Outcome of Soil Nutrient Balancing in Sustainable Vegetable Production

            In Virginia and other southeastern states, many cultivated soils show Ca base saturation below 65%, with Mg and/or K well above their  recommended  ranges.  This  imbalance  is believed to "tighten" the soil and degrade crumb structure, hamper aeration and drainage, cause surface crusting and hardpans, inhibit beneficial soil organisms and humus formation, aggravate weed, pest and disease problems, and hurt crop and livestock health. Applications of high calcium lime or gypsum to restore the balance are claimed to correct these problems; to enhance soil biological activity and organic matter levels; to increase availability of  phosphorus  (P), nitrogen (N) and other nutrients; and to improve produce flavor, nutritional value and shelf life.   

            Between 1998 and 2000, on-farm studies and a literature review were conducted to evaluate some of these claims. Field trials were conducted on five organic vegetable farms in Virginia and eastern Tennessee to determine whether applying Ca amendments to soils showing high Mg (average 24%) and slightly low Ca (average 63%) would benefit soil tilth, soil life or marketable vegetable yields. Treatments (low-Ca = control; high-Ca = Ca amendments applied four times between summer 1998 and summer 2000) were replicated three times at each site.   

            The high-Ca treatment shifted the average base saturation ratio to 70% Ca and 18%Mg, and slightly reduced K saturation. Vegetables grown on the amended soil had slightly higher foliar Ca and lower Mg levels. However, the high-Ca treatment had no detectable effect on soil organic matter, biological activity, crop uptake of N, P and micronutrients, abundance of weeds, incidence of disease or insect pest damage, or Brix (percent soluble solids, an index of produce quality) in broccoli or tomato. Broccoli yielded about 11% more in the high Ca treatment in the 2000 season, whereas treatment effects on tomato and squash yield have been inconsistent. 

            Soil bulk density (degree of compaction), moisture content, water infiltration rate (indicates drainage and porosity) and soil strength (resistance to root growth) were measured in fall 1999, and spring and fall 2000. When results from the five sites were averaged, the high-Ca treatment did not seem to affect any of these soil attributes. However, when results were considered site by site, some possible trends emerged at two sites. On a clay-loam soil in the Blue Ridge foothill region, the high-Ca treatment seems to have improved water infiltration and slightly  loosened  a  pre-existing  subsurface  hardpan.  Conversely,  the  high-Ca  treatment  apparently tightened hardpan and slowed water infiltration on a Tidewater sandy loam.