| Watermlon,as a chlorine resistant crop,is extremely sensitive to chlorine.When the chlorine input reaches a certain level,the growth of watermelon would be inhibited,and produce toxic effects,and the yield and quality would decrease significantly.This study aimed at the problem of chlorine toxicity caused by the long-term use of subsurface briny water containing chloride ions for irrigation of watermelons in NingXia,through field experiment were carried out with five levels of Cl0(0 kg·hm-2)、Cl1(30 kg·hm-2)、Cl2(60 kg·hm-2)、Cl3(90 kg·hm-2)、Cl4(120 kg·hm-2)chlorine,respectively,and the effects of chlorine application on growth,nutrient absorption,yield and quality of watermelon were studied,in order to provide a theoretical basis for the determination of chloride ion toxicity threshold and the safe use of subsurface briny water irrigation of watermelons.Results showed that:1.The chlorine in soil was mainly concentrated in 20-40 cm soil layer,while the nitrate nitrogen,ammonium,available phosphorus and available potassium were mainly concentrated in 0-20 cm soil layer,and accumulated to 20-40 cm in the later stage.When the chlorine application rate was 60-90 kg·hm-2,the nutrient content in soil was the highest,more than 90 kg·hm-2,the nitrate nitrogen content decreased significantly,and the content of chlorine,ammonium,available phosphorus and available potassium decreased.2.Appropriate amount of chlorine fertilizer could promote the growth of watermelon vines,stems and leaves.The vines of C14 treatment was the longest,which was 11.28%higher than that of Cl0.At the later growth stage,the vines of ClO treatment decreased gradually,while that of chlorine treatment still increasing.At the later growth stage,the stems of watermelon were 0.70 mm、0.44 mm、0.70 mm、0.69 mm higher than that of C10(no chlorine application).The numbers of leaves increased by 376,372,382,385,410 for Cl0,Cl1,Cl2,Cl3 and Cl4 treatments,respectively.In the early growth period,the SPAD value of watermelon leaves was middle leaf>top leaf>basal leaf,and the later growth period was middle leaf>basal leaf>top leaf.When the chlorine application amount reached 120 kg·hm-2,the SPAD value of watermelon leaves was the lowest.3.The chlorine content in different organs of watermelon was root>stem>leaf,skin>pulp>seed.In the early growth stage,there was no significant deifference.In the middle growth stage,when the chlorine application was 60-90 kg·hm-2,the chlorine content was the highest,if the chlorine fertilizer was applied continuously,the content would decrease on the contrary.In the harvest stage,the content of C14 treatment was the highest,and the contents of root,stem,leaf were 34.44 g·kg-1、29.68 g-kg-1、23.22 g·kg-1,resoectively.The content of total nitrogen was leaf>stem>root,peel>seed>pulp,and the content and accumulation of total nitrogen in root,stem and leaf were 60 kg·hm-2.In the early growth stage,the total phosphorus content was mainly concentrated in the leaves and stems,and in the late growth stage,it was mainly in the roots,when the chlorine application rate was 60-90 kg·hm-2,the total phosphorus content was the highest,and the total phosphorus content in the seeds was the highest,reaching 41.59 g·kg-1.The content and accumulation of total potassium in different organs of watermelon were stem>leaf>root,the content and accumulation of total potassium were the highest at 60 kg·hm-2 and decreased significantly at 120 kg·hm-2.4.The yield of watermelon in gravel-mulched field reached the highest of 33302 kg·hm-2 at 94.68 kg·hm-2 chlorine rate,which was 13.54%higher than that of Cl0 treatment.The morphological quality of watermelon was the best at 60 kg·hm-2,and the nutritional quality was the best at 60-90 kg·hm-2,the reasonable application of chlorine fertilizer had a greater impact on soluble solids,hardness and vitamin C content,therefore,the chlorine application rate should be between 60-90 kg·hm-2,which is beneficial to the growth、yield and quality of watermelon,while more than 90 kg·hm-2 will inhibit the growth and reduce the yield and quality of watermelon.In a word,the regulation of chorine input is crecial to the growth、yeild and quality of watermelon in gravel-mulched field.Under brine water irrigation,when the amount of chlorine applied is 60-90 kg·hm-2,it is beneficial to the growth of watermelon.When the amount of chlorine applied is more than 90 kg·hm-2,the content of chlorine ion in the soil from the watermelon sitting period to the harvest period reaches 22.09-26.63 mg kg-1,the growth,yield and quality of watermelon were obviously inhibite. |
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