Cropping System Effects on Soil Monosaccharides in Western Burkina Faso

Labile pools of soil organic matter (SOM), including soil sugars, are important to the formation and stabilization of soil aggregates and to microbial activity and nutrient cycling. The effects of cropping systems at farm level in tropical areas on SOM labile pool dynamics have not been adequately studied and the results are sparse and inconsistent. The objective of this study was to determine the effects of soil management intensity on soil sugar monomers derived from plant debris or microbial activity in cotton (Gossypium herbaceum)-based cropping systems of western Burkina Faso. Thirty-three (33) plots were sampled at 0-15 cm soil depth considering field-fallow successions and tillage intensity. Two pentose (arabinose, xylose) and four hexose (glucose, galactose, mannose, glucosamine) monomers accounted for 2 to 18% of soil organic carbon (SOC) content. Total sugar content was significantly less with tillage, especially for the hexose monomeric sugars glucose and mannose, the latter of microbial origin. Soil mannose was 63 and 80% less after 10 years of cultivation, without and with annual ploughing respectively, compared with fallow conditions. Soil monosaccharide content was rapidly restored with fallow and soon approached the equilibrium level observed under old fallow lands. Therefore, the soil monosaccharides, in particular galactose and mannose from microbial synthesis are early indicators of changes in SOC.