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WINTER ANNUAL COVER CROPS
IN A WHEAT-GRAIN SORGHUM ROTATION:
ON-FARM AND ON-STATION RESEARCH, 1995/97

Rhonda Janke, Mark Claassen, William Heer,
Jerry Jost, Stan Freyenberger, and David Norman

Kansas Sustainable Agriculture Series, Paper #6

ABSTRACT

This paper reports the results of a study in central and south central Kansas, investigating the agronomic and economic implications of adding a winter annual legume cover crop to a winter wheat-grain sorghum rotation. Experiments included researcher-managed on-station trials and farmer-managed on-farm trials using hairy vetch and Austrian winter pea.

(Contribution No. 99-389-D from the Kansas Agricultural Experiment Station. Rhonda Janke is an Associate Professor of Horticulture, Forestry and Recreational Resources, Mark Claassen and William Heer are Agronomists-in-Charge of the Harvey County Experiment Field and the South Central Experiment Field respectively, Jerry Jost is Coordinator of the Heartland Project, Kansas Rural Center, Whiting, KS, Stan Freyenberger is Extension Associate in Agronomy, and David Norman is a Professor in Agricultural Economics, Kansas State University, Manhattan, KS, 66506.)

CONTENTS

ABSTRACT

INTRODUCTION

MATERIALS AND METHODS

Hutchinson Site: Date of Termination Study, 1995/96
Hesston Site: Date of Termination Study, 1995/96
Hesston Site: Date of Termination Study, 1996/97
Hesston Site: Seeding Rate Study, 1995/96
Hesston Site: Tillage x N Rate Study, 1996/97
On-Farm Research, 1995/96 and 1996/97
Economic Analysis, 1995/96 and 1996/97

RESULTS

Hutchinson Site: Date of Termination Study, 1995/96
Hesston Site: Date of Termination Study, 1995/96
Hesston Site: Date of Termination Study 1996/97
Hesston Site: Seeding Rate Study, 1995/96
Hesston Site: Tillage x N Rate Study, 1996/97
On-Farm Research, 1995/96 and 1996/97
Economic Analysis, 1995/96 and 1996/97

DISCUSSION

CONCLUSIONS

ACKNOWLEDGEMENTS

REFERENCES

LIST OF TABLES

Table 1. Date of Termination Trial, Hutchinson, 1996/97
Table 2. Date of Termination Trial, Hesston, 1995/96
Table 3. Date of Termination Trial, Hesston, 1996/97
Table 4. Seeding Rate Trial, Hesston, 1995/96
Table 5. Tillage x N Rate Trial, Hesston, 1997/98
Table 6. On-Farm Trials, Agronomic Results, 1995/96 and 1996/97
Table 7. On-Farm Trials, Soils Data, 1995/96 and 1996/97
Table 8. On-Farm Trials, Economic Data, 1995/96
Table 9. On-Farm Trials, Economic Data, 1996/97
Table 10. On-Farm Trials, Means and Significance of Economic Data, 1995/96 and 1996/97

WINTER ANNUAL COVER CROPS
IN A WHEAT-GRAIN SORGHUM ROTATION:
ON-FARM AND ON-STATION RESEARCH, 1995/97

Rhonda Janke, Mark Claassen, William Heer,
Jerry Jost, Stan Freyenberger, and David Norman

ABSTRACT

Winter annual legumes in humid regions of the country can have a positive effect on subsequent corn (Zea mays) and grain sorghum (Sorghum bicolor) crops, mainly through N contribution of the legume and, in some cases, soil improvement. However, water use by the cover crop in drier regions has the potential to reduce yields in subsequent crops. This study was initiated in central and south-central Kansas to look at both the agronomic and economic implications of adding a winter annual legume cover crop to a winter wheat (Triticum aestivum)-grain sorghum rotation. Experiments included researcher-managed on-station trials and cooperative (i.e., farmer-managed) trials with farmers using hairy vetch (Vicia villosa) and Austrian winter pea (Pisum arvense). Results showed that in good rainfall years, establishment of cover crop was adequate, and no significant difference occurs between sorghum yields following cover crops versus following wheat with fertilization. On-station trials showed a significant nitrogen (N) contribution from hairy vetch and benefits to sorghum in both tilled and no-till systems. During years with low rainfall, cover crop establishment was poor, N contribution from the cover crop was low, and grain sorghum yields were reduced because of water use by the cover crop. Variable costs were similar between cover crop and fertilized treatments, but gross returns and, consequently, net returns were lower in the cover crop plots because of this yield reduction. For cover crops to be attractive options for farmers in this part of Kansas: they must be used also for livestock feed and/or for early spring grazing; other cultivars or management systems that use less water must be developed; experiments must be conducted to ascertain benefits of cover crops during the second rotation cycle; and the price of N fertilizer must increase to the point that use of alternative sources is economic. Also, the use of cover crops by farmers in regions of variable rainfall should not be "recipe driven" but "response driven", using cover crops in years where rainfall is adequate, and not planting or destroying stands during dry years to conserve water for the cash crop.

WINTER ANNUAL COVER CROPS
IN A WHEAT-GRAIN SORGHUM ROTATION:
ON-FARM AND ON-STATION RESEARCH, 1995/97

Rhonda Janke, Mark Claassen, William Heer,
Jerry Jost, Stan Freyenberger, and David Norman

INTRODUCTION

Annual legumes have been tested widely in many regions of the U.S. (Smith et al., 1987) and have been largely successful in providing or supplementing nitrogen (N) to corn (Power et al., 1991; Utomo et al., 1990; Frye et al., 1983; Holderbaum et al., 1990; Decker et al., 1994; Ebelhar et al., 1984 ); sorghum (Sweeney and Moyer, 1994; Hargrove, 1986; Schlegel and Havlin, 1997); and tomatoes (Stivers and Shennan, 1991). In some cases, the N release occurs later in the season from cover crops than from fertilizer N (Huntington et al., 1985). Though plant uptake is initially higher from fertilizers than from cover crop sources, more cover crop N remains in the soil organic and microbial pools and may be released later (Harris et al., 1994). In addition to the N benefit, yield increases have been documented when fertilizer is combined with cover crop use (Utomo et al., 1990; Blevins et al., 1990), possibly because of soil quality enhancement (Sweeney and Moyer, 1995; McVay et al., 1989). Additional benefits of cover crops are reduced erosion (Bilbro, 1989); greater uptake of N left over from the preceding crop (McCracken et al., 1994); and providing habitat for soil-improving organisms such as mycorrhizal fungi (Galvez et al., 1995; Harris et al., 1966; Tisdall and Oades, 1982).

However, water use by cover crops also can decrease yields in subsequent crops in dry regions or during dry years (Schlegel and Havlin, 1997; Ebelhar et al., 1984) and can require more water under irrigated conditions (Stivers and Shennan, 1991), though early termination of the cover crop can reduce this negative effect (Munawar et al., 1990). Economic analyzes have shown that diverse crop rotations of feed grains including red clover as a cover crop are profitable compared to conventional continuous cropping (Diebel et al., 1993; Hanson et al., 1990), but analysis of a wheat-vetch/sorghum rotation in Kansas (Diebel et al., 1993) found that net profit was negative under some conditions. Other economic studies of winter annual cover crops in rotation have shown that profitability depends on the region of the country where the study was conducted, whether or not the cover crop reduced or enhanced crop yields, the relative prices of the cover crop seed and N fertilizer, and the value of the field crop or gross return (Hanson et al., 1993; Frye et al., 1985; Shurley 1987; Ott and Hargrove, 1989).

The above-mentioned work was all based on researchers' field plot data and/or county average yields. Within the discipline known as "farming systems research," the idea of farmer involvement and control over field research on their farms has been promoted internationally for several decades and more recently in the U.S. (Norman et al, 1994). The real synergism lies, however, in the combination of the two types of research. Studies have shown that farmers already do a fair amount of experimentation on their own, like being part of larger projects (Norman et al., 1998), and find experimental results more believable if economic data are presented. In addition, a study based on the farmer's own experience has a high degree of "plausibility" to the farmer (Walter, 1993).

Our major objectives were to:

• Determine the effects of date of establishment, seeding rate, and tillage system on establishment of cover crops and N accumulation in above ground biomass.
• Determine the effect of cover crop termination date and N contribution on subsequent grain sorghum yields in a wheat-sorghum rotation in on-station trials.
• Compare with versus without cover crops in the system with a network of farmer cooperators, each having a set of paired plots. Analyze the economics of the on-farm data.

Additional goals were to promote more farmer-researcher interaction, prioritize future research directions, and take advantage of the complementarity of on-farm and on-station research data.

MATERIALS AND METHODS

To fulfill the objectives of the study, one researcher managed trial was implemented at the KSU South Central Experiment Field, Hutchinson, and four others were implemented at the KSU Harvey County Experiment Field, Hesston. In addition a total of 20 farmer implemented, farmer managed comparisons were performed over the period of 1995/97. Details of the trials are as follows.

Hutchinson Site: Date of Termination Study, 1995/96
The site of the trial consisted of an Ost loam soil where wheat had been grown in 1994/95. The research used a randomized block design and was replicated four times. Cover crop treatments consisted of fall-planted winter peas with intended termination dates in April and May and no cover crop (fallow). The winter peas were planted on 14 September, 1995 at a rate of 35 lb/a in 10-inch rows with a double-disk opener grain drill. Actual dates of termination were 16 May, 1996 and 4 June, 1996. Prior to termination of the cover crop, above ground biomass samples were taken from a 10.76ft² area. These samples were used to determine forage yield (winter pea and other) and forage N and phosphorous (P) contents for the winter pea portion. Weeds were controlled with a broadcast application of propachlor and atrazine after planting. Fertilizer treatments consisted of a control (zero N) and three N levels (30, 60, and 90 lb N/a) that were broadcast and applied as ammonium nitrate (34-0-0) prior to planting of grain sorghum on 17 June, 1996. Phosphate was applied at a rate of 40 lbs/a P₂O₅ in the row at planting. Grain sorghum plots were harvested on November 25 (replications 1 and 2) and December 8, 1996 (replications 3 and 4) to determine yield, moisture, test weight, and N and P contents of grain.

Hesston Site: Date of Termination Study, 1995/96
The trial site consisted of a Geary silt loam soil on which unfertilized winter wheat was grown in 1995. Detailed soil sampling was done in the fall prior to vetch planting to establish soil nutrient and moisture status. Additional soil sampling was done at vetch termination and grain sorghum planting, as well as at the end of the season. Reduced tillage practices with a disk and field cultivator were used to control weeds and prepare a seedbed. Hairy vetch plots were roller harrowed and planted at 15 lb/a in 8 in. rows with a grain drill equipped with double-disk openers on 15 September, 1995. Rainfall shortly after planting favored fall stand establishment of hairy vetch. Volunteer wheat was controlled by a mid-October application of Fusilade + crop oil concentrate (2 oz ai/a + 1% v/v). Fall, winter, and early spring months were very dry. Consequently, hairy vetch had too little growth to merit termination in early April, the first target date. Subsequent wet weather delayed initial termination by disking until 20 May. Hairy vetch in a second set of plots was terminated in a like manner on 11 June, about 5 weeks later than intended.

Vetch forage yield was determined by harvesting a 10.76 ft² area in plots on 16 May and 11 June. Nitrogen fertilizer was broadcast as ammonium nitrate, at similar levels as in the Hutchinson site, on specified plots before the last preplant tillage on 14 June. Pioneer 8505 grain sorghum treated with Concep III safener and Gaucho insecticide was planted at approximately 42,000 seeds/a on 14 June. Weeds were controlled with a preemergence application of Microtech + atrazine (2.5 + 0.25 lb ai/a). Grain sorghum was combine harvested on 27 October.

Hesston Site: Date of Termination Study, 1996/97
The experiment was established on a Geary silt loam soil on which unfertilized winter wheat was grown in 1995 and 1996. Reduced tillage practices with a disk and field cultivator were used to control weeds and prepare a seedbed. Hairy vetch plots were planted at 15 lb/a in 8 in. rows with a grain drill equipped with double-disk openers on 13 September, 1996. Rainfall shortly after planting favored fall stand establishment of hairy vetch. Precipitation during the entire vetch growing season was near to or slightly above normal. Volunteer wheat was controlled by a mid-March application of Fusilade + crop oil concentrate (2 oz ai/a + 1% v/v). One set of vetch plots was terminated early by disking on 25 April. Hairy vetch in a second set of plots was terminated in like manner on 14 May. Vetch forage yield was determined by harvesting a 10.76 ft² area from each plot immediately before termination. Nitrogen fertilizer treatments were broadcast as ammonium nitrate on 23 June, 1997. All plots received 35 lb/a of P₂O₅, which was banded as 0-46-0 at planting. Pioneer 8505 grain sorghum treated with Concep III safener and Gaucho insecticide was planted after a rain delay at approximately 42,000 seeds/a on 3 July, 1997. Weeds were controlled with a preemergence application of Microtech + atrazine (2.5 + 0.25 lb ai/a). Grain sorghum was combine harvested on 6 November.

Hesston Site: Seeding Rate Study, 1995/96
Spring oats were grown on a Smolan silt loam soil in 1994. Stubble mulch tillage practices, initiated with a V-blade, were used after oat harvest. Relatively high temperatures and dry soil in late summer made it necessary to postpone vetch planting. The experimental design was a 3-way factorial with three replications of each treatment (combination). Factors included vetch seeding rate (none, 25 and 40 lbs/a), no-till (NT) versus disk tillage system for vetch and sorghum establishment, and nitrogen (N) fertilizer rates (0 and 50 lb/a) for grain sorghum A grain drill with double - disk openers on 7 in. spacing was used to seed the vetch at 25 and 40 lb/a on 8 October, 1994. A substantial crop of volunteer oats was eliminated by an early November application of Fusilade + crop oil concentrate (2 ox ai/a + 1% v/v). Spring termination of hairy vetch was delayed by cool and wet conditions. Vetch forage yield was determined by harvesting a 10.76 ft² area in each plot on June 7. The entire site then was sprayed with Roundup + 2,4-D LVE + Pen-A-Trate II nonionic surfactant (0.375 + 0.71 lb ae/a + 0.5%). Nitrogen fertilizer was broadcast as ammonium nitrate on specified plots prior to tillage (disk, roller harrow) later in June after some soil drying had occurred. Pioneer 8500 grain sorghum treated with Concep II safener and Gaucho insecticide was planted at approximately 30,000 seeds/a on 27 June. Temik 15G insecticide at 7 lb/a was applied in the furrow with the seed at planting. Weeds were controlled with a preemergence application of Lasso + atrazine (2.0 + 0.5 lb ai/a). Grain sorghum was combine harvested on 27 October.

Wheat cultivar 2163 was no-till planted into sorghum stubble at 75 lb/a on 6 November, 1995. No fertilizer was applied. The N status of wheat was determined from whole-plant samples of three tillers from six locations within each plot collected when the plants were fully headed. Wheat was harvested on 5 July, 1996.

Hesston Site: Tillage x N Rate Study, 1996/97
The experiment site was located on a Smolan silt loam on which a vetch-grain sorghum-winter wheat cropping system had been established in the fall of 1994 (the seeding rate is described in the previous section). Wheat grown in 1996 had not been fertilized. In this second cycle, hairy vetch was no-till planted on 13 September, 1996, into wheat stubble in which weeds and volunteer plants had been controlled with Roundup. The experimental design consisted of with versus without vetch, disk till versus no-till, and three rates of N in a factorial design with three replications. A grain drill with double-disk openers on 8 in. spacing was used to seed the vetch at 15 lb/a. In the following spring, vetch forage yield was determined by harvesting a 10.76 ft² area in 12 representative plots just prior to vetch termination. Vetch was sprayed on 15 May at very early bloom stage with Roundup + 2,4-DLVE + Premier 90 nonionic surfactant (0.375 + 0.71 lb ae/a + 0.5%). Tillage plots were disked on 17 May. Rains delayed N application and planting. Nitrogen fertilizer treatments (zero, 60 and 90 lbs/a) were broadcast as ammonium nitrate on 4 July. Pioneer 8500 grain sorghum treated with Concep 11 safener and Gaucho insecticide was planted at approximately 42,000 seeds/a on the same day. Weeds were controlled with a preemergence application of Microtech + atrazine (2.0 + 0.25 lb ai/a). Grain sorghum was combine harvested on 7 November.

On-Farm Research, 1995/96 and 1996/97
Farms were selected as research sites based on the interest of the cooperator in growing cover crops and in participating in the trial and willingness to follow agreed-upon protocols and collect yield data. Eleven farms participated in 1995/96, and 10 in 1996/97 with some of the farmers being involved both years. Research staff collected the soil samples, leaves for tissue nutrient analysis, and cover crop biomass and nutrient data. Farmers collected yield data and did all field preparation, planting, fertilizer applications, and weed control. Protocols were developed through a series of meetings with researchers and farmers. Rainfall data and economic data were recorded by the farmers and compiled and summarized by researchers.

In 1995/96, seven farms used hairy vetch, and five grew Austrian winter pea. Two of the five farms with winter pea collected economic data, but did not participate in the agronomic trials. In 1996/97, five grew hairy vetch, and five grew Austrian winter pea. Most farms grew one species or the other, but in 1995/96 one farm had plots of each and in 1996/97 two farms had plots of each. All farms in each year planted an adjacent control plot with no cover crop. Each farmer chose the rate of fertilizer for the control plot generally based on local recommended rates and their typical best management practice. Some farms also applied a small amount, usually as starter, to the cover crop plot. The same variety of grain sorghum (Pioneer 8505) was used in all plots in both years. Tillage methods in the cover crop plots and the control plots were identical within each farm each year but varied slightly from farm to farm, with each farmer using his or her normal practice. In all cases except one, the cover crop was killed with the preplant tillage operation. One farmer killed the cover crop with herbicide prior to no-till planting the sorghum. Soil samples were collected in the late fall after cover crop planting but prior to maximum biomass production as a "before" measurement of soil nutrient status. Soil samples were collected again the next year in the late fall after sorghum harvest as an "after" measurement. All soil samples were collected to a depth of 24" in increments of 0-6", 6-12", and 12-24" using a hand corer. One end of the experimental plots was designated for intensive sampling for all measurements. Five cores per plot were collected and bulked for analysis. Similar subsamples were collected for cover crop percent cover using a rope-knot counting method (two transects per plot), cover crop biomass (4 ft. sq. subsamples), and sorghum leaf tissue analysis at early heading (10 leaves per plot). Soil water content was measured using an 'Aquaterr' soil water capacitance probe at depths of 0-6" and 6-12" (5 samples per plot). All data were analyzed using analysis of variance with two treatments (with and without cover crop). Farms served as replicates in the analysis, with seven and three replicates in 1996 for hairy vetch and winter pea, respectively, and five each in 1997.

Economic Analysis, 1995/96 and 1996/97
The same data set of farms was used for the economic analysis, with the exception of 1996; five farms contributed economic data on winter pea, whereas only three were used in the agronomic analysis (see Table 8, Austrian winter pea farms 1-3). Records kept by each farmer were used to calculate costs and returns for production with versus without cover crop plots. Actual tillage operations, seeding rates, fertilizer and herbicide costs, and time were tracked for each farm. Uniform values for the costs of sorghum seed, hairy vetch seed, and winter pea seed and grain sorghum were used across all farms in each year and were based on current market prices. Labor costs were incorporated into the equipment custom rate costs. A spreadsheet program was used to record all costs and calculate the gross return, variable costs (i.e., which includes labor costs), and net return.

RESULTS

Hutchinson Site: Date of Termination Study, 1995/96
Soil conditions at planting of the winter peas were excellent with good moisture. However, the mid-September planting date was later than desired because of above-normal rainfall in late August and early September. After planting, temperatures cooled and limited fall growth of winter peas. Fall ground cover ranged from 26 to 36% with no significant differences across treatments (Table 1). The winter months were cool and dry. This limited growth and delayed the first date of termination from early April to 16 May. The second termination date also was delayed to 4 June by wet conditions in May. Winter pea above ground biomass on 4 June was more than double that on 16 May (Table 1). Nitrogen credited to the cover crop generally doubled between 16 May and 4 June but ranged from 10 to 32 lb N/a. These N levels are considered low and did not result in increased grain yields in the grain sorghum crop. Flag leaf N (%) and whole plant N (%) were lowest in the no-N treatments with or without cover crop. Generally, the first increment of fertilizer N (30 lbs/a) had the greatest effect on leaf and whole plant N and grain yield. However, the overall effects of the cover crop and N fertilizer on flag leaf and whole plant N and grain yield were not always significant or consistent.

Hesston Site: Date of Termination Study, 1995/96
Initial soil nitrate N and available P averaged 36 lb/a and 51 lb/a, respectively, and organic matter was 2.8%. Hairy vetch provided adequate late-fall ground cover (40%) to protect the soil from erosion (Table 2). Rainfall in late April and early May encouraged growth of hairy vetch, which was about 21 in. tall and had reached the 20 to 30% bloom stage on 20 May. It ranged from late bloom to early seed formation stages by June 11. Average dry matter yields were just under 2 tons/a on May 20 and nearly 2.5 tons/a by June 11. The average N contents were 2.73% and 2.59%, respectively (data not shown). Consequently, the average amount of N in the above-ground biomass was 105 to 127 lb/a.

Disking to terminate hairy vetch growth reduced soil moisture at the surface, particularly on 11 June. Sorghum stands averaged about 8000 fewer plants in the June 11 treatment than in the May 20 date of termination and the no-vetch plots. Leaf N at boot to early heading stage tended to be highest at the highest N rates, and was statistically significant in the absence of vetch and the June 11 date of termination. Sorghum following vetch required 2 to 4 days longer to reach half bloom than sorghum without a preceding cover crop. Averaged over N rates, sorghum yields were 6 to 12 bu/a lower after vetch than where no cover crop had been grown. This negative effect of hairy vetch was accounted for by adjusting sorghum yields for soil P removal by vetch and may also be due to water use by the cover crop prior to sorghum planting. Yields tended to increase with N rate in sorghum after vetch, mainly at the 60 lb/a.

Hesston Site: Date of Termination Study 1996/97
Initial soil nitrate N (0 to 2 ft) and available P (0 to 6 in.) averaged 19 lb/a and 40 lb/a, respectively, with an organic matter level of 2.1%. Hairy vetch provided excellent fall ground cover (63%) to protect the soil from erosion (Table 3). On 25 April, vetch was about 16 to 18 in. tall and had not reached bloom stage. A few plants were beginning to bloom by 14 May. Average dry matter yield of hairy vetch was 2.66 tons/a on April 25 and nearly 3.0 tons/a on May 14. The average N contents were 2.76% and 3.15%, respectively. Consequently, the average potential amounts of N in the above-ground biomass were 147 lb/a and 188 lb/a, respectively. Disking to terminate hairy vetch growth did not adversely affect soil moisture at the surface because of ample spring rains, which ultimately delayed planting. Sorghum stands averaged 39,560 plants/a and were relatively uniform across treatments. At low N rates, leaf N at boot to early heading stage was higher in sorghum after vetch than in sorghum without vetch. The highest leaf N values occurred in sorghum following vetch in the 14 May termination date treatment. However, the effects of vetch termination date on leaf N were not always significant or consistent. The overall effect of N fertilizer rate on leaf N was significant. A trend for increasing leaf N as N rate increased was consistent in sorghum without prior vetch. In sorghum following vetch, leaf N did not increase meaningfully above an N rate of 30 lb/a. Sorghum following vetch required 1 to 2 days fewer to reach half bloom than sorghum without a preceding cover crop. Averaged over N rates, sorghum yields were 6 to 10 bu/a more after vetch than where no cover crop had been grown. The positive effects of 25 April and 14 May vetch on the yield of sorghum without fertilizer N were equivalent to those of about 70 lb/a and 89 lb/a of N, respectively. A small, but significant, increase in the number of panicles per plant accounted for most of the treatment effects on yield. The trend for increasing yields at the second termination date may indicate a response to the higher N contribution from the additional vetch.

Hesston Site: Seeding Rate Study, 1995/96
Mid-October rain in 1995 enabled vetch to emerge, but fall growth remained rather limited. However, cool wet conditions allowed considerable spring growth. At the time when it was controlled with herbicide, vetch was about 22 in. tall and had reached late bloom stage. Hairy vetch production was not affected by seeding rate. The average dry matter yield was 2.54 tons/a (Table 4), and the average N content was 2.62%. Consequently, the average potential amount of N to be mineralized was 133 lb/a. The thick mat formed by dead vetch material kept the soil wet for some time. A large population of armyworms (Spodoptera frugiperda) present under the vetch did not impact the later emerging sorghum seedlings. Sorghum stands averaged about 2000 plant/a more in plots with hairy vetch than where no cover crop had grown (data not presented). However, sorghum following vetch tended to reach half bloom 1 to 2 days later than after no cover crop (data not presented). Also, half bloom for no-till sorghum was delayed about 3 days in comparison with sorghum in tilled plots. Nitrogen concentration of sorghum flag leaves was slightly higher with the 50 lb N/a treatment than with no fertilizer. Despite late June planting and an early fall frost, sorghum yields averaged 84 bu/a. However, hairy vetch, tillage, and N rate had no significant effects on yield.

Wheat emergence was delayed by late planting and dry conditions in the fall of 1995. Little or no tillering occurred until spring. An extremely dry winter as well as cyclical periods of warm and cold temperatures caused considerable stress. However, favorable spring moisture and temperatures allowed late tillering to occur and development of reasonable yields. Residual effects of hairy vetch produced an average increase of 6.5 bu/a in wheat yield. Vetch seeding rate had no effect. At the zero level of fertilizer on the previous sorghum crop, vetch increased wheat yield by 7.9 bu/a. The prior tillage system for grain sorghum had no effect on yield of wheat. The residual effect of 50 lb N/a on sorghum improved wheat production by 2.8 bu/a. Whole-plant analysis showed a significant increase of 0.41% N in wheat that followed sorghum after vetch. Residual no-till and N fertilizer effects on plant N content also were significant but smaller. Similar trends in treatment effects on grain N levels also occurred. Residual effects of vetch on wheat grain represented a 1% increase of protein.

Hesston Site: Tillage x N Rate Study, 1996/97
Fall rains promoted vetch emergence and stand establishment and was near to or slightly above normal in the fall of 1996. At the time of termination, vetch was 22 to 25 in. tall and had produced an average dry matter yield of about 2 tons/a (Table 5) and the average N content was 3.12%. As a result, the potential amount of N to be mineralized averaged 128 lb/a. Sorghum stands averaged about 36,700 plants/a and were not affected by tillage or vetch treatments. Rainfall during the summer months was above normal. Sorghum following vetch reached half bloom 1 day earlier than sorghum after no cover crop. Also, half bloom for no-till sorghum was about 1 day earlier in comparison with sorghum in tilled plots. Vetch significantly increased the N concentration of sorghum flag leaves at the zero N rate but not at 60 or 90 lb N/a. Tillage had no effect on leaf N level in sorghum. Grain yields increased by nearly 22 bu/a in unfertilized sorghum after vetch versus that with no vetch. This positive effect was equivalent to approximately 58 lb/a of N. The yield increase correlated with a slight increase in the number of heads per plant. Both vetch and N fertilizer slightly increased sorghum grain test weight (not shown).

On-Farm Research, 1995/96 and 1996/97
Dry growing conditions in the fall and winter of 1995-1996 resulted in poor stand establishment of both cover crops on most farm sites. The average biomass of cover crops prior to spring tillage was less than 0.5 ton/a, and the N contribution from that biomass averaged 26-27 lb/a (Table 6). The resulting sorghum yields in 1996 were lower with cover crop than without (14.8 bu/a lower with hairy vetch and 30.1 bu/a lower with winter pea), though leaf tissue N levels were adequate in both treatments. Soil water measurements during the growing season indicated lower soil moisture in the vetch plots at the 6-12" depth, perhaps because of depletion in spring prior to destruction of the cover crop. This result was somewhat surprising in this particular growing season, because late spring rains delayed cover crop destruction and tilling. However, the cumulative effect of low rainfall throughout the winter could explain this result. Rainfall data were recorded consistently on four farms, in representative locations within the study area. The average cumulative rainfall during the 1995/96 vetch growing season (Sept - May) was 14.8 inches, compared to 20.3 inches for the same time period in 1996/97. Thus, moisture may have been a limiting factor. The amounts of rain during the sorghum growing season (June - Sept.) were similar for both years, averaging 17.8 inches and 17.5 inches in 1996 and 1997, respectively.

Cover crop establishment was much better in the fall and winter of 1996-1997, resulting in an average of over 1.54 and 0.76 tons of cover crop above ground biomass, which contributed averages of 91.8 and 51.8 lb/a N from vetch and winter pea, respectively. The range for vetch was from 22 lb/a to 164 lb/a N. Few conclusions can be made from a comparison of vetch and pea at this point. That comparison was not an objective of this study, because the choice of cover crop depends more on how it fits into the overall farm system rather than just biomass or N produced as a rotation crop. However, on the two farms where both cover crops were planted side-by-side, the vetch produced more biomass and N than the pea.

Subsequent sorghum yields were relatively higher in the cover crop plots in 1997 as compared to 1996. The sorghum following winter pea was not significantly different from the yields of the fertilized control plots but the yield of sorghum following vetch was significantly lower (9.7 bu/a) than the control plot (significant at P=0.05). Leaf tissue N also indicated adequate N status in both treatments. Soil water measurements in 1997 also were not different between plots. Observations by the farmer participants indicated that the apparent timing of N release differed between the cover crop and fertilizer, and in some cases, the sorghum in plots following cover crops did not develop a dark green color until fairly late in the season.

Soil pH, organic matter, and levels of P, K, and other cations, were not different between the cover crop and control plots in either year within each farm site, for the "before" or the "after" samples. Mineral N, total N, and organic matter levels, also not significantly different, are presented in Table 7. Though not significant, a trend occurred for slightly lower mineral N levels following cover crops as compared to the fertilized plots. From these data, we do not know if the plots had lower N status overall, or if the N was simply tied up in organic forms (i.e., plant residue and microbial biomass). The study also was not able to determine if this potentially stored N could be released for crop growth later in the rotation cycle. Some samples were analyzed for soil quality factors such as water infiltration rate and water stable aggregates. After only one year of cover crop, no differences were seen in these factors. Other data sets have indicated that two or more cycles through the legume portion of the rotation may be required to change these soil physical factors significantly (Peters et al., 1992).

Economic Analysis, 1995/96 and 1996/97
Individual farm data are shown in Table 8 and Table 9, and the means and significance levels based on analysis of variance of aggregated data are shown in Table 10. Seeding costs were $15.41/a (i.e., seed plus equipment and labor) for cover crops, averaged over the two cover crops and two years (Table 10). Fertilizer costs averaged $23.84/a for the control plots and $6.16/a for the cover crop plots. Thus, total N costs were $21.57/a in the cover crop plots and $23.48/a in the fertilizer only plots. However, because of establishment problems in 1995/96, average N contribution from the cover crop plots was less than the fertilizer added in the control plots (i.e., 52.8 lb/a N from cover crop versus 73.6 lb/a N from fertilizer). This N difference, the availability of the N, and water use by the cover crops partially explain the lower sorghum yields in the cover crop plots; 82.1 bu/a versus 94.6 bu/a averaged over all years and both cover crops. This 12.5 bushel difference is responsible for the differences in gross income (i.e., $225.01/a for control versus $194.77/a with cover crops) and net income (i.e., $120.12/a versus $90.32/a), because the total variable costs were virtually identical between the two treatments ($104.89/a versus $104.45/a, respectively).

Quite a bit of farm-to-farm variability can be noted in Tables 8 and 9, including higher herbicide costs for the no-till farmer (winter pea site number 1 in 1995/96, and vetch and winter pea site number 3 in 1996/97). The no-till farmer required much less time for field operations (i.e., only applying herbicides, in addition to the planting, fertilizer, and harvest requirements) than the other farmers (i.e., 30 versus 74 minutes), who used a variety of mechanical operations (i.e., disk, spring-tooth, chisel, and/or field cultivator, in addition to possible use of herbicides) for field preparations and weed control (data not shown). Generally with cover crops, more time was required compared to the fallow plots (76 versus 60 minutes/a). This increase in time requirement can be accounted for by the additional operations of drilling the cover crop and then later killing it in preparation for planting sorghum.

DISCUSSION

For farmers, costs are similar for cover crop use as compared to fertilizer, though there is a small trade-off of increased time as an input versus other off-farm purchased inputs. Lower yields with cover crop use in this experiment resulted in lower net returns from grain sorghum in a wheat-cover crop-sorghum rotation. Soil-improving benefits of the cover crop in this rotation were not found after one rotation cycle in either increased organic matter, total N, or mineral N. Two or more rotation cycles through the legume may be needed to observe this soil quality benefit. Questions that farmers brought to this study as ranked in a research priority setting exercise in a group meeting shifted from economics and nitrogen fixation to establishment success and grazing opportunities, which would result in an economic benefit as yet not taken into account. Moisture conservation and soil quality were high on the list of research questions both at the beginning and end of the project.

Agronomic data from the farm sites showed that moisture may have been a limiting factor in vetch plots in 1996, but not in 1997. Good cover crop establishment was achieved in 1996/97, but poor stands occurred in 1995/96 as a result of dry winter conditions. Results for leaf tissue N at the early heading stage indicate that N was not limiting at this point in the growing season, but farmer observations of later greening of the sorghum in the cover crop plots indicates that the N from the cover crop may have been available only later in the growing season, and the timing of N release may have influenced yield.

The hairy vetch data from the KSU Hesston field is encouraging. The vetch provided an overall average of 116 and 168 lb N/a in the above ground biomass in the Termination Date experiments in 1996 and 1997, and 134 and 128 lb N/a in the Seeding Rate and Tillage x N experiments, respectively. The N provided by the vetch generally resulted in little to no response to N fertilizer in the plots with vetch, whereas typical yield responses to N fertilizer were observed in the control plots without vetch. Hairy vetch seeding rate (Table 4) had no significant effect on vetch biomass, N contribution, or subsequent sorghum or wheat yields, showing that 25 lb/a is an adequate seeding rate, as compared to 40 lb/a. The farmers involved in the experiments used an average seeding rate of 17 lb/a, based on their own prior experience with vetch and a desire to save as much money on seed as possible. On one farm where observation data were collected on vetch seeding rates of 26 versus 13 lb/a, both plots resulted in similar spring vetch biomass and N levels, but the fall percent ground cover was higher with the higher seeding rate (data not shown).

The use of a cover crop generally appears to be compatible with either standard tillage or no-till. In the Seeding Rate and the N x Tillage experiments at Hesston (Tables 4 and 5), no significant differences in sorghum or wheat yields occurred with disk tillage versus no-till planting into hairy vetch. The no-till farmer involved in the on-farm experiment obtained sorghum yields similar to averages over all farms with winter peas in 1996, and yields higher than average in 1997.

The later cover crop termination date in the hairy vetch experiments at Hesston (Tables 2 and 3) resulted in more total vetch biomass, lower percentage N in the tissue (data not shown), but overall higher levels of N in the above ground biomass. Grain sorghum yields were 6 and 4 bu/a higher in 1996 and 1997 at the second termination date, respectively. Although not statistically significant, this trend may indicate a response to the higher N contribution by the extra vetch. Attempting the termination date experiments pointed out one of the difficulties of handling cover crops in a wet spring, since cover crop kill and subsequent sorghum planting often must be delayed. Some farmer participants felt that the lack of dramatic yield increase or decrease due to termination date makes it less important exactly when the cover crop is killed, only that it is killed. However, data from western Kansas, where rainfall is even more limiting, point out the importance of vetch termination date in a rotation that includes fallow for moisture conservation purposes (Schlegel and Havlin 1997).

The termination date experiment at Hutchinson found that the N contribution from winter peas nearly doubled from 14 to 27 lb N/a with a termination date of May 16 versus June 4. Grain sorghum yields increased from 85 to 90 bu/a with cover crops at the two termination dates, respectively, but this difference was not statistically significant. Overall, the winter pea N contributions from both the Hutchinson trial and the on-farm data were not impressive during these 2 years. The maximum N contributions averaged only 32 lb/a in the Hutchinson trial and 26 lb/a in 1996 and 52 lb/a in 1997 in the on-farm plots, although one farm achieved a level of 142 lb/a in 1997. Many of the farmers who use winter peas will continue to use them despite their low N contribution as compared to vetch, because they feel that they are easier to control in the spring and offer grazing opportunities for livestock on their farms. An on-farm observation study with grazing winter peas suggested that taking peas off early in the form of forage can help conserve soil moisture as compared to leaving them until preplant tillage.

CONCLUSIONS

More research is needed on the long-term benefits of legumes in rotation, including perennial legumes as well as winter and summer annuals. When a farmer first starts to use cover crops, if rainfall is adequate and a good stand is obtained, the cover crop can substitute for all or part of the N requirement for the sorghum crop. However, in a dry year, sorghum yields may be reduced. Long-term soil improvements from repeated cover cropping may eliminate this yield reduction in time, but in the short-term farmers need to be prepared for it. Some of the farmers in this project expressed interest in reducing the risk of cover crops and enhancing their profitability by introducing spring grazing with livestock. This would remove the top growth early in the spring, lessen moisture competition with the crop, and provide an additional return from the cover crop.

On-farm data can give meaningful results and complement field station data. Farmers benefited from seeing how their farm compared to others in the trial, and several farmers commented that they plan to continue using cover crops. Most would not do replicated on-farm research, or even establish a "control" plot, without an incentive to pool their data with others. Many also would not have collected the required soils data without Rural Center and KSU researcher time and muscle power. The sharing of planting, tilling, and other problem-solving experiences was a valuable part of the annual meetings where the actual field trial data were presented.

Our conclusions concerning the technical results are that to make cover crops attractive options for farmers in this part of Kansas: they must be used also for livestock feed and/or for early spring grazing; other cultivars or management systems that use less water must be developed; experiments must be conducted to ascertain benefits of cover crops during the second rotation cycle; and the price of N fertilizer must increase to the point that use of alternative sources is economic. Also, the use of cover crops by farmers in regions of variable rainfall should not be "recipe driven" but "response driven", using cover crops in years where rainfall is adequate, and not planting or destroying stands during dry years to conserve water for the cash crop.

ACKNOWLEDGEMENTS

This project would not have been possible without funding from the USDA/SARE (Sustainable Agriculture Research and Education) program and support from the Kansas State University College of Agriculture. Thanks also to Pioneer for providing seed for this project, and most of all, thanks to the farmer cooperators: Arnold Busenitz, Marlo Duerksen, Larry and Carol Entz, Jim and Lisa French, Jaime Funke, Rick and Bill Granzow, Ron Jacques, Ron Miller, Arlyn and Mike Miller, Steve Sears, Nathan Stillwell, Russ and Gail Toevs, Fred Traskowsky, Leon Unruh, Lewis and Carrie Unruh, and Delton Voth.

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Table 1. Date of Termination Trial, Hutchinson, 1995/96

a. Harvested May 16 or June 4.

Table 2. Date of Termination Trial, Hesston, 1995/96

Table 3. Date of Termination Trial, Hesston, 1996/97

Table 4. Seeding Rate Trial, Hesston, 1995/96

Table 5. Tillage x N Rate Trial, Hesston, 1996/97

Table 6. On-Farm Trials, Agronomic Results, 1995/96 and 1996/97

* = 5%
a. Though there were 5 farms in 1996 having Austrian winter pea trials with economic data (including yield data) collected, agronomic data (cover crop biomass, soil tests, etc.) was only collected on 3 farms. Thus for this table, only the 3 farms agronomic and yield data are included in the analysis. These numbers and their significance are different from Table 10 economic data where all 5 farm yields are considered.

Table 7. On-Farm Trials, Soil Data. 1995/96 and 1996/97