Flush of CO2 As a Short-Term Biological Indicator of Soil Nitrogen Mineralization in the Southeast.

Determining the appropriate nitrogen (N) rate is critical to farm economics and environmental protection. In North Carolina, N fertilizer recommendations are not modified by residual inorganic N or biologically active N, but only by realistic yield expectation set for each soil type by crop. However, due to increasingly popular conservation management practices such as cover cropping and no-till farming, residual N can remain in the soil in a biologically active form for potential plant uptake, resulting in greater supply of N than expected. Measuring biologically active carbon (C) is faster, more accurate, and less expensive than measuring biologically active N. Soil samples (120) were collected from field stations representing the three physiographic regions of North Carolina (coastal plain, piedmont, and mountains) to use in a greenhouse trial. Unfertilized Sorghum bicolor was planted for the greenhouse trial and harvested at 4 and 8 weeks. Dry matter accumulation and N concentration were measured, which allowed for determination of N uptake. Carbon mineralization, or the “flush of CO₂”, was measured for each soil, as was microbial biomass C using fumigation-incubation, prior to the greenhouse trial. Mean plant dry matter accumulation was linearly related to the flush of CO₂ with an r² of 0.78. Soil microbial biomass C was linearly related to the flush of CO₂ with an r² value of 0.80. These data, as well as total, particulate, and inorganic N, will contribute to a larger database of laboratory incubations and greenhouse trials to help understand nutrient dynamics and improve accuracy of fertilizer N recommendations in the Mid-Atlantic and southeastern USA.