reduced Pseudomonas and Streptomyces relative to those receiving synthetic fertilizer treatments. Long-term fertilization markedly raised ALP activity, which was significantly and positively correlated with the relative abundance of the phylum Proteobacteria as represented by the genera Methylobacterium and Lysobacter. ALP was closely associated with moderately labile Po, followed by enzyme P, recalcitrant Po, and labile Po. The changes in phoD bacteria and ALP were mainly driven by soil organic carbon, Olsen P and pH. We concluded that the long-term fertilization, especially the addition of organic supplements, profoundly modified the soil properties and subsequently changed the diversity and relative abundance of phoD gene harboring bacteria, which promoted the activity of ALP, and thus the mineralization of various forms of Po (mainly moderately labile Po) to enhance the P availability.

Abstract Background Mixed pigment analysis is an important and complex subject in preserving and restoring Chinese paintings since the colors observed by our naked eyes or instruments such as hyperspectral cameras are usually a mixture of several kinds of pigments. The purpose of this study was to explore a more effective method to confirm the type of every pure pigment and their proportion in pigment mixtures on the surface of paintings. Methods Two endmember extraction algorithms were adopted to identify the types of pigments and an improved method of ratio spectra derivative spectrophotometry was used to determine their proportion. Main works (1) Extracting the pure pigment components from mixed spectrum by adopting two blind source separation algorithms: Independent Component Analysis and Non-negative Matrix Factorization; (2) matching the separated pure spectrum with the pigment spectral library built in our laboratory to determine the pigment type; and (3) calculating the proportions of mixed pigments using the Ratio Spectra Derivative Spectrophotometry based on Mode, which is improved based on the original algorithm. Finally, a comparison was made with two abundance inversion algorithms: Least Squares Algorithm and Minimum Volume Simplex Analysis. The correlation coefficient and root mean square error were used to provide evidence for accuracy evaluation. Conclusions (1) Non-negative matrix factorization is more suitable for endmember extraction; and (2) Ratio spectra derivative spectrophotometry based on mode is more suitable for abundance inversion.

The combination of organic manure and inorganic fertilizer plays a role in increasing crop yield and nutrient efficiency, but such effectiveness varies with crop, soil, management, and climate. Here, a 6-year field experiment was conducted to evaluate the effects of substituting organic manure with inorganic fertilizer on crop yield, grain protein content, and nitrogen and phosphorus efficiency under a winter wheat-summer maize cropping system on Anthrosol. Five treatments were included: recommended nitrogen (N), phosphorus (P) and potassium (K) fertilizers (NPK), 75% NPK + 25% organic manure (M), 50% NPK + 50% M, 25% NPK + 75% M, and 100% M, respectively. Wheat, maize, and annual yield were 1643–8438 kg ha−1, 4847–11,104 kg ha−1, and 10,007–17,496 kg ha−1. Organic manure treatments produced the same crop yield as NPK treatment except for 100% M. Grain protein content of wheat and maize was 7.9–15.1% and 5.6–12.6%. Organic manure treatments yielded significantly lower wheat grain protein content but had no significant effect on maize grain protein content relative to NPK treatment. Nitrogen uptake efficiency and nitrogen use efficiency at the cropping system level were 0.67–1.16 and 35.7–60.5 kg kg−1. Phosphorus uptake efficiency and phosphorus use efficiency were 0.28–0.75 and 167–531 kg kg−1. Compared with NPK treatment, 50% M, 75% M, and 100% M improved nitrogen use efficiency but decreased nitrogen uptake efficiency and phosphorus efficiencies. Annual N and P budgets were −1.3–79.1 kg ha−1 a−1 and 25.6–100.1 kg ha−1a−1, and both increased with the increase in organic manure input. Based on crop yield, grain protein content, nitrogen, and phosphorus efficiency and their budget, substitution of 25% inorganic fertilizer with organic manure is the rational combination under the winter wheat–summer maize system on an Anthrosol.

Phosphate (P) rock is a finite natural resource, and its use for P fertilizer production has resulted in its rapid depletion worldwide. In order to reduce the use of natural P resources, reducing the input of P into agricultural systems is necessary. The assessment of legacy P in soil is an option to maintain crop yield with low P fertilizer input. Many models have been tested to assess the contribution of legacy soil P to crop uptake. However, these models face a common challenge as conceptual soil P pools in models cannot be accurately initiated and evaluated using measured soil P indexes. In this study, a novel legacy P assessment (LePA) model was developed according to empirical equations about crop P uptake, soil Olsen-P, and total P from two long-term fertilizer experiments in typical calcareous and acidic soils in China. We used the DPPS (dynamic phosphorus pool simulator) model as a contrast model to estimate the simulation accuracy of the new LePA model. The calibration and validation datasets for both models were set-up by collecting data from two long-term fertilizer experiments in typical calcareous and acidic soils in China. The results showed that the LePA model simulated crop P uptake similar to the DPPS model in calcareous soil. While the DPPS model failed to depict crop P uptake under low pH conditions, the LePA model worked well after modification when limited crop growth caused by acidic conditions was considered. Moreover, the LePA model can also predict changes in soil TP and Olsen-P with P fertilizer application, which are new functions compared with the DPPS model. Based on a scenario analysis generated by the LePA model, P fertilizer application could be reduced by 52% in Yangling and 46% in Qiyang compared with the conventional application rate during this period to maintain the current yields if soil legacy P can be utilized efficiently. The LePA model is a useful tool for guiding soil P management from the field to country scales.

Temporal changes in the concentrations of plant-available phosphorus (P) in soil (Olsen-P), total soil-P and P activation coefficient (the ratio of Olsen-P to residual-P (i.e. an approximation to total-P)) were measured in plots that received consistent inorganic nitrogen, phosphorus and potassium plus organic fertilizers annually. Maize and winter wheat crops were grown in rotation for 24 years. Olsen-P and P activation coefficient declined significantly in the earlier years (< 12 years) for treatments that did not include any P fertilizer, and increased over the same period for the P-fertilized treatments. The rates of change in the Olsen-P and P activation coefficient values were positively related to P balance. In the later years, the Olsen-P and P activation coefficient plateau values were positively related to the P balance.

To understand the mechanisms affecting water balance partitioning during fallow on drylands could improve the fallow management practices in arable land ecosystems. A three-year field experiment was conducted to evaluate the effects of field management regimes on water balance partitioning and fallow efficiency during the fallow periods under a winter wheat (Triticum aestivum L.) fallow system on the Loess Plateau, China. The fallow management regimes tested were: (i) conventional practice, (ii) catch cropping, and (iii) no tillage with wheat straw mulching. A process-oriented ecosystem model (CoupModel) was calibrated with field measurements and then used to generate comparative simulations of the water balance partitioning. The simulations indicated that mulching increased the soil water storage change by 38-71 mm during the three fallow periods, thus resulting in higher fallow efficiency by 9-12%, and decreased soil evaporation by 22-72 mm, compared with the conventional practice. Furthermore, water reached deeper horizons, resulting in 7 mm deep percolation in a wet year under mulching but not under conventional practice or catch cropping. The simulation results also showed that the catch cropping decreased the soil water storage change by 13-21 mm, although it lowered soil evaporation by 11-51 mm, and altogether reduced the fallow efficiency by 3-9%, compared to conventional practice. On the Loess Plateau of China mulching proved to be a sound measure for ensuring certain fallow efficiency and possibly benefit to the water cycle, while catch cropping negatively partitioned the water balance. The catch cropping under mulching might be another management regime to be considered.

Streptococcus agalactiae is one of the important causative agents of bovine mastitis. Studies on molecular epidemiology, virulence factors and antimicrobial susceptibility profiles of S. agalactiae isolates from mastitis in China are scarce. Thus, this study was carried out to investigate prevalence of S. agalactiae associated with subclinical mastitis, to determine antimicrobial susceptibility profile, and to analyze their phenotypic and genotypic profiles. Capsular serotypes and genotypes by multilocus serotyping and virulence genes (hemolysin III, C-β protein, C-α protein, surface protein rib, hyaluronate lyase, and C5a peptidase) were determined using molecular assays. Additionally, susceptibility of S. agalactiae isolates to antimicrobial agents was accessed through standard disc diffusion method. A total of 2225 milk samples were collected from 21 large dairy herds located in 10 provinces of China. Overall, 133 (14.1%) S. agalactiae isolates were recovered from 946 (42.5%) subclinical mastitis milk samples. Serotype Ia and ST103 were the most prevalent serotypes and genotypes. Five of the six virulence genes were detected in 22.6% isolates with only two virulence genes and 6.8% of isolates with three genes. There were no significant geographical differences in the distribution of virulence genes. Moreover, 63.9% of S. agalactiae exhibited resistance to levofloxacin, 3.8% isolates were resistant to cefepime, 2.3% were resistant to chloramphenicol and ampicillin. Additionally, two ampicillin/cefotaxime/ levofloxacin-resistant isolates, one vancomycin-resistant isolate and one ampicillin/cefotaxime-resistant isolate were identified. This study concludes high prevalence of S. agalactiae from subclinical mastitis carrying virulence genes and mainly belonging to Serotype Ia and ST103. [ABSTRACT FROM AUTHOR]

This study assessed changes in nitrogen (N) and phosphorus (P) uptake and partitioning in response to selection for yield in milestone varieties of Chinese winter wheat (Triticum aestivum L.). We established a factorial trial combining 11 nutrient–water regimes with three (2013–14) and five (2014–15) varieties released from 1970 to 2005. Grain yield increased at a rate of 0.46% year–1, with no apparent increase in the uptake of nutrients. Nitrogen harvest index did not change, and P harvest index increased at a rate of 0.15% year–1. Consequently, yield per unit N uptake and yield per unit P uptake increased at similar rates (0.4% year–1) at the expense of nutrient concentration in grain, which declined at a rate of 0.47% year–1 for N and 0.31% year–1 for P. No trends in N nutrition index were found. Selection for yield in wheat increased the yield per unit nutrient uptake at the expense of grain nutrient concentration. Further gains in yield need to be matched by increasing N uptake to maintain grain protein. Dilution of P in grain needs to be considered in terms of the putatively undesirable role of phytate for human nutrition, and the need for P reserves in seed for crop establishment. [ABSTRACT FROM AUTHOR]

Improving N use efficiency (NUE) and reducing the negative impact of N fertilization on the environment are essential for sustaining agricultural production in many intensive farming regions around the world. The objective of this research was to investigate the effect of various fertilization regimes on yield, N uptake, and NUE by maize (Zea mays L.) in long-term (15-yr) experiments performed at four sites (Changping, Zhengzhou, Yangling, and Qiyang) in China. Eight treatments were examined: unfertilized control (CK); inorganic fertilizer (manufactured source) N, N and P, N and K, and N, P, and K; inorganic N, P, and K with manure (NPKM); 1.5′ the rate of NPKM (1.5NPKM); and N, P, and K with maize stover returned (NPKS). Compared with inorganic fertilization, mixed inorganic and manure fertilization (NPKM and 1.5NPKM) resulted in more stable and significantly higher yield and NUE as well as increases in soil nutrient storage at all sites, with the most significant improvement in the acid soil (pH = 5.7) at Qiyang. Phosphorous was identified as one of the most important limiting factors in maize NUE because the NUE at all four sites increased from about 20 to 45% by increasing the available P in the soil. Higher NUEs (up to 70%) were observed mostly from the continuous manure applications. We conclude that manure and P applications are the most important and effective nutrient management strategies for both the acid and alkaline soils in this study for maize production in China. [ABSTRACT FROM AUTHOR]

labile organic pools, soluble organic matter and soil microbial biomass are sensitive to changes in soil management and therefore good indicators of soil quality. Effects of a 17-year long-term fertilization on soil microbial biomass C (SMBC) and N (SMBN), soluble organic C, and soluble organic N during the maize growing season were evaluated in a loess soil (Eum-Orthic Anthrosol) in northwest China. The fertilization treatments included no fertilizer (CK), inorganic N, P, and K fertilizer (NPK), cattle manure plus NPK fertilizer (MNPK), and straw plus NPK fertilizer (SNPK). Our results showed that C storage in the 0-20 cm soil layer was 28% to 81% higher in the fertilized treatments compared to the unfertilized treatment. In the 0-10 cm soil layer, SMBC and SMBN in the three fertilized treatments were higher than in the unfertilized treatment on all sampling dates, while microbial biomass C and N in the 0−10 cm soil layers were the highest at grain filling. In the same soil layer, soil-soluble organic C generally decreased in the order MNPK > SNPK > NPK > CK, while soluble organic N was the highest in the MNPK followed by the SNPK treatment. There was no significant difference in soluble organic N in the NPK and CK treatments throughout most of the maize growing season. Changes in soluble organic N occurred along the growing season and were more significant than those for soluble organic C. Soluble organic N was the highest at grain filling and the lowest at harvest. Overall, our results indicated that microbial biomass and soluble organic N in the surface soil were generally the highest at grain filling when maize growth was most vigorous. Significant positive relationships were found between soluble organic C and SMBC and between soluble organic N and SMBN. [ABSTRACT FROM AUTHOR]

Microbial biomass phosphorus (MBP) and its relationships with other biological and chemical properties were studied on loess soil with an 11-year long-term fertilization experiment. The results indicated that inorganic fertilizers (F) improved soil microbial biomass carbon (MBC), nitrogen (MBN), and MBP levels and F plus maize stalk (SNPK) improved MBC and MBN. Manuring markedly increased soil MBC, MBN, and MBP levels. Fertilization decreased the ratios of MBC/MBN, MBC/MBP, and MBN/MBP. Microbial biomass phosphorus was positively and linearly correlated with MBC, MBN, organic carbon (SOC), total phosphorus (TP), water-soluble P, and Olsen P but negatively correlated with soil pH. Microbial biomass phosphorus constituted 2% of TP on control (CK) and inorganic fertilizer treatments and 12% on manure plots. Microbial biomass phosphorus to Olsen P ratios were 50% on CK, F, and SNPK and 80% on manure treatments. Measurements of MBP in soil containing high Olsen P were subject to analytical problems of unknown reasons. [ABSTRACT FROM AUTHOR]

The critical value of soil Olsen-P is the point above which the probability of crop yield response to fertilizer P is small or nil. Determining this critical value is fundamental when making appropriate P fertilizer recommendations. In this study, the critical values were determined for continuous maize ( Zea mays L.)-winter wheat ( Triticum aestivum L.) cropping systems from a 15-year field experiment across three sites in China using linear-linear, linear-plateau and Mitscherlich models. The mean critical values for maize using the three models ranged from 12.1 to 17.3 mg P kg−1 (average 15.3 mg P kg−1) and for winter wheat from 12.5 to 19.0 mg P kg−1 (average 16.3 mg P kg−1) among study sites. The mean critical value for maize was approximately 7% lower than that for winter wheat across all sites based on the three models. Critical values identified by the Mitscherlich model were 1.4 to 2.1 times those from linear-linear and 1.3 to 1.9 times of those from linear-plateau and were crop and site dependent. There was a significant negative correlation ( P < 0.05) between the mean critical value from the three models and the observed P uptake by either maize or wheat. Our study shows that the critical values can vary with sites, crops and models used, and thus caution should be taken when selecting the most appropriate one when making P fertilizer recommendations for agronomic return and to minimize chances of negative environment impact from overfertilization. [ABSTRACT FROM AUTHOR]

Wheat, rice, and maize collectively provide the bulk of energy and protein to the human diet worldwide. Over the last seven decades, China increased 5.8-fold the aggregated production of the three cereals, but further gains are required to meet the predicted demand of 776 Mt. by 2030. Here, we report the rate of genetic gain in yield of 0.65% year-1 for wheat between 1937 and 2012, 0.69% year-1 for rice between 1934 and 2011, and 0.77% year-1 for maize between 1950 and 2014 in China. National farm yield in the same periods increased 1.38% year-1 for wheat, 1.15% year-1 for rice and 1.32% year-1 for maize. Hence, genetic improvement (G) accounted for 47%-60% of the increase in farm yield, with improved management (M) and G × M interaction accounting for the balance. The absolute rate of genetic gain (kg ha-1 year-1) was proportional to environmental potential. Genetic gain in nitrogen utilization efficiency (yield per unit nitrogen uptake) was significant for all three crops and was achieved at the expense in grain N concentration that decreased at 0.19% year-1 in rice and 0.47% year-1 in maize. To guarantee future food security and environmental sustainability, breeding and agronomic efforts need to increase the rate of gain in yield and revert the declining trends in grain protein by improving nitrogen uptake and nitrogen harvest index. [ABSTRACT FROM AUTHOR]