施氮量对太湖地区设施菜地年氮素淋失的影响

采用田间小区试验,研究了太湖地区设施菜地一年三季作物(番茄-莴苣-芹菜)氮素淋失特征.结果表明:太湖地区设施菜地氮淋失以NO3--N为主,氮素淋洗量受施氮量的直接影响,以农民习惯施氮量(N5)处理下的淋洗总量最高,全年TN淋失总量高达193.6 kg· hm-2.在N5基础上减施N40％(N3)可分别减少番茄、莴苣和芹菜季TN淋洗损失40.4％、49.2％和57.5％,同时可分别增产15.1％、39.0％和27.8％.设施菜地氮素淋洗高峰发生在揭棚期(7—11月),其中包括揭棚休闲期和莴苣生长前期.揭棚期淋洗液TN平均浓度为51.1 mg·L-1,是盖棚期TN浓度的1.7倍；TN淋洗量为129.2 kg· hm-2,约占全年总氮淋洗量的66.7％.

Effect of Nitrogen Fertilizer Application Rates on Annual Nitrogen Leaching Loss from Protected Vegetable Production System in Tai Lake Region, China

A field experiment was conducted to evaluate the effect of nitrogen(N) fertilizer application rates on N leaching loss from protected vegetable soil in Tai Lake region,China.Five N treatments,including N1(no fertilizer),N5(conventional N application rate at 1 560 kg·hm-2·a-1),N2(at 40% of N5 the N rate),N3(at 60% of the N5 N rate),and N4(at 75% of the N5 N rate),were applied to a tomato,lettuce and celery rotation,a typical protected vegetable cropping system in the region.It was found that the main form of the N leached was nitrate-N,and the leaching loss increased with the N rates.The highest annual total N leaching loss at 193.6 kg·hm-2 ocurred in the N5 treatment.Compared with the N5 treatment,the N leaching loss in the N3 treatment reduced by 40%,49% and 58%,and yield increased by 15%,39% and 28%,in the tomato,lettuce and celery season,respectively.The leaching loss of N peaked in the open period,from July to November when the plastic cover was removed and the soil was subject to rainfall,including fallow period and early stage of lettuce.The average total N concentration in the leachate was 51.1 mg·L-1 during the open period,which was 1.7 times greater than that in the covered period.The total N leaching loss was 129.2 kg·hm-2 in the open period,which accounted for 67% of the total annual loss.Our results demonstrate that the technique of reducing N fertilizer application rate can greatly minimize the environmental risk of N loss from protected vegetable field without any negative effect on vegetable yields.The fallow period should be the most critical period for controlling the total N leaching loss.