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.

Field experiments were carried out in split plot design during the dry and wet seasons for two years (two seasons each in 2016–2017 and 2017–2018) with two genotypes (SH4 and SUIN053), two plant geometry (30×15 cm and 45×15 cm main plots) and three levels of NPK (20 kg N ha^–1, 40 kg P ha^–1 and 40 kg K ha^–1; 20 kg N ha^–1, 60 kg P ha^–1 and 60 kg K ha^–1; 20 kg N ha^–1, 80 kg P ha^–1 and 80 kg K ha^–1) with an objective to study the relationship between fibre yield of sunhmep and thermal indices.  The results indicated that the thermal units such as cumulative heat unit (CHU), photo thermal unit (PTU) and  helio thermal unit (HTU) were the highest during dry seasons, while relative temperature disparity (RTD) was the highest during wet seasons irrespective of the genotypes, plant geometry and fertilizer levels.  The combined analysis of variance showed that the suitability of sunnhemp genotypes for obtaining fibre and seed yields varied with season.  The results further indicated that sunnhemp grew during dry seasons with longer photoperiod and higher values of growing degree days (GDD), HTU and PTU resulted in a higher fibre yield, while a higher seed yield and relatively longer, finer and stronger fibres were obtained during wet seasons with higher RTD values.  Regression analysis indicated that CHU was positively related to fibre yield, while RTD was positively related to seed yield.   CHU beyond 2 000 °C d reduced seed yield and favoured fibre production.  In contrary to CHU, RTD values were positively related to seed yield and negatively related to fibre yield.   Similarly, HTU had an inverse relationship with fibre yield while PTU had a positive relationship with fibre yield.  The genotype SH4 produced a seed yield of 1 361 kg ha^–1 during wet seasons, which was significantly higher than SUIN053, while a fibre yield of 990 kg ha^–1 (significantly higher than that of SH4) was obtained for SUIN053 that required less CHU to attain the phenological events during dry seasons.  The per unit area yields of seed and fibre with the closer spacing (30 cm×15 cm)  by virtue of higher plant density were 17.0 and 14.9% higher than those with the spacing of 45 cm×15 cm, respectively.  Higher doses of P and K resulted in higher seed and fibre yields.

 

The yield and nitrogen use efficiency (NUE) of hybrid rice combinations are closely related to restorer line.  Therefore, it is essential to evaluate the agronomic characteristics of restorer lines with high yield and high NUE (HYHN).  However, it is unclear which restorer lines are HYHN, and neither have the common agronomic traits of the HYHN restorer lines been identified.  Aiming to address this issue, we conducted two filed experiments using three nitrogen applications, which screened five HYHN restorer lines from 15 indica restorer lines.  Yield, NUE and nutrient transportation of restorer lines with different yields and NUE types were examined.  Yield and total nitrogen absorption in aboveground biomass (TNA) increased, whereas NUE for grain production decreased with increasing nitrogen application levels.  The HYHN restorer lines had large spikelets and high weight per panicle that were significantly positively correlated with yield and NUE.  Therefore, large sink potential may be beneficial for both yield and NUE.  We further studied the differences in nutrient transportation to panicles between the HYHN and low yield and low NUE (LYLN) restorer lines and found that the former had a higher nitrogen absorption level and dry matter weight ratios of panicle in maturity.  Moreover, the HYHN lines also had a higher root and neck-panicle node bleeding intensity per stem after heading and more developed vascular bundles of neck-panicle nodes and leaves than the LYLN lines, which could contribute to the transportation of nutrients from root to ground and from stem and leaf to spike.  Therefore, the advantages of large sink potential of the HYHN restorer lines include large nutrient accumulation in and distribution to the panicles and smooth flow of nutrients along the transportation channels.

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.