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Estimating soil nitrogen (N) availability is important for developing effective N fertilizer recommendations for plant growth. We examined the ability of various soil biological properties to predict soil N availability, and plant dry matter and N uptake in two greenhouse trials with sorghum-sudangrass (Sorghum bicolor (L.) Moench ssp. Drummondii) as test crop using soils (0–10 cm) from 57 tall fescue (Schedonorus arundinaceus (Schreb.) Dumort.) pastures mostly in North Carolina and Virginia. Soil biological properties, the flush of CO2, cumulative carbon (C) mineralization, soil microbial biomass C, basal soil respiration, and plant available N were positively correlated with net N mineralization, plant dry matter, and N uptake in both the greenhouse trials. The flush of CO2, which is the measure of carbon dioxide released from dried and rewetted soil during the first 3 days of aerobic incubation, explained 77% and 72% of the variation in the plant N uptake in Greenhouse Trial 1 and 2, respectively. Total soil N and residual inorganic N in both trials and manganese in Trial 1 and particulate organic C in Trial 2 added minor contributions to explaining variation in plant N uptake. The flush of CO2 was reflective of management history and soil texture. We conclude that the flush of CO2 is a reliable predictor of soil N availability across diverse pasture soils because (a) it was highly correlated with net N mineralization, plant dry matter, and N uptake, and (b) it was less laborious and more cost-effective than other direct indicators of soil N availability. [ABSTRACT FROM AUTHOR]

Estimating soil nitrogen (N) availability is important for developing effective N fertilizer recommendations for plant growth. We examined the ability of various soil biological properties to predict soil N availability, and plant dry matter and N uptake in two greenhouse trials with sorghum-sudangrass (Sorghum bicolor (L.) Moench ssp. Drummondii) as test crop using soils (0–10 cm) from 57 tall fescue (Schedonorus arundinaceus (Schreb.) Dumort.) pastures mostly in North Carolina and Virginia. Soil biological properties, the flush of CO2, cumulative carbon (C) mineralization, soil microbial biomass C, basal soil respiration, and plant available N were positively correlated with net N mineralization, plant dry matter, and N uptake in both the greenhouse trials. The flush of CO2, which is the measure of carbon dioxide released from dried and rewetted soil during the first 3 days of aerobic incubation, explained 77% and 72% of the variation in the plant N uptake in Greenhouse Trial 1 and 2, respectively. Total soil N and residual inorganic N in both trials and manganese in Trial 1 and particulate organic C in Trial 2 added minor contributions to explaining variation in plant N uptake. The flush of CO2 was reflective of management history and soil texture. We conclude that the flush of CO2 is a reliable predictor of soil N availability across diverse pasture soils because (a) it was highly correlated with net N mineralization, plant dry matter, and N uptake, and (b) it was less laborious and more cost-effective than other direct indicators of soil N availability. [ABSTRACT FROM AUTHOR]