| Summary: | Due to a growing poultry industry in the Fraser Valley of British Columbia, an abundance of manure is shipped to Delta, B.C. Delta farmers are concerned that large quantities of poultry manure may harm crop quality and cause nitrogen leaching losses. This study tested the effects of organic fertilizer applications on agronomic indicators of crop quality and the potential for nitrate leaching in Delta, and sought tools for predicting appropriate manure application rates. Field trials on commercial certified organic sweet corn (Zea mays L. saccarata Sturt), green bean (Phaseolus vulgaris L.) and broccoli (Brassica oleracea var. italica L.) fields in Delta, B.C. tested poultry manure at rates of 10 and 20 t/ha, and composted yard trimmings and a mixture of the two materials, at rates of about 10 t/ha. Weeds in the corn and bean experiments and insect pests on broccoli were not affected by treatments. Clubroot in broccoli was suppressed by manure treatments. Diagnostic levels of crop tissue nitrogen were within the sufficiency range for corn and beans. Yields were not affected by treatments, relative to controls. In corn and broccoli fields, the potential for nitrate leaching increased disproportionately at manure rates above 25 m³/ha. This may be a result of application rate exceeding the maximum crop N uptake, which was 140 kg/ha for corn and 110 kg/ha for broccoli. Available soil N in control plots (soil mineral N + crop N at harvest) was about 115 kg/ha in the corn and bean experiments, and 89 kg/ha in broccoli. Laboratory incubation experiments showed that poultry manure can mineralize 160 kg N/ha over 74 days, and that composted yard trimmings reduces the N application when mixed with manure. Composted yard trimmings alone caused N immobilization after 31 d, but not after 60 d. It is recommended that the capacity of compost and manure to contribute to soil available N be better quantified in Delta, and that rates not exceed 25 m³/ha for crops with similar uptake patterns to those studied. Annual inputs are not necessary on fields which have a large store of soil available N due to management history.
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