| In recent years,farmers applied excessive nitrogen fertilizer to pursue high yield,the behavior leads to soil unbalance nutrients supply and fertility reduction in gravel-mulched field,the yield and quality of watermelon have decreased.The field experiment and indoor soil column simulation test were carried out to study the effects of watermelon growth and nitrogen uptake on nitrogen application rate,as well as nitrogen release and transformation in gravel-mulched field.The objective was to provide a theoretical basis for rational nitrogen application in gravel-mulched field and improved yield and quality of watermelon in gravel-mulched field.In the field experiment,5 nitrogen treatments were applied(nitrogen application of 0 kg/hm2,45 kg/hm2,90 kg/hm2,135 kg/hm2,180 kg/hm2).The soil column simulation test set three soil water content levels(10%,20%,30%)and four nitrogen levels(nitrogen application of 0 kg/hm2,60 kg/hm2,120 kg/hm2,240 kg/hm2)which were completely combined,and a total of 12 treatments were performed,study on soil nitrogen release in gravel-mulched field.The results show that:1.The stem diameter,number of leaves and vine length are the maximum when the nitrogen application rate is 90-180 kg/hm2.The yield was 40582.02-40993.4440582 kg/hm2 when nitrogen application rate is 124.87-135 kg/hm2.The amount of nitrogen applied was significantly correlated with the yield and was in the relationship of a one-dimensional quadratic curve with an open downward.Propriate nitrogen application can increase the Vc.sugar/acid ratio,soluble solids and soluble sugar of watermelon in gravel-mulched field.2.Nitrogen accumulation in plants reached highest when nitrogen application rate wasl57-180 kg/hm2.The nitrogen accumulation in leaves reached the highest when nitrogen was applied at 125-150 kg/hm2.The nitrogen content of the leaves and yield were significantly correlated with the SPAD of the middle leaves during the stage of expanding.The nitrogen content of the leaves was highest when the SPAD value of the middle leaves was 61.04-62.13,and yield was highest when the SPAD value of the middle leaves was 62.75-64.48.3.The depth of soil 0-100 cm,nitrogen,ammonium,nitrate nitrogen,soluble organic nitrogen,microbial biomass nitrogen content was the highest when nitrogen application rate from 135 to 180 kg/hm2.In the depth of soil 0-40 cm,ammonium nitrogen and nitrate nitrogen accumulation were the highest when nitrogen application rate 125-180 kg/hm2,and the accumulation of ammonium nitrogen and nitrate nitrogen increased with the increase of nitrogen application rate.The nitrogen content and yield of the pressed sand watermelon were higher when the soil ammonium nitrogen accumulation was 4.50-5.73 kg/hm2.The nitrogen content and yield of the pressed sand watermelon were higher when the soil nitrate nitrogen accumulation was 19.88-23.70 kg/hm2.4.The content of ammonium nitrogen and nitrate nitrogen increased continuously and reached the highest when days from 1 to 5 after nitrogen application,which began to decrease at 5 d.The content of soluble organic nitrogen decreased gradually when the water content was 10%within days from 1 to 30.When the water content was 20%and 30%,the content of soluble organic nitrogen increased first and then decreased.Therefore,nitrogen application promoted the growth of watermelon stems,vines and leaves,which improved the quality and yield of watermelon,and nitrogen application could increase the active nitrogen content and nitrogen supply capacity of gravel-mulched field.The nitrogen content and yield of the leaves were higher when the SPAD value of the middle leaf was 62.13-64.48 in the period of expanding.The nitrogen nutrition diagnosis and yield prediction could be carried out by the SPAD value of the middle leaf of the expending.Comprehensive the growth,yield,quality of watermelon and nitrogen supply capacity of gravel-mulched field,the optimum nitrogen application rate is 135-180 kg/hm2. |
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