太湖地区绿肥还田与无机氮追肥配施的环境效应分析

通过太湖地区绿肥还田与不同用量的无机氮追肥配施小区试验,研究了水稻苗期、分蘖期和抽穗期田面水氮素不同形态的变化特征、径流损失及水稻产量。结果表明:绿肥还田后,水稻苗期田面水中总氮浓度出现先减小后增加的变化,总氮浓度增加的原因主要是有机氮浓度的增加,而无机氮浓度先升后降;分蘖肥和穗肥施用后,田面水氮素浓度随施肥量的增加而升高,田面水总氮和有机氮在施肥后第1天达到最大,随后快速下降,而无机氮在施肥后则经历了一个先升后降的变化过程;随着施肥量的增加,稻季氮素径流损失不断增大,无机氮是氮素径流损失的主要形态,且径流水中无机氮以铵态氮为主,故应将铵态氮作为农田排水污染检测的主要指标;绿肥还田模式下,施用氮素基肥可大大提高田面水的氮素含量,增加氮素流失风险,而不施氮素追肥或者过量减施均可影响作物的产量。绿肥还田,稻季配施140 kg hm-2无机氮追肥,可减少48%无机氮肥投入,降低38.5%氮肥流失率,实现水稻产量效应和环境效应的协调,是水体污染严重地区值得尝试的一种农作方式。

Environmental Benefits of Green Manure Crop and Inorganic Nitrogen Fertilizer Combined Application in Paddy Fields of Taihu Area

The study focused on the nitrogen lose via runoff,grain yield,and change of nitrogen in different forms in surface water in paddy field at seedling stage,tillering and heading stage,through green manure crop and applications of different amounts of inorganic nitrogen fertilizer combined.Results showed that after green manure returned to soil,the total N(TN) content in surface water of rice field firstly decreased and then increased at seedling stage,and the main reason that the TN content increased was that the organic N content increased in paddy water,however,inorganic N showed opposite trend with the TN.After tillering and earing fertilizer practices,N content increased as increase in nitrogen application.The TN and organic N content in the paddy water reached peak values the first day after each fertilizer management,and then dropped sharply inorganic N content.The N losses through runoff continually increased as the increasing rate of fertilizer input.The ammonia nitrogen(NH4+-N) was the main form of N losses via runoff,thus it should be considered as the best index for farmland drainage pollution detection.In green manure-rice rotation system,basic fertilizer application greatly increases the concentrations of N in surface water of rice field,which increased the risk of N loss as well.On the other side,the grain yield will decrease if topdressing nitrogen do not input or the rate of topdressing nitrogen excessive reduces.After all,It is a worthwhile farming method in serious water pollution area to realize harmonization of grain yield and environmental benefits,with 140 kg ha-1 inorganic N fertilizer input after return of green manure to soil.This method could reduce both 48% of N fertilizer input and 38.5% of N loss.