Decomposition of 14C-labelled plant residues in different soils and climates of Costa Rica

The decomposition of 14C-labelled wheat straw has been studied under field and laboratory conditions since 1975 in 13 Orthents, Andepts, Tropepts, Ustolls, and other soils of Costa Rica, representing its most important groups and production zones. No reliable predictions about the degradation rate of plant residues in field soils at their natural locations can be made from data obtained under controlled laboratory studies. Although, in some cases the decomposition rates of the laboratory experiment corresponded fairly well with the ones obtained in the field, there were instances where the laboratory decomposition lags behind. The reasons for this discrepancy have not yet been clearly interpreted, but will certainly have to do with the natural climatic conditions prevailing at the particular location. It is important to do such experiments in the open field, no matter how complicated this may be. It was found after a year, that from 23 to 36 per cent of the 14C added in the wheat straw remained in the soils under field conditions. Four years later, the residual 14C was from 11 to 23 per cent. From this information it is assumed that a considerable fraction of the organic carbon in the plant residues ramains undecomposed during several years in these tropical soils, as it occurs in other soils from temperate areas of the world. (Author)