- Agronomic: corn, oats, potatoes, rye, grass (misc. perennial), hay
- Vegetables: cucurbits, peas (culinary)
- Animal Production: feed/forage
- Soil Management: nutrient mineralization, organic matter, soil quality/health
Protecting soil and water quality is an integral part of agricultural sustainability, which could be accomplished with winter cover cropping systems particularly in the areas with high rainfall activity during the winter months. This study used winter cover cropping systems that consist of mono-culture of cereal rye, annual ryegrass, spring oats, triticale, and hairy vetch and of bi-culture of hairy vetch and cereal rye, annual ryegrass, spring oats, or triticale that are or are not susceptible to winter kill. The goal was to determine whether or not the bi-culture cover cropping systems are as effective as the mono-culture systems in minimizing nitrate leaching during the winter high rainfall period, but also more effective than the mono-culture of the non-leguminous cover crops in increasing soil N availability and crop productivity. The accompanied economic analysis determined the costs and estimated benefits from the cover cropping system and the potential barriers that the growers could face in utilizing the cover cropping systems.
Cover crop had variable effect on the growth of corn, depending on the cover cropping systems and the amount of N fertilizer applied to the corn during the growing season. The effect was pronounced when the amount of N fertilizer applied was low. All bi-cultures increased soil N availability over the mono-cultures of any of the non-leguminous cover crops, although the increase was generally smaller compared to the mono-culture of the vetch. However, while the mono-culture of the vetch was most effective in enhancing soil N availability and corn yield at low rates of N fertilizer application, it accentuated nitrate leaching during the winter. This is in sharp contrast to mono-culture of rye or ryegrass cover crop, which, while being least effective in improving soil N availability and crop productivity, was most effective in reducing nitrate leaching. Inclusion of hairy vetch with rye, ryegrass, spring oat, or triticale in bi-cultures not only improved corn yields in on-farm and on-station trials, but also decreased residual soil inorganic N after fall harvest and nitrate leaching during the winter. With this cover cropping system, nitrate concentration of the leachates from the bi-culture of hairy vetch and rye or ryegrass cover crop treatment never exceeded the 10 ppm NO3-N water quality standard even at the highest rate of N fertilizer addition (202 kg N/ha). The bi-culture is the type of winter cover cropping system that improved water quality, soil N availability, and the productivity of the corn crop. The cover cropping system was not as effective if the cover crop was planted after winter wheat and there was excessive growth of volunteer winter wheat to lower residue N content, which decreased residue net N mineralization potential in the soil.
Pea root rot is common in this coastal region of Pacific Northwest. The mixture of hairy vetch and rye was found to be effective in reducing pea root rot rated early or late in the growing season and in increasing pea yield, compared to the fallow treatment. This type of cover cropping helped delay and diminish root rot development in pea. It is not clear at this time if the effectiveness was attributed to the changes of soil physical and/or biological reactions caused by hairy vetch. A more in-depth study would be needed to elucidate this. There is a potential cost saving for growers using this type of cover cropping system, rather than chemical treatments, to control pea root rot.
The cover crop that generated the largest comparative returns for the cover cropping systems was the bi-culture of the ryegrass and the vetch, provided that N fertilizer applied to corn was 134 kg N ha-¹ or higher. From an economic-environmental perspective, the scenarios that performed the best overall for comparative returns and nitrogen uptake, were those in which N fertilizer was applied. Future study would be needed that incorporate additional measures for more conclusive results. The additional measures are soil nitrogen retention property and the risk or the cost to society resulting from nitrate leaching.
1. Determine the biological and environmental impact of hairy vetch mixed with various types of non-leguminous winter cover crops that are or are not susceptible to winter kill.
2. Perform economic analyses of the production systems that utilize mixed leguminous and non-leguminous cover crops.
3. Involve growers in on-farm research and develop programs to educate other growers, Master Gardeners, and interested citizens in the value of mixed cover cropping systems to facilitate their adoption.