Content And Distribution Of Exchangeable Magnesium In Main Farmland Soils Of Hainan Province And Interaction Of Potassium And Magnesium

Hainan belongs to the northern edge of the tropics.Due to the special light and temperature conditions in winter,it is most suitable to develop melons and vegetables in winter to supply cold areas in the north.Winter melon,as one of the main varieties of winter melons and vegetables in Hainan,has a planting area about 8000hm².Winter melons needs more magnesium,which is only slightly lower than phosphorus.In recent years,magnesium deficiency has frequently occurred in production.Excessive application of nitrogen,phosphorus and potassium fertilizers in winter melon production is very common,resulting in high content of available nitrogen,phosphorus and potassium in the soil.A large number of studies have shown that high potassium antagonizes magnesium absorption,but the interactive effects of potassium and magnesium in the soil and different treatments of potassium and magnesium in the effect of potassium and magnesium absorption of winter gourd has not been reported,so we collected soil samples from the main farmland in Hainan,studied systematically the content and distribution of exchangeable magnesium in the soil,studied the potassium after applying different amounts of potassium and magnesium fertilizers to the soil through indoor cultivation experiments,and studied the effects of different potassium and magnesium ratios on winter melon growth and potassium and magnesium absorption and transport through hydroponic experiments,which can provide a theoretical basis for the rational application of potassium and magnesium fertilizers on magnesium-deficient soils in Hainan,thus promoting winter melon High-yield and high-quality production.The research results are as follows:（1）The lowest exchangeable magnesium content in the main farmland soils of Hainan Province is only 1.42 mg/kg,and the soils in the extremely deficient,deficient and relatively deficient state account for 86.75%,so the extent and scope of magnesium deficiency in Hainan soil are very serious.Reasonable application of magnesium fertilizer on magnesium-deficient soil has become a necessary condition for high yield and quality of crops.The two cities（counties）of Wen chang and Tun chang have the lowest soil exchangeable magnesium content,with average values of only 42.46 and 37.8mg/kg,both of which are in extremely deficient levels.Dan zhou soil has high exchangeable magnesium content,with an average value of 363.66mg/kg,but 65.63%of the soil is deficient in magnesium to varying degrees,36.88%of which is at the extreme deficiency level.The exchangeable magnesium content in the soil of planting fruit trees and vegetables is relatively high,and the lowest are the soil of planting forest trees and peanuts,both of which are lower than 50mg/kg.This may be related to its extensive management and not applying basically organic fertilizer and magnesium fertilizer.（2）The application of potassium and magnesium fertilizers is an effective method to increase the content of available potassium and exchangeable magnesium in the soil;when no potassium fertilizer is applied,whether magnesium fertilizer is applied or not,there is no effect on the content of available potassium in the soil.At 50 and 250 mg/kg,the application of high magnesium fertilizer（150 mg/kg）has an antagonistic effect on potassium;when no magnesium fertilizer or a small amount of magnesium fertilizer（30mg/kg）is applied,whether potassium fertilizer is applied or not,The medium exchangeable magnesium content has no effect,but when applying a high amount of magnesium fertilizer,potassium has an antagonistic effect on magnesium,but with the extension of the cultivation time,the antagonistic effect weakens.（3）The stem length,biomass,and root activity of winter melon treated with Mg2（1.5m M）were the largest,indicating that too high or too low magnesium concentration is unfavorable for winter melon growth.The SPAD values of the upper and lower leaves of Mg3（4.5m M）and Mg2（1.5Mm）were almost significantly higher than those of Mg1 and Mg0,which indicates that no or insufficient magnesium application affects chlorophyll synthesis.When cultured to 40 days,the SPAD value of the upper leaves of Mg0 was significantly higher than that of the lower leaves,and Mg1 was similar,but there was no significant difference in the SPAD values of the upper leaves and lower leaves of Mg2,Mg3,indicating that when magnesium was not applied or insufficient,magnesium was transfered from inferior lobe to superior lobe.（4）increasing Properly the concentration of potassium or magnesium treatment can increase significantly the potassium or magnesium content and accumulation of winter melon plants.Magnesium can promote the absorption of potassium in the root system under high potassium conditions,but has little effect on the absorption of potassium in the ground;When the ratio of K⁺/Mg²⁺is small,the magnesium absorbed is transferred through the root system to the ground,easily.and high potassium inhibits magnesium absorption.