What is it about manure?

Anna Cates

Manure not only supplies nutrients in a corn production system, it can help improve soil health as well. In particular, manure has been shown to have outsized effects on soil carbon pools relative to its total carbon content. As interest in understanding soil health has grown, we have access to an increasing number of carbon pool assays, including permanganate oxidizable carbon, particulate organic matter carbon, and lignin, cellulose, and hemicellulose. We propose to explore the carbon pools in various types of dairy manure. This will provide a foundation for future work building towards predicting the soil carbon, nitrogen, and phosphorous response in soil to application of various types of manure. It can be challenging to synchronize nutrient availability with plant needs because of variability in the timing of organic N and P mineralization into plant-available inorganic forms. This variability in mineralization rates depends upon factors such as temperature, soil moisture, soil properties, microbial activity, and manure characteristics (Eghball et al., 2002). The C:N ratio of the manure is particularly important in determining the patterns of nutrient release in soil (Probert et al., 2005). In addition, it is unclear how the forms of organic carbon bound to N and P might affect mineralization rate or nutrient availability. On-farm manure storage and handling procedures can have large impacts on the C content and quality of manures, and can therefore impact nutrient availability, crop yield, and soil health. For example, solid-liquid separation can reduce total C content of manure by 30% (Holly et al., 2017), mostly by removing cellulose and hemicellulose (Rico et al., 2007). Similarly, anaerobic digestion can consume 50 to 65% of the cellulose and > 80% of the hemicellulose in manure (Molinuevo-Salces et al., 2013; Moller, 2015). Manure has the potential to harm water quality if mis-handled, but can also stimulate soil biological activity and diversity (Liu et al., 2016) and boost soil organic matter, which can subsequently improve soil structure. The carbon pools explored in this work have the potential to better characterize what effect manure will have on soil properties. The long-term goal is to recommend application procedures to do most to improve soil health while minimizing water quality risks.