| Long-term supplementary irrigation with brackish water containing a lot of chloride ions would inhibit the growth of watermelon because it is a kind of chlorine-free crop,while the application of nitrogen fertilizers could alleviate the toxic effects of chloride ions to some extent.In this study,a gravel-mulched field experiment with watermelon was carried out,in which 3 nitrogen levels(N0:no nitrogen fertilizer,N1:nitrogen 225 kg/hm2,N2:nitrogen 300 kg/hm2)and 3 chlorine levels(C10:Chlorine-free,Cll:Chlorine concentration 30 mmol/l,C12:Chlorine concentration 60 mmol/1)were set for complete combination,to explore the interaction between nitrogen and chlorine and its influence on soil nutrients,watermelon growth,yield and quality,and provide a basis for regulating and alleviating the harm of chloride ions in gravel-mulched watermelon under brackish water irrigation.The main results were as follows:1.Combined application of nitrogen and chlorine could affect the release and distribution of nitrogen,phosphorus and potassium available nutrients and chloride ions in the soil.Nitrogen application could significantly increase the content of nitrate nitrogen and available phosphorus in the soil,while chlorine application could significantly inhibit the formation of nitrate nitrogen and available P in the soil,and promote the migration of nitrate N and available P to the deep soil.There were a significant negative interaction between them.Appropriate amount of nitrogen application and chlorine application were both beneficial to the ammonization of the soil and promote the generation of ammonium nitrogen,and there were a positive interaction between them.Both nitrogen application and chlorine application could promote the release of soil available potassium,and there were a positive interaction between them.Chlorine application could obviously increase the chloride ion content in the soil,while the appropriate amount of nitrogen application reduced the chloride ion content in the soil,and nitrogen and chlorine were a negative interaction effect on the existence of soil chloride ions.2.The application of nitrogen fertilizer could obviously increase the length of the main vine and the number of leaves of watermelon,while the chloride ion showed a significant inhibitory effect.The application of nitrogen fertilizer at a high amount could alleviate the inhibitory effect of chloride ion to a certain extent.From flowering to maturity,the main vines of N2C10 treatment were the longest,increasing by 7.6%,12.9%,18.8%,and 19.1%respectively compared with N0Cl0,while the lowest was treated with N1Cl2.The number of leaves in each period was higher in N2Cl0 treatment,and the lowest in N0Cl2 treatment.There was a difference of 345 leaves between the two in the mature period.Appropriate nitrogen and chlorine combined application were beneficial to the thickening of the main vines of watermelon.When no nitrogen is applied,the treatment with a chlorine concentration of 30 mmol/1 can increase the thickness of the main vines.The medium application of N1(225 kg/hm2)and the high application of nitrogen could increase the thickness of the main vine.When nitrogen was N2(300kg/hm2),the application of chlorine inhibits the thickening of the main vine.The right amount of nitrogen and chlorine could also increase the SPAD value of leaves.For the upper leaves,the treatment with N2Cl1 was higher during the whole period;the SPAD value of nitrogen fertilizer on the middle leaves showed a significant promotion effect during the whole growth period,and the treatment with N2Cl0 during the vine and flowering period was higher,and the SPAD value of the middle leaves was higher.The N2Cl2 treatment was higher at the maturity stage;the SPAD value of the lower leaves was the highest in the N2Cl0 treatment from the vine stage to the swelling period stage,and the highest was the N2Cl1 and N2Cl2 treatment at the maturity stage.3.The application of nitrogen fertilizer could increase the total nitrogen content of the leaves,and the influence of chloride ions varied with the amount of nitrogen applied.When nitrogen was not applied,chloride ions could significantly increase the total nitrogen content of the upper leaves(expanding period)and lower leaves(flowering and maturity periods);when nitrogen was applied at a moderate amount(N1),the chlorine concentration promoted the increase in the expansion period.The total nitrogen content of the middle and lower leaves;when applying high amounts of nitrogen,the appropriate amount of chlorine could increase the total nitrogen content of the upper leaves during the flowering period and reduce the total nitrogen content of the middle leaves during the melon setting period.The medium chlorine is beneficial to the nitrogen content of the lower leaves.The right amount of nitrogen and chlorine could also increase the total phosphorus content of leaves.For the upper leaves,the interaction between nitrogen and chlorine reached a significant level during the setting stage,that is,when no nitrogen is applied,the total phosphorus content increases with the increase of the amount of chlorine applied,and when the amount of nitrogen was applied,it decreased with the increasing of the amount of chlorine;The total phosphorus content of the middle leaves showed a significant inhibitory effect at the melon setting stage,and the highest treatment with N1Cl0;the chlorine concentration showed a very significant inhibitory effect on the total phosphorus content of the lower leaves at the melon setting stage and the swelling period stage.The effect of nitrogen and chlorine on the total potassium content of leaves varied with leaf position.Appropriate nitrogen application could increase the total potassium content of leaves,while increasing the chlorine concentration had a significant inhibitory effect,which was more significant in the mature stage.Nitrogen had an inhibitory effect on the chlorine content of leaves,and chlorine had an accelerating effect,with the middle leaves being the most obvious.4.Appropriate amount of nitrogen application could increase the dry matter quality and yield of watermelon,while chlorine application would significantly reduce the dry matter quality and yield,and the application of nitrogen fertilizer would reduce the inhibitory effect of chlorine to a certain extent.The total dry matter quality and yield of watermelon were both the highest in N1Cl0 and the lowest in N0Cl2,with a difference of 72.6%and 81.2%respectively.From the point of view of watermelon quality,the application of nitrogen fertilizer would greatly increase the total acidity of the flesh,but the combined application of chlorine would reduce the total acidity;the protein content of the flesh was the highest in N1Cl0 treatment,which was 7.4%higher than N0Cl0,and the lowest in N0Cl2 treatment,which was lower than N0Cl0 13.2%;Watermelon soluble sugar content was the highest under N1Cl2 treatment,11.4%higher than N0Cl0;Vitamin C content of watermelon treated with N0Cl1 reached 16.31mg/kg,30.0%higher than N0Cl0;moderate nitrogen fertilizer combined with chlorine would also increase watermelon lycopene content.However,high-level nitrogen application had an inhibitory effect;the effects of nitrogen and chlorine on the soluble solid content of watermelon were also shown as mutual inhibition.Nitrogen has a promoting effect and chlorine has an inhibitory effect.It is concluded that the effects of nitrogen and chlorine on the release of soil nutrients and the growth of watermelon were shown as mutual inhibition.Exogenous chlorine would greatly increase the chloride ion content in the soil,inhibit the release of soil nitrate nitrogen and available phosphorus,and promote the release of ammonium nitrogen and available potassium.Appropriate nitrogen application would reduce the chloride ion content in the soil and plants,,and then relieve the inhibitory effect of chlorine on the growth of watermelon,thereby promoting watermelon growth and nutrient absorption,and increasing yield.At the same time,proper amount of nitrogen and chlorine could also improve the quality of watermelon,reduce acidity and increase the content of soluble sugar. |
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