Evaluation of the Topsoil Nutrient Content and Fertility of Paddy Land in Laos
A more comprehensive survey was conducted to understand the changes in soil nutrients in rice fields in Laos and to provide a basis for scientific and rational fertilization of rice fields in Laos.Forty soil samples were collected from 11 provinces and cities in northern,central,and southern Laos in typical rice-producing areas and analyzed for organic matter,nitrogen,phosphorus,potassium,calcium,magnesium,zinc,and pH.The organic matter and exchangeable magnesium con-tents ranged from 3.3 to 56.0 g/kg and 3.6 to 184.8 mg·kg-1,respectively,which were in the middle to high levels;the soil effective phosphorus and quick-acting potassium contents ranged from 2.1 to 38.7 and 8.8 to 204.5 mg·kg-1,respectively,which were low with high variability;the exchangeable calcium content ranged from 22.0 to 2 370.0 mg·kg-1,with high vari-ability;and the content distribution was not uniform.The exchangeable calcium content of the southern rice field soil was low,and the effective phosphorus content was low;the exchangeable magnesium content of the central rice field soil was low,and the quick-acting potassium content of the northern rice field soil was low.The overall acidity and strong acidity of Lao paddy soils,the low content of quick-acting potassium and effective phosphorus,and the uneven distribution of exchangeable cal-cium are the main nutrient problems in Lao paddy soils at present;the soil nutrient content varies greatly in different rice eco-logical planting areas.Lime and alkaline fertilizers should be applied to increase the soil pH;chemical fertilizers such as cal-cium,magnesium,phosphorus,and potash fertilizers should be increased in different planting areas;and organic fertilizer applications should be considered.
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