Effection Of Nitrogen Fertilizer Application And Organic-inorganic Mixed Fertilizer On Yield And Quality Of Lettuce

In order for development and extension of organic-inorganic mixed fertilizer for lettuce, theeffects of nitrogen fertilizer application rate on yield and quality (nitrate content, protein content,soluble sugar content, rough fiber content and Vitamin C content) of lettuce and nitrogen fertilizerutilization ration have been studied by pot experiment using ¹⁵N trace technique. Underguaranteeing high yield, good quality and low pollution, the rational nitrogen application rate oflettuce has been obtained. And the effects of organic-inorganic mixed fertilizer on thephotosynthetic characteristic, key enzymes (such as sucrose synthase, sucrose phosphate synthaseand nitrate reductase) of carbon-nitrogen metabolism, yields and quality (such as the content ofvitamin C, soluble sugar, nitrate, inferior nitrate, coarse fibred and amino acids) of lettuce by fieldplot experiment on the basis of this research conclusion. The results were shown as follows:There was significantly correlation between vegetables yield (?)(g/pot) and nitrogen fertilizerapplication rate x (gN/kg soil); the parabola model regression equation could be expressed as: FW:=104.21+2476.31x-5181.97x², DW: (?)=0.95+179.58x-390.60x². The yield of lettuceincreased with increasing of nitrogen application rate. While exceeding certain nitrogenapplication rate, the yield of lettuce decreased. Rational nitrogen application rate could increasethe yield lettuce.Increasing the application rate of nitrogen fertilizer could increase Vitamin C content ofthe esculent part of lettuce in certain nitrogen application rate range; but increasing the nitrogenapplication rate would decrease content of Vitamin C after exceeding certain nitrogen applicationrate. Rational nitrogen application rate could promote the synthesis and accumulation of protein,increase the content of soluble sugar, and chlorophyll content in functional leaves of lettuce,lengthen the functional period of functional leaves, strengthen the activation of NR, reduce theaccumulation of nitrate, change inherent quality and mouthfeel of the esculent part of lettuce.With the increasing of nitrogen application rate, total nitrogen absorption and ¹⁵N% of lettucewere increased. Rational nitrogen application rate could significantly improve the absorption from nitrogen and from soil nitrogen. The nitrogen utilization ratio, residual ratio and recovery ratio inthe soil would decrease with the increasing of nitrogen application rate, while the loss rateincreased. Rational nitrogen rate could improve the utilization ratio of the nitrogen, reduce theloss ratio of the nitrogen. Under guaranteeing high yield, good quality and low pollution, therational nitrogen application rate of lettuce is 0.1750～0.2125gN/kg soil.Organic-inorganic mixed fertilizer could increase the content of chlorophyll and netphotosynthetic rate in the functional leaves during middle and late growth stages of lettuce.Organic-inorganic mixed fertilizer could significantly enhance the activities of sucrosesynthase(SS), sucrose phosphate synthase(SPS) and nitrate reductase(NR) in the functional leavesduring middle and late growth stages of lettuce as compared to the treatments of chemicalfertilizer and farmer fertilization practice.Organic-inorganic mixed fertilizer could promote the growth and thus increase the yields andquality of lettuce. There was not significant difference for the yield of lettuce between thetreatments with organic-inorganic mixed fertilizer and farmer fertilization practice; while therewas significant at 1% level between the treatments with organic-inorganic mixed fertilizer andfertilizer. Organic-inorganic mixed fertilizer could significantly increase the content of Vc andsoluble sugar, decrease the accumulation of nitrate, inferior nitrate, remain adequate coarse fibrecontent in esculent part of lettuce. It could obviously promote nutrient and health quality of lettuce.Net incomes and output/input ratio from the treatment of organic-inorganic mixed fertilizer wasthe highest among three treatments. Organic-inorganic mixed fertilizer could significantly increaseeconomic profit of lettuce production.Protein content in esculent part of lettuce with organic-inorganic mixed fertilizer wasincreased as compared to the treatments with chemical fertilizer and farmer fertilization practice;but there was not significant effect on aspartic acid, phenylalanine, isoleucine and tyrosine.