Analysis of slow-release nitrogen fraction in maize specialized fertilizer for mild-saline alkaline soils

Currently, the fertilization of maize is not pertinent to actual local situations in northern Shanxi. To solve this problem, a maize specialized fertilizer formula for mild-saline-alkaline soils in northern Shanxi was studied to explore the proper ratio of slow-release nitrogen (SRN) and rapid-release nitrogen (RRN) in maize production in this region and the effectiveness of the formula validated for spring maize. The treatments were 100% RRN and 25%, 33%, 50%, 67%, 75% and 100% SRN, and no nitrogen application was the control. The grain production and dry matter weight at different growth stages, nitrogen uptake, transport and utilization of maize plant, as well as post-harvest nitrate nitrogen accumulation in soil were analyzed. The results showed that with increasing SRN ratio in the maize specialized fertilizer, physiological parameters of maize increased and then decreased at different growth stages. The peaked values of different indicators all occurred under the treatment with 33% SRN. The addition of 33% SRN effectively increased grain production, dry matter weight, nitrogen uptake and nitrogen use efficiency of maize, and with the highest yield of maize of 14 897.46 kg?hm^-2. The yield of maize increased by 42.23% compared with 100% RRN treatment. Meanwhile compared with 100% RRN, yield components such as ear length, ear grain number, diameter, 100-seed weight in 33% SRN treatment were higher by 55.34%, 39.30%, 53.57% and 52.57%, respectively. Moreover, in the same treatment, the length of bald tip was shorten by 0.38 cm, while nitrogen use efficiency, nitrogen partial productivity and agronomic efficiency of nitrogen fertilizer were 39.79%, 66.20 kg.kg^-1 and 47.03 kg.kg^-1, respectively; all of which were the highest in the treatments. The transport rate of nitrogen in different organs of maize was higher in 33% SRN treatment compared with 100% RRN treatment. Specifically, the rates of nitrogen transport in leaf and stem were respectively 76.08% and 49.39%, and the rate of nitrogen transfer and nitrogen harvest index were 67.76% and 77.40%, respectively; all of which were significantly higher than those in 100% RRN treatment. The 33% SRN treatment effectively improved nitrate nitrogen accumulation in the soil, which was different at different soil depths with the least in deep soil layers. It was therefore concluded that for spring maize cultivated in mild-saline-alkali soils in northern Shanxi, the addition of 33% of SRN to the existing maize specialized fertilizer increased maize production and fertilizer use efficiency, and protected the environment. This method was promising in enhancing the conditions (yield and environment) of maize production of the region.