Objective  The soil magnetic susceptibility is a common parameter for monitoring environmental pollution, and usually measured on the surface of bare soil. The farmland soil is often covered with crop straw, and this paper mainly studies the influence of straw mulching on farmland soil magnetic susceptibility measurement.

Method  The measuring points were set in paddy field, sugarcane field 1, sugarcane field 2 and corn field respectively, and piled up with straws artificially and evenly. The soil magnetic susceptibility values were measured under different straw materials and straw mulching thicknesses to analyze the influence of straw mulching on farmland soil magnetic susceptibility measurement.

Result  The soil magnetic susceptibilities decreased constantly with the increase of straw mulching thickness. When the thicknesses ranged from 0 to 5 cm, soil magnetic susceptibilities attenuated rapidly, but the values could reflect the magnetic susceptibility of bare soil to a certain extent. When the thicknesses exceeded 6 cm, soil magnetic susceptibilities attenuated slowly and when the thicknesses exceeded 10 cm, soil magnetic susceptibilities tended to zero. The test data of most measuring points were fitted with index model, while that of a few points were fitted with linear model. Data of all measuring points in paddy field, sugarcane field 1, sugarcane field 2 and corn field were respectively integrated, and the relationships between soil magnetic susceptibility and straw mulching thickness in above fields were characterized by index, index, index and linear negative correlations. The corresponding detection distances of different straw mulching thicknesses were the main factors causing the attenuation of soil magnetization susceptibilities, and the influences of straw materials on the measured value were very small.

Conclusion  When measuring soil magnetic susceptibility with MS2D magnetic susceptibility meter, it is best to measure bare soil directly. If there is straw mulching, the mulching thickness should not exceed 5 cm. The influence of straw mulching thickness on soil magnetic susceptibility can be characterized by index function or linear negative correction model.