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Effects of Cover Crop Mixtures on Biological Indicators of Soil Health under Conservation Systems




Ucar, Gokhan

Type of Degree

Master's Thesis


Crop Soils and Environmental Sciences


Soil management practices affect the health and productivity of agroecosystems. Cover crops, which are grown between periods of cash crop production, play a critical role in building healthy soil. The most obvious benefit of cover crops is protection against soil erosion. Other benefits include nutrient retention, weed suppression, and increase of soil organic matter. Moreover, cover crops can alter soil habitat for living organisms by improving moisture status and soil aggregation. Although there is evidence that cover crops enhance soil microbial diversity and activity, limited information is available about the impact of cover crops on biological indicators of soil health. The use of multi-species cover crop mixtures has been promoted nationwide to enhance soil health; however, little data are available demonstrating the benefits of cover crop mixtures compared with a single species in the Southeastern U.S. This project examined the effects of three winter cover crop species grown singly and combined in multispecies mixtures on selected biological indicators of soil health and determined the changes of these indicators over a three-year period. The cover crops included single species and mixtures of cereal rye (Secale cereale L.), crimson clover (Trifolium incarnatum L.), and radish (Raphanus sativus L.) in a soybean (Glycine max L.)–cotton (Gossypium hirsutum L.) rotation system under strip tillage. The field experiment was a randomized complete block design with four replications and included the following treatments: fallow (no cover crop), rye, rye/clover, rye/radish, clover/radish, and rye/clover/radish (3-way mixtures) mixtures. Soil samples collected in the spring at the 0–15 cm depth were analyzed for microbial biomass C (MBC) and arbuscular mycorrhizal fungi (AMF) colonization of cotton roots; those collected in the fall at 0–5, 5–10, 10–15, 15–30, and 30–45 cm depth were analyzed for active C, soil respiration, and glomalin-related soil protein (GRSP). In the first two years, significant treatment differences were observed only for the AMF colonization of cotton. In the third year, overall treatment effects were found for all of the parameters measured; however, there were no significant differences among cover crop types. There was an overall decreasing trend for active C, soil respiration, and GRSP with increasing soil depth. Winter cover crops did not influence metabolic quotients significantly. Active C was highly correlated with SOC (r = 0.86), soil respiration (r = 0.91), and GRSP (r = 0.92). Our results show that the beneficial effects of cover crops on biological soil health became more pronounced over time. Active C, soil respiration, and AMF colonization can be useful indicators of soil health reflecting short-term changes; AMF colonization of cotton responded to cover cropping most quickly. Within the three-year study period, biological indicators of soil health measured did not increase with the number of cover crop species used and a longer duration for cover crop treatments may be needed to detect effects of cover crops.