Research On Effects Of Organic Fertilizer On Yield And Quality Of Lettuce

Lettuce is the leafy vegetable widespread grown in the south China. There are large areas of lettuce in Chongqing. At present, during the process of planting vegetable, people pay more attentainon to applying more chemical fertilizer on vegetable while ignore the effects of organic fertilizer on yield, quality, soil fertility and so on. Combining with field experiment, pot experiment, indoor chemical analysis and statistic analysis, this research was conduced to study the effects of different kind and different rate of organic fertilizer (peat, common rapeseed cake and yellow rapeseed cake) on growth, yield, quality and physiological-biochemical characteristics of lettuce. In order to filtrate the suitable kind and rate of organic fertilizer which was fitting to the garden soil of Chongqing. Also academic reasons were provided by the research for reasonably fertilizing and growing high quality vegetable. The main results were as follows:1.The application with different rate of peat, common rapeseed cake(CRc) and yellow rapeseed cake(YRc) increased the yield of lettuce from 11.1%-89.7% and 6.8%-54.7% in the early and later growth stage of rosette leaf. And the treatment of which the application of CRC was 8g/kg got the highest yield. The leaf number of which applied organic fertilizer were more than CK, when the rate of organic fertilizer was from 1g/kg-4g/kg, the numbers of leaf number were in the order of YRc＞CRc＞peat. Except treatment M_H4, the height of lettuce with the treatments which applied organic fertilizer were all taller than CK in the early and later growth stage of rosette leaf. It indicated that from the rate of 1g/kg-8g/kg, the organic fertilizer of peat and CRc accelerated the growth of lettuce, maked the best biological properties of lettuce. When the fertilizer rate of YRc was higher than 8g/kg would inhibit the growth of lettuce in early stage of rosette leaf.2. The application of peat, CRc and YRc increased the nitrate content of lettuce leaf during the growth stage of rosette leaf. And the heavier the organic fertilizer was applied, the higher the content of nitrate would be. But the highest content of nitrate was no more than 3000mg/kg. The content of Vc in peat treatments was higher than CRc and YRc treatments, and the increase scope was from 6.5%-8.2% during the early growth stage of rosette leaf. While in the later growth stage of rosette leaf, the YRc treatments got the highest content of Vc. The application of peat and CRc increased the reductive sugar content of lettuce leaf during the early growth stage of rosette leaf. The highest content of reductive sugar appeared in M₄ treatment, and the increase degree was 50.2%. During the later growth stage of rosette leaf, as the rate of organic fertilizer increased, the content of reductive sugar decreased. As comparison to CK, the content of amino acid was increased from 19.0%-202.5% during the early growth stage of rosette leaf. And the treatment M₄ got the highest content of amino acid. The content of amino acid was enhanced directly as the rate of YRc increased, and the content of which was higher than the other two kinds of organic fertilizer with the same rate. As comparison to CK, the content of protein increased in lettuce leaf in all treatments. And the YRc treatments got the highest content of amino acid in the same rate compared with peat and CRc treatments during the growth stage of rosette leaf. The content of phosphorus was higher than CK during the early growth stage of rosette leaf, and lower than CK during the later growth stage. The content of potassium was higher than CK during the whole growth stage of rosette leaf.3. The content of chlorophylla, chlorophyllb and chlorophylla+b of lettuce leaf increased by application of organic fertilizer during the growth stage of rosette leaf. And the content of chlorophylla, chlorophyllb and chlorophylla+b were all positively related to the application rate of peat and CRc significantly. During the early growth stage of rosette leaf, the activities of nitrate reductase(NR) rised from 30.8%-86.2% by adding low rate of CRc(lg/kg-4g/kg) and YRc(lg/kg-2g/kg). While the activities of NR was lower than CK by adding organic fertilizer during the later growth stage, and as the rate of organic fertilizer increased, the activities of NR declined. The superoxidase activities increased from 3.5%-192.2% and 2.5%-116.7% by the application of organic fertilizer during the early and later growth stage of rosette leaf. And the activities were in the order of YRc＞CRc＞peat. During the whole growth stage of rosette leaf, the catalase activities rised as the rate of organic fertilizer increased. When the application rate of YRc was 8g/kg, the increase degree of catalase activities was 61.3% and 46.1%,respectively.4. The application of CRc and YRc improved the pH of soil, and the pH was negatively related to the application rate of organic fertilizer significantly. The application of CRc and YRc also increased the content of available nitrogen from16.3%-69.4% and 10.4%-51.7%. The effects of peat on pH and available nitrogen were not obvious. The content of available phosphorus and organic matter all increased significantly by application of organic fertilizer. There's no effect on enhancing the available patassium of the soil by application of organic fertilizer.5. In field experiment, the variation of the quality index in lettuce leaf during the three stages showed that the highest content of nitrate, Vc and potassium appeared in growth stage, the highest content of reductive sugar appeared in harvest stage, and the highest content of protein existed in growth stage of rosette leaf. The application of peat, rapeseed cake increased the yield of lettuce , and the increase degree were 50.9% and 66.4%,respectively. The application of peat, rapeseed cake decreased the content of nitrate in lettuce stem, increased the content of Vc in lettuce leaf and stem, enhanced the content of reductive sugar(22.4%-26.1%), phosphorus(8.2%-14.0%) and patassium (16.9% -17.2%)in lettuce stem, as well as the ratio of fresh ammo acid/total amino acid in lettuce stem and ratio of sweet amino acid/total amino acid, flavorous amino acid/total amino acid in lettuce leaf. As far as the effect of organic fertilizer on improving the nutrition value of lettuce leaf and stem was concered, only the peat treatment expressed some positive effects.