Final Report for SW97-011
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.
Objective 1. Determine the biological and environmental impact of hairy vetch mixed with various types of non-leguminous cover crops that are or are not susceptible to winter kill.
This on-station study was conducted on a Sultan silt loam in Puyallup of Pierce County Washington. The treatments included four nitrogen fertilizer rates (0, 67, 134, and 201 kg N ha-¹ as NH4NO3), five to 7 cover crop species, depending on the year, and two cover crop residue management practices (incorporation and residue removal). Of the amount of N fertilizer applied, 67 kg N ha-¹ was applied to the corn at planting, with the remaining amounts at 134 and 201kg N ha-¹ applied as sidedress late in June. The cover crop species included hairy vetch, cereal rye, annual ryegrass, triticale, and spring oat. The seeding rate for mono-culture was about 134 kg ha-¹ for rye, 28 kg ha-¹ for ryegrass, 35 kg ha–¹ for vetch, 112 kg ha-¹ for spring oat, and 134 kg ha-¹ for triticale. For bi-culture, the seeding rate for each species was about 70% of that used for mono-culture. They were planted in the fall after corn harvested as mono-culture and as bi-culture of the vetch and cereal rye, annual ryegrass, spring oat, or triticale and harvested late in April for determining the cover crop biomass production and total N accumulation in the above-ground biomass. Corn was seeded (75,000 seeds ha-¹) in mid-May and harvested late in September. Corn yield and N concentration in the harvested plant material were determined. Each treatment was replicated three times in a randomized block design. Other nutrients than N were applied to the soil as recommended before corn planting. Soil samples were taken from 0-15 and 15-30 cm depths late in June and after fall harvest. The soils were analyzed for total C and N, and for nitrate-N.
Lysimeters were installed in the control without any cover crops and in the mono-culture of the vetch, cereal rye, and annual ryegrass and in the bi-culture of vetch/rye and vetch/ryegrass that had N fertilizer treatments of 0, 134, or 201 kg N ha-¹ applied to corn during the growing season. The leachates was collected from each lysimeter, beginning late in October or early in November, depending on the rainfall activity and analyzed for nitrate-N. The sampling of leachates was terminated when the nitrate-N concentration was consistently at the trace level (3 mg N L-¹) or lower.
Another on-station research was conducted on a Puget silt loam at Mount Vernon in Skagit County of Washington, to determine the cover crop species effect on cucumber and potato yields and on pea root rot. The study included mono-culture of the vetch and rye and bi-culture of the vetch and rye. The seeding rates for mono-culture and bi-culture were same- 30 kg ha-¹ for vetch, and 80 kg ha-¹ for rye. A control without the cover crop was included for comparison. The cover crops were seeded in the fall and incorporated into the soil in the spring. Cucumber (Calypso) and potato (Red Lasoda) were seeded in mid-June. And harvested late in August for cucumber and mid-October for potato. The N fertilizer rates for the summer crops were 0, 40, and 80 kg N ha-¹. All other nutrients than N were applied as recommended. Each treatment was replicated four times in a randomized block design. Pea (Charo) (220 kg seeds ha-¹) was planted to the control and to the bi-culture of vetch/rye. Yield of pea was determined at harvest and the average root rot was rated.
The on-farm trials were conducted at four farm sites, two in Grays Harbor County in southwestern Washington and two at Skagit County of Northwestern Washington. The cover crops planted included mono-cultured vetch, cereal rye, and spring oat, and bi-cultured vetch/rye, and vetch/spring oat at the Grays Harbor County sites. The seeding rates for the cover crops were the same as those used in the on-station trial at Puyallup. The summer crop was sweet corn in the trials at Grays Harbor County and Pea at one of the Skagit County sites. Sweet corn and pea yields were determined at harvest. The degree of pea root rot was also rated. The trial at another site in Skagit County was terminated soon after the cover crops were seeded. This resulted from the grower’s decision to shift the farmland to small fruit instead of vegetable crop production as initially planed.
Cover crop effects on soil N availability and crop productivity
The study at the Puyallup site showed that hairy vetch seeded early in October each year from 1997 to 1999, alone or in bi-culture with cereal rye, annual ryegrass, spring oat, or triticale, did not establish as quickly as did the non-leguminous species in this western Washington region. With a lack of sufficient plant growth to remove the residual nitrate-N, nitrate-N leaching was consistently elevated in the monoculture of the vetch and the control without any of the cover crops throughout the study. The magnitude of nitrate N leaching increased with increasing amounts of N fertilizer applied to the corn during the growing season. At the same N fertilizer rate, the highest nitrate-N leaching was not in the control, but in the monoculture of the vetch possibly because the continued N mineralization from the vetch incorporated into the soil prior to corn planting in the spring. At the peak of nitrate-N leaching, which occurred between late in October to early in December depending on the year, the nitrate-N concentration of leachates attained a level as high as 42 mg L-¹ with the application of 201 kg N/ha of N fertilizer to corn. This was almost twice the level for the control without cover crop (22 mgL-¹) at the same high N fertilizer rate. Also, the breadth of the peak widened at the high N fertilizer rate of 202 kg N ha–¹, which indicated more residual inorganic N was available for leaching in the soil after fall harvest of corn. If high rates of N fertilizer are used to sustain the corn growth and productivity, the soil should not be left in fallow or planted with the vetch as a cover crop. Neither practice is effective in preventing nitrate leaching.
In contrast to the fallow or vetch cover crop, the rye or ryegrass cover crop markedly reduced nitrate-N leaching. Even at the highest N fertilizer rate (201 kg N ha-¹) used, the nitrate-N concentration of the leachates was close to 10 mg N L-¹ even during the high leaching period between late in October and early in December. Rye and ryegrass germinated quickly after fall seeding and absorbed sufficient residual soil nitrate-N to minimize its leaching during the winter.
As with rye or ryegrass in mono-culture, the rye or ryegrass component in the bi-culture was effective in minimizing nitrate-N leaching in the soil. The nitrate-N concentration of leachates in the vetch/rye or vetch/ryegrass cover cropping system seldom exceeded 10 mg N kg-¹ water quality standard even at the highest N fertilizer rate used and during the high leaching period in all three years of this study. The result clearly demonstrates the ability of these bi-culture cover crop systems to protect water quality when used as part of the agricultural production practice.
Even though the growth of the vetch was very slow during the winter period, it accelerated early in the spring to produce an average aboveground biomass of 1.83 Mg ha-¹, as compared to 1.40 Mg ha-¹ for rye, 1.53 Mg ha-¹ for ryegrass. For the bi-culture of vetch/rye and vetch/ryegrass, the respective biomass yields were 2.33 and 2.15 Mg ha-¹. The average N accumulation of N in the aboveground biomass was 20.9 and 19.0kg N ha-¹ for rye and ryegrass, respectively, which was two to three times lower than that of monoculture vetch (58.3 kg N ha-¹), rye/vetch (50.0) or ryegrass/vetch (56.3 Mg N ha-¹). Inclusion of vetch with the non-leguminous cover crop effectively increased the tissue concentration of N and lower the C:N ratio, which are important indices of the mineralization potential of N in the residues. The same result was found in the cover cropping study that included in addition to the above cover crop species, mono-cultured oat and triticale and bi-cultured triticale/vetch and oat/vetch. The average N accumulation in the aboveground biomass was more than four times higher in the mono-cultured vetch and bi-cultured rye/vetch, triticale/vetch, and oat/vetch than in the mono-culture of these non-leguminous cover crops. Oat was winter killed in 1999, but not in 1998. The winter kill produced a much lower biomass production in oat as mono-culture, but increased residue N concentration, compared to the rye/vetch or triticale/vetch in which neither rye or triticale was winter killed.
Incorporation of cover crop residues in the spring two weeks prior to corn planting had a variable effect on the presidedress nitrate-N level (PSNT). The control soil without any of the cover crops had a PSNT level of 35 kg N ha-¹. Rye residue did not increase the PSNT, whereas ryegrass residue depressed PSNT due primarily to its high concentration of carbohydrate content that promoted rapid microbial growth and N immobilization in the soil. In contrast, the bi-culture increased the PSNT level by 27 to 50% over the control, as compared to 146% for mono-cultured vetch. As the proportion of the non-leguminous cover crop residue in the mixture of vetch and the non-leguminous cover crop was increased, less residue N was mineralized. Removing the cover crop residue to simulate animal grazing had essential no effect on PSNT for any of the mono-culture of the non-leguminous cover crops, but PSNT for the bi-culture and mono-culture vetch in particular was significantly depressed regardless of whether the field trial was done on-station or on-farm. The portion of N associated with the vetch in the aboveground biomass that can be readily mineralized was lost from the soil in the simulated grazing. The result also shows that if these non-leguminous species are used as cover crop, their aboveground biomass could be utilized for forage without affecting the soil N fertility in the short term. However, because the soil N accumulation is intimately associated with C or total residue input, removing cover crop residues decreased soil C and N accumulation, thereby decreasing soil N mineralization potential over the long term.
The differential effect of the cover crop species on PSNT was also well reflected in crop yield when insufficient amount of N fertilizer was applied to corn during the mid-growing season. With 0 N fertilizer addition to corn, vetch increased the average corn yield over the control by 75%, compared to 44% for rye/vetch, and 27% for ryegrass/vetch. Rye had no effect on the average corn yield, and ryegrass even lowered it by about 6%. The beneficial effect of vetch and the bi-cultures diminished when the aboveground portion of the cover crops was removed from the field for use as forage. This decreased the input of readily mineralizable N into the soil and reduced PSNT.
The on-station trials at the Mount Vernon site also showed the effectiveness of rye and bi-culture of rye/vetch cover crops in decreasing residual soil nitrate-N in both the surface (0 to 30 cm) and subsurface soil (30 to 60 cm) early in the winter. It also showed the effectiveness of mono-cultured vetch (204 kg N ha-¹) and bi-cultured rye/vetch (166 kg Nha-¹) in increasing PSNT of the soil over the mono-cultured rye (130 kg N ha-¹) during the growing season. The amount of N accumulated in the cover crops was very high, being 136 kg N ha-¹ for rye, 160 kg N ha-¹ for vetch, and 220 kg N ha-¹ for rye/vetch before the cover crops were incorporated into the soil early in April. The high availability of N from the soil itself could explain the high N accumulation in the cover crops and why there was no positive effect of even the mono-culture vetch or bi-culture of rye/vetch on the yields of cucumber or potato. In fact, the amount of soil available N appeared to be far in excess of crop requirements as the yield of either crop generally decreased with increasing rates of N fertilizer addition to the crop. This emphasizes that for the soil with a high amount of available N, mono-cultured rye is preferred to mono-cultured vetch or bi-cultured rye/vetch as a cover crop.
The on-farm trial at one of the sites at Grays Harbor County showed very much the same result as the on-station trials. The incorporation of the cover crop residues into the soil increased nitrate-N concentration of the surface soil (0 to 15 cm) from 10.4 mg N kg-¹ in the control without any cover crops to 15.3 mg N kg-¹ for rye/vetch, 19.1 for oat/vetch, and 22.3 for vetch. Spring oat was mostly winter killed so that the residue in oat/vetch bi-culture contained almost entirely vetch. This increased residue N concentration to a level (4.07%) as high as mono-cultured vetch (3.62%), and brought soil nitrate-N concentration to the level higher than bi-cultured rye/vetch, which had a residue N concentration of only 1.34%. Sweet corn yield was higher in mono-cultured vetch and bi-culture oat/vetch and rye/vetch, compared to the control or mono-cultured rye and oat at low N fertilizer input.
In the area such as Grays Harbor County of coastal Washington, the annual precipitation is quite high (about 200 to 250 cm annually), with close to 75% of the precipitation falling during the winter period. The soil drainage could become a factor for cover crop growth. This was illustrated in the poor growth of cover crops at another on-farm trial in this county, where soil drainage was inadequate. The cover crop particularly affected in the fine-textured soil was hairy vetch. This led to a total N concentration of the residue in the bi-cultured rye/vetch (1.82%) and oat/vetch (1.77%) same as that of mono-cultured rye (1.67%) and oat (1.97%). The total amount of N accumulated by those cover crops including mono-cultured vetch was low, ranging from 15 to 34 kg N ha-¹, and no apparent effect of the cover crop residues on the yield of the succeeding sweet corn was found.
Cover crop effects on pea root rot
Pea yield in some soils infested with a high population of pea cyst nematode (PCN) can be severely reduced. The on-farm trial in Skagit County from 1997 to 1998 showed that cyst nematodes were detected in the vetch cover crop. With the fall-planted vetch cover crop, there was a significant reduction in the population of PCN in the soil and the degree of pea root rot measured late in March or late in April. As a result, there was an increase in the number of pods and pod weight where vetch cover crop was planted the preceding fall. The vetch could provide roots to trap nemas from soil in the fall or the incorporated residue could have delayed hatching and infestation of pea roots in the study.
Another cover crop effect on pea root rot disease conducted on-station in the same county showed that the particular root rot had symptoms typical of the Pythium species/Fusarium solani f. sp. Pisi complex common to this region. While root rot developed in all cover crop treatments, root rot ratings at the early growth (June 15) and late growth (July 20) states showed a significant reduction in the root rot on pea in the bi-cultured rye/vetch than in the fallow treatment. The bi-cultured cover crop helped delay and diminish root rot development in pea. As a result, the pea yield was higher in rye/vetch than in the fallow even though a nearly 40% reduction in plant counts in the bi-culture was due to the use of drill inappropriate for pea seeding in the soil containing high amounts of residue from the cover crop. It is not clear if the reduction in pea root rot in the rye/vetch is related to any change in soil physical or biological reactions or both. Given a potential cost saving for pea growers to use the cover crop, instead of chemical treatments, to control the disease, a more thorough study to gain a better understanding of the relationship is needed.
The result of the on-station and on-farm trials clearly showed the advantages and disadvantages of various cover cropping systems including the mono-cultured vetch and various non-leguminous cover crops. While mono-cultured vetch increased soil N availability more than any other cover crops, it accentuated nitrate-N leaching during the winter, which makes it less desirable as a cover crop than the non-leguminous cover crops if protecting water quality is also an objective. In contrast, the non-leguminous cover crops were effective in minimizing nitrate-N leaching during the winter, but ineffective in improving soil N availability during the growing season. When combing the vetch with any one of the non-leguminous cover crops, the bi-cultured cover crop possessed an unique characteristic of protecting water quality by minimizing nitrate-N leaching during the winter and increasing soil N fertility during the growing season. Spring oat was winter killed one out of the three years. When the biomass was reduced by winter kill, the oat/vetch was better than rye/vetch, ryegrass/vetch or triticale/vetch in improving soil N fertility. Even though the non-leguminous cover crops were ineffective in increasing the amount of soil available N in the short term, incorporation of their residues into the soil enhanced soil C, and, thereby, N accumulation in the soil on the long term. Soil C and N is an important index of soil quality. While removing the non-leguminous cover crop for forage is advantageous in term of economic incentive, this practice may not be as viable if protecting soil quality is also considered.
Another important benefit of the bi-cultured rye/vetch cover crop system is its ability to reduce the pea root rot, which could lead to a severe yield reduction unless controlled. This could be a cost-effective biological control of pea root rot disease for the pea growers confronted with this disease in this and perhaps, other regions as well.
Objective 2. Perform economic analysis of the production systems that utilize mixed leguminous and non-leguminous cover crop.
Although numerous studies have assessed the tradeoff between returns and environmental risk, a review of the literature failed to locate studies that assessed the economics of leguminous and non-leguminous winter cover crops for corn productivity nitrate-N leaching abatement in this region. This economic analysis determined comparative economic costs, revenues, and returns for the cover cropping systems, and economic-environmental tradeoffs. Enterprise budgeting techniques were employed for assessing the economic cost. Costs such as corn seed, planting, and fertilizer application were assumed to be constant in all scenarios and not incorporated into the analysis. Indifference maps were utilized for the assessment the economic-environmental tradeoffs. This enabled a comparison and ranking of the various combinations. It was assumed an increase in nitrogen uptake was preferred since this would limit the amount available for leaching.
Yields or total physical product (TPP) were analyzed for deriving the production functions for each scenario. In addition, average physical product (APP), marginal physical product (MPP), total value product (TVP), average value product (AVP), marginal value product (MVP), and marginal factor cost (MFC) were calculated for each scenario. It was hypothesized that increasing rates of N fertilizer (X) for each scenario would exhibit diminishing marginal returns for corn.
The analysis of the production function showed that in 1998, as more N fertilizer was added, diminishing returns existed for rye/vetch and vetch. This was also true for rye/vetch, ryegrass/vetch and vetch in 2000. It appears that all scenarios were operating in stage two, since all were beyond the point where APP=MPP. Comparative revenues (TVP) were derived by multiplying yields by corn prices generating a direct correlation between revenues and yields. TVA was utilized to derive AVP and MVP, and the point where MVP=MFC represents the optimal level of N fertilizer input. For the control, mono-cultured rye and ryegrass, additional fertilizer was needed to attain maximum returns. For the bi-cultured ryegrass/vetch and mono-cultured vetch, the optimal amount of fertilizer input for maximum returns would be an amount between 134 and 201 kg N ha-¹. The returns was highest ($625.90) for ryegrass/vetch at 134 kg N ha-¹ in 1998 and at 201 kg ha-¹ in 2000 and lowest for mono-cultured ryegrass with 0 N fertilizer addition ($156.05) in both 1998 and 2000.
From an economic-environmental perspective, the scenarios that performed the best overall for comparative returns and N uptake were those in which N fertilizer were added. The vetch performed the best for 0 N fertilizer addition scenario in 1998, whereas bi-cultured rye/vetch was the best in 2000 at the 0 N fertilizer addition. The results from this analysis are based on only two years. Further time-series data would be needed to have more conclusive results.
Objective 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.
Demonstration plots were established on two grower’s fields in Grays Harbor County in southwestern Washington and on two grower’s fields in Skagit County in northwestern Washington so that the growers had first-hand observation of the responses of crops to various cover crop species. In addition, we directly interacted with other growers and Master Gardeners from various locations through workshop and Focus Group meeting, and presentations at various conferences. Washington State University-Pierce County Master Gardeners had established a cover crop trial on their own demonstration garden.
Improving crop and water quality is an integral part of sustainable agriculture and the primary goal of this research. The results of this study clearly showed the benefits of using mixed leguminous and non-leguminous cover crops to improve soil N availability and crop productivity during the summer growing season, and to minimize nitrate leaching during the winter in this coastal Pacific Northwest region. This cover cropping system also improved soil C and N accumulation, thereby improving the soil quality on the long-term. Then growers can utilize this type of cover cropping system to protect soil and water quality, as well as to improve the crop productivity. Regulatory solutions of imposing a tax on N fertilizer, as some studies suggested, may not be necessary if this bi-culture 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 very cost-effective alternative to chemical treatments for pea growers.
Education and Outreach
The field day, demonstration plots on the grower’s fields, and direct interaction with growers were intended to allow growers and other interested citizens to become familiar with our research objectives and findings. Press coverage and interview by a freelance writer from California also carried the research information to growers and interested citizens in this and other states. Publications in the Pacific Northwest Sustainable Agriculture and Dairy News concerning how various types of cover crops affected 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 on 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.
Presentations at various regional and national conferences and publishing research findings in the scientific journals are avenues to reach the scientific communities throughout the country and the world. At present, two scientific articles related to cover crops and cover crop residues on soil N availability and crop yields have been published in the journal of Soil Biology and Soil Fertility. Another article related to the long-term cover cropping effects and residue management has been submitted to Agronomy Journal for publication. The effect of legumes on pea cyst nematode was published in the Journal of Nematode. There are five abstracts prepared for various conferences. It is anticipated that more publications in both the technical and scientific journals on the effects of various cover crops on nitrate leaching are forthcoming.
List of presentations and publications
1. Kuo, S., and W. C. Anderson. 1998. Influence of winter cover cropping on soil nitrogen availability and cucumber yields. Potato and cucumber field days. Mt. Vernon, WA, August 26, 1998.
2. Kuo, S. 1998. Developing and testing a simple nitrogen test for evaluating nitrogen requirements and the need for winter cover cropping. Northwest Agricultural Research Foundation.
3. Kuo, S. 1998. Winter cover cropping and cover crop species effects on soil N availability and nitrate-N leaching. Western Regional Technical Research Committee meeting. January 14, 1998.
4. Kuo, S. 1998. Winter cover crop influences on soil N availability and crop productivity. SARE Conference. March 3-4, 1998, Austin, TX.
5. Kuo, S. 2000. Influence of winter cover crop species and residue management on N leaching and soil N availability. Presented at the American Society of Agronomy annual meeting. November 5-9, Minneapolis, MN.
6. Kuo, S. 2000. The benefits of mixed leguminous and non-leguminous cover crops to soil nitrogen availability and water quality. Presented to Agriculture, Fish and Water (AFW) process FOGO Executive Committee workshop. August 23-24, Mt. Vernon, WA.
7. Kuo, S. 2000. Sustainable crop production practices with mixed leguminous and non-leguminous cover crops. Western SARE Conference, Portland, OR. March 8-10, 2000.
8. Anderson, W. C., and S. Kuo. Cover crop species effects on soil quality and nitrate leaching. Presented to a Focus Group at Mt. Vernon, WA. May 3, 2000.
9. Huang, B., and S. Kuo. 2000. Effects of phosphorus fertilization, cover crop and residue management on soil phosphorus transformation under a continuous corn production system. Presented at the American Society of Agronomy annual meeting. November 5-9, Minneapolis, MN.
10. Anderson, W. C. 2000. Cover crop and soil erosion. Presented to Agriculture, Fish, and Water (AFW) process FOGO Executive Committee workshop. August 23-24, Mt. Vernon, WA.
1. Kuo, S., and U. M. Sainju. 1998. Nitrogen mineralization and availability of mixed leguminous and non-leguminous cover crop residues in soil. Biol. Fertil. Soil. 26:346-353.
2. Inglis, D. A. 1998. Pea Cyst Nematode: Biology and prevention. Washington State University Cooperative Extension Bulletin 1872.
3. Kuo, S. 1999. Improving crop productivity and water quality with winter cover cropping of mixed leguminous and non-leguminous species. PNW Sustainable Agriculture 11(2):1-4.
4. Kuo, S. 1999. Effects of winter cover crop species and soil nitrogen availability on silage corn production in western Washington. Dairy News 8 (10):1-3.
5. Tedford, E. C., and D. A. Inglis. 1999. Evaluation of important legumes in the Pacific Northwest as hosts for the pea cyst nematodes. J. Nematol. 31:155-163.
6. Inglis, D. A. Pea cyst nematode: Management and research findings. Proc. 1999 West. Wash. Hort. Assoc. Mtg. Seatac., WA.
7. Kuo, S. 2000. Factors to consider in managing cover crop residues. Dairy News. 9 (6):1-3.
8. Anderson, W. C., S. Kuo, D. Bulthuis. 2000. Benefits of fall-planted cover crops in the Puget Sound rows crop production system. Washington State University Cooperative Extension Bulletin 1900.
9. Kuo, S., and E. J. Jellum. 2000. Long-term winter cover cropping effects on corn (zea mays L.) production and soil nitrogen availability. Biol. Fertil. Soils. 31:470-477.
10. Kuo, S., and E. J. Jellum. 2000. Influence of winter cover cropping and residue management on N leaching and soil N availability. Agron. Abstr., p. 45.
11. Huang, B., and S. Kuo. 2000. Effects of phosphorus fertilization, cover crop and residue management on soil phosphorus transformation under a continuous corn production system. Agron. Abstr., p. 225.
12. Kuo, S., and E. J. Jellum. 2001. Influence of winter cover crop species and residue management on soil N availability and corn yield. Agron. J. (Submitted).
13. Kuo, S., B. Huang, J. W. S. Barnes, and R. Bembenek. 2001. Effects of long-term phsophorus fertilization and winter cover cropping on phosphorus transformation under continuous corn production. Soil Sci. Soc. Am. J. (Submitted)
14. Kuo, S. 2001. Factors to consider in managing cover crop residues. PNW Sustainable Agriculture 12 (4) 5-7.
15. Inglis, D. A. 2001. Pea diseases caused by nematodes. In: Compendium of pea disease. J. M. Kraft (ed.) American Phytopathological Soc. Press, St. Paul, Mn.
Education and Outreach Outcomes
Areas needing additional study
The economic analysis of this study is based on only two years. Further time-series data would be needed to have more conclusive results. The economic and environmental tradeoff is the critical component in deciding whether or not cover cropping should be encouraged. In the future study, the tradeoff analysis needs to include the risk or the cost to society of nitrate leaching to improve its accuracy.
While the effectiveness of the mixed leguminous and non-leguminous cover crop to protect soil and water quality has been proven in this study, one needs to expand the on-farm trials. The trials should be initiated and managed by the growers themselves. This will provide results that strengthen their belief in the value of the bi-cultured cover cropping system and their belief that hairy vetch will not become a weed if the legume is used as a green manure cover crop for the row crop production. Including other legumes in future study of the bi-cultures may be needed to determine if other legumes are equally effective as hairy vetch to increase soil N availability and compatible with the non-leguminous species. This may lead to more bi-culture cover crop options for the growers to choose from, if necessary.