Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/27/2010
Publication Date: 3/1/2011
Citation: Pritchett, K., Kennedy, A.C., Cogger, C. 2011. Management effects on soil quality in organic vegetable systems in western Washington. Soil Biology and Biochemistry 75:605–615. doi:10.2136/sssaj2009.0294.
Interpretive Summary: The National Organic Program encourages practices that create sustainability in organic production systems; however, it is not always apparent that these practices benefit the soil and environment. Soil quality can be used to indicate functioning of a soil under various management regimes. We investigated the sensitivity of biological, biochemical and physical measures of soil quality in the early stages of contrasting organic crop management systems. Our goal was to provide baseline data for future system comparisons of soil quality. We found that soil quality indicators responded to short-term management practices in the second and third years of treatment establishment. Enzyme assays were more sensitive than microbial communities to changes in management. Recent tillage, however, masked cover-cropping and amendment effects. High carbon amendment increased soil carbon and decreased bulk density compared to the low carbon amendment. Understanding the changes in soil quality properties with management may lead to early identification of differences in sustainability among farming practices and assist producers using organic management systems.
Technical Abstract: Management practices in organic vegetable cropping systems and their contributions toward sustainable farming practices can differ greatly. Soil quality monitoring may help organic farmers evaluate and choose best management practices. This study 1) assessed the sensitivity of soil biological properties under organic management systems and 2) provided baseline data for future comparisons. Data were collected from a field experiment comparing cropping systems (pasture every other year, relay cover crop, and post-harvest cover crop), tillage strategies (conventional tillage and modified tillage with a rotary spader), and amendments (low carbon chicken manure, and high carbon on-farm compost) arranged in a split-split plot design. Microbiological analyses included dehydrogenase, Beta-glucosidase, phospholipid fatty acid methyl esters (PLFA) and carbon substrate utilization. Biochemical and physical determinations included total carbon, particulate organic matter carbon, bulk density, and aggregate stability. All soil quality indicators tested, except aggregate stability, responded to short-term management practices in the second and third years of treatment establishment. Beta-glucosidase increased with relay cropping and minimum tillage later in the study. Dehydrogenase and PLFA profiles were similar in that they responded to the large differences in cover cropping systems in August 2004. Recent tillage, however, masked cover-cropping and amendment effects. High carbon amendment increased soil carbon and decreased bulk density compared to the low carbon amendment in July 2005. Understanding the changes in soil microbial properties with management may lead to early identification of differences in sustainability among farming practices.