Status Of Soil Exchangeable Mg And Yield Response Of Rice To Mg Fertilizer In Fujian Province,China

Magnesium（Mg）is an essential nutrient for crop growth and plays an important role in the formation of photosynthetic products,yield,and quality of crops.Hence,it is important to clarify the status of soil exchangeable Mg content,Mg fertilizer efficiency and recommended dosage to guide the scientific management of Mg fertilizer.In this study,we collected 9200 samples of soil exchangeable Mg data from Fujian province from 2016 to 2019.We conducted a comprehensive analysis of soil exchangeable Mg content,including its abundance,deficiency,and the influencing factors,at the provincial scale.The effect of Mg fertilizer application was explored in the main rice-producing areas of the Fujian province.A regression analysis established the recommended amount of Mg fertilizer based on varying levels of exchangeable Mg content.Subsequently,a comparative trial of different types of Mg fertilizer was conducted on soils with varying exchangeable Mg content,ultimately determining the best Mg fertilizer type.These findings could provide a scientific basis for the judicious application of Mg fertilizer in the main rice-producing areas of Fujian province.The main research results were as follows:（1）The average soil exchangeable Mg content in Fujian province was 80.3 mg kg^-1(2.02～601 mg kg^-1).Approximately 49.3%of the soils exhibited soil exchangeable Mg content less than 60 mg kg^-1.The rice soils had a significantly higher exchangeable Mg content than red soils and laterites.The random forest model showed that soil organic matter,altitude,and p H were the most important factors influencing soil exchangeable Mg.（2）The results of field trials（2020-2021）on Mg fertilizer dosage and type showed that applying Mg fertilizer could significantly improve rice yield,fertilizer utilization,and economic efficiency and substantially reduce nitrogen surplus.The degree of yield increase with different Mg fertilizer dosages was as follows;Mg3(43.8 kg MgO ha^-1)>Mg2(29.2 kg MgO ha^-1)>Mg1(14.6 kg MgO ha^-1)>CK.Rice yield was significantly increased under Mg2 and Mg3 treatments by 6.97%and 7.15%,respectively,compared to the control,but there was no significant difference between them.In contrast,different types of Mg fertilizer showed the following pattern for the increase in yield;Mg（OH）₂>Mg SO₄>CK.（3）The threshold level for deficient exchangeable magnesium（Mg）in rice soils was80 mg kg^-1.Through a maximum return to Mg,the recommended regional Mg fertilizer dosage in Fujian province was 31.59 kg MgO ha^-1.When the exchangeable Mg in soil is below 80 mg kg^-1,the Mg fertilizer dosage should be increased to 33.18 kg MgO ha^-1.Conversely,when exchangeable Mg in the soil exceeds 80 mg kg^-1,the Mg fertilizer dosage should be reduced to 27.25 kg MgO ha^-1.Based on the soil Mg status in the rice area of Fujian province,the preliminary Mg fertilizer requirement is 19655 t MgO.