Effects Of The Combined Application Of Organic Manure And Chemical Fertilizer On The Contents Of Nitrate And Nitrite In Leaf Vegetable

The effects of combined application of organic manure and chemical fertilizer on the nitrate , nitrite contents , the activity of nitrate reductase and the content of Vc in vegetable, and die content of nitrate in soil was studied by plot experiment in the winter of 2002 and the summer of 2003 .The soils used in experiments are red vegetable soil derived from quaternary red clay(the Donghu experimental site) and alluvial vegetable soil derived from alluvial deposit (HAU experimental site), and the crop used in experiments was pakchoi. The results are summarized as follows:1. the experiment result in 2002 and 2003 showed that when the ratio of combined application of organic manure and chemical fertilizer was 1:1 the nitrate content in pakchoi was lower and the yield of pakchoi was higher. The yield of 1/2M treatment (the treatment that the ratio of the combined application of organic manure and chemical fertilizer was 1 :l)was the highest and the nitrate content was lowest in 2002 when the amount of N fertilizer was 300kg.hm-2 .When the amount of N fertilizer was 180 kg.hm-2, the yield of the 1/2M treatment at Donghu experimental site and the CF treatment at HAU experimental site was higher and the nitrate content was lower. In the two year's experiment, the variation of the Vc content and the activity of nitrate reductase was uncertain.2.The nitrate content in soil varied with the ratio of combined application of organic manure and chemical fertilizer. At the early growth stage, the nitrate content in soil increased with the ratio of chemical fertilizer increasing at HAU experimental site and Donghu experimental site, but at later growth stage, the variation of the nitrate content in soil is different with the ratio of organic manure applied in soils at the two experimental site. The nitrate content in soil increased with the increasing ratio of organic manure at HAU experimental site, but it was highest in soil with the CF treatment (the treatment that only chemical fertilizer was applied ) at Donghu experimental site. At the growth stage, the variation of the nitrate content in soil at the two experiment sites was different. The nitrate content in soil increased at the earlystage and decreased at the later stage at HAU experimental site, but af Donghu experimental site it was increased until harvest.3.There is closely positive relation between the nitrate contents in soil and in pakchoi, especially in the early growth stage. At the later growth stage, the relation between the nitrate content in pakchoi and in soil becomes insignificant. It was because that the nitrate content in pakchoi at the later growth stage was mainly affected by the nitrate content in soil at the early growth stage.