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Soil nitrogen (N) mineralization is variably affected by management and edaphic conditions. A routine soil test that reflects both soil biological activity and N mineralization could improve predictions for N fertilizer recommendations to cereal grains on different soil types and landscape settings. We collected soils from 47 corn production fields in North Carolina and Virginia at depths of 0 to 10, 10 to 20, and 20 to 30 cm and evaluated soil C and N characteristics in association with sorghum-sudangrass [Sorghum bicolor (L.) Moench ssp. Drummondii] dry matter production and N uptake during 6 to 8 wk of growth in the greenhouse. Plant dry matter and N uptake were strongly associated, as expected. Plant available N (sum of net N mineralization during 24 d of aerobic incubation + residual inorganic N) had the strongest association with plant dry matter production (r² = 0.76) and N uptake (r² = 0.85). However, the flush of CO2 during a 0- to 3-d period following rewetting of dried soil was nearly equally effective at r² = 0.74 and r² = 0.76, respectively. Multiple regression models with 4 ± 2 additional variables led to r² = 0.88 ± 0.10 among different separations of data based on depth, region, and soil textural class. We suggest the optimum combination of variables to predict soil N availability would be the flush of CO2, residual inorganic N, and total soil N concentration, as they balance relevant scientific information with limited soil-testing resources (time and labor). We demonstrated that the flush of CO2 was a rapid and reliable indicator of soil N availability. [ABSTRACT FROM AUTHOR]

Nitrogen limits crop production when insufficient and harms the environment when excessive. Tailoring N inputs to cropping systems remains a high priority to achieve production and environmental goals. We collected soils from 47 corn (Zea mays L.) production fields in North Carolina and Virginia at depths of 0 to 10, 10 to 20, and 20 to 30 cm and evaluated soil C and N characteristics in association with soil N mineralization. Soil organic C at a depth of 0 to 10 cm varied among sites from ~10 to 80 g kg–1, and generally declined with depth because of many sites with no-tillage management. Net N mineralization during 24 d of aerobic incubation (25°C, 50% waterfilled pore space) was 54 to 114 mg N kg–1 (24 d)–1 at 0 to 10 cm, 22 to 41 mg N kg–1 (24 d)–1 at 10 to 20 cm, and 12 to 22 mg N kg–1 (24 d)–1 at 20 to 30 cm (middle 50% of observations at each depth). Total soil N was positively associated with net N mineralization (r² = 0.58), but the flush of CO2 during 3 d was even more closely associated with net N mineralization (r² = 0.77). Association between the flush of CO2 and net N mineralization did not change significantly when data were sorted by different regions or soil textural classes. The flush of CO2 is a rapid, reliable, and robust indicator of soil-test biological activity. The strong association of the flush of CO2 with net N mineralization also corroborated use of the flush of CO2 as a rapid and reliable indicator of soil N availability. [ABSTRACT FROM AUTHOR]