Soil‐test biological activity with short‐term and long‐term carbon contributions

Soil‐test biological activity (STBA) is a key indicator of soil health because of its relevance to ecosystem processing, broad applicability, and simple and rapid analysis. Short‐term and long‐term influences of carbon (C) availability on STBA were assessed. A short‐term factor was root‐derived C inputs from a sudangrass (Sorghum × drummondii) test crop grown under greenhouse conditions. Long‐term factors were from soil at two depths in three sections of a field varying in soil texture and exposed to 16 yr of different pasture–crop rotation management. Soil‐test biological activity was determined after 0, 14, 21, 31, and 45 d of greenhouse growth. Total variation in STBA was 7% from the short‐term factor and 81% from the long‐term factors. Soil depth was the primary long‐term factor influencing STBA (57%) and soil texture was intermediate (24%). Results indicate that short‐term changes in STBA are important but modest compared with variations due to soil depth and texture.