Soil‐Test Biological Activity with the Flush of CO2: I. C and N Characteristics of Soils in Corn Production

Core Ideas Soil nitrogen mineralization can be predicted with the flush of CO₂. Soil texture does not alter the relationship between the flush of CO₂ and N mineralization. Large quantity of mineralizable N in surface soils is possible with conservation management. The flush of CO₂ is an appropriate indicator for soil‐test biological activity. The flush of CO₂ is a rapid and reliable indicator of soil N availability. 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% water‐filled 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.