Accumulation Of Chlorine In Soil Under Brackish Water Irrigation And Study On Chlorine Absorption Characteristics And Critical Value Of Chlorine Tolerance In Watermelon

In order to determine the critical value of chlorine tolerance of soil and watermelon and to use brackish water safely,this paper takes the sand-pressed land in Xingren Town,Shapotou District,Ningxia and the sand-pressed watermelon No.5 in Jincheng as the research objects,and set five chlorine levels to simulate long-term the accumulation of chloride ions caused by chlorine supplemental irrigation with brackish water,based on the experiments of the previous year(2020).Field location experiments were conducted to explore the accumulation and distribution of chlorine in soil and watermelon plants under brackish water irrigation,the effect of chlorine on watermelon growth and development,yield and quality,and chlorine the effects on soil nutrient enzyme activities and microbial community structure are expected to explore the critical value of chlorine toxicity of watermelon and provide theoretical reference for the safe use of chlorine-containing brackish water and chlorine-containing fertilizers.The main findings are as follows:(1)The content of nitrate nitrogen in the soil after harvesting was lower than that before sowing in the soil layer of 0-60 cm,and its content was mainly higher in the soil layer of 40-100 cm with the increase of soil depth.The ammonium nitrogen content in the soil also showed a decreasing trend after harvest.Compared with before sowing,the ammonium nitrogen content in the 0-20 cm soil layer during the harvest period decreased by 36.8%～68.3%.High levels of chlorine(240 kg·hm-2)also had a certain inhibitory effect on soil enzymes.The catalase,urease and phosphatase in the soil after harvesting were all lower than those before sowing.The dominant flora of soil bacteria and fungi under different chlorine levels were completely different,and the relative abundances were also different to some extent.There were more bacterial phyla and genera than fungi,but they were both treated at 60 and 120 kg·hm-2 the best abundance.Moderate chlorine level(60～120 kg·hm-2)can increase soil flora abundance,diversity and species,but high chlorine level(240 kg·hm-2)reduces its abundance and diversity,It has a great impact on soil microbial community structure.(2)Under the condition of brackish water irrigation,the chlorine level of 0～120 kg·hm-2 had no obvious inhibitory effect on the growth of watermelon plants,and even had a certain growth promotion effect.When the chlorine level exceeded 120 kg·hm-2,the growth of the main vine and the synthesis of biomass were inhibited.When the chloride level exceeded 180 kg·hm-2,the thickening of the main vine of watermelon was obviously inhibited.With the increase of chlorine level,the nitrogen content in watermelon plants decreased significantly,and the absorption of nitrogen by various organs of watermelon was inhibited when chlorine was applied at 240 kg·hm-2.When the chloride level was 60～120 kg·hm-2,the absorption of phosphorus by various organs of watermelon could be promoted,but the absorption of phosphorus by various organs of watermelon was also inhibited when the chlorine level was 240 kg·hm-2.From the perspective of the whole watermelon plant,the appropriate chlorine level(60～180 kg·hm-2)can promote the absorption of potassium content in watermelon.(3)Appropriate amount of chlorine(60～120 kg·hm-2)can maintain the higher stomatal conductance and transpiration rate of leaves to increase the net photosynthetic rate,and also improve the yield and quality of watermelon.High chloride level(240 kg·hm-2)inhibited the synthesis of chlorophyll in watermelon leaves,affected the stomatal conductance,and reduced the photosynthetic rate.And it has an adverse effect on the quality and significantly reduces the sugar-acid ratio.By fitting the relationship between yield and chlorine application,it was found that there was a significant correlation between them.When the yield reached the highest,the chlorine application level was 98.3 kg·hm-2,and the yield decreased when it exceeded 120 kg·hm-2.(4)There was a significant positive correlation between the chloride ion content of the whole watermelon plant and the chlorine application level at the harvest stage.The chloride content reached the highest at 240 kg·hm-2.At this time,the chloride content in leaves was the highest,and the chloride content in roots,stems and grains was less.At 60 kg-hm-2 chlorine level,the chlorine accumulation in plants reached the highest,and the chlorine accumulation in leaves was the highest The content of chloride ions in soil is less before sowing,and most of them migrate to deep soil with water.After fertilization and brackish water irrigation,the content of chloride in soil increases after harvest.During the harvest period,soil chloride ions accumulated more in 0-40 cm soil layer,and the chloride accumulation in 0-100 cm soil layer was higher than that before sowing.By fitting the relationship equation between relative yield of watermelon and chlorine concentration of plant and soil,it is concluded that the critical value of chlorine tolerance of watermelon plant is 86.55～89.60 g·kg-1,and the chlorine concentration of soil is 128.80～141.0 mg·kg-1.The critical chlorine application amount is 120～180 kg·hm-2,if it exceeds,it will adversely affect watermelon plants.