Study on the changes of soil properties, plant pests and diseases population in conventional farming converted into organic farming

In order to develop organic farming in Bali [Indonesia], a series of organic vegetable cultivation experiments consisting of 9 (nine) plantings was conducted in Bangli village, Baturiti District, Tabanan, Bali, a main vegetative cultivating area in Bali for three years, from 2005 to 2007. The land used in this study had been used for conventional vegetable cultivation, in which synthetic fertilizers and pesticides had been intensively applied. In each planting, the experiment was designed in Randomized Block Design (RBD) consisting of nine treatments of a combination between cow manure at 20, 30 and 40 tons/ha, and application of botanical pesticides such as Frontir (containing the extracts of Eugenia aromatica and Pometia pinnata), Bali species (a mixture of several spices such as Alpinia galonga, Curcuma sp. salt, prawn paste, oil, Piper retrofractum, Eugenia aromatica etc) and neem extract. Cabbage is generally planted as monoculture or in mix cropping with leek and carrot, and potato as monoculture farming. The change of soil properties and the main pests and diseases, beneficial microorganisms and the crop yield were evaluated and determined to know the effect of the treatments. The treatment with cow manure at 40 tons/ha resulted in the increase of the concentration of soil nutrients such as N, P, K, Ca, Mg, Fe and Mn. The C/N ratio in the soil of this treatment obviously decreased, indicated that the concentration of Nitrogen in the soil increased. Population of beneficial microorganisms (antagonists) namely Bacillus sp. and Pseudomonas fluorescens on this treatment was found to be the highest among other treatments. Treatment with cow manure at 40 tons/ha in combination with application with application of Bali spices obviously reduced leaf rot disease on cabbage caused by Xanthomonas sp. Population of diamondback moth (Plutella xylostella) on the treatment with 40 tons/ha cow manure in combination with neem extract was found to be the lowest among other treatments. In general, the yield of cabbage in the second and fourth planting with cow manure treatment was consistently higher in comparison with the conventional farming system. Results of present study suggested that continual organic farming system application after a certain period improves soil properties, increases the population of beneficial microorganisms, reduces the pest and diseases and increases the yield of crop.