Effect Of Urease & Nitrification Inhibitors On Yield,Nutrients Uptake And Leaching Of Field Vegetables Under Reduced Application Of Nitrogen Fertilizer

As a large agricultural country,China consumed a huge number of chemical fertilizers in the agricultural production process every year.Excessive application of chemical fertilizer causes a waste of resources and increases the risk of environment pollution.Therefore,in 2015,the Ministry of Agriculture issued the"zero-growth action plan for fertilizers by 2020".It is very common that the amount of chemical fertilizer used in vegetable crops exceeds the standard,especially the excessive application of nitrogen fertilizer,in order to obtain higher yield and benefit.The reduction of fertilizer application on vegetables is very critical.During the pratices of fertilizer reducing,new fertilization strategies should be adopted to ensure the yield and quality of vegetables.Pot experiment and field experiment were carried out to study the effect of urease/nitrification inhibitors on yield,nutrient uptake and leaching of field vegetables under reduced application of nitrogen fertilizer(pot experiment:water spinach;Field experiment:cabbage,wax gourd and lettuce),aiming to screen and optimize the application of urease/nitrification inhibitors in combination with chemical fertilizer reduction for field vegetables.The major results are as follows:1.The results of pot experiment showed that there was no yield decrease under the application of urease/nitrification inhibitor on the basis of nitrogen fertilizer reduction for the water spinach.In the first harvest experiment of water spinach,there was no significant difference in plant height and yield between N70 treatment(30%reduction of nitrogen fertilizer)and N100 treatment(normal fertilization),indicating that 30%reduction of nitrogen fertilizer had no significant effect on water spinach yield,but the plant height and yield of water spinach improved through using urease/nitrification inhibitor.In the second harvest experiment of water spinach,the treatment was adjusted to reduce nitrogen fertilizer application by 50%,the result showed that nitrogen fertilizer application reduced the yield of water spinach.However,the application of 45.0 kg/hm~2nitrification inhibitor based on 50%reduction of nitrogen fertilizer alleviated the yield reduction caused by the application of nitrogen fertilizer only.Compared with 50%reduction of nitrogen fertilizer and the treatment of normal fertilization,the yield increased by 40.7%and 6.9%,respectively,demonstrating a beneficial outcome on reducing fertilization and increasing yield.2.The nitrification inhibitor were used in the first season field experiment of cabbage under 40%reduction of nitrogen fertilizer.The results showed that 40%reduction of nitrogen fertilizer resulted in 26.4%yield decrease in cabbage.And compared with normal fertilization treatment,application of nitrification inhibitor on the basis of 40%reduction of nitrogen fertilizer still resulted in a reduction in the yield of cabbage,indicating that under a significant reduction of chemical fertilizer,application of nitrification inhibitor alone was not ideal for increasing the yield of cabbage in the southern area.3.The nitrification inhibitor and urease inhibitor were used in the second season field experiment of wax gourd under 30%reduction of nitrogen fertilizer.The results indicated combined application of urease/nitrification inhibitor significantly increased the yield of wax gourd,suggesting the combination of nitrification inhibitor and urease inhibitor had more positive effect on the yield than that of single application of nitrification inhibitor.And compared with normal fertilization treatment,30%reduction of nitrogen fertilizer resulted in 12.2%yield reduction in wax gourd.Compared with 30%reduction of nitrogen fertilizer and normal fertilization treatment,the combination of urease inhibitor and nitrification inhibitor treatment increased the yield of wax gourd by 29.0%and 13.2%,respectively,demonstrating a beneficial outcome on reducing fertilization and increasing yield.4.The nitrification inhibitor and urease inhibitor were also used in the third season field experiment of lettuce under 30%reduction of nitrogen fertilizer.The result proved that nitrification inhibitor and urease inhibitor significantly increased the yield of lettuce based on 30%reduction of nitrogen fertilizer.The average yield of the normal fertilization treatment plot was 570516.8 kg/hm~2,the average yield was643086.0 kg/hm~2after using the nitrification inhibitor,with an increase yield of35.3%.Compared with 30%reduction of nitrogen fertilizer,the yield of lettuce treated with urease/nitrification inhibitor increased by 8.0%,indicating a positive effect on reducing fertilization and increasing yield.5.Urease/nitrification inhibitors reduced the nitrate nitrogen leaching amount and nitrite content in both cabbage and wax gourd fields,promoted the uptake of nitrogen nutrients by vegetables.Compared with the 40%reduction of nitrogen fertilizer,the amount of nitrate leaching in cabbage field under the application of nitrification inhibitor decreased by 38.1%,and the nitrogen content of cabbage increased by 0.3%.Compared with the normal fertilization treatment,the nitrate leaching amount of the wax gourd field treated with single application of nitrification inhibitor and the combination of nitrification inhibitor and urease inhibitor decreased by 48.7%and 26.8%respectively,the nitrite content of wax gourd decreased by66.6%and 53.3%respectively,and the nitrite content of lettuce decreased by 63.1%and 56.09%respectively.Compared with 30%reduction of nitrogen fertilizer,the nitrogen content of lettuce treated with both nitrification inhibitor and urease inhibitor increased by 0.7%.Based on the overall results of field and pot experiments,it was found that the effect of different urease/nitrification inhibitor varied among various vegetable types.The reduction range of nitrogen fertilizer in pot experiment could be up to 50%,and the effect of nitrification inhibitor treatment alone NMAX30(45.0 kg/hm~2)or the application of inhibitor NAMX15+UR had better effect.It showed that the reduction of the nitrogen fertilizer application to about 30%was appropriate for planting vegetables in the field,and the effect of NAMX15+UR treated with nitrification inhibitor and urease inhibitor together verified better result.In summary,urease/nitrification inhibitors could be adopted to maintain or increase yield under the practice of nitrogen fertilizer reduction.