Subsoiling is an important management practice for improving maize yield, especially for maize planted at high plant density. However, the affected physiological processes have yet to be specifically identified. In this study, field experiments with two soil tillage (CK: no-tillage, SS: subsoiling) and three planting densities (low: 45000 plants ha⁻¹, medium: 67500plants ha⁻¹, and high: 90000 plants ha⁻¹) were conducted from 2010 to 2012 at Xinxiang, Henan province. Yield, canopy function, and root system were investigated to determine the associated physiological processes for improving maize production affected by soil tillage and plant density. Subsoiling significantly increased the grain yield of the low-, medium-, and high-planting densities by 6.21%, 8.92%, and 10.09%, respectively. Yield increase in the SS plots was mainly attributed to greater post-anthesis DMA and improved grain filling compared to CK plots. Greater green leaf area, leaf net photosynthetic rate, F_V/F_m and ΦPSII in the SS plots were mainly contributed to enhanced dry matter production post-anthesis. This is mainly because subsoiling increased density of root dry weight in deep soil and root bleeding sap amount due to decreased the bulk density of the 0–30 cm soil profile layer. Density of root dry weight at 10–50 cm depth with SS increased by 40.68%, 32.17%, and 20.14% at low, medium, and high planting densities compared to CK, respectively, while the root bleeding sap amount increased by 17.41%, 15.82%, and 20.91%. These results indicate that subsoiling could change the root distribution and improve soil layer environment for root growth, thus maintaining a higher canopy photosynthetic capacity post-anthesis and in turn promoting DMA and yield, particularly at higher planting densities.

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.

Both compact planting and selecting superior maize (Zea mays L.) hybrids can greatly optimize the source–sink relationship and enhance maize productivity. However, the underlying physiological mechanism for regulating carbon (C) assimilate transport and influencing grain yield between maize cultivars has remained unclear under contrasting plant densities. A two-year field experiment was conducted to investigate grain yield, vascular bundle character, grain filling, C allocation in grains and other tissues, and hormone level and enzyme activity in grains under 60,000 (ND) and 90,000 plants ha⁻¹ (HD) densities using Xianyu 335 (XY335) and Zhengdan958 (ZD958) hybrids. Compared to the ZD958, XY335 increased grain yield, kernel number per plant (KNP), and sink capacity by 11.4%, 15.7%, and 7.4%, respectively. Moreover, XY335 performed higher net photosynthetic rate and sucrose synthase activities in grains than those in ZD958, and higher levels of sucrose phosphate synthase and soluble acid invertase activity were mainly exhibited in the middle of the grain filling stage, which contributed to increasing the proportion of grain in total dry matter, grain C content and leaf C transport efficiency by 4.3%, 12.2%, and 52.9%, respectively, under HD conditions. Additionally, a greater area and number of small vascular bundle in ear of XY335 resulted in 21.3% higher matter transport efficiency and 4.8% higher maximum grain filling rate than ZD958 under HD conditions. In addition, grains of XY335 exhibited generally higher levels of indole acetic acid (IAA) and abscisic acid (ABA), as well as ABA/GA₃ ratio after maize pollination relative to those from ZD958, conducive to regulating C translocation from leaves to grains. Overall, our study illustrates that stronger source activity, sink characteristics, and matter transport channels for maize hybrids are significant for C assimilate transport to grain for achieving high grain yield under higher plant density.

Elucidating the mechanisms underlying the relationships between root growth and water use efficiency is important for achieving full yield potential. We conducted a field experiment with maize under high planting density (105,000 plants ha⁻¹) in 2013 and 2014. Four treatments were implemented: traditional cultivation, root optimization cultivation, canopy optimization cultivation, and shoot–root optimization cultivation. Compared to the treatments involving rotary tillage, subsoil tillage significantly improved the soil structure and promoted soil water storage. Moreover, the distribution of roots was significantly deeper under shoot–root optimization cultivation than traditional cultivation treatment. Shoot dry matter and leaf area were slightly higher under the plant growth-regulator treatments than that under the other treatments. Thus, relative to the shoot–root optimization cultivation treatment, the root optimization cultivation and canopy optimization cultivation treatments reduced the shoot–root area ratio by 8% and 4%, respectively, and these reductions were significantly lower than the reduction under the traditional cultivation treatment (16%). Rainfall storage can be enhanced by improving tillage practices, promoting root growth (particularly at depths >20 cm), promoting access to water, and regulating plant growth by the foliar spraying of ECK (ethylene-chlormequat-potassium). This approach has the potential to achieve highly efficient resource utilization without additional inputs, thereby increasing yield.