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Returning crop residues to the field after harvesting is a proven effective strategy for improving soil fertility, carbon sequestration, and crop productivity. However, the relationships between crop residue return modes, SOC and nutrient contents, and crop yields are still unclear. In this study, a field trial was conducted to investigate the effects of different maize straw return modes, i.e., straw mulching (SMU), straw deep ploughing (SDP), and control without straw return (CK), on soil organic carbon (SOC) and nutrient contents in soil layers of 0–40 cm in a Mollisol. The relationships between straw return modes, SOC and nutrient contents, and maize yield were evaluated. Compared with CK, SMU and SDP significantly increased SOC, total nitrogen (N), available N, total phosphorus (P), and available P contents in all soil layers. Relative to SMU, SOC, total N, available N, total P, and available P contents were significantly lower in soil layers of 0–10 cm, but they were significantly higher in soil layers of 20–40 cm in SDP. Redundancy analysis indicated that total N, available N, and SOC were major factors controlling maize yield. Structural equation modeling further showed that straw return modes indirectly affected maize yield by directly and preferentially affecting total N and available N contents. The results indicated that SMU and SDP were beneficial for increasing SOC and nutrient contents at the surface and subsurface soils, respectively. Optimizing a nitrogen management strategy is important to achieve high maize yield with straw return. [ABSTRACT FROM AUTHOR]

Plastic pollution in farmland soil has become a significant concern for scientists studying farmland ecosystems. However, the current research focus on the environmental impacts of plastics in soil overlooks crucial factors such as sources, distribution, and persistence. In this study, we examined the distribution of residual film after eight years of film mulching in mid-April 2018. We also assessed changes in spatial distribution from 2018 to 2020. Our findings reveal that eight years of film mulching significantly increased the quantity of agricultural mulch film residues in the soil. The size of residual film fragments varied from 0.25 cm2 to 109 cm2, and the average size, number, and quantity of residues were influenced by soil depth. There was a noticeable downward trend in the quantity of agricultural mulch film residues, decreasing annually by 0.525 kg·ha−1. In contrast, the number of residual films showed an average annual growth rate of 2.13 × 105 p·ha−1. Importantly, we observed a substantial accumulation of residual film fragments below the 10 cm soil layer over time. Fragments ranging from 1–5 cm2 were the most abundant and gradually accumulated in deeper soil layers, enhancing mulching film recovery efficiency. This study provides valuable insights into the influence of mulch cycles on farmland soil profiles, identifying the key locations and size-to-shape ratios of residual films. These findings serve as a theoretical foundation for implementing effective measures to control mulch film pollution in agricultural practices. [ABSTRACT FROM AUTHOR]

In order to test the short-term effects of straw amendment on soil organic C (SOC) stabilization, SOC protection mechanisms, and soil bacterial community, we examined which bacterial taxonomic groups were associated with protected C fractions via different soil depths. We conducted a 5-year field experiment including a total of four treatments: S0 (no straw amendment), S1 (0–20 cm straw-amended soil), S2 (0–40 cm straw-amended soil) and S3 (0–60 cm straw-amended soil). The core method was used for soil sampling, and 180 soil samples was collected. Our results showed that straw amendment significantly increased bulk soil C content, enhanced the constituents of physically separated fractions and their OC contents, and changed the soil bacterial community composition at different soil depths. SOC was more accelerated in macroaggregate-derived unprotected and microaggregate-derived physically protected fractions at soil depths of 0–20 cm. Physically protected and physico-biochemically protected fractions were the major C protection mechanisms at soil depths of 20–40 cm and 40–60 cm soil depths. Our study also provides evidence that straw amendment significantly increases the bacterial phyla abundance of Proteobacteria and Bacteroidetes at each soil depth. Moreover, straw amendment enhanced the relative abundances of Gemmatimonadetes and Nitrospirae at soil depths of 40–60 cm and have a positive correlation with physically and physico-biochemically protected C pools. These results indicate that straw amendment can regulate C sequestration processes by enhancing SOC physical protection and modulating bacterial community, especially in the deep soil. In addition, straw amendment in subsoil (0–40 cm or 0–60 cm) is more beneficial for C storage and stabilization. [ABSTRACT FROM AUTHOR]

Soil enzymes strongly affect soil organic carbon (SOC) and nitrogen (TN) storage. However, few studies have focused on their relationships in aggregates, especially in sodic-alkali agricultural fields. In the current study, we hypothesized that the impact of soil enzymes on SOC and TN were different within aggregates for their heterogeneous distribution. Soils collected from the surface (0–20 cm) and subsurface (20–40 cm) layers of sodic-alkali agricultural fields in the northeast of China were separated via the dry sieve method into macro-aggregates (>2000 μm), meso-aggregates (250–2000 μm), and micro-aggregates (<250 μm). SOC, TN, microbial biomass carbon (MBC) and nitrogen (MBN), and C- and N-cycling enzymes, namely amylase (AMY), invertase (INV), β-glucosidase (GLU), catalase (CAT), β-N-acetylglucosaminidase (NAG), and urease (URE) in soil aggregates were tested and analyzed. High content of SOC and TN were observed in macro- and meso-aggregates in both layers, with the largest amount detected in meso-aggregates. The highest values of MBC and MBN were observed in meso-aggregates, followed by micro-aggregates for MBC and macro-aggregates for MBN. Soil enzymes were distributed heterogeneously in soil aggregates, where the activities of AMY, INV, and URE in both layers were in the order of meso-aggregates > macro-aggregates > micro-aggregates. The same trend was followed by NAG of surface soils, while in the subsurface soils, NAG activities increased with the increasing aggregate sizes. NAG activities in both layers decreased with decreasing aggregate sizes. The GLU activity rose with the decreasing aggregate sizes in both layers, contrary to CAT. Enzyme activities affect SOC and TN in soil aggregates, for NAG, INV, GLU, and URE are closely related to SOC and TN across aggregate sizes. The test indices mentioned above in the surface layer were higher than those in the subsurface layer. These results indicate that biophysical processes associated with C- and N-cycling enzymes may be vital to the SOC and TN sequestration within soil aggregates in sodic-alkali agricultural fields. [ABSTRACT FROM AUTHOR]

Maize ( Zea mays L.) root morphology exhibits a high degree of phenotypic plasticity to nitrogen (N) deficiency, but the underlying genetic architecture remains to be investigated. Using an advanced BC4F3 population, we investigated the root growth plasticity under two contrasted N levels and identified the quantitative trait loci (QTLs) with QTL-environment (Q × E) interaction effects. Principal components analysis (PCA) on changes of root traits to N deficiency (ΔLN-HN) showed that root length and biomass contributed for 45.8% in the same magnitude and direction on the first PC, while root traits scattered highly on PC2 and PC3. Hierarchical cluster analysis on traits for ΔLN-HN further assigned the BC4F3 lines into six groups, in which the special phenotypic responses to N deficiency was presented. These results revealed the complicated root plasticity of maize in response to N deficiency that can be caused by genotype-environment (G × E) interactions. Furthermore, QTL mapping using a multi-environment analysis identified 35 QTLs for root traits. Nine of these QTLs exhibited significant Q × E interaction effects. Taken together, our findings contribute to understanding the phenotypic and genotypic pattern of root plasticity to N deficiency, which will be useful for developing maize tolerance cultivars to N deficiency. [ABSTRACT FROM AUTHOR]

With 2 figures and 2 tables Abstract Plant height (PH), ear height (EH) and the PH/EH ratio have a great effect on plant lodging in maize ( Zea mays L.) under intensive cropping systems. To understand the genetic mechanisms controlling PH, EH and the PH/EH ratio in response to nitrogen (N) or phosphorus (P) supply, a set of 218 recombinant inbred lines (RILs) was used to evaluate PH, EH, PH/EH ratio and grain yield (GY) and grain yield components under low N, low P and normal N and P supply (NP). A total of 100 QTLs (quantitative trait loci) were detected for the traits investigated. Several QTLs were found to be associated with PH (bin 1.06/1.07) only, both PH and EH (umc1692 at bin 5.01/5.03; umc2313-umc1006 at bin 6.02) and the PH/EH ratio (bnlg1484-bnlg1866 at bin 1.03; umc1164-um1757 at bin 4.01) which was also associated with grain yield. N- or P-inducible QTLs for PH, EH and the PH/EH ratio were found in both years and are sensitive to weather conditions. [ABSTRACT FROM AUTHOR]

Application of organic amendments, such as maize straw and its derived biochar and compost are considered as effective strategies for sustaining soil productivity. However, limited information available on the variation of soil carbon sequestration, soil quality and crop yield responses to these amendments, especially in the highly rich organic matter soils. The field experiment was conducted in a Mollisol since the fall of 2011 to evaluate the impact of chemical fertilizer plus maize residue driven materials amendments on continuous maize yield, soil carbon sequestration and soil quality parameters. The experiment consisted of five treatments: CK (no fertilizer), NPK (chemical fertilizer), NPK+ST (NPK plus maize straw), NPK+CP (NPK plus straw compost), and NPK+BR (NPK plus straw biochar). The organic materials were applied on an equal carbon input basis (3.2 Mg ha−1 per year). Soil samples were collected from 0 to 10 cm and 10–20 cm soil depths in 2017, and analyzed for contents of soil organic carbon (SOC), readily oxidizable organic carbon (ROC), dissolved organic carbon (DOC), microbial biomass carbon (MBC), nutrients and aggregates-size distribution. The NPK+BR and NPK+CP significantly increased SOC stock at the topsoil (0–20 cm) relative to CK and NPK treatments. The amount of soil carbon sequestration (relative to SOC baseline in 2011) associated with different treatments was as follow: NPK+BR (13.1 Mg ha−1) > NPK+CP (5.60 Mg ha−1) > NPK+ST (2.90 Mg ha−1) > NPK (0.50 Mg ha−1) > CK (−1.90 Mg ha−1). However, the greatest concentrations of ROC, DOC and MBC at the topsoil were observed in NPK+CP treatment, with greater supply of available nutrients than other treatments. The NPK+BR reduced the fraction percentage of microaggregates significantly (<0.25 mm), and in greater mean weight diameter and geometrical mean diameter than NPK+ST and NPK+CP treatments. The NPK plus straw or compost increased grain yield during the first year of application significantly as compared to NPK treatment, but no apparent change in yield observed in the first 3 years under biochar treatment. There is no considerable difference was found over six-year average of grain yield between the three organic treatments. Our results suggest that over six years the maize-derived organic materials use have led to significant improvement in soil quality and maize yield, where straw derived biochar was more effective for soil carbon sequestration in Mollisol of Northeast China. • Biochar application sequestrated 4.5 times of C of that under straw treatment. • Compost input resulted in greater labile organic C pool and available nutrients. • Biochar application contributed greatest aggregate stability. • Biochar treatment had no significant change in maize yield in the first 3 years. • Maize yield positively correlated with labile organic C content. [ABSTRACT FROM AUTHOR]

Selection of high-yielding and nitrogen (N)-efficient cultivars under realistic agronomic conditions can benefit farmers in their production practices. In addition, phenotyping the root characteristics of high-yielding and N-efficient cultivars under N stress conditions is important to guide maize breeding for abiotic stress tolerance. The objective of this study was to (1) evaluate the potential increase in yield and reduction in required fertilizer input in maize cultivars, and (2) examine the root characteristics of high-yielding and N-efficient cultivars. Under the high-N (240 kg N ha−1) and the low-N (no N supplied) conditions, grain yield and nodal root traits of 10–67 dominant maize cultivars grown in North and Northeast China were investigated in field trials at six environments. The low-N conditions reduced grain yield by 24%, crown root number (CRN, shoot-borne roots formed at consecutive underground shoot nodes) by 8%, brace root number (BRN, shoot-borne roots formed at consecutive aboveground shoot nodes) by 44%, and brace root whorl number (BRWN, whorls of roots that arise from aboveground shoot nodes) by 50%. The grain yield showed a significant positive correlation with CRN and crown root length (CRL) under both N treatments. The cultivars were classified into four types based on the average grain yield under high-N and low-N treatments: EE, efficient under both high-N and low-N treatments; HNE, N efficient only under high-N treatment; LNE, N efficient only under low-N treatment; and NN, inefficient under both high-N and low-N treatments. The cultivars with EE and HNE types had 5%–10% greater grain yield and reduced N fertilizer input requirements by 11%–50%. Under the low-N conditions, the cultivars classified as EE and HNE types showed 4%–20% higher CRN and 14%–22% longer CRL compared with NN types. Cultivation of the EE and HNE maize cultivars in Northeast and North China may reduce N input requirements without compromising yield. Compared with NN type cultivars, the EE and HNE cultivars had greater CRN and CRL, which may be contributed to improving N acquisition and grain yield formation in response to N stress. [ABSTRACT FROM AUTHOR]