Chemical N fertilizer replaced with organic fertilizer affecting yield and quality of leaf vegetable and N leaching in soils

Abstract: Application of organic nitrogen amendments and reduction of chemical fertilizer are considered as an effective approach in sustainable agriculture. 5 field experiments were conducted to evaluate the effects of nitrogen in organic fertilizer instead of chemical fertilizer nitrogen (0, 25%, 50%, 75% and 100%, and marked as 100CF, 25OM75CF, 50OM50CF, 75OM25CF and 100OM) on the yields and qualities of leaf vegetables and soil nitrogen residues. The results list as follow: when compared with conventional fertilization (100CF), the similar leaf vegetables yield of pakchoi was obtained by the organic N fertilizer instead of 25% chemical N fertilizer in the first season, and 25%-100% in the second and fifth season. The treatments with the organic N fertilizer instead of 25% chemical N fertilizer gained the same yield of lettuce comparing with 100CF. For Chinese cabbage seeding, there was no difference on the yield among these different treatments. The nitrate content of pakchoi could be significantly reduced when the substitution ratio of organic nitrogen was above 50%. Only the treatments of organic N fertilizer instead of 100% chemical N fertilizer could significantly reduce the nitrate content of the Chinese cabbage seeding and the lettuce leaf. Among the 3 leafy vegetables, the highest nitrate content was obtained by pakchoi, and the lowest nitrate content was gotten by lettuce. But the treatments with organic nitrogen instead obtained much more Vitamin C (Vc) content compared with chemical fertilizer treatment in the fifth season. There was no difference on free amino acid, soluble sugar and sugar-acid ratio of lettuce among these different treatments. The treatments with high organic N fertilizer replaced chemical N fertilizer ratio (50% - 100%) mainly affected the soluble sugar and sugar-acid ratio of pakchoi in the first season. The treatment with 100% organic N fertilizer instead ratio could increase the soluble sugar and total acid content of Chinese cabbage seeding. After fertilization, the accumulation of nitrate nitrogen and ammonia nitrogen mainly concentrated in the 0-20 cm plough layer. After 2 a 5-season planting, the nitrate nitrogen content in 0-20 cm soil layer treated with 100CF, 25OM75CF, 50OM50CF, 75OM25CF and 100OM increased by 5.25%, 24.09%, 100.52%, 318.81% and 439.10%, and that increased by 142.11%, 59.54%, 376.18%, 543.06% and 120.48% for ammonium respectively compared with that in the first season. With the increase of organic nitrogen substitution ratio, the soil nitrate and ammonium contents decreased gradually. Compared with 100CF, the soil nitrate and ammonium reduced by 10.67%-16.11% and 23.13%-69.03% with the treatments of organic N fertilizer replacement in 0-20 cm, respectively. In addition, the soil nitrate and ammonium content in >20-40 cm reduced by 21.15%-60.77% and 2.04%-10.20% comparing with 100CF. Therefore, for the leafy vegetables, the nitrogen in organic N fertilizer instead of 25%-50% chemical N fertilizer could obtain better yield, meanwhile reducing the environmental risk of nitrate nitrogen.