Effects of Rhizobium Inoculation and Cropping systems on Leaf Litter Decomposition of Two legumes (Common bean and Lablab)

Abstract

Crop litter residues decompose and provide nutrients in to the soil. Decomposition is a process which is accelerated by sufficient soil conditions (good soil physical properties, soil moisture and microorganisms) and residues litter quality. However, the quantitative knowledge on decomposition of different legumes under such conditions when litter residues are placed above and below (10 cm) soil is insufficient. Therefore, the decomposition study of the two inoculated legumes residues, common bean (P. vulgaris) and lablab (D. lablab) collected from two cropping seasons (2015-2016) was set using litterbag experiments at the screen house of Selian Agricultural Research Institute (SARI). The residues were applied on the surface and on sub soils and then retrieved after 10, 20 and 30 days. The parameters determined from the legume residues included; mass loss, decay rate constant (k), and Carbon and Nitrogen concentrations. Results showed lower decomposition of legume residues collected from two cropping seasons when the litterbags were placed on the soil surface compared to subsoil. Mass loss was higher in Rhizobium inoculated legumes than uninoculated legumes of residues collected from both cropping seasons. D. lablab had higher mass loss than P. vulgaris on the soil surface and in sub soil of litter residues collected from both cropping seasons. The residues decay rate ranged from 0.97 to 0.99 for all treatments in screen house across the litter residues collected from the two cropping seasons. Lablab recorded the high decomposition rate than common bean in all sampling times as a result of high initial N and C content in the litter residues. This predicts that, the mass loss, nutrient content, and litter quality were all changed mostly in the first 0-30 days, which indicates that early stage of litter residues incorporation is important in nutrients release into the soil. These findings showed the effect of plant residues on the supply of mineral N to crops growing during subsequent seasons.