Soil organic matter and nitrogen transformation mediated by plant residues of different qualities in sandy acid upland and paddy soils

Abstract

Organic matter management is believed to solve many of the chemical and physical problems of coarse-textured, low fertility soils of NE Thailand. The influence of different plant residues available in this area on soil C and N dynamics in upland (Oxic Paleustult) and lowland (Aeric Paleaquult) soils was tested. Residues included groundnut (upland) or Sesbania rostrata stover (lowland), rice straw, Tamarindus indica and Dipterocarpus tuberculatus leaves applied at 10 t ha-1 (dry matter). For the former three residues additional application rates of 20 t ha-1 were included as well as a mixture (50:50) of groundnut/Sesbania - rice straw treatment. Groundnut stover and Sesbania had C:N ratios 17%) and polyphenol (>4.5%) contents. These latter residues, despite slow decomposition, apparently resulted in only moderate soil C (1 mm). Thus the mixture of groundnut/Sesbania with straw was among those residue treatments that led to the highest soil C (