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Purpose: Keystone taxa play an important role in soil nutrient cycling and crop growth and can be influenced by soil tillage. We investigated the composition of keystone taxa and their relationships with soil properties under different long-term tillage practices. Methods: Four tillage treatments (i.e., CT, conventional tillage; NT, no tillage with mulch; RT, reduced tillage; and SS, subsoiling with mulch) were maintained for twenty-one years. Co-occurrence network (CoNet) was constructed to identify the keystone taxa, and redundancy analysis (RDA) was carried out to explore the relationships between keystone taxa and soil properties under the four tillage practices at two growth stages (elongation and grain filling stages) of winter wheat. Results: Compared with CT, RT had no significant effect on the microbial community and the keystone microbiome, while NT and SS remarkably altered the microbial community structure and the keystone microbiome at both growth stages. Massilia was the keystone genus under CT and RT, while Sphingomonas, Asanoa and Hoeflea were the keystone genera under NT and SS. RDA results showed that keystone genera were significantly correlated with soil organic carbon (SOC), dissolved organic carbon (DOC) and microbial biomass nitrogen (MBN) at both stages, especially at the elongation stage. Our results further revealed that the effects of NT and SS on crop growth might be related to the changes in keystone microbiome. Conclusion: Our study suggests that NT and SS may contribute to the development of sustainable agricultural production in the Chinese Loess Plateau. [ABSTRACT FROM AUTHOR]

As soil and soilless culture systems are highly dynamic environments, the structure of rhizosphere microbial communities is consistently adapting. There is a knowledge gap between the microbial community structure of soil based and soilless culture systems and thus we aimed at surveying their impact on diversity and composition of bacterial communities across a 10-month period in a tomato cultivation system. We compared community metrics between an soil based culture system fertilized with malt sprouts and blood meal, known for its slow and high mineralization rate, respectively and a soilless culture system fertilized with fish effluent or supplemented with an liquid organic fertilizer. Bacterial and fungal community composition was followed over time using two complementary techniques, phospholipid fatty acid analysis and 16S rRNA amplicon sequencing. Nitrogen dynamics and plant performance were assessed to provide insight on how bacterial diversity of soil and soilless microbial communities ultimately impacts productivity. Similar plant performance was observed in soilless culture systems and soil based system and yield was the highest with the aquaponics-derived fertilizer. Soil and soilless cultivating systems supplemented with different nitrogen-rich fertilizers differed on its characteristics throughout the experimental period. Fast-paced fluctuations in pH(H2O) and nutrient cycling processes were observed in growing medium. Physicochemical characteristics changed over time and interacted with bacterial community metrics. Multivariate analysis showed that plant length, pH, Flavisolibacter , phosphorus, chloride, ammonium, potassium, calcium, magnesium, sodium, electrical conductivity, nitrate, sulfate, and the bacterial genera Desulfotomaculum , Solirubrobacter , Dehalococcoides , Bythopirellula , Steroidobacter , Litorilinea , Nonomuraea were the most significant factors discriminating between natural soils supplemented with animal and plant by-products. Long-term fertilizer regimes significantly changed the PLFA fingerprints in both the soilless culture and soil based culture system. The use of these by-products in the soil was positively associated with arbuscular mycorrhizal fungi (AMF), which may influence rhizosphere communities through root exudates and C translocation. Community structure was distinct and consistently different over time, despite the fertilizer supplementation. The fungal microbial community composition was less affected by pH, while the composition of the bacterial communities (Actinomycetes, Gram-negative bacteria, and Gram-positive bacteria) was closely defined by soil pH, demonstrating the significance of pH as driver of bacterial community composition. Fertilizer application may be responsible for variations over time in the ecosystem. Knowledge about the microbial interactions in tomato cultivating systems opens a window of opportunity for designing targeted fertilizers supporting sustainable crop production. [ABSTRACT FROM AUTHOR]

In open-field vegetable production, high quantities of soil mineral nitrogen (Nmin) and N-rich crop residues often remain in the field at harvest. After the harvest of crops in autumn, this N can lead to considerable nitrate (NO3−) losses during the subsequent winter leaching period. In four field trials, different tillage depths (3–4, 10, 30 cm) and dates (early autumn, late autumn, early spring) were investigated to reduce N losses after growing spinach in the autumn. In a further treatment, the nitrification inhibitor 3,4-Dimethylpyrazole phosphate (DMPP) was directly applied to the crop residues. Potential N losses were calculated by a balance sheet approach based on Nmin concentration (0–90 cm), measured N mineralization and N uptake by catch crops. By postponing the tillage date from early to late autumn or spring, resprouting spinach stubbles acted as a catch crop, reducing N losses by up to 61 kg ha−1. However, if the spinach biomass collapsed, the N losses increased by up to 33 kg ha−1 even without tillage. The application of DMPP as well as the tillage depth were less effective. Overall, postponing tillage to spring seems to be the most promising approach for reducing N losses during the off-season. [ABSTRACT FROM AUTHOR]

We examined the effects of 10 yr of reduced tillage (RT) management, compared with conventional tillage (CT), on the chemical composition of soil organic matter (SOM) using a combination of physical fractionation and pyrolysis-field ionization mass spectroscopy (Py-FIMS). Surface soil samples (0-10 cm), which were collected from two adjacent CT and RT managed fields, were separated into particulate organic matter (POM) fractions and sand, silt, and clay size separates. Higher amounts of C (77%) and N (64%) were observed in all size separates of the RT soil and, in particular, the proportion of intramicroaggregate POM was two times as large as in the CT soil. The Py-FIMS spectra showed that larger proportions of free fatty acids, sterols, and N-containing compounds were present in the RT soil's sand fraction than in the CT soil. Similar observations were also made for both free and intramicroaggregate POM fractions. In the silt and clay size fractions, no substantial differences in SOM composition were measured between tillage treatments, except that the RT soil's clay fraction had a higher proportion of N-containing compounds and a lower proportion of alkylaromatics. Ratios of carbohydrate hexose to pentose subunits and of lignin monomers + phenols to lignin dimers confirmed a less decomposed character of the SOM in the silt and clay size fractions of the RT soil. These observations can be logically linked to the reduced mixing of crop residues and manure in the soil profile and higher surface soil microbial biomass under RT. [ABSTRACT FROM AUTHOR]

Judicious management of organic matter supply and tillage practice is crucial for sustaining soil quality in horticulture. We have studied whether N fertilization of vegetable crops should be adapted in the short term when soil management changes to include compost application and reduced tillage as soil quality improving factors. The experimental setup was a multiyear field trial on a sandy loam soil with a vegetable crop rotation. Soil tillage in spring was either conventional (moldboard plough) or reduced, non-inversion tillage (with a specially designed chisel plough). Starting in 2008, farm compost was applied each autumn at three rates: 0, 15 and 45 Mg per hectare. The three-year crop rotation (2009–2011) consisted of broccoli ( Brassica oleracea , var. Italica Group), carrots ( Daucus carota ) and leek ( Allium porrum ). Small but significant differences in N dynamics were found between treatments. Broccoli had a higher N uptake and biomass production under reduced compared to conventional tillage. In accordance with this, the apparent net N mineralization tended to be higher for reduced tillage compared to conventional tillage. In contrast, for leek, N uptake did not differ between tillage practices despite a higher apparent net N mineralization under conventional tillage. A tendency for a higher biomass production under conventional tillage was in line with a tendency for a higher amount of residual soil mineral N that might have increased the risk of N losses. In the carrot crop, a higher amount of mineral N under conventional tillage did not increase root yield. Compost application maintained soil organic matter content and did not result in a higher amount of residual soil mineral N. Only in the carrot growing season, compost application increased soil mineral N content to a limited extent. The small short-term changes in overall N availability observed between treatments do not necessitate changes in N fertilization strategy or additional precautions regarding residual soil mineral N. [ABSTRACT FROM AUTHOR]

Abstract: To evaluate the effect of tillage intensity on the N mineralization pattern of winter wheat residues, sugar beet residues, Italian ryegrass and maize residues undisturbed soil samples were taken from six sites under different tillage management. Site NTK had been managed for 10 years under reduced tillage (RT), whereby the last 4 years the crops were sown using direct seeding (NT). Site RTCSE had been managed for 20 years under reduced tillage (RT) and site RTH for 3 years. For each site under RT a nearby site under conventional tillage (CT) was selected (CTK, CTCSE and CTH). On site NTK and site RTCSE a significantly higher amount of SOC in the 0–10cm was accumulated compared to the respective CT sites. Between site RTH and site CTH no such significant difference was found. However, the content of microbial biomass C (MB-C) and the β-glucosidase and urease activities were higher on all RT sites compared to the respective CT sites. This indicates that these microbiological and biochemical parameters seem to be very sensitive for alterations in management intensity. After 98 days, more N was immobilized under NTK than under CTK by adding winter wheat residues (expressed as kgha−1 and as % of total added N). This higher immobilization potential can be explained by a higher microbial activity and a change in microbial population. Under RTCSE and RTH net N immobilization of the winter wheat residues was found, but the pattern was less pronounced than for NTK. However, when expressed as % of total N added, N immobilization of winter wheat residues was higher under CT than under RT, which indicates that high C:N residues when incorporated, decompose more slowly under RT than under CT. Similar results were found comparing the N mineralization pattern of maize residues under RTH and CTH. The residues of sugar beet and Italian ryegrass at site CTH released N more rapidly and to a higher extent, 74.1% and 66.2%, respectively (expressed as % of total N added) than under RTH at the end of the incubation. The slower mineralization of N rich crop residues under RT compared to CT means that there is less potential risk for nitrate leaching to occur, which may result in a higher N efficiency in RT compared to CT. [Copyright &y& Elsevier]

Long-term field experiments have confirmed belowground plant carbon (C) to be two to three times more efficient precursor of soil organic carbon (SOC) than aboveground plant residues. But it remains elusive just when this belowground biomass is relatively stabilized against mineralization: during the initial fast degradation, or on the longer term? A one-year field experiment was set up with biweekly follow-up of the in-situ mineralization of maize (Zea mays L.) C-inputs, either above- or belowground biomass based on soil δ 13C resolved CO 2 emissions. In addition, a treatment with maize roots and post-harvest remnant rhizodeposited-C left undisturbed in the field was included as well as a corresponding control that was physically disturbance as in the other treatments. We found that most maize-C was mineralized within a year with peaks in late fall and spring, i.e. 1 and 8 months after incorporation. Shoot-C decomposed only 1.4 times faster than root-C though statistically insignificant, which shows that on the short term (i.e. within a single year) the 2–3 fold stability of belowground biomass C is not manifested. Total maize-derived CO 2 emissions of soil amended with only roots and with roots and post-harvest rhizodeposits were equal, likely because the rhizodeposited-C had already degraded quickly. A much smaller share of root- and rhizodeposited-C (43%) was mineralized when soil was not disturbed after harvest. We hypothesize that such a delayed physical disturbance, which in practice would only occur in early spring, could be key in stabilizing belowground biomass C in the field. Overall, our findings show a limited difference in degradability of roots and shoots under field conditions on the short term, and a large effect of tillage timing. • Mineralization of maize-C was assessed using on-site resolved soil δ 13C-CO 2 emissions. • Annual degradability of shoots and roots cannot explain reported long-term stability. • Delayed tillage could slow down the mineralization of belowground biomass. • Delayed tillage may co-explain the higher longevity of root-C vs. shoot-C in soil. [ABSTRACT FROM AUTHOR]

Abstract: In the scope of the increasing concern for soil conservation, reduced tillage (RT) agriculture is growing more important in today''s agriculture in Western Europe. However, crop rotations often include beets and potatoes, crops that are generally assumed to be less suitable under RT agriculture because they result in a high disturbance of the soil at the formation of the ridges and at harvest. Therefore, the short- and long-term effect of RT agriculture on bulk density (BD), water retention curve (WRC), aggregate stability and field-saturated hydraulic conductivity of silt loam soils with crop rotations including root crops was evaluated. Ten fields at seven locations representing the important RT types, applied for a different number of years, and eight fields under conventional tillage (CT) agriculture with similar soil type and crop rotation were selected. At each location, BD of the 5–10cm layer was mostly lower in the RT fields (1.42±0.05Mgm−3 [average with standard deviation]) compared to the CT fields (1.44±0.09Mgm−3) and the water content at saturation was mostly higher (0.394±0.027m3 m−3 and 0.382±0.021m3 m−3 for RT and CT fields, respectively). No differences in BD (1.53±0.03Mgm−3) or WRC could be found in the 25–30cm soil layer when comparing the RT with the CT fields. The stability index of the 0–10cm layer measured by ‘dry and wet sieving’ [De Leenheer, L., De Boodt, M., 1959. Determination of aggregate stability by the change in mean weight diameter. Mededelingen van landbouwhogeschool en de opzoekingstations van de staat te Gent 24, 290–300] was 40% higher under RT than CT agriculture. The mean weight diameter (MWD) [Le Bissonnais, Y., 1996. Aggregate stability and assessment of soil crustability and erodibility: I. Theory and methodology. Eur. J. Soil Sci. 47, 425–437] was significantly higher even after short-term RT compared to CT agriculture. The MWD after a heavy shower, a slow wetting of the soil and stirring the soil after prewetting was 19%, 38% and 34% higher for RT than CT fields, respectively. The field-saturated hydraulic conductivity tended to be higher under RT compared to the CT fields. Despite the high disturbance of the soil every 2 or 3 years of crop rotations including sugar beets or potatoes, RT agriculture had a positive effect on the investigated physical soil properties. [Copyright &y& Elsevier]

Abstract: Field experiments were carried out to study the effects of different soil management practices on the water balance, precipitation use efficiency (PUE), and crop yield (i.e. winter wheat and peanut) on a loess soil near Luoyang (east edge of the Chinese Loess Plateau, Henan Province, China). Field plots were set up in 1999 including following soil management practices: subsoiling with mulch (SS), no-till with mulch (NT), reduced tillage (RT), two crops per year (i.e. winter wheat and peanut, TC), and a conventional tillage control (CT). The field plots were equipped to monitor all components of the soil–water balance except evapotranspiration, which was computed by solving the water balance equation. The results showed that although soil management had smaller influence on the magnitude of the water balance components than did precipitation variations, small influences of the applied soil management practices on water conservation during the fallow period can greatly affect winter wheat yield. SS increased consistently precipitation storage efficiency (PSE) and PUE over the 5 years compared to CT except during the wettest year. NT also had a noticeable effect on postharvest water storage during the fallow period; however, the influence on yield of NT depended on the amount of precipitation. TC lowered the winter wheat yield mainly due to the unfavorable soil moisture conditions after growing peanut in summer; however, the harvested peanut gained an extra profit for the local farmer. No matter which kind of soil management practices was adapted, PSE never exceeded 41.6%, which was primarily attributed to high evapotranspiration. From data of five consecutive agricultural years between 2000 and 2005, it could be concluded that SS resulted in the highest PSE, PUE and crop yield. TC also showed promising results considering the economic value of the second crop. NT performed slightly less as SS. CT gave intermediate results, whereas RT was the worst alternative. [Copyright &y& Elsevier]

Soil quality in vegetable cropping systems is seriously threatened by intensive tillage and fertilization practices and by limited crop rotations. Inclusion of cover crops, compost application and reduced tillage may help to sustain soil quality. A three-year field trial was set up on horticultural land to explore the combined effects of compost amendment at three rates (0, 15 and 45 Mg ha-1 year-1) and tillage practices (reduced tillage versus conventional ploughing) on soil quality. Cover crop was not a factor in the experiment, but cover crops were included in the rotation for reasons of good agricultural practice. The highest compost dose supported the initial level of total organic carbon in the arable layer. The decrease in pH in the arable layer was considerably limited by compost application, irrespective of the dose applied. Reduced tillage resulted in a favorable stratification for different soil quality indicators both by placement of organic inputs near the soil surface and by a reduction of leaching of base cations and organic carbon compounds. Differences between tillage practices and compost doses were most striking in the 0-10 cm soil layer. Compost application at the highest rate enhanced organic C content by 16% compared to the content in the non-amended soil. Reduced tillage induced a 13% higher organic C content in the 0-10 cm soil layer than that in the underlying 10-30 cm layer. Combining reduced tillage and recurrent compost application resulted in a different soil microbial community structure in the 0-10 cm surface layer, as revealed by phospholipid fatty acids analysis. Total microbial biomass was 44% higher under reduced compared to conventional tillage and increased by 27% due to compost application at a rate of 45 Mg ha-1 year-1. Fungal biomass doubled in the surface layer by reduced tillage. Actinomycetes and arbuscular mycorrhizal fungi were favored by both reduced tillage and compost application. Conversion to reduced tillage allowed for sustaining crop production in this intensive vegetable cropping system. Compost application and reduced tillage counteracted soil degradation. [ABSTRACT FROM AUTHOR]