Effects of Cover Crop Mixtures on Biological Indicators of Soil Health.

The use of cover mixtures in agronomic systems has been widely promoted since increasing plant diversity may enhance ecosystem services leading to better soil health. In this study, effects of cover crop mixtures on biological indicators of soil health were examined in a conservation cotton (Gossypium hirsutum L.) production system. Biological indicators of soil health evaluated were active C, soil respiration, glomalin-related soil proteins (GRSP), and arbuscular mycorrhizal colonization of cotton. Winter cover crop treatments included fallow, cereal rye (Secale cereal L.), cereal rye + crimson clover (Trifolium incarnatum L.), cereal rye + radish (Raphanus sativus L.), crimson clover + radish, and a mixture of all three cover crops. These treatments had been in place for one year when soil samples were taken at depths of 0–5, 5–10, 10–15, 15–30, and 30–45 cm. Amounts of active C ranged between 80 and 442 mg/kg soil and GRSP between 1.2 and 5.1 g/kg soil from the lowest depth to the surface. Active C accounted for 2.2 to 5.1% of the total C. There were no significant differences in active C, soil respiration and GRSP among the six treatments at any soil depth, but mycorrhizal colonization of cotton following the cereal rye + crimson clover treatment was higher than that after the fallow treatment. Overall positive correlations were observed between active and total C (r = 0.60), active C and soil respiration (r = 0.82), GRSP and active C (r = 0.91), as well as GRSP and soil respiration (r = 0.68). A longer duration for cover crop treatments may be needed to detect changes in biological indicators of soil health.