CO2 Respiration, Soluble Carbon and Nutrient Tests Measure Fertility Flux in Commercial Multi-Crop Organic Faming.

Commercial organic farming which employs compost as a principle means of fertility must factor in uncertainty about nutrient and particularly nitrogen release, and also consider natural soil release. The measurement of soil CO₂ respiration has been shown to be a means to gauge biological soil fertility, and the assumption that soil-carbon turnover corresponds to soil-N release is common. We previously compared results of testing CO₂ respiration using alkali-trap titration, infrared gas analysis (IRGA) and the Solvita® CO₂ gel system and found all three methods highly correlated with each other. In this study we acquire a series of soils from a commercial organic farm to which successive applications of compost with multiple-cropping is practiced. The approach is to compare crop performance for arugula, spinach and beet greens with soil tests for soluble nitrogen, WSOC, WSON, and 24-hr CO₂ respiration on soils that have been dried and rewetted using the commercial Solvita system to measure CO₂. Soil test results show small but detectable increases in soil soluble nitrate following each compost application, and significant yield increase from these small increments. The data suggest that the Solvita gel system for soil CO₂ analysis could be combined with basic soil tests for soluble fractions of nutrients to aid commercial organic growers optimize yields with conservative nutrient and manure-compost applications.