Optimal planting density and proper fertilization method are important factors to improve maize yield and nutrient utilization.  A two-year (2016 and 2017) field experiment was conducted with three plant densities (6.0, 7.5 and 9.0 plants m⁻²) and three fertilization modes (no fertilizer, 0F; one-off application of slow-released fertilizer, SF; twice application of conventional fertilizer, CF).  Results indicated that the grain yields and N, P and K use efficiencies under SF with the optimal planting density (7.5 plants m⁻²) were the highest among all the treatments in 2016 and 2017.  Compared with CF, SF could increase post-silking dry matter accumulation and promote N, P and K uptake at pre- and post-silking stages; this treatment increased grain N, P and K concentrations and resulted in high N, P and K use efficiencies.  Nutrient (N, P and K) absorption efficiencies and partial productivity, and nutrient (N and P) recovery efficiency in SF treatment were significantly higher than those in CF treatments under the planting density of 7.5 plants m⁻².  Under both SF and CF conditions, the grain yield, total N accumulation and nutrient use efficiencies initially increased, peaked at planting density of 7.5 plants m⁻², and then decreased with increasing plant density.  Based on the yield and nutrient use efficiency in two years, plant density of 7.5 plants m⁻² with SF can improve both the grain yield and N, P and K use efficiency of spring maize in Jiangsu Province, China.

 

Waxy maize is widely cultivated under rainfed conditions and frequently suffers water shortage during the late growth stage.  In this study, a pot trial was conducted to examine the effects of post-silking drought on leaf photosynthesis and senescence and its influence on grain yield.  Two waxy maize hybrids, Suyunuo 5 (SYN5) and Yunuo 7 (YN7), were grown under the control and drought (soil moisture content was 70–80% and 50–60%, respectively) conditions after silking in 2016 and 2017.  The decrease in yield was 11.1 and 15.4% for YN7 and SYN5, respectively, owing to the decreased grain weight and number.  Post-silking dry matter accumulation was reduced by 27.2% in YN7 and 26.3% in SYN5.  The contribution rate of pre-silking photoassimilates transferred to grain yield was increased by 15.6% in YN7 and 10.2% in SYN5, respectively.  Post-silking drought increased the malondialdehyde content, but decreased the contents of water, soluble protein, chlorophyll, and carotenoid in the leaves.  The weakened activities of enzymes involved in photosynthesis (ribulose-1,5-bisphosphate carboxylase and phosphoenolpyruvate carboxylase) and antioxidant system (catalase, superoxide dismutase and peroxidase) reduced the photosynthetic rate (P_n) and accelerated leaf senescence.  The correlation results indicated that reduced P_n and catalase activity and increased malondialdehyde content under drought conditions induced the decrease of post-silking photoassimilates deposition, ultimately resulted in the grain yield loss.

Post-silking high temperature is one of the abiotic factors that affects waxy maize (Zea mays L. sinensis Kulesh) growth in southern China.  We conducted a pot trial in 2016–2017 to study the effects of post-silking daytime heat stress (35°C) on the activities of enzymes involved in leaf carbon and nitrogen metabolisms and leaf reactive oxygen species (ROS) and water contents.  This study could improve our understanding on dry matter accumulation and translocation and grain yield production.  Results indicated that decreased grain number and weight under heat stress led to yield loss, which decreased by 20.8 and 20.0% in 2016 and 2017, respectively.  High temperature reduced post-silking dry matter accumulation (16.1 and 29.5% in 2016 and 2017, respectively) and promoted translocation of pre-silking photoassimilates stored in vegetative organs, especially in leaf.  The lower leaf water content and chlorophyll SPAD value, and higher ROS (H₂O₂ and O₂^-·) content under heat stress conditions indicated accelerated senescent rate.  The weak activities of phosphoenolpyruvate carboxylase (PEPCase), Ribulose-1,5-bisphosphate carboxylase (RuBPCase), nitrate reductase (NR), and glutamine synthase (GS) indicated that leaf carbon and nitrogen metabolisms were suppressed when the plants suffered from a high temperature during grain filling.  Correlation analysis results indicated that the reduced grain yield was mainly caused by the decreased leaf water content, weakened NR activity, and increased H₂O₂ content.  The increased accumulation of grain weight and post-silking dry matter and the reduced translocation amount in leaf was mainly due to the increased chlorophyll SPAD value and NR activity.  Reduced PEPCase and RuBPCase activities did not affect dry matter accumulation and translocation and grain yield.  In conclusion, post-silking heat stress down-regulated the leaf NR and GS activities, increased the leaf water loss rate, increased ROS generation, and induced pre-silking carbohydrate translocation.  However, it reduced the post-silking direct photoassimilate deposition, ultimately, leading to grain yield loss.