Abstract
To explore the response of summer maize leaf senescence, photosynthetic characteristics, and yield to the depth of one-time base application of controlled-release urea, which provides a theoretical basis for the light and simplified production of summer maize. Seven treatments were set up with Zhengdan 958 as the material under field conditions, including no nitrogen fertilizer (CK), surface spreading (DP0), furrow application depth of 5 cm (DP5), 10 cm (DP10), 15 cm (DP15), 20 cm (DP20), 25 cm (DP25). The results showed that under the same nitrogen application rate, there are significant differences in the effects of summer maize leaf senescence and photosynthetic characteristics with the increase of fertilization depth, and DP10 and DP15 have the best effects. The LAI of DP10 and DP15 increased by 5.1% and 5.5% compared to DP0 at tasseling stage, and chlorophyll content increased by 6.8% and 7.3% in 10 days after tasseling. Compared with DP0, superoxide dismutase (SOD) increased by 13.1% and 10.5%, the content of soluble protein increased significantly, while the content of malondialdehyde (MDA) decreased by 9.8% and 10.8%, respectively. In addition, Pn and Gs of the ear-leaf significantly increased by 13.9%, 16.5%, and 26.1% and 31.9% at tasseling stage, respectively, over DP0, while Ci decreased by 22.3% and 26.4%, respectively; meanwhile, the photochemical quenching (qP) and quantum yield (ΦPSII) of the reaction center of photosystem II (PSII) of the ear-leaf were significantly improved, the non-photochemical quenching (NPQ) was significantly reduced. The yield of DP10 and DP15 heightened significantly; two-year average value increased by 5.7% and 6.0% compared with DP0; the kernels per spike and 1000-kernels weight increased by 4.8%, 5.2%, and 4.1%, 5.2%, respectively. Comprehensive analysis of LAI, chlorophyll content, various protective enzyme activities and MDA, soluble protein content showed that 10–15 cm is the appropriate fertilization depth when the nitrogen application rate of controlled-release urea is 225 kg N per hectare. In consequence, optimizing fertilization depth of controlled-release urea as a simplified fertilization mode could improve the nitrogen utilization efficiency and obtain higher yield in summer maize, which provides technical support for large-scale application of controlled-release urea.
Highlights
Nitrogen is one of the key nutrients that limit crop growth and yield potential, and the rational application of nitrogen fertilizer is essential for achieving high crop yields [1]
In 2013 and 2014, the one-time base application of controlled-release urea significantly increased the yield by 14% on average compared to CK (p < 0.05) (Table 1)
Compared with the two-year average value of DP0, the kernels per spike in the treatments of DP10 and DP15 increased by 4.8% and 5.2%, respectively, and the 1000-kernels weight increased by 4.1% and 5.2% (p < 0.05); the kernels per spike and 1000kernels weight of DP25 decreased by 1.5% and 0.7% compared with DP0
Summary
Nitrogen is one of the key nutrients that limit crop growth and yield potential, and the rational application of nitrogen fertilizer is essential for achieving high crop yields [1]. Compared with common urea, controlled-release urea saves more time, labor, and cost. It can reduce soil ammonia volatilization and greenhouse gas emissions, reducing environmental pollution [7,8]. Studies have shown that under the same nitrogen application rate, one-time basal application of controlled-release urea can significantly improve the nitrogen use efficiency of maize, reduce nitrogen loss; controlled-release urea showed stable and increased yield compared to the traditional split fertilization of common urea [9–11]. The nutrient release cycle is longer and the release time is relatively controllable, thereby increasing the nitrogen utilization rate [13], but to improve its fertilizer utilization rate, it needs to be combined with fertilization technology. Different fertilization depths have great differences in the conversion of soil available nutrients and the uptake of nutrients by plants [16]
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