Potential of Cover Crop Influence on Water Repellency and the Sustainability of Southern U.S. Soils

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Commodities

Practices

• Crop Production: cover crops, crop rotation, nutrient cycling
• Soil Management: soil quality/health

Integrating cover crops into a crop rotation improves soil properties, including increasing soil organic carbon and soil structure, promoting nutrient cycling and credit to the subsequent cash crop, and reducing soil loss via surface runoff and erosion. Cover crops affect soil water content during cover crop and subsequent cash crop growth. There is little information on the effects of cover crop residues on soil water repellency (SWR). Southern USA surface soils are susceptible to developing water repellency due to their sand-dominated textures and lack of organic matter. Water repellency affects soil hydrology, altering water infiltration and distribution uniformity throughout the soil. Results include water and chemical loss via deep percolation and via surface runoff and soil erosion. Cash crops become water-stressed and cannot efficiently utilize nutrients and chemicals, impacting quality and yield. Producers must increase inputs to compensate, reducing sustainability of the field, surrounding environment, and the producer’s livelihood. Hotter temperatures, short intense droughts and rising CO₂ levels are factors that are directly and secondarily associated with increasing SWR presence. This project aims to identify if residues from five common Southern USA cover crops include water repellent compounds, their short-term soil impacts, identify the potential for longer term impacts considering climate change, and educate a broad range of stakeholders on SWR and which cover crops to utilize. We will disseminate results via articles, webinars, and workshops. The results of this project will help Southern USA producers a make educated decisions on which cover crop to use for their field soils.

OBJ 1. Identify if the composition of fresh biomass, as well as residue and the soil under commonly used cover crops in the Southern USA before the cash crop is planted. This includes determining compounds that potentially contribute to SWR (cellulose, hemicellulose, lignin, and suberin).  Importance: Identifying the presence and concentration of these compounds in cover crops can allow us to determine if they could potentially cause SWR. Typically, cash crops are planted four to eight weeks after cover crop termination. Most SWR compounds are recalcitrant and thus do not degrade quickly. They may result in longer residues on the surface. Some SWR compounds may be partially degraded and migrate into the soil, where they may either add to the aggregation of coarse sands and or eventually build up and contribute to SWR. We hypothesize that cover crops with higher amounts of hydrophobic components will be more reluctant to decomposition, and therefore will be more likely to contribute to the occurrence and development of SWR within a field.  

OBJ 2. Identify baseline SWR and how quickly it can affect two related soil properties: infiltration rates and aggregate stability. Importance: research shows that SWR development is thought to occur primarily over the long term, as the SWR plant compounds “build up” in the soil. Short-term characterization of SWR and its effects are poorly understood and previously minimally investigated. We hypothesize that cover crops with more hydrophobic plant components will induce SWR and influence short-term soil-water dynamics (infiltration rates and aggregate stability).

OBJ 3. Deliver outreach and extension of project results to stakeholders and underrepresented groups. Importance: This objective contributes to sustainable agriculture as it helps to educate others on SWR and the influence SWR has on different factors, including water use efficiency, runoff, and nutrient efficiency. Often research is conducted, and results are published in peer-reviewed scientific journals and scientific conferences. Yet, there is a minimal translation of the science to practical application. Stakeholders’ change in knowledge of SWR and how (if) commonly used cover crops may impact its occurrence can result in a change in practice, thus increasing the sustainability of soil and water natural resources and stakeholder livelihood.