To understand the long-term effects of combined organic and chemical nitrogen fertilization on soil organic C (SOC) and total N (TN), we conducted a 30-year field experiment with a wheat–maize rotation system on the Huang-Huai-Hai Plain during 1990–2019.  The experimental treatments consisted of five fertilizer regimes: no fertilizer (control), chemical fertilizer only (NPK), chemical fertilizer with straw (NPKS), chemical fertilizer with manure (NPKM), and 1.5 times the rate of NPKM (1.5NPKM).  The NPK, NPKS, and NPKM treatments had equal N inputs.  The crop yields were measured over the whole experimental duration.  Soil samples were collected from the topsoil (0–10 and 10–20 cm) and subsoil (20–40 cm) layers for assessing soil aggregates and taking SOC and TN measurements.  Compared with the NPK treatment, the SOC and TN contents increased significantly in both the topsoil (24.1–44.4% for SOC and 22.8–47.7% for TN) and subsoil layers (22.0–47.9% for SOC and 19.8–41.8% for TN) for the organically amended treatments (NPKS, NPKM and 1.5NPKM) after 30 years, while no significant differences were found for the average annual crop yields over the 30 years of the experiment.  The 0–10 cm layer of the NPKS treatment and the 20–40 cm layer of the NPKM treatment had significantly higher macroaggregate fraction mass proportions (19.8 and 27.0%) than the NPK treatment.  However, the 0–10 and 20–40 cm layers of the 1.5NPKM treatment had significantly lower macroaggregate fraction mass proportions (–19.2 and –29.1%) than the control.  The analysis showed that the higher SOC and TN in the soil of organically amended treatments compared to the NPK treatment were related to the increases in SOC and TN protected in the stable fractions (i.e., free microaggregates and microaggregates within macroaggregates), in which the contributions of the stable fractions were 81.1–91.7% of the increase in SOC and 83.3–94.0% of the increase in TN, respectively.  The relationships between average C inputs and both stable SOC and TN stocks were significantly positive with R² values of 0.74 and 0.72 (P<0.01) for the whole 40 cm soil profile, which indicates the importance of N for soil C storage.  The results of our study provide key evidence that long-term combined organic and chemical nitrogen fertilization, while maintaining reasonable total N inputs, benefited soil C and N storage in both the topsoil and subsoil layers.

Nutrient balance is essential for attaining high yield and improving profits in agricultural farming systems, and crop nutrient uptake ratio and stoichiometry can indicate crop nutrient limitations in the field.  We collected a large amount of field data to study the variations in yield, nutrient uptake and nutrient stoichiometry of peanut (Arachis hypogaea L.) in Southeast China (SEC), North-central China (NCC), and Northeast China (NEC), during 1993 to 2018.  Peanut pod yield gradually increased from 1993 to 2018, with average yields of 4 148, 5 138, and 4 635 kg ha^–1 in SEC, NCC, and NEC, respectively.  The nitrogen (N) internal efficiency (NIE, yield to N uptake ratio) was similar among the three regions, but phosphorus (P) IE (PIE, yield to P uptake ratio) changed from low to high among regions: NCC<SEC<NEC, while potassium (K) IE (KIE, yield to K uptake ratio) portrayed a different pattern of SEC<NCC<NEC.  Based on the nutrient IE, to produce 1 Mg of pod yield, the average N, P, and K requirements of the above-ground parts of peanut were roughly 47.2, 5.1, and 25.5 kg in SEC, 44.8, 5.7, and 20.6 kg in NCC, and 44.6, 4.4, and 14.7 kg in NEC, respectively.  The N/P ratio changed in the sequence NCC<SEC<NEC, and the N/K ratio was similar in NEC and NCC, but lower in SEC.  The N harvest index (HI) and KHI declined with increasing nutrient uptake across all regions under high nutrient uptake.  The low PIE and N/P ratios in NCC could be explained by the high P accumulation in stover, and high KIE and N/K ratios in NEC may be attributed to the low soil K supply.  The frontier analysis approach provides a practical framework and allows documentation of a decline in nutrient HI as nutrient uptake increases.  Lastly, this study reveals the limitation and surplus of nutrients of peanut in different regions of China.

Microbes are decomposers of crop residues, and climatic factors and residue composition are known to influence microbial growth and community composition, which in turn regulate residue decomposition.  However, the succession of the bacterial community during residue decomposition in Northeast China is not well understood.  To clarify the property of bacterial community succession and the corresponding factors regulating this succession, bags containing maize residue were buried in soil in Northeast China in October, and then at different intervals over the next 2 years, samples were analyzed for residue mass and bacterial community composition.  After residue burial in the soil, the cumulative residue mass loss rates were 18, 69, and 77% after 5, 12, and 24 months, respectively.  The release of residue nitrogen, phosphorus, and carbon followed a similar pattern as mass loss, but 79% of residue potassium was released after only 1 month.  The abundance, richness, and community diversity of bacteria in the residue increased rapidly and peaked after 9 or 20 months.  Residue decomposition was mainly influenced by temperature and chemical composition in the early stage, and was influenced by chemical composition in the later stage.  Phyla Actinobacteria, Bacteroidetes, and Firmicutes dominated the bacterial community composition in residue in the early stage, and the abundances of phyla Chloroflexi, Acidobacteria, and Saccharibacteria gradually increased in the later stage of decomposition.  In conclusion, maize residue decomposition in soil was greatly influenced by temperature and residue composition in Northeast China, and the bacterial community shifted from dominance of copiotrophic populations in the early stage to an increase in oligotrophic populations in the later stage. 

 

Quantification of currently attainable yield and fertilizer requirements can provide detailed information for assessing the food supply capacity and offer data support for agricultural decision-making.  Datasets from a total of 5 408 field experiments were collected from 2000 to 2015 across the major wheat production regions in China to analyze the spatial distribution of wheat yield, the soil nutrient supply capacity (represented by relative yield, defined as the ratio of the yield under the omission of one of nitrogen (N), phosphorus (P) and potassium (K) to the yield under the full NPK fertilizer application), and N, P and K fertilizer requirements by combining the kriging interpolation method with the Nutrient Expert Decision Support System for Wheat.  The results indicated that the average attainable yield was 6.4 t ha⁻¹, with a coefficient of variation (CV) of 24.9% across all sites.  The yields in North-central China (NCC) and the northern part of the Middle and Lower reaches of the Yangtze River (MLYR) were generally higher than 7 t ha⁻¹, whereas the yields in Southwest China (SWC), Northeast China (NEC), and the eastern part of Northwest China (NWC) were usually less than 6 t ha⁻¹.  The precentage of area having a relative yield above 0.70, 0.85, and 0.85 for N, P, and K fertilizers accounted for 52.3, 74.7, and 95.9%, respectively.  Variation existed in N, P, and K fertilizer requirements, with a CV of 24.8, 23.9, and 29.9%, respectively, across all sites.  More fertilizer was needed in NCC and the northern part of the MLYR than in other regions.  The average fertilizer requirement was 162, 72, and 57 kg ha⁻¹ for N, P₂O₅, and K₂O fertilizers, respectively, across all sites.  The incorporation of the spatial variation of attainable yield and fertilizer requirements into wheat production practices would benefit sustainable wheat production and environmental safety.