Reducing nitrogen input and improving yield and quality of rape through combination of fertigation and nitrification/urease inhibitor addition

ObjectivesThe paper was aimed at the selection of the optimum reduction of nitrogen with nitrification and urease inhibitors application, to provide theoretical basis for reducing nitrogen losses, improving nitrogen use efficiencies and reducing nitrate contents in vegetables with fertigation management.

MethodsA pot experiment was carried out using negative pressure irrigation (–5 ± 1) kPa method. Five treatments were set up as: no N (T1), urea 150 kg/hm² (T2), urea 150 kg/hm² + 10%DCD (dicyandiamide) + 1%HQ (hydroquinone) (T3), urea 127.5 kg/hm² + 10%DCD + 1%HQ (T4), and urea 105 kg/hm² + 10%DCD + 1%HQ (T5). Water supply amounts, soil moisture contents, rape growth indicators, soil nitrate nitrogen and ammonium nitrogen contents during the period of rape growth were analyzed, and the yield, quality, nutrient content of rape after the harvest were determined. The optimum formula was acquired through comprehensive analysis.

ResultsDuring the rape growth, the total water yield amounts were very close among the treatments (12174–13869 mL). In the condition of the same fertilizing amount, compared with the no inhibitor added treatment (T2), T3 could effectively inhibit the conversion of ammonium nitrogen to nitrate nitrogen in the soil, increase the leaf length, leaf width and chlorophyll contents, promote rape plants to absorb nutrients, significantly increase the rape yield by 25.2% and nitrogen use efficiency significantly by 85.2%, and at the same time significantly reduce the nitrate content by 51.9%. Compared with the no inhibitor added treatment (T2), decreasing 15%–30% of nitrogen input rate and adding nitrification and urease inhibitors also had similar effect on rape yield, quality and nutrient absorption, and could restrain the nitrofication process and reduce nitrate accumulation in the soil. Among them, the treatment T5 improved rape yield by 15.9%, increased total N, P and K contents by 8.4%, 21.5% and 27.8%, which led to 1.26 times of increase in the nitrogen use efficiency, and 66.6% of reduce in the nitrate content in rape.

ConclusionsUnder the condition of negative pressure irrigation, moderate reduction of nitrogen with addition of nitrification and urease inhibitors have obvious promoting effect on yield and nitrogen use efficiency of rape, and reducing effect on the nitrate content of rape and soil nitrate accumulation. Under the experimental condition, urea 105 kg/hm² + 10%DCD + 1%HQ, reducing 30% of nitrogen with addition of 10%DCD and 1%HQ shows the best effect, reducing the risks of nitrate accumulation caused by high nitrogen input at the same time.