Wednesday, 9 November 2005
14

Organic Vegetable Cropping System Effects on Soil Properties.

Kerianne Pritchett1, Ann C. Kennedy2, and Craig G. Cogger1. (1) Washington State University, 233W Johnson Hall, Washington State University, Pullman, WA 99163, (2) USDA - ARS, 217 Johnson Hall, Washington State University, Pullman, WA WA99164-6421

Organic vegetable crop production practices, suitable for small-scale farms, can improve soil properties and provide conditions for optimal crop production; however, little research has been conducted on these systems. This study investigates short-term changes in soil biological properties of 12 management schemes. The treatments were selected with the input of local farmers in Western Washington, and included three treatment factors in a split-split plot design. The main treatments include three cover cropping systems: 1-) pasture every other year, 2-) relay cover cropping, and 3-) post-harvest cover cropping. There were two tillage operations: 1-) high disturbance tillage (conventionally tilled) and 2-) low disturbance tillage (spader tilled) and two amendments: 1-) chicken manure applied at a low rate (4-5 dry Mg/ha), and 2-) on-farm compost applied at a high rate (30 dry Mg/ha). Microbiological activity was determined by dehydrogenase and B-glucosidase enzyme assays on three dates: mid-season of vegetable crop growth in 2004, three weeks after incorporation of cover crop and amendments in 2005, and mid-season of vegetable crop growth in 2005. Phospholipid fatty acids (PLFA's) and carbon substrate utilization profiles were used to detect community changes due to management (samples from first two dates above). Dehydrogenase activity from pasture was greater than other systems, regardless of tillage. Dehydrogenase activity was greater in the pasture system with minimal tillage, compared to pasture with conventional tillage. The high rate amendment had greater dehydrogenase activity than the low rate. Amendment did not affect B-glucosidase activity, but the relay system had higher activity, when compared to the other systems. Carbon substrate utilization profiles separated the relay from other systems during the 2004 sampling; however, after cover crop incorporation in 2005, a separation was found between tillage treatments. PLFA profile treatment differences were found in 2004 only, with post-harvest separating from other systems.


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