Evaluating the Impact of Integrated Nutrient Management Practices on Land Productivity, Crop Residue Decomposition and Abundance of Soil Organisms in a Banana Plantation in Sri Lanka

The fertilization practices heavily influence the decomposition rate of organic materials added to soil. Hence, the nutrient management strategies that aim to improve crop yields may not necessarily support organic carbon accumulation in soil and overall soil fertility. This study investigated how land productivity, crop residue decomposition and diversity of soil organisms were affected by the combined use of chemical fertilizers (CF) and poultry manure (PM) in a banana plantation in Buttala, Sri Lanka. Banana yield, soil properties and decomposition of crop residues were studied in six treatments as, CF1+PM1, CF1+PM2, CF1+PM3, CF2 +PM1, CF2+PM2, and CF2+PM3. CF1 and CF2 correspond with 75% and 100% of recommended CF application rate. PM1, PM2 and PM3 correspond with PM application rates of 0, 2.5 and 5 kg/plant. Crop residue decomposition was assessed using litter bags containing two litter materials as banana pseudo-stem pieces and banana leaves and placed at two depths (surface and at 7.5 cm depth). Litter bags were recovered at 17, 31 and 45 days after placement (DAP) and weight loss of crop residues was determined. The application of poultry manure significantly increased (P<0.01) banana yield at first harvest and decreased (P<0.1) bulk density. Type of material and time of exposure to decomposition had significant effects (P<0.05) on litter decomposition but depth of placement and nutrient management strategy had no significant effect (P>0.05) on decomposition. By 45 DAP pseudo-stems were degraded more than leaves (67.47±13.99 % and 46.90±5.76 %, respectively). The abundance of culturable bacteria and cellulose decomposers in soil and the abundance of soil fauna in decomposing litter were significantly (P<0.1) increased with the PM application to soil. In conclusion, in the studied banana plantation, incorporation of PM in nutrient management increased land productivity and had positive impact on some soil properties, which are important determinants of soil fertility but did not register any effects on crop residue decomposition during the study period.