Comparison of various technical measures for controlling nitrogen leaching from tomato-grown soil in greenhouse facilities

Tomatoe is the vegetable with the largest planting area in China. The soils in which the tomato is grown experience heavy nitrogen leaching owing to the application of large amounts of nitrogen fertilizer and irrigation, which aggravate nitrate pollution of the groundwater. To effectively reduce soil nitrogen leaching caused by excessive nitrogen application and irrigation in tomato production facilities, we compared various control methods in this study by integrating physical barrier materials, fertilizer synergists, enzyme preparations, microbial preparations, and other products with fertilizer application technologies developed by the National Key Research and Development Project of China “Nitrogen and Phosphorus Pollution Load Reduction Technology and Product Development in Agricultural Facilities”. The best control technology was then developed to provide a reference for controlling soil nitrogen leaching in vegetable fields. In this study, six treatments, which were conventional fertilization (FP), optimal fertilization (OPT), physicochemical regulation (PCT), bioecological regulation (BET), water and fertilizer regulation (WRT) and comprehensive regulation (CRT), were set up to control soil ntrogen leaching. The FP treatment used 18 t∙hm⁻² of chiken manure with 50% organic matter content, and the application rates of chemical fertilizers N, P₂O₅ and K₂O were 225 kg∙hm⁻², 150 kg∙hm⁻² and 450 kg∙hm⁻². The total irrigation amount was 2700 m³∙hm⁻². Under OPT treatment, same amount of commercial organic fertilizer with 60% organic matter content was used, and application amount of chemical fertilizer were ajusted. Compared to OPT treatment, physical barrier blocks and nitrification inhibitors (dicyandiamide) were used under PCT treatment, enzyme preparations and microbial preparations were added under BET treatment, fertilizer synergists (DY-ET100) was added under WRT treatment, and all the addtitions above were added under CRT treatment. Tomato yield, soil nitrogen leaching and nitrogen form in the leachat as well as the economic benefits from farmland growing tomatoes under different treatments were determined. The methods were compared and screened for the best in controlling soil nitrogen leaching. The results showed that tomatoes yield under OPT and FP treatments were similar, while tomatoes yield under CRT treatment was significant higher than that under FP, OPT and BET treatments. Compared to FP treatment, tomato yields under PCT, BET, WRT and CRT treatments increased by 4.70%, 2.05%, 7.93% and 9.28%, respectively. The CRT treatment resulted in the highest total revenue, followed by WRT, PCT and BET treatments, whereas the FP treatment had the lowest total revenue. However, WRT treatment showed the highest net income. The FP treatment showed the highest total nitrogen content (114.8 kg∙hm⁻²) in soil leachate, which were 25.6%, 35.6%, 34.5%, 40.5% and 40.9% higher than those of the OPT, PCT, BET, WRT and CRT treatments, respectively. The nitrate nitrogen leaching from the FP treatment was the highest (49.0 kg∙hm⁻²), and nitrate nitrogen leaching under OPT, PCT, BET, WRT and CRT treatments decreasd by 31.5%, 32.7%, 38.4%, 43.9% and 49.2%, respectively. The FP treatment resulted in the highest organic nitrogen leaching (65.8 kg∙hm⁻²), and organic nitrogen leaching under OPT, PCT, BET, WRT and CRT decreased by 21.2%, 37.7%, 31.5%, 38.0% and 34.7%, respectively. Organic nitrogen and nitrate nitrogen leaching accounted for 55.2%–62.9% and 36.7%–44.6% of total nitrogen leaching in the different treatments, respectively, whereas ammonium nitrogen accounted for less than 0.5% of total nitrogen leaching. Nitrate nitrogen and ammonium nitrogen contents in the 0–100 cm soil layer under FP treatment were both higher than that under OPT treatment. Moreover, the nitrate nitrogen content in the 20–100 cm soil layer was in the order of WRT>CRT>BET>PCT>OPT. In conclusion, in terms of both economic and environmental benefits, water and fertilizer regulation would be the best technology for controlling soil nitrogen leaching in tomato cultivation facilities.