Optimal application rates of controlled release urea for high yield and high nitrogen use efficiency of summer maize under different soil water conditions

Objectives Both water and nitrogen managements are very important to increase maize yield. In this paper, the coordinated appropriate application amount of controlled release urea was studied under different soil water conditions, aiming for the high maize yield and nitrogen use efficiency.

Methods The experiment was conducted in the rainout shelter, located in the Experimental Farm of Shandong Agricultural University, using a maize cultivar ‘Zhengdan 958’ (a popular summer maize hybrid) as tested material. Soil columns, 1 m high and 30 cm in inner diameter, were used for the experiment. The main treatment was soil water capacity (SWC), three levels of SWC were setup: 35% ± 5% (severe stress, W1), 55% ± 5% (mild stress, W2), and 75% ± 5% (adequate, W3). Sub-treatment was controlled release urea fertilizer amount, N levels of 0, 105, 210 and 315 kg/hm² were setup, recorded as N0, N1, N2 and N3, respectively. The maize yield, dry matter and nitrogen accumulation were investigated, and the nitrogen use efficiencies were calculated.

Results Under adequate and mild water stress condition, the yields showed an increasing trend with the amounts of N application increased. Under the same amount of N application, the yields were also improved with the increase of soil moisture. Under severe water stress, the dry matter and nitrogen accumulation amounts in maize plants were generally low, especially at post-silking stage. The yields of N1, N2 and N3 were similar in 2014, while the yield of N3 was significantly higher than those of N1 and N2 in 2015. Nitrogen use efficiencies for grain production (NGPEs) and nitrogen use efficiencies (NUEs) were decreased with the increase of N. Under the mild water stress, the dry matter and N accumulation showed increasing trends with the increase of N application, and the rates of post-silking were relatively higher, and the yield and N accumulation of W2N3 were similar to W3N3. In 2014, there was no significant difference in NGPE and NUE between N3 and N2, the NUE of N3 was significantly higher than that in N2 in 2015. Under adequate water condition, the yields of N3 and N2 were similar, and both were significantly higher than that of N1; at the post-silking stage, the agronomic efficiency of nitrogen (ANUE), NUE and physiological nitrogen use efficiency (PNUE) of N2 were significantly higher than those of N3.

Conclusions Comprehensively, relatively high input of nitrogen fertilizer could alleviate the yield reduction caused by mild water stress, and appropriated nitrogen input could achieve high yield and efficient utilization of nitrogen under adequate water supply. Under the experimental condition, the suitable rate of controlled release urea is N 210 kg/hm² for the soil moisture content of 75% ± 5% of field capacity, and 315 kg/hm² for the soil moisture content of 55% ± 5% of field capacity in summer maize production.