Soil Nutrient Balancing in Sustainable Vegetable Production

The purpose of this project is to determine whether an unfavorable balance among soil 

potassium (K), sodium (Na), calcium (Ca) and magnesium (Mg) might be limiting vegetable production on some organic farms in the southeastern United States. These cation (positively charged) nutrients are held in exchangeable (plant-available) form on  the  soil's  negatively- charged clay and humus particles. The Albrecht formula, utilized by "eco-farming" consultants and by many private soil test labs, recommends that the soil's cation exchange capacity (CEC) be occupies by cations in approximately the following ratios: Ca 65-75%, Mg 10-15%, K 2-5%, Na 0.5-3%, and hydrogen (H, or acid) 10-15%.   This is called "base saturation ratio." 

Project Objectives

The overall objectives of the project are: (1) to document the long term (5 year) effects of adjusting soil base saturation ratio toward the Albrecht formula on soil properties and vegetable crop production on five organic farms; and (2) to develop, disseminate and periodically update practical guidelines to help growers determine whether and how to implement soil cation balancing measures on their farms. Specific objectives for the 2000 season (plain text), with comments (italics) on progress toward, and changes in, those objectives follow.

A. to document the effects on soil exchangeable K, Mg and Ca, and on crop foliar nutrient levels, of two treatments designed to produce different soil base saturation ratios in field experiments at five farms. Completed.

B. to collect third-season data on soil physical properties in the two treatments at each farm. Completed. Soil biological properties also measured.

C. to evaluate treatment effects on marketable yields, quality, and Ca-stress disorder symptoms of three crops known to have high Ca requirements: tomato, broccoli and Chinese cabbage. Yield and quality data taken for tomato (2 sites), broccoli (4 sites) and winter squash (1 site). Insufficient Chinese cabbage was established in plots to collect data.

D. to evaluate the effects of low-K and high-K mulches on soil base saturation ratio and asparagus yields at one farm. Base saturation ratio and soil strength measured. No yield data taken because of time constraints.

E. to continue case studies at three farms, in which soil management practices based on cation nutrient balancing and organic matter optimization are implemented in selected fields. Limited monitoring only in these fields, again due to time constraints.

F. to continue to develop and refine soil cation balancing guidelines. Information sheets revised and published Dec. 1, 2000. Copies attached.

G. to communicate interim results and findings to growers and agricultural professionals through farm field days, presentations at conferences, semi-annual written project updates, and information sheets. Completed.