Conventional fertilization with most N applied before or during early maize (Zea maysL.) growth stages can negatively affect production if soil N is insufficient after silking. Here, drip irrigation with a split application of N (drip fertigation) was evaluated to determine whether the effect on yield and N use efficiency (NUE) differs with cropping practice. Compared with conventional fertilization, drip fertigation increased yield by 13 and 14% at a low planting density under a low N rate (L) and by 15% at a high planting density under a high N rate (H) in 2012 and 2013, respectively. Yield increases under drip fertigation were attributed to 18 and 17% increases in postsilking dry matter (DM) accumulation under L, and 12 and 10% increases in presilking DM accumulation, and 17 and 16% increases in postsilking DM accumulation under H in 2012 and 2013, respectively. Increased postsilking N accumulation under drip fertigation, promoted by greater root length and soil mineral N after silking, maintained increased leaf area index (LAI) and DM accumulation rate to improve postsilking DM accumulation under L. Greater N accumulation under drip fertigation from the 12‐leaf stage to silking and after silking promoted greater LAI and DM accumulation rate to increase pre‐ and postsilking DM accumulation under H. Because of greater grain yield and N uptake and less water consumption, drip irrigation improved NUE and irrigation water use efficiency. Drip fertigation can effectively improving maize grain yield and NUE resulting from improved DM accumulation with increased early‐season N uptake.

Exploring suitable maize straw-return measures is essential for the new double-cropping system of maize (Zea mays L.)–rice (Oryza sativa L.) rotation in the middle reaches of Yangtze River in China, which can increase crop yield by improving soil quality. In this study, four straw-return measures were evaluated by investigating the soil bulk density (BD), organic matter (OM), microbial community, and nutrients from 2016 to 2018. The four straw-return treatments were as follows: (1) no straw-return (CK), (2) only rice straw incorporated into the field (M₀R_i), (3) both maize and rice straw incorporated to field (M_iR_i), and (4) maize straw mulched and rice straw incorporated into the field (M_mR_i). Compared to CK, two-season crop straw-return treatments changed soil microbial community composition, and increased soil total organic carbon (TOC) and dissolved organic carbon (DOC), microbial biomass carbon (MBC), mineralized nitrogen (N_min), available phosphorus (P) and exchangeable potassium (K) in the 0–20 cm soil layer by 3.6%, 63.4%, 38.8%, 12.4%, 39.7%, and 21.6%, respectively, averaged across M_mR_i and M_iR_i treatments. In addition, M_mR_i and M_iR_i increased annual yield by 9.1% and 15.2% in 2017 and 11.7% and 12.9% compared to CK in 2018, respectively. M_mR_i exhibited superiority in the soil microbial community, enzyme activities, DOC, MBC, N_min, available P, and exchangeable K in contrast to M_iR_i. We concluded that M_mR_i is the best measure to implement for straw-return in maize–rice rotation systems.

High temperature during May to July is a major hurdle for production of sorghum as fodder in Pakistan, ultimately resulting in a deficit with respect to the demand of meat and milk for increasing population. A field study was conducted to investigate the impact of exogenous application of natural plant growth-promoting substances on forage yield and quality of sorghum. Seed priming and foliar application (alone or in combination) with 1% sorghum water extract (SWE), 3% moringa leaf extract (MLE) and water were applied. Two foliar applications, the first at one month after sowing and the second at 45 days after sowing were carried out. Untreated seeds were used as control. The results indicated that priming and foliar spray performed best in combination as compared to priming or foliar application alone. All MLE applications (priming plus foliar application, priming alone, foliar spray alone) enhanced growth parameters and chlorophyll contents, which ultimately improved forage yield and total dry matter production of sorghum plants. An increase in crude protein and total ash and decrease in crude fiber was also recorded in plants treated with MLE. The results of this study revealed that exogenous application of MLE at 3% concentration (priming plus foliar application, priming alone, foliar spray alone) significantly enhanced the yield through improvement in sorghum growth.

Increasing planting density is the main method and key management to enhance the grain yield. Preventing lodging and premature senescence in high planting density, and screening and enhancing the density-tolerance of maize variety is the main goal of agronomy. Differential response of maize hybrids to high plant density greatly affect the dry matter accumulation and its allocation to maize kernel, depending upon various traits responsible for crowding stress tolerance, of which ear characteristics are pivotal. Density resistance as a quality appraisal of certain variety permits the construction of a simple and accurate method to determine this value, useful for plant breeding. Therefore, we created a new quantitative method, which tested several maize varieties planted populary in China (e.g. Zhengdan 958, Xianyu 335, and Denghai 661) to quantify their response to crowding stress through model. We established 13 planting densities (ranging 1.67–16.67 plants m⁻²) by adopting fixed line spacing (80 × 40 cm) and then gradually increasing row spacing from 1 m to increasing planting density. A conventional standard plot was also established for verification and evaluation of the plant morphologic characteristics, ear traits, and the yield of maize at various standard densities during 5-year study period. By studying the density–yield relationship, a quantitative model was constructed to identify the density resistance of maize. Grain yield of maize varieties under varying planting densities were simulated, and models of population yield and yield per plant that fitted the data well with high biological significance were produced. From the models, the optimal density of the popular main maize varieties planted in China and the morphological characteristics of each variety at that density were identified. The density-resistance of each variety was referred to as the ear-sensitivity classification. With the highest yield at the optimal density, the plant height of each variety reached 98% to that of tallest plant. The ear/plant ratio was about 0.45, and the ratio between the stem diameter and the largest stem diameter was 0.65–0.80. During the harvest period, the ratio between average single-plant yield and the highest single-plant yield was 0.40–0.50. By gradually increasing planting density, the density resistance of the maize and the changes in yield with density were quantified. Present study provides a convenient tool for the effective selection of varieties by plant breeders through this method and model will help to rapidly identify the density resistance for a new variety and accurate confirmation to optimal planting density, it could be optimized to enable practical production at reasonable planting densities.

Soil compaction due to field trafficking involves a complex interplay of machine-soil properties. In contrast to previous studies simulating worst field scenarios, this two-year field experiment investigated the effects of traffic-induced compaction involving moderate machine operational specifications (axle load, 3.16 Mg; mean ground contact pressure, 77.5 kPa) and lower field moisture contents (< field capacity) at the time of trafficking on soil physical properties, spatial root distribution, and corresponding maize growth and grain yield in sandy loam soil. Two compaction levels, i.e. two (C2) and six (C6) vehicle passes, were compared with a control (C0). Two maize (Zea mays L.) cultivars, i.e. ZD-958 and XY-335, were used. Results showed topsoil (< 30 cm) compaction with increases in bulk density (BD) and penetration resistance (PR) up to 16.42% and 127.76%, respectively, in the 10-20 cm soil layer in 2017. Field trafficking resulted in a shallower and stronger hardpan. An increased number of traffic passes (C6) aggravated the effects, and the carryover effect was found. Higher BD and PR impaired root proliferation in deeper layers of topsoil (10-30 cm) and promoted shallow horizontal root distribution. However, XY-335, compared with ZD-958, showed deeper root distribution under compaction. Compaction-induced reductions in root biomass and length densities were respectively up to 41% and 36% in 10-20 cm and 58% and 42% in the 20-30 cm soil layer. Consequent yield penalties (7.6%-15.5%) underscore the detriments of compaction, even only in topsoil. In crux, despite their low magnitude, the negative impacts of field trafficking under moderate machine-field conditions after just two years of annual trafficking foreground the challenge of soil compaction.