Leaching Characteristics Of Chloride In Soil And Its Effects On Citrus Growth

Citrus is an important economic crop in China,and it has always been regarded as a"chlorine-avoiding crop".K₂SO₄ is used as potassium fertilizer for a long time in production,resulting in the accumulation of S and soil acidification in citrus orchards.Chlorine is also one of the essential elements for citrus growth.In this experiment,a large soil column test was used to set different chlorine levels to study the effect of chlorine-containing potassium fertilizer on the growth of Satsuma Mandarin and the leaching characteristics of soil Cl^-.And on this basis,the field test of chlorine-containing fertilizer combined with biogas slurry was carried out on white pomelo.In order to clarify whether citrus is a chlorine-sensitive crop and the amount of chlorine fertilizer application,which provides theoretical and practical basis for citrus nutrient management.The main findings are as follows:（1）The results of leaf photosynthesis and nutrient absorption of Satsuma Mandarin in large undisturbed soil column experiments under different chlorine levels showed that with the increase of chlorine application rate,the Cl^-content of Satsuma Mandarin leaves increased exponentially,and it reached the critical level of chlorine toxicity when the chlorine application rate was 1200 kg/hm²,which applied is 4.8 times that of KCl instead of K₂SO₄ in the actual production of citrus.The application of chlorine-containing fertilizers significantly increased the contents of N,Ca,Mg,Mn and decreased the contents of K,Cu,and Zn in the leaves of Satsuma Mandarin.When the chlorine application rate was less than 488 kg/hm²,chlorine promoted the photosynthesis of Satsuma Mandarin leaves by increasing Pn,Tr and Ci.However,when the chlorine application rate exceeded488 kg/hm²,chlorine inhibited leaf photosynthesis by limiting Gs.（2）The results of soil nutrients of Satsuma Mandarin in large undisturbed soil column experiments under different chlorine levels showed that with the increase of chlorine application,soil Cl^-residue increased logarithmically,and within the chlorine application range set in this experiment,soil Cl^-residue did not cause toxicity to citrus growth.Application of chlorine-containing fertilizer can increase the content of alkaline hydrolyzed N,available K and EC in 0-40 cm soil,and reduce the content of alkaline hydrolyzed N,in40-60 cm soil.When the soil Cl^-content of the root layer exceeds 55 mg/kg,soil Ca and Mg will easily migrate downward with Cl-,reducing the supply capacity of soil exchangeable Ca and Mg,resulting in the lack of soil Ca and Mg in the root layer.（3）The soil leachate results of soil column test under different chlorine levels showed that the leaching concentration of soil Cl^-,K⁺,Ca²⁺,NO₃^--N in leachate showed the trend that first increased and then decreased,and reached the highest during the second leaching.Soil Cl^-leaching concentration and total leaching losses increased significantly with the increase of chlorine application rate,and Cl^-leaching rate was between 66%-75%.But soil NO₃^--N,K⁺,Ca²⁺,Mg²⁺leaching losses showed first decrease and then increase,when chlorine was applied from 140 kg/hm² to 266.67 kg/hm²,the leaching losses of them could keep a low level.During the whole leaching process,with the increase of Cl^-content in the leachate,the leaching amount of K⁺and Mg²⁺showed a trend of first decrease and then increase,while Ca²⁺showed an exponential increase trend,and the total amount of base ion leaching showed Ca²⁺>Mg²⁺>K⁺,indicating that Ca²⁺is the main accompanying ion when Cl^-is leaching.（4）The results of the field application experiment of chlorine-containing biogas slurry on the yield and quality of white pomelo showed that the application of chlorine-containing biogas slurry significantly increased the yield of white pomelo,and the medium-chlorine and high-chlorine treatments increased by 27.15%and 75.84%,respectively,compared with XG;The application of chlorine-containing biogas slurry can improve the soluble solids,titratable acid,peel thickness and fruit shape index of white pomelo fruit,while high amount of chlorine-containing biogas slurry decreased the VC,juice yield and edible rate of white pomelo fruit by 17.99%,7.69%and 6.19%,respectively.（5）The results of the field application test of chlorine-containing biogas slurry on the growth of white pomelo showed that the application of low-chlorine biogas slurry significantly improved the photosynthetic capacity of white pomelo leaves,but high-chlorine biogas slurry weakened the photosynthetic capacity of white pomelo leaves by reducing leaf Gs and Tr,the application of chlorine-containing biogas slurry has a tendency to increase soil p H,significantly improve soil fertility level,and will not cause more accumulation of Cl^-in the soil.Although it will increase the Cl-content of leaves,it does not reach the level of toxicity;the application of chlorine-containing biogas slurry improved the absorption of P,K,Fe,Mn and Zn by leaves,and increased K and reduced Mg carried-out amount of the fruit.