Effect of Organic Farming on Soil Fertility , Yield and Quality of Crops in the Tropics
To elucidate the advantages of organic farming over inorganic farming in sustainable agriculture, experiments were conducted at Kerala Agricultural University, College of Agriculture, Vellayani using Cowpea (Vigna unguiculata subsp. sesquipedalis (L.) Verdcort) as a test crop. The experiments were carried out in a loamy skeletal kaolinitic rhodic haplustult soil. Different treatments tested were T1:Full recommended dose as per Package of practices recommendation (20 kg N ha-1, 30 kg P2O5ha-1 & 10 kg K2O ha-1 with 20 t FYM ha-1), T2: Full recommended dose as Farm Yard Manure, T3:Full recommended dose as FYM + P Solubilizing Micro-organisms, T4: Full recommended dose as Vermi compost, T5: Full recommended dose as Vermi compost + P Solubilizing Micro organisms, T6:Full recommended dose as Poultry manure, T7: Full recommended dose as Poultry manure + P Solubilizing Micro organisms, T8: Inorganic alone (20kg N ha-1, 30 kg P2O5ha-1 & 10 kg K2O ha-1). Farmyard manure, vermicompost and poultry manure were applied on the N content basis and additional requirements of P and K were met through application of rock phosphate and ash according to treatments. Phosphorus Solubilizing Microorganisms consisted of a mixture of Pseudomonas, Aspergillus and Azospirillum. Phosphorus Solubilizing Micro organisms @1 g plant -1 was applied in T3, T5 and T7 treatments. Entire P and K were applied basally and half the recommended N as basal and rest after two weeks of planting for all the treatments. The experiments were laid out in randomized block design with eight treatments and three replications. Lime was uniformly applied to all plots @ 250kg ha-1 to reduce the soil acidity. The results showed that organic farming practices improved physical, chemical and biological properties of the soil and helped for carbon sequestration. Organic manures also enhanced the soil enzyme activities such as dehydrogenase and phosphatase. All growth characters like height of plant, number and weight of nodules and leaf area index were found to be significantly boosted by organic treatments. The highest pod yield has been observed in Package of Practices recommendation treatment (T1) followed by vermi compost + P Solubilizing Micro organism’s application (T5). But these two treatments were on par statistically. Vermi compost + P Solubilizing Micro-organisms application showed pronounced effect on bhusa (total shoot weight) yield and total dry matter production. Pod nutrient composition as obtained from chemical analysis projected the role of organic manures in enhancing the pod nutrient content- N, P, K, Ca, Mg, Mn, Zn and Cu. Sulphur content was highest in poultry manure treatment. The influence of organic manure addition over inorganic nutrition was clearly highlighted in pod quality. Vermi compost application registered lowest value for crude fibre in cowpea. Regarding protein content, shelf life and organoleptic evaluation, organic treatments showed superior values over inorganic alone. The study revealed the favourable effect of organic nutrition in enhancing soil fertility and the quality aspects of cowpea pod in comparison with inorganic and integrated nutrition.