2019 ASHS Annual Conference

A 7-year soil health survey from 2012-2018 assessed soil chemistry and microbial respiration in the rhizosphere of a diversity of horticultural systems. Over 1000 soil samples of both annual and perennial crops were compared in organic and conventional farms and native forestlands. Representative crop categories of vegetable crops included sweet corn, pepper and tomato; agronomic crops were field corn and soybeans; small-fruit crops were blueberry and strawberry; grass crops included equine pasture, bioenergy grasses, home-lawns and golf-course greens/fairways. Soil probes were inserted 6-8 inches deep with 8 sub-samples per replication. All sites had similar sandy loam or clay loam soils such as Sassafras, Downer and Berryland types. Chemical laboratory analysis and estimated crop needs are used to recommend fertilizer rates. Not typically measured is the ability of farmland soils to produce their own nutrients such as nitrogen through mineralization by soil microbes. This biological process is a key factor in soil building methods used in organic and sustainable farm production. The Solvita® CO₂ aerobic respiration test measured the release of carbon dioxide from the soil as a measure of microbial biomass and nitrogen nutrient mineralization. Among the grass crops, the perennial bio-energy crop, Miscanthus giganteus, had the highest CO₂ burst of 23 ppm; similar to field corn-soybean-cover crop rotations but significantly different at P>.05 than the 11 ppm of golf course bent-grass greens, Agrostis stolonifera. Sweet corn, Zea mays convar. Saccharata var. rugosa were slightly higher at 14.0 ppm. Untilled, perennial sites as golf course fairways, equine pastures and residential lawns, all with bluegrass mixes, Poa pratensis, averaged higher at 21 ppm. Significantly higher soil respiration levels averaging 37, 41, and 31 ppm reached an ideal microbial activity and soil health. These results were achieved in organic blueberry operations (Vaccinium corymbosum), natural forestlands and organic lawns with no-tillage and standard practices like “feeding the soil” with composted amendments. Conversely, most conventional blueberry soil respiration levels were under 10 ppm. Significant correlations were found with increased pH and higher organic matter. These related high levels of microbial CO₂ respiration can return 30-40 lbs. of naturally produced nitrogen per acre per year. This low-cost, biological soil test may be used to measure any changes over time from farm management practices such as cover cropping, tillage systems, fertilizers, liming, municipal leaf additions and organic compost amendments.