Application of slow-release fertilizer (SF) is a nutrient-management measure aimed at improving maize nutrient use and yield and saving labor cost. One-time application of SF at sowing usually results in nutrient deficiency during the post-silking stage, owing to the long growth period of spring maize. This study was conducted to investigate the effects on spring maize of SF application stage (zero, three-, and six-leaf stages, designated as SF0, SF3, and SF6, respectively) on grain yield, total soil rhizosphere nitrogen (N) content, and root activity, in comparison with the conventional fertilization mode (CF, application of compound fertilizer at sowing time, and topdressing urea at six-leaf and tasseling stages) at the same fertilization level as the control. Compared with no fertilization (F0) and CF, SF increased grain number and weight. The maize cultivars Suyu 30 (SY30) and Jiangyu 877 (JY877) produced the highest grain yield and net return under SF6 treatment over the three years. SF6 increased enzymatic activities including oxidoreductase, hydrolase, transferase, and lyase in rhizosphere soil at silking (R1) and milking stages (R3). SF6 increased the total N contents of rhizosphere soil by 7.1% at R1 and 9.2% R3 stages compared with SF0. The activities of antioxidant enzymes in roots were increased under SF6 treatments at R1 and R3. The mean root activities of SF0, SF3, and SF6 increased by 7.1%, 12.8%, and 20.5% compared with CF at R1 and by 8.8%, 13.0%, and 23.5% at R3. Delaying the application time of SF could increase grain yield by increasing total N content of rhizosphere soil, delaying root senescence, and increasing root activity at the late reproductive stage. Applying SF at the six-leaf stage is recommended as an effective fertilization strategy for the sustainable production of spring maize in southern China.

High temperature (HT) during grain filling is one of the most important environmental factors limiting maize yield and grain quality. Nitrogen (N) fertilizer is essential for maintaining normal plant growth and defense against environmental stresses. The effects of three N rates and two temperature regimes on the grain yield and quality of fresh waxy maize were studied using the hybrids Suyunuo 5 (SYN5) and Yunuo 7 (YN7) as materials. N application rates were 1.5, 4.5, and 7.5 g plant⁻¹, representing low, moderate, and high N levels (LN, MN, and HN, respectively). Mean day/night temperatures during the grain filling of spring- and summer-sown plants were 27.6/21.0 ℃ and 28.6/20.0 ℃ for ambient temperature (AT) and 35/21.0 ℃ and 35/20.0 ℃ for HT, respectively. On average, HT reduced kernel number, weight, yield, and moisture content by 29.8%, 17.9%, 38.7%, and 3.3%, respectively. Kernel number, weight, yield, moisture, and starch contents were highest under MN among the three N rates under both temperature regimes. HT reduced grain starch content at all N levels. HT increased grain protein content, which gradually increased with N rate. Mean starch granule size under MN was larger (10.9 μm) than that under LN and HN (both 10.4 μm) at AT. However, the mean size of starch granules was higher under LN (11.7 μm) and lower under MN (11.2 μm) at HT. Iodine binding capacity (IBC) was lowest under MN and highest under HN among the three N levels under both temperature regimes. In general, IBC at all N rates was increased by HT. Peak viscosity (PV) was gradually reduced with increasing N rate at AT. In comparison with LN, PV was increased by MN and decreased by HN at HT. Retrogradation percentage gradually increased with N rate at AT, but was lowest under MN among the three N rates at HT. LN + AT and MN + HT produced grain with high pasting viscosity and low retrogradation tendency. MN application could alleviate the negative effects of HT on the grain yield and quality of fresh waxy maize.

Understanding the effects of shading after pollination on kernel filling and physicochemical properties of waxy maize could improve kernel quality. Experiments were conducted to investigate the effects of shading (30% and 50% light deprivation, taken plants without shading as control) on kernel weight, size, and physicochemical properties during kernel development in 2013 and 2014 using two waxy maize varieties (Suyunuo 5 and Yunuo 7). Results indicated that shading reduced kernel filling rate and decreased kernel size and weight, and the influence was large under severe light deprivation conditions. The large reduction in kernel weight and volume of Suyunuo 5 in response to shading indicated that it was more sensitive to shading than Yunuo 7. Starch content was reduced and protein content was increased by shading, especially under severe shading after 22 days after pollination (DAP). The iodine binding capacity of Yunuo 7 was not affected by shading at fresh and maturity stages but was gradually decreased by shading at the newly formed stage, while the values for Suyunuo 5 were decreased at 7 and 40 DAP only by moderate shading and were similar among three treatments at 22 DAP. Severe shading decreased crystallinity at all kernel development stages, whereas moderate shading decreased crystallinity at fresh stage and increased it at mature stage for Suyunuo 5. Crystallinity in Yunuo 7 was increased by shading at 7 DAP and decreased by shading at 40 DAP, whereas the value at 22 DAP was increased by moderate shading and reduced by severe shading, respectively. The average gelatinization temperatures at different stages were decreased by shading and showed no difference between two shading levels. The retrogradation percentage at 7 DAP for both varieties was increased by shading. The value at 22 DAP was increased by moderate shading for Suyunuo 5 and decreased by severe shading for Yunuo 7, respectively. The retrogradation percentage at 40 DAP was decreased by shading treatments for Suyunuo 5 and reduced only by moderate shading for Yunuo 7. Peak viscosity was decreased by shading at fresh stage for Yunuo 7 and at maturity for Suyunuo 5. In conclusion, shading after pollination inhibited kernel filling of waxy maize and reduced paste viscosity quality, but kernel retrograde quality, crystallinity and starch iodine binding capacity in response to shading were dependent on stage and variety.