Author: Anna Marie CatesPublisher:
ISBN:
Category :
Languages : en
Pages : 128
Book Description
Cover crops, or the practice of adding an unharvested crop to an annual crop rotation, are increasing in popularity and widely recommended to help retain soil, water, and nutrients on agricultural land. However, the ability of cover crops to improve soil health and sequester soil C remains unknown. Cover crops are thought likely to increase soil C because they add diversity in C inputs and increase the total growing season, but the magnitude and probability of this effect in different systems is critical for informing our understanding of cover crop efficacy and making recommendations to growers. In addition, cover crops may impact biogeochemical cycling and soil processes via changing the abiotic environment. Motivated by the need for detailed evidence of cover crop efficacy at multiple scales, I combined field-based evaluation of cover crop effects on the C cycle with an investigation into mechanisms of C storage under varying abiotic conditions. In Chapter 1, I review establishment constraints and variability in production to argue that cover cropping in northern climates requires specific agronomic systems and "buy-in" from farmers and government agencies. In Chapter 2, I used a biometric approach to the net ecosystem C balanced (NECB) of maize-cover crop and found that grain maize's NECB hovered near zero, suggesting that with or without cover crops the systems had marginal ability to increase soil C. Silage maize's NECB was always negative, despite greater rye biomass. In Chapter 3, I carried out a litterbag experiment on maize residue decomposition, soil or litter microbial decomposer community and analyzed particulate organic matter (POM) and potentially mineralizable C (PMC) as indices of active C. We found that cover crops did not alter microbial composition or maize residue decomposition rate. We observed increases in PMC and POM-C with cover crops, which were correlated with total NPP. In Chapter 4, we report on a laboratory incubation evaluating whether temperature and moisture effect on physical protection of decomposing plant litter C. We found that higher temperatures increased C mineralization, shifted bacterial composition, and decreased efficiency of conversion of litter C to soil C, but dry conditions increased soil aggregation.
