Effect Of Nitrogen Application On Chlorine Absorption And Distribution In Watermelon Growing In Gravel-Mulched Field Under Supplementary Irrigation With Brackish Water

Watermelon growing in gravel-mulched field in Ningxia has been used for long-term supplement irrigation with underground brackish water,which leads to salinization of soil cultivation layer,and a large amount of chloride ion accumulation in soil,thus inhibiting the growth and development of chlorine free crops,reducing yield and quality.However,nitrogen could alleviate the toxicity of chloride ion to a certain extent.In this study,five nitrogen levels were set up through field experiments:NO(0kg/hm2),N1(45kg/hm2),N2(90kg/hm2),N3(135kg/hm2),N4(180kg/hm2).Under the condition of brackish water irrigation,the effects of different nitrogen application on the accumulation and distribution of chloride ions in watermelon plants were studied,and the effect and mechanism of nitrogen fertilizer on the toxicity of chloride ion were explored,The results are expected to provide theoretical basis for safe use of brackish water and rational application of nitrogen fertilizer.The results show that:1.The content of chloride in the soil during leisure period was low,but it had the phenomenon of surface aggregation;After the irrigation with brackish water,the content of chloride in soil increased significantly in the harvest period,and the content of 0-20 cm and 80-100 cm soil layer was higher.With the increase of nitrogen application,the chloride ion in each layer of soil decreased.The content of Cl-in soil was the lowest when the nitrogen application amount was 135 kg/hm2,which was 27.5%lower than that of no nitrogen treatment.It is suggested that the irrigation of brackish water will increase the content of chloride in soil,while nitrogen fertilizer will reduce the content of chloride in soil profile.2.In the period of melon expansion and harvest,the chloride content in the leaves of sand pressed watermelon decreased first and then increased with the increase of nitrogen application.When the nitrogen application amount was 135 kg/hm2 the content was the lowest,which was 15.3%and 29.8%lower than that without nitrogen application;The highest chlorine ion accumulation was 180 kg/hm2 and no nitrogen treatment,and the lowest was when 135 kg/hm2 was applied.The content of chloride in stem increased with the increase of nitrogen application.When nitrogen was applied 180 kg/hm2,the accumulation of chloride in stem was the highest.With the increase of nitrogen application,the content and accumulation of chloride in root system decreased,and the lowest was when nitrogen was applied 135kg/hm2.In general,the order of chloride content was leaf>stem>root.3.The content of chloride ion in different parts of the watermelon leaves was negatively correlated with the nitrogen application.With the increase of nitrogen application,the content of chloride in different parts of the leaves decreased with the increase of nitrogen application.The lowest chlorine content was N3 treatment,the nitrogen application was 150 kg/hm2,while the content of chloride in leaves increased with increasing nitrogen application(under N4 treatment).The content of chloride in upper leaves is 25%-30%,that of middle leaves is 30%,and that of lower leaves is 35%-40%.The distribution of chloride in leaves was lower than middle leaf>upper leaf.4.The nitrogen application amount was positively correlated with the chlorine content in different parts of watermelon leaves.In the early stage of growth,nitrogen application mainly affected the chlorine content of the base leaves,and the middle stage had a great influence on the chlorine content in the middle leaves,while the later stage was closely related to the chlorine content in the top leaves.The content of mineral nitrogen in soil is closely related to the top part,and the harvest period is inhibited.For watermelon yield,the chlorine content in the middle leaves was positively correlated with the fruit yield of watermelon.