Abstract:
Soil nitrogen leaching has been the main pathway of reactive nitrogen loss, which was caused by the accumulation of nitrate nitrogen in the soil profile below the dense layer of the root system. However, it is still unclear on the systemic effects of different nutrient managements on the soil nitrate accumulation and leaching in vegetable fields. In this study, a Meta-analysis was used to clarify the effects of reduced nitrogen application (RF), combined application of organic and inorganic fertilizers (OF), and inhibitor regulation (IF) on the accumulation and leaching of nitrate in vegetable soil. Taking the conventional nitrogen application (TF), single fertilizer application (CF) and no inhibitor application (WI) as confrol, respectively. Published studies from 2000 to 2021 were collected from the CNKI, Wanfang, Weipu (Chinese databases), and Web of Science database. A systematic literature search was conducted with the key words “organic and inorganic combined application” and “nitrate or nitrate nitrogen”, “optimal fertilization or reduced nitrogen application” and “nitrate or nitrate nitrogen”, “inhibitor (nitrification inhibitor, urease inhibitor, nitrogen regulators)” and “nitrate or nitrate nitrogen”. In the end, a total of 62 literatures were selected to obtain the 377 groups of nitrate accumulation data from 0-100 cm soil profile, and 202 groups of nitrate leaching data. The results showed that the three nutrient managements were effectively reduced the concentration of nitrate accumulation and leaching in the 0-100 cm soil profile, compared with the control. Specifically, the concentration of nitrate accumulation significantly decreased in the 0-100 cm soil profile for the RF, the 60-80 cm for the OF, and 0-80 cm for the IF, respectively, compared with the conventional TF, CF and WI. Among them, the RF showed the greatest inhibiting effect of soil nitrogen leaching, with an effect size of -4.301 and a decrease rate of 43.19%. The inhibiting effect size of nitrogen leaching and decrease rate were -4.279 and 36.79% in the OF, respectively. However, the inhibiting effect decreased significantly, when the substitution rate of organic nitrogen fertilizer was over 60%. There was a significant inhibiting effect in the IF treatment on the nitrate leaching, compared with the WI, especially, the combination of urease and nitrification inhibitor, with the effect size of-4.373, and the decrease rate of 37.12%, respectively. A software package “Random Forest” in the R programming language was used to determine the contribution rates of various influencing factors to nitrate leaching. Data analysis results showed that the nitrogen application rate and water input were the main influencing factors on the nitrate leaching, indicating the total contribution rates 43.2%-47.3% of the variance. In the RF, the contribution rates of soil texture and nitrate content to the nitrate leaching was the second, accounting for 17.4% and 15.2%, respectively. In the OF, the soil organic matter, soil nitrate content, and soil texture presented a great effect on the nitrate leaching, accounting for 17.3%, 14.5%, and 12.3%, respectively. Nevertheless, there was a relatively small effect of pH with a contribution rate of 10.3%. In the IF, the soil nitrate content, soil texture, and organic matter content shared the relatively high contribution to the nitrate leaching, accounting for 18.0%, 16.2%, and 12.2%, respectively. A comprehensive evaluation demonstrated that the appropriate nitrogen reduction ratio ranged from 30% to 50% for reduced nitrogen application measures, when the input amounts of water and nitrogen were 430.74 mm and 646.53 kg/hm2, respectively. In the soil with high content organic matter, when the input amounts of water and nitrogen were 360.28 mm and 432.18 kg/hm2, respectively, the application proportion of organic fertilizer instead of chemical fertilizer was from 30% to 60% for combined application of organic and inorganic fertilizers measures. A combination of urease and nitrification inhibitor showed the greatest inhibiting effect for inhibitor regulation. This finding can provide valuable information for the decision-making on the appropriate strategies of nutrient management in vegetable production.