Effects of Lime Content on Soil Acidity,Soil Nutrients and Crop Growth in Rice-Rape Rotation System

【Objective】Soil acidification is becoming more and more serious, which reducing crop yield in rice-rape rotation system of southern of China. In this study, the effects of lime application on soil nutrients and crop growth in acidic soil were studied, and the response relationship between soil available nutrients, yield and crop nutrient uptake to soil pH was clarified, so as to provide theoretical basis for the improvement of acidified soil in paddy fields. 【Method】 From 2015 to 2018, the paddy field with soil pH 4.5 was selected in Jinxian county, Jiangxi province, and hydrated lime was used as acid soil modifier. Through laboratory simulation, the amount of hydrated lime under different soil pH values was calculated. Then field experiments were carried out with six soil pH gradients of pH 4.5, pH 5.0, pH 5.6, pH 6.3, pH 6.8, and pH 7.3. In 2015, in order to ensure that the pH value of the treated soil was basically consistent with the measured pH value, one year after the soil was uniformly planted, the hydrated lime was used for quantitative adjustment with a period of one year. 【Result】 (1) With the amounts of lime and soil pH increase, the contents of soil available nitrogen increased first and then decreased, the content of soil exchangeable Ca ²⁺ and exchangeable Mg ²⁺ increased significantly, and the content of soil available potassium and available phosphorus decreased significantly. (2) With the increase of lime contents and soil pH, crop yield first increased and then decreased. At pH 6.4 (equivalent to the amount of 6 145 kg·hm ^-2hydrated lime), the yield of rape reached the highest; compared with pH 4.5, the yield increased by 202.2%. At pH 6.8 (equivalent to the amount of 7 474 kg·hm ^-2hydrated lime), the rice yield reached the highest; compared with pH 4.5, the yield increased by 61.2%. When the yield was reduced by 50%, the soil pH thresholds of rape and rice were 4.7 and 4.2, respectively. (3) Soil pH significantly affected crop nutrient uptake content. With the increase of the amount of hydrated lime, the nitrogen, phosphorus and potassium uptake contents in rape increased first and then decreased. The average increase of nitrogen, phosphorus and potassium uptake contents in rape from 2016 to 2018 was 59.5%-181.4%, 36.2%-188.8% and 65.7%-198.9%, respectively. The nitrogen, phosphorus and potassium uptake contents in rice first increased and then decreased. The uptake content of rice was the highest at pH 6.8. Compared with that without lime application the average increase of nitrogen, phosphorus and potassium uptake of rice from 2016 to 2018 was 11.1%-88.6%, 13.5%-68.5% and 9.7%-66.1%, respectively.【Conclusion】Under the application of lime conditioner, the contents of soil available nitrogen and exchangeable Ca ²⁺ and exchangeable Mg ²⁺ were increased with the increase of soil pH, which promoted the uptake of nitrogen, phosphorus and potassium nutrients of crops and increased the crop yield. Under the experiments conditions, the optimal dosage of lime in acid soil (pH 4.5) of rice -rape rotation system was about 6 500 kg·hm ^-2, which could obtain stable and high yield of crops in rice-rape rotation system of southern China.