Effects Of Long-term Fertilization On Calcium Effective Forms And Availability In Greenhouse Soil

Facility cultivation is one of the important ways of vegetable production in China.It has developed extremely rapidly in the past 40 years.However,with the increase of planting years,the accumulation of NPK elements has led to secondary salinization,acidification and nutrient imbalance and consolidation.The problem of continuous cropping,such as knotting,has led to soil-borne diseases and plant physiological diseases,which seriously affect the yield and quality of crops.At present,although the content of calcium in the soil in the north is rich,the application of organic fertilizer in the facility cultivation supplements the content of total calcium and exchangeable calcium in the soil to some extent,but the physiological diseases caused by calcium deficiency in the vegetable crops were not uncommon.Therefore,the soil should be studied,whether nutrient accumulation has an effect on the effective forms and availability of soil calcium can provide a scientific basis for balanced fertilization in facilities to increase the effectiveness of calcium.In this study,the changes of soil available calcium content and the leaching process of calcium under the conditions of nitrogen,phosphorus and potassium were monitored by laboratory culture and leaching tests.The tomato experimental site located in Shenyang Agricultural University for long-term fertilization was the research object.By collecting soil and tomato plants accumulated by different nutrients,the content of available calcium in the soil,the growth of tomato and the absorption of calcium were determined to analyze the effects of different nutrient accumulation on the calcium effctives and availability.Below are key research findings:?1?Nitrogen and potassium application at different levels were affected by NH₄⁺,NO₃^-and K⁺,respectively.Water-soluble calcium was increased while exchangeable calcium content was decreased.The combination of water-soluble calcium with phosphorus application at different levels decreased the availability of soil calcium.?2?Because of the influence of NH₄⁺,NO₃^-and K⁺,the migration of calcium in soil was strengthened under different levels of N and K application.At the same level,when N and K were applied alone,the total leaching amount of calcium was slightly greater than that of K under the condition of N,and the leaching amount of calcium was reduced by the application of P.?3?In plot experiment,with the increase of nutrient accumulation in soil,total calcium in soil was similar,water-soluble calcium content in soil increases,exchangeable calcium and calcium saturation decreases,water soluble and exchangeable Ca/K and Ca/NH₄⁺ show a downward trend,and the ratio of available calcium to nitrogen,phosphorus and potassium in soil decreases,showed a relative lack.?4?Through the study on the growth of tomatoes under different nutrient accumulation after long-term fertilization,it was found that when the content of available nitrogen,available phosphorus and available potassium in the soil exceeded 394.5,289.1 and 452.33 mg·kg^-1,the dry matter and yield of tomatoes were inhibited,and the occurrence of tomato BER increased with the increase of soil nutrient accumulation.?5?The increase of soil nutrient accumulation and the decrease of available calcium ratio will affect the uptake of calcium in tomato.The upward transport of calcium was inhibited.The calcium content in tomato leaves and fruits decreases first,followed by stems and finally roots.The proportion of calcium in tomato stems,leaves and fruits decreased.Tomatoes were susceptible to BER when the calcium content in tomato fruit was less than 1 g·kg^-1,Ca/N,Ca/P and Ca/K were less than 0.05,0.3 and 0.03,respectively.?6?The incidence of tomato umbilical rot was less than 6% when the content of available nitrogen and phosphorus,available potassium was 205²73,117¹47 and 168²21 mg·kg^-1,Ca/N was 17.5⁶5,Ca/P was 32.5⁹4,Ca/K was 11.7³4.6,and the comprehensive yield and incidence of tomato umbilical rot were less than 6%.It was more appropriate to apply nitrogen,phosphorus and potassium fertilizer 483,161 and 691 mg·kg^-1 for 7 years.?7?The amount of calcium absorbed by tomato in this experiment was 1 640²707 kg·hm^-2 per year when cow manure and chicken manure were mixed at a ratio of 1:1.The total amount of calcium absorbed by cattle manure and chicken manure was 3284⁵428 kg·hm^-2,which was not enough to supplement the available calcium taken away by tomato.