Soil Nutrient Balancing in Vegetable Production
The purpose of this project was to determine whether an unfavorable balance among soil potassium (K), calcium (Ca), sodium (Na), and magnesium (Mg) might be limiting vegetable production on some organic farms in the southeastern United States. Low soil Ca levels and unbalanced ratios of exchangeable Ca, Mg, and K have been advocated as constraints to sustainable vegetable production. And while sufficient available Ca is essential for a healthy soil microbiota, as well as crop vigor and disease resistance, some say that even in the absence of crop Ca deficiency, the low Ca:K or Ca:Mg ratios in many soils may cause a loss of soil tilth, increased compaction, poor aeration and reduced microbial and earthworm activity.
The Virginia Biological Farming Association established experimental plots at five farms in Virginia and eastern Tennessee to document and illustrate the effects of differing soil Ca:Mg ratios on soil health and vegetable crop nutrition, yield and quality. Two experimental soil amendment regimes, designed to maintain different Ca:Mg ratios, were implemented in adjacent plots at each farm.
The project was initially undertaken to validate the Albrecht formula in organic production in the southeastern U.S. The project findings have not led to a validation of that approach. The results to date have led instead to a shift in focus toward developing a holistic, site specific and resource-conserving approach to soil nutrient balancing. The association found that growers can remedy nutrient balances by reducing inputs and may not need purchased Ca amendments to “correct” high soil Mg if soil and crops are healthy. This results in a savings to the grower by not having to buy and add unnecessary soil amendments.