Optimum compost application for raised bed organic vegetables

Yield of organically grown vegetables, crop biomass, cover crop biomass, and various soil chemical nutrient levels including N, P, K, Ca, Mg, pH, soil organic matter and soil nitrate were measured against four compost rates to determine the optimum compost application rates for raised bed organic farming. Organic poultry mortality compost was applied at rates of 0, 10.7, 32.2, and 53.7 Mg/ha. Compost treatments were fall applied for two consecutive years in three cropping blocks with nine 33 m rows per block and fall seeded with a winter rye, Secale cereale/hairy vetch, Vicia villosa/crimson clover, Trifolium incarnatum cover crop. In 2008 squash Cucurbita pepo, variety "Green Wave;" tomato Lycopersicon esculentum, variety "Mountain Fresh;" and bell peppers Capsicum annuum, variety "Revolution," were planted and rotated in 2009 with cabbage Brassica oleracea, variety "Artost;" onion Allium cepa, variety "Yellow Granex;" bush green beans "Phaseolus vulgaris, variety "Bush Blue Lake," and beets Beta vulgaris, variety "Detroit Dark Red." Vegetables were spring planted into crimped cover crop mulch in the cropping blocks. Crop and cover crop biomass were measured in the spring before vegetable harvest and showed significant and positive correlation with crop yield and significantly higher yields between the zero compost treatment and the other three treatments. Vegetable yield was also significantly and positively correlated to compost rate for both years. Few significantly different yield means were found using Tukey's Honestly Significantly Different (HSD) Test at the p = 0.05 level, although crop yield did increase with increasing compost rate. The highest rate (53.7 Mg/ha) did not give significantly higher yield results than the low (10.7 Mg/ha) and medium (32.2 Mg/ha) rates to justify this level of treatment. Measured soil properties were also found to be significantly and positively correlated to crop yield. In particular soil P showed significant differences between all compost rate means. Compost was also spring applied in one cropping block to test for differences in season of application. In 2008 tomato, variety "Mountain Fresh," and in 2009, sweet corn Zea mays, variety "Xtra-Tender 270A," were planted two weeks after compost application. The lower compost rate showed higher yield for 2008 and the medium compost rate showed higher yield for 2009 with much lower yields for the high rate of compost application. Yield for both years were positively but not significantly correlated to compost rate. Fall applied compost between the low (10.7 Mg/ha) to medium (32.2 Mg/ha) application rate or approximately (20 Mg/ha) with fall seeded winter cover crop appear to be the optimum soil management practice in this study.