Since the initiation of reform and opening up policy in the late 1970s, agriculture has developed rapidly in China, producing substantial economic benefits while being accompanied by grievous pollution and food safety issues mainly due to the immoderate use of fertilizer and pesticide [1, 2]. More specifically, the amount of fertilizer application to land use in 1978 was 8.84 million tons, which has grown to 60.23 million tons in 2015, with approximately five times of net increase [3]. The pesticides and chemical fertilizers not absorbed entering the surrounding environment generate soil

The effects of polyaspartic acid and different controlled-release fertilizers with urea on dry matter accumulation and distribution, nitrogen absorption and accumulation, and the activities of enzymes involved nitrogen metabolism and yield of corn were studied by using xianyu (XY688), a maize nitrogen efficient cultivar, and Jifeng NO.2 (JF2), a maize nitrogen-inefficient cultivar, as experimental materials and through random blocks experimental design in 2019. For XY688, polyaspartic acid chelated nitrogen fertilizer (PASPN) had the highest yield, which was 21.34% higher than N0 treatment. For JF2, it also had the highest yield under PASPN combined urea treatment, which was 23.44% higher than N0 (no nitrogen fertilizer), and JF2 had a 9.7% lower yield under XY688 treatment. For XY688, PASPN treatment had the largest nitrogen uptake in grain, up to 3.14 kg/hm 2 , and PASPN treatment increased 17.4% compared with N0. For JF2, grain nitrogen uptake was also the highest under PASPN treatment, which was significantly different from other treatments. Nitrogen uptake was 3.16 kg/hm 2 , which increased 37.4% compared with N0. Compared with JF2, XY688 showed higher nitrogen uptake efficiency, nitrogen utilization efficiency, and partial nitrogen productivity. For XY688, the highest nitrogen absorption efficiency was SU3 (slow-release urea and ordinary urea) treatment (0.36 kg/kg). The partial nitrogen productivity and harvest index of PASPN treatment were the highest and significantly different from other treatments. The partial nitrogen productivity of PASPN treatment was 57.02 kg/kg. These results can provide help for the further researches of the rational utilization and absorption of nitrogen fertilizer.

Controlled-release urea (CRU-N) fertilizer application is a solution to improve the utilization rate of nitrogen (N), reduce economic costs and improve crop yields. It is significant to study the effects of release CRU-N reduction and the combined application of conventional urea on soil N control and the large-scale maize planting system. In this study, the effects of controlled-release nitrogen fertilizer reduction and postponement on soil nitrogen components, enzyme activities, and yields were investigated. Seven treatments were set up in this study, including no N fertilizer (CK), 100% conventional urea (U), 100% controlled-release urea (S), 30% controlled-release urea (SU 3/7 ), 50% controlled-release urea (SU 5/5 ), 70% controlled-release urea (SU 7/3 ) and Sodium Salt of Polyaspartic Acid (PASP)-N. The results showed that mixed CRU-N and urea increased yields and net benefits compared with conventional urea at the same application rate of N, and reduced N loss. The application of CRU-N at 70% for maize represented the best overall effects. Compared with U treatment, soil ammonium nitrogen (NH 4 -N), soil nitrate-nitrogen (NO 3 -N), and microbial biomass nitrogen (SMB-N) of CRU-N at 70% (SU 7/3 ) increased by 35.00%, 15.53%, and 25.04%. However, soil nitrate reductase (S-NR) and urease (S-UA) were the best in SU 5/5 and significantly higher than other treatments. The applications of CRU-N would effectively increase soil N; CRU-N in 50% proportion can promote the maize root growth and improve the efficient utilization of N by soil microorganisms. Like the yields (9186.61 kg/hm 2 ), expertly in the proportion of 70% CRU-N (SU 7/3 ) plays a vital role in a wheat-maize rotation system, which can potentially be used to improve the yields, nitrogen use efficiency, and net benefit with low N losses. In conclusion, using CRU-N fertilize effectively improves soil nitrogen, and various ratios of CRU-N can ensure the continuous release the nutrients during the growing period. And among the different proportions of CRU-N, it is optimal in SU 7/3 .

Understanding the physiological processes associated with leaf photosynthetic characteristics and nitrogen (N) assimilation during grain-filling stage are helpful for enhancing nitrogen utilization efficiency (NUtE) of maize. In this study, the leaf photosynthetic and N assimilation parameters in maize, including Zhengdan 958 (ZD958), a low-N tolerance cultivar and Huanong 138 (HN138), a low-N sensitive cultivar under different N rates were examined. Results showed that ZD958 displayed significant increases on grain yield and NUtE than that in HN138. Analyses on the leaf photosynthetic and N assimilation-associated processes indicated that ZD958 had higher leaf N remobilization (Rem N), net photosynthetic rate (Pn) and photosynthetic N use efficiency (PNUE) with respect to those of HN138 during grain-filling stage. In addition, ZD958 was also shown to be higher activities of leaf nitrate reductase (NR), glutamine synthetase (GS), nitrate reductase (GDH) and glutamine synthetase (GAGOT) than those of HN138. The leaf PNUE was significantly positively correlated with NR, GS, GDH, GOGAT suggesting that leaf PNUE and NR, GS, GDH, GOGAT jointly determined the N remobilization efficiency and the leaf N remobilization during post-silking. These results suggested that ZD958 possessed improved PNUE, NR and GS activities in leaves during grain-filling stage that contributes improve grain weights and yield formation capacities upon under low-N conditions.

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