1997 Annual Report for SW97-011
Sustainable Crop Production Practices with Mixed Leguminous and Non-leguminous Cover Crops
Summary
Objectives
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 killed.
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.
Abstract
This study is on winter cover cropping systems consisting of hairy vetch mixed with various non-leguminous cover crops that include cereal rye, annual ryegrass, spring oats, triticale that are or are not susceptible to winter kill. The goal is to determine if the mixed cover cropping systems are effective in minimizing nitrate leaching during the winter high rainfall period and increasing soil nitrogen (N) availability during the growing season to enhance crop productivity. Economic analysis will determine the costs and estimated benefits from the cover cropping system and the potential barriers that the growers may face in utilizing the cover cropping system.
The growth of corn during the growing season and nitrate leaching during the winter high rainfall period were very much affected by N fertilizer rate and the type of winter cover cropping system used, similar to the results of the study in 1998. Corn yields increased with increasing N fertilizer rates up to 202 kilograms of nitrogen per hectare (kg N/ha). Whereas the winter cover cropping with hairy vetch alone was most effective in enhancing soil N availability and corn yield under zero N or low rates of N fertilizer, it accentuated nitrate leaching during the winter. In contrast, rye or ryegrass cover crop was very effective in reducing nitrate leaching but was ineffective in promoting corn production when available N in the soil was low. Including hairy vetch with rye, ryegrass, spring oat, or triticale as cover crop improved corn yields in on-farm and on-station trials, and was effective in reducing nitrate leaching during the winter. Even at the highest rate of N fertilizer addition (202 kg N/ha), nitrate concentration of the leachates from the mixed hairy vetch with rye or ryegrass cover crop treatment never exceeded the 10 parts per million (ppm) nitrates (NO3-N) water quality standard. Spring oats were winter killed. This gave the mixed hairy vetch and spring oat cover cropping system an advantage in enhancing soil N availability over the other cover cropping systems, which included hairy vetch with rye or triticale that is not susceptible to winter kill in the coastal Pacific Northwest region.
Type of crop rotation can affect the effectiveness of the mixed leguminous and non-leguminous cover cropping system in increasing soil N availability and crop productivity. The mixture of hairy vetch and rye cover crop planted to the soil after a crop of winter wheat did not affect the amount of soil available N or the succeeding cucumber or potato yield. Presumably, this resulted from the excessive growth of volunteer winter wheat, which produced a large amount of residue with low N contents to lower the N content of the combined residue from hairy vetch and rye and its N mineralization potential.
Pea root rot is common in this region. 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 economics of the use of leguminous and non-leguminous cover crops for corn production in Western Washington was assessed. At zero N fertilizer, comparative returns were lowest for rye or annual ryegrass treatment, intermediate for hairy vetch mixed with rye or annual ryegrass, and highest for hairy vetch alone. At the high N fertilizer rate, the comparative returns for the mixed species cover cropping systems were as good as the single species cover cropping systems, if not better. The lack of data for measuring environmental impacts from nitrate leaching precluded an assessment of the cost to society of nitrate leaching or the benefits from the prevention of groundwater contamination. This is an area in which additional research is needed.
Dissemination of Findings
The field day, demonstration plot on the grower’s field, and direct interaction with growers were intended to allow growers and other interested citizens to become familiar with our research objectives and findings. Publications in the Pacific Northwest Sustainable Agriculture and dairy newsletters concerning how various types of cover crops affect soil and crop productivity and nitrate leaching were distributed to all county extension offices and many dairy farms. These publication were also given to the growers attending the King and Pierce Counties Farm Bureau annual meeting at the City of Fife in October 1999. The possible benefit of using hairy vetch as a cover crop in the control of pea cyst nematode was presented at the Western Washington Horticultural association annual meeting and in one extension bulletin.
Two scientific articles related to cover crops and cover crop residues on soil N availability and crop yields have been submitted to the journal of Soil Biology and Soil Fertility. One has been published and the other is being reviewed. Another article related to the effect of legumes on pea cyst nematode was published in the Journal of Nematode.
Potential Benefits
Improving crop and water quality is an integral part of sustainable agriculture and the primary goal of this research. The results of the second year of this research in general re-enforces the findings of our first year research—the use of mixed leguminous and non-leguminous cover crops can improve soil N availability and crop productivity during the summer growing season, and minimized nitrate leaching during the winter in this coastal Pacific Northwest region. Regulatory solutions of imposing a tax on N fertilizer, as some studies suggested, may not be necessary if the use of mixed leguminous and non-leguminous cover cropping systems is implemented on a large scale. Any tax imposed on N fertilizers will eventually be passed on to the growers, which would further raise production cost.
Hairy vetch mixed with rye was found to significantly reduce pea root rot. This biological approach to control pea root rot may be a cost-saving alternative to chemical treatments for pea growers.
Reaction from Farmers and Ranchers
Farmers are paying more attention to the potential benefits of this mixed leguminous and non-leguminous cover cropping system and would be willing to adopt it if we can prove to them that it is cost effective to use this cover cropping practice.
Producer Involvement
Two growers were involved in the on-farm trial in the fall of 1999. Cover crops were established on their fields. On-farm trial on one of the fields was discontinued because the field was rotated to another crop not originally planned and involved soil fumigation which changed the dynamics of soil nitrogen.
Approximately 15 growers attended a field day on pea root rot and the control of the root rot by hairy vetch mixed with rye. Some sweet corn growers and vegetable growers also visited the on-farm and on-station cover crop trials to see the responses of corn to various cover crops.
This summary was prepared by the project coordinator for the 2000 reporting cycle.