Abstract
As the Green Revolution initiated in the late 1960s was expected to affect paddy soil fertility considerably, information on the long-term changes of the total content of elements and micronutrient status of paddy soils in Thailand were investigated. Totally, 65 soil samples were collected in 2015 and 2016 from the surface layer of paddy fields in the northeast, north, central plain, and Bangkok Plain of Thailand. Total content of 13 elements (Si, Fe, K, Ca, Mg, Na, Mn, P, Cl, S, Ni, Cu, Zn) and available Mn, Fe, Cu, Zn, S and B contents were determined, and compared with those in the 1960s collected at or near the same locations. Total contents of the 13 elements in the 2010s were relatively lower than those of the world soil except for Si, and the total contents in the northeastern region were considerably lower than other regions except for Si. Total K, Mn and Si contents in 2010s were significantly lower than those in the 1960s (p < 0.01), suggesting the possibility of accelerated weathering by agricultural intensification. The available Mn and Fe contents were sufficiently present in all the fields, whereas available Cu, Zn, S and B contents of dominant soils in the northeastern region were below the threshold for deficiency. It is, therefore, recommended to apply more K fertilizer to maintain the level of soil K, and to apply more organic fertilizers with a variety of micronutrients, especially in the northeastern region.
