QUANTITATIVE ESTIMATION OF CROP RESIDUES, THEIR NPK POTENTIAL AND MANURIAL VALUE

A field study was undertaken during 2008-09 and 2009-10 to quantify production of various crop residues and their total NPK potentiality for recycling and manurial value in composts. Rice (Oryza sativa) produced the highest mean dry crop biomass (4.94 t/ha) with C content (36.44%) while the lowest C content (15.90%)  in potato (Solanum tuberosum) haulm. The total N content (1.33%) was maximum in tapioca (Manihot esculenta)  leaves followed by black gram (Vigna mungo) (0.86%). Wheat (Triticum aestivum) crop residue exhibited the highest C:N ratio (75.26) while tapioca leaves showed lowest C:N ratio (19.17). The total P content of all crop residues was minimum. The highest total potassium content (1.23%) was recorded in maize (Zea mays)  crop biomass. The highest total N, P, K potential (91.39 kg/ha) was estimated in rice residues followed by that in maize residues (69.96 kg/ha). Chemical compositions in compost of various crop residues indicated that pH of the composts ranged from 5.48 -5.91. The compost of tapioca leaves showed the highest organic carbon (7.10%) and N (1.38%) contents. Niger (Guizotia abyssinica) biomass compost recorded the highest C:N ratio (11.15). The highest P2O5 (0.15%) however, was found in buckwheat (Fagopyrum esculentum L.) compost while that from wheat residue registered the highest K2O (0.29%). The rice crop residue compost contained highest Ca (75.0 ppm), Mg (41.0 ppm) and S (52.0 ppm) contents. The Fe content (18.60 ppm) was the highest in compost from wheat. Other micronutrients, such as Mn content (8.10 ppm) in toria (Brassica campestris), Cu content (5.33 ppm) in sesamum (Sesamum indicum), Zn content (5.70 ppm) and Mo content (4.26 ppm) in buckwheat, and B content (2.50 ppm) in niger were recorded as highest. Thus, crop residues may be adopted to increase the status of organic C and nutrients recycling in the agricultural soil.