Effects of Nitrogen Application Rates on Soil Nitrogen Content, Nutrient Uptake and Utilization of Cotton in Low Fertility Fields
- Qin Yukun, Li Pengcheng, Zheng Cangsong, Sun Miao, Liu Shuai, Dong Helin , Xu Wenxiu
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[Objective] The effects of nitrogen (N) application rates on cotton yield, nutrient uptake and utilization rate, soil available N and urease activity were investigated in low-fertility cotton fields of the Yellow River Basin. [Methods] Six N application rate treatments, 0, 90, 180, 270, 360 and 450 kg·hm－2 (N0, N90, N180, N270, N360 and N450, respectively), were established using cotton CCRI 79 in the field during 2016 and 2017. The cotton yield, dry matter quality, N, phosphorus and potassium accumulation levels, N use efficiency, 0–100-cm soil layer ammonium and nitrate N contents, 0–100-cm soil layer urease activity and other indicators were investigated. [Results] (1) Compared with N0, the N treatments significantly increased seed cotton yield, except the N90 treatment in 2016. Two years of N360 treatments significantly increased the number of bolls per cotton plant, while no significant differences were found among the seed cotton yields with other N treatments. The N application rates had no significant effect on lint percentage. (2) Compared with N0, N applications significantly increased the cotton dry matter accumulation. The accumulation of N, phosphorus and potassium in cotton increased along with the N application rates in the 90–360 kg·hm－2 range. The levels of N, phosphorus and potassium in N450-treated cotton decreased compared with N360-treated cotton. As the N application rates increased, the N agronomic efficiency and N fertilizer partial productivity of cotton decreased. When the N application rates exceeded 360 kg·hm－2, the N physiological efficiency began to decrease, but there were no significant differences among treatments. (3) The nitrate N contents in the 41–80-cm soil layers of the treatments, except for N90, significantly increased compared with N0. The nitrate N contents in the 41–80-cm soil layers of N270-, N360- and N450-treated cotton were significantly increased compared with those of N0, N90 and N180. However, N applications had no significant effects on the ammonium N contents in the soil. (4) The soil urease activities increased when N application rates were less than 360 kg·hm－2, and then decreased when the N application rates were greater than 360 kg·hm－2. [Conclusion] The optimum N application rate was 277.0 kg·hm－2. When the N application rates were greater than 360 kg·hm－2, the nitrate N contents in the soil increased. However, the nutrient accumulation levels and the N fertilization efficiencies decreased, and the soil urease activities were inhibited. No obvious increase in cotton yield was observed.