Final Report for SW96-029
Advantages of an inter-cropping farming system, which contains a legume species, includes reduced soil erosion, weed suppression, improved soil fertility and improved forage quality. Many of the farmers in the central high great plains USA graze corn (Zea mays L.) stalks and are looking at ways to improve this fall pasture resource. However, no information is available on inter-cropping annual legumes with irrigated corn in the region. The objective was to evaluate for the most appropriate pasture legume species, which could be used in the development of a irrigated corn/legume system. To accomplish this experiments were conducted under irrigation at three sites in year 1. Eight legume species were evaluated in corn in comparison to mono culture corn under both a weed-free and weedy condition. Corn yields were reduced by the presence of legume in some treatments while others were comparable to the check yields. Medicago lupulina L. reduced corn yields by 4% whereas Medicago truncatula Gaertn. reduced corn yields by 17%. Corn yields were reduced approximately 62% by the presence of weeds regardless of legume species. The legumes did not significantly suppress weed growth. The results indicate that a mostly weed free field will be required to maximize corn and legume production. M. lupulina appears to offer the greatest potential for intercropping with irrigated corn in the central high great plains USA. Based on the finding of the year 1 trial 'George' (Medicago lupulina L.) and 'Orion' (Medicago sphacrocarpus L.) medics were selected for further study. The objectives of year 2 research were to (i) evaluate the effects of planting date and seeding rate of 'George' and 'Orion' medics on grain and forage yield of corn under irrigated conditions, (ii) determine the effect of planting date and seeding rate on 'George' and 'Orion' forage production when intercropped with grain and silage corn under irrigated conditions. Replicated field experiments were conducted at the University of Wyoming Research and Extension Center at Torrington. The results from these experiments provided further evidence that a corn-medic intercropping system may be a viable option for producers in the central high great plains USA. The system worked for both silage and grain corn production. A silage production system would be more suitable if the main objective of the producer is to get good quality fall grazing for livestock. If grain corn production is the goal of the farmer then 'George' medic is the best medic species to incorporate into the intercropping system. 'George' medic allows for increased forage production while having the least effect on corn yields. To allow for optimal corn and medic production 'George' medic should be planted at a seeding rate of 32 pure live seed/ft² at the time of corn planting, and bentazon should be added to a herbicide tank mixture with imazethapyr, pendimethalin, and NIS. In year three, 'George' medic and alfalfa were evaluated for intercropping potential with corn. The objectives of the research were to (i) evaluate the effects of these legumes on forage yield of corn under irrigated conditions, (ii) determine the yielding potential as a forage when intercropped with silage corn under irrigated conditions. Replicated field experiments were conducted at the University of Wyoming Extension Center at Torrington, WY and the Chuck Jones farm near Huntley, WY. The results from these experiments provided evidence that a corn-medic intercropping system has varied performance from year to year. The forage potential of annual medics under a corn silage system in 1998-1999 did not perform to a level that was anticipated indicating that further refinement of the practice is needed. The spring regenerative ability of 'George' medic is encouraging. The year following interseeding populations were 24 plants/ft², 2 years following interseeding seedling populations could be as high as 66 plants/ft². The year 2 results are preliminary. We plan further data collection later this spring. The regeneration is 3 and perhaps 8 times the initial interseeded seedling population.
1. Evaluate the most appropriate pasture legume species for effective weed suppression when undersown in irrigated corn.
2. Determine the appropriate seeding rate and sowing time of the selected annual medic to maximize weed suppression.
3. Investigate the regenerative capabilities of the selected annual medic and its potential to compete with weeds in a continuous-corn cropping system.
4. Establish the potential for improving livestock production from grazing the corn stubble/legume pasture mix in autumn following corn harvest.
A recent study in Minnesota found that farmers generally perceived companion-cropping systems to be highly desirable (17). Increased forage production, reduced soil erosion, and weed suppression were the main reasons given for using this system. Several studies have shown that there was little yield reduction when annual medics were inter-cropped with corn (2, 8). Further, at a seeding rate of 250 plants/m², medics suppressed weed growth 46% (8). Similarly, annual medics inter-cropped with barley in Minnesota reduced weed biomass 65% (7). Forage yields were increased, and soil erosion reduced 90%, when alfalfa was inter-cropped with sorghum, compared to a monoculture of sorghum (4). Further, several researchers (3,6, 1,19) have indicated that seeding date, seeding rate and herbicide treatments were important factors influencing the success of an intercropping system. For example forage production of annual legume species was generally better in intercropped systems with sweet corn with earlier compared to later planting dates, yet planting date had no significant effect on sweet corn yield or quality (3). Similarly, trials in North Dakota indicated that vetch (Vicia villosa Roth) biomass production in intercropped systems with sunflowers (Helianthus annuus L.) was greatest when vetch was planted at the same time as sunflowers (6). Further when vetch was intercropped with cereal rye (Secale cereale L.) production increased with increasing seeding rates (1). Intercropping medic with barley (Hordeum vulgare L.) has shown that forage production is influenced by species (Moynihan et. al., 1996). Additionally, an evaluation of 34 Medicago species conducted in Utah indicated that Medicago lupulina was the best adapted medic species for production in the Northern Great Plains (16).
During the first year of this SARE-funded project the objective was the evaluation for the most appropriate pasture legume species for effective weed suppression when interseeded in irrigated corn. The specific objectives were to (i) evaluate the effects of eight inter-cropped annual legume species on weed populations, weed growth, and corn yield, when sown at one seeding rate and (ii) determine the effect of weeds and corn on medic forage production.
Based on the finding from the year 1, two pasture legume species were selected for further study.
The objectives in year 2 were to (i) evaluate the effects of planting date and seeding rate of legume species on grain and forage yield of corn under irrigated conditions, (ii) determine the effect of planting date and seeding rate on legume species production when intercropped with grain and silage corn under irrigated conditions.
Based on the findings from the year 2 trials, a single species medic was selected for further analysis. The objectives of this research were to (i) Evaluate this medic and alfalfa intercropping potential for effective weed suppression when intersown in irrigated corn. Investigating the forage capabilities of the annual medic and alfalfa in a silage corn cropping system. (ii) Evaluate the forage yielding potential of an annual medic under a producer silage corn management system. Investigating the germination capabilities of the selected annual medic under drill or broadcast seeding applications. (iii) Monitor the regenerative capabilities of the annual medic.
In year one, field experiments were conducted at four locations in Goshen County, Wyoming. Two locations (designated TREC-1 & TREC-2) were on the University of Wyoming Research and Extension Center at Torrington, with a Valentine sandy loamy (mixed mesic, Ustic, Torripsamment) soil. Two locations were established on producer fields, one at Lingle, WY, with a Hargrave loamy sand (fine-loamy sandy, mixed, calcareous, mesic, Ustic Torrifluvents) soil, and the other at Huntley, WY, with a Mitchell sandy clay loam (coarse-silty, mixed, calcareous, mesic, Ustic Torriorthents) soil. The TREC and Huntley locations were sprinkler irrigated, while the Lingle location was furrow irrigated. Pioneer 3751 IR seed corn was planted on May 2, 10, 15, and 16 at TREC-1, Lingle, Huntley and TREC-2 respectively. Corn was inter-seeded with each of the species in Table 1 in 10 x 20 ft plots. A weedy, medic free plot, plus a weed and medic free check plot was included as a basis for comparison.
Table 1 Legume species interseeded with corn.
Common Name, Scientific Name, Cultivar
Black medic, Medicago lupulina L., George
Alfalfa, Medicago sativa L., Wrangler
Sweetclover, Melilotus officinalis Lam., Yellow Blossom
Gama medic, Medicago rugosa Desr., Paraponto
Snail medic, Medicago scutallata (L.) Mill., Sava
Barrel medic, Medicago truncatula Gaertn., Caliph
Spineless burr medic, Medicago polymorpha L., Santiago
Sphere medic, Medicago sphacrocarpus L., Orion
A brief description of each medic is provided, using information from various sources (5,7,12,14,15,18). Black medic has procumbent stems that are 12 to 28 in long. This cultivar was developed in Montana and is adapted to approximately 15.75 in precipitation. The other medics are from Australia. Gama medic has erect stems that become lax with growth, and is suited to heavy soils. It matures in 4.5 months (short days), and is adapted to areas receiving 12+ in annual precipitation. Snail medic has semi erect growth, branching at the base, and becomes lax with growth. It will produce flowers in 35 to 45 days in the Northern Great Plains. This species is best suited to regions receiving 12 to 20 in precipitation, and heavy soils with neutral to alkaline conditions. Barrel medic has a semi erect growth habit, branching near the base, branches are 6 to 32 in long. This species flowers in 41 days and is suited to areas receiving 11+ in precipitation that have neutral to alkaline soils. Spineless burr medic is prostrate in growth, with central stems weakly erect and branches up to 3 ft long. The plant produces flowers in 43 days, and is adapted for slightly acid to alkaline soils in areas receiving 15.75 in of precipitation. Sphere medic has semi erect growth, branching near the base, with branches 12 to 36 in long. This species is suited to light, moderately acid soils in areas receiving 14+ in precipitation.
Medic treatments were split into weedy and weed free treatments. To supplement existing weed seed soil banks ensuring adequate weed populations weeds were seeded in the weedy treatments. The weeds selected for planting were redroot pigweed (Amaranthus retroflexus L.), common lambsquarters (Chenopodium album L.), kochia (Kochia scoparia (L) Schrad.), field sandbur (Cenchrus longispinus (Hack.) Fern.), and yellow foxtail (Setaria glauca (L.) Beauv.). Weeds that were already present in the plots were also allowed to grow. The medics and weed seeds were broadcast over the plots prior to corn planting and shallow (<1in) incorporated using a 'Lely' vertical tine tiller. The medics were seeded at an appropriate rate to obtain a target population of 16 pure live seed (PLS)/ft². Following incorporation, corn was planted using a John Deere Maximerge vacuum planter. Weed free treatments received one application of imazethapyr [(+)-2-[4,5-dihydro-4-methyl-4 (methylethyl)-5-oxo-1H-imidazol-2-yl]-5-ethyl-3-pyridine carboxylic acid] “Pursuit” (4 oz/acre) + pendimethalin [N-(1-ethylpropyl)-3,4-imethyl-2,6-dinitrobenzenamine] “Prowl” (2.4 pt/acre) + NIS “X-77” (0.25% V/V) to control weeds when the corn had four to six leaves and weeds were less than three inches tall. Each treatment was replicated four times in a split plot (weedy or weed free) arrangement with a RCB design. Medic and weed counts were made approximately one month after planting at each location. Four counts in each plot, for medics and weeds, were made in each plot using a 95 in² quadrant. Two corn population counts were made on a 5 ft section of row at the same time. A medic and weed biomass sample was taken at mid season, and a second medic biomass sample was taken at the time of corn harvest, using a 3.3 x 1 ft quadrant over the corn row. Twice during the season light measurements were taken using a LI-COR linear photon flux meter. Corn yields were determined by harvesting an 18 ft section of row in each plot using an Almaco plot combine. Samples were weighed and yield expressed at 15% moisture.
In year two, field experiments were again conducted at the University of Wyoming Research and Extension Center at Torrington (TREC). Two studies were established at TREC, one looking at grain production (TREC 1), and the second at silage production (TREC 2). Pioneer 3751 IR corn was planted on May 6, in both studies at a population of 32,000 plants/acre. The experiments were conducted utilizing a RCB design with a split plot arrangement. Main plots were seeding date and subplots a factorial arrangement of medic species, seeding rate and herbicide input level. The medic species included Black medic (Medicago lupulina L.) cv. George and Sphere medic (Medicago sphacrocarpus L. ) cv. Orion, three medic planting dates, planting date one (PD1) two weeks prior to corn, on April 22, PD2 at corn planting, on May 6 and, PD3 two weeks after corn planting, on May 20 and three medic seeding rates of 8, 16, and 32 PLS/ft² in both studies. Seeding rates in 1997 were based on our 1996 rate of 16 PLS/ ft² and consisted of a ½X, X, and 2X rate. In addition, there were two herbicide input levels utilized in this study. The low input treatment consisted of the same herbicide treatment as used in year 1, and the high input treatment consisted of: imazethapyr “Pursuit” (4 oz/acre) + pendimethalin “Prowl” (2.4 pt/acre) + bentazon [3-(1-methyl)-(1H)-2,1,3-benzothiasiazon-4(3H)-one,2,2-dioxide] “Basagran” ( 1 pt oz/acre), + NIS “X-77” (0.25% V/V). The bentazon was included in the high input treatment to improve common lambsquarters (Chenopodium album L.) control.
The medics were broadcast over 10 x 20 ft plots and shallow (< 1 in) incorporated using two passes of a rotary hoe tiller. Corn was planted using a John Deere Maximerge vacuum planter. Each treatment was replicated four times in the study. Medic counts were made in each plot approximately one month after medic planting. Four counts in each plot were made using a 95 in² quadrant. Two corn population counts were made in each plot on a 5 ft section of row at the same time medic counts were made. A medic biomass sample was taken at mid season (June 1), a second sample taken after silage corn harvest (September 24), and a final sample taken after grain corn harvest (October 29). The samples were taken by clipping the medics that were rooted within two 95 in² quadrants. The medic samples were dried for 48 hours at 140oF, and dry weight measured. Silage corn yields were determined by harvesting a 5 ft section of corn row in the middle two rows of each four row plot. A fresh weight of the samples was taken and weighed to determine silage production. Sub-samples of silage were taken and dried for 48 hours at 140°F to calculate corn moisture content, and silage yields were adjusted to 65% moisture. Grain corn yields were determined by harvesting an 18 ft section of row in the center of each plot using an Almaco plot combine. Samples were weighed, moisture measured and grain yield adjusted to 15% moisture. The data was analyzed statistically using an ANOVA. Only main effect means are reported as no interactions were significantly different.
In year three and four, field experiments were conducted at the TREC and the Chuck Jones farm (Huntley). In 1998 a 150 ft x 600 ft field was divided into nine plots 50 ft x 170 ft with a 30 ft border between replications at TREC utilizing a RCB design. In 1999 two ten acre blocks were used for experimentation at Huntley. All treatments were compared to a check plot without medics. Pioneer 3751 IR corn was planted on April 24 at TREC and May 15 at Huntley. Applications of herbicide consisted of the high input treatment as used in year 2. The medic 'George' and the alfalfa were planted on April 24 at Torrington and the medic species on May 26 at the cooperators. The medic was Brillion drill seeded at 3.5 lbs/A, alfalfa at 9.0 lbs/A at TREC. On the cooperator's land medic was seeded at 7.2 lbs/A. 'George' medic was also broadcast at this location on part of one block at first cultivation to determine the yield potential of medics broadcast seeded after corn matured to the 4 to 5 leaf stage.
Four medic counts were made randomly using a 95 in² quadrant in each 10 acre block at the cooperators farm on August 24. Counts were made in medic/silage plots (drill seeded) and medic/silage plots (broadcast seeded) at the same time. Medics were harvested on November 17 to determine forage yield after the removal of silage corn. At the TREC location counts were taken in a 6 inch band 5 ft long over the corn row on June 6 to determine corn, medic, alfalfa and weed populations. Corn silage yield was determined on August 27 by harvesting two 5 ft sections of row. The entire area was combined on October 23. Each plot was evaluated for weight, test weight (TWT), and moisture content. Corn and medic dry weight was determined October 27 by clipping two 95 in² samples per plot. Samples were dried, weighed and statistical analyzed separately. The intention was to graze the TREC location with sheep and the Huntley location with cattle after corn silage removal.
Corn yields and weeds populations were adjusted according to medic populations using covariant analysis with the SAS statistical program. The adjustment for medic population was made because the populations were not uniform across species (9).
Reaction of Weeds to Medics
None of the medic species significantly reduced weed populations at any of the locations (P = 0.30), or weed biomass (P = 0.20) data not shown, alpha = 0.05 (9).
The presence of weeds reduced corn yields. Weeds reduced corn yields 56 to 64%, when compared to weed free treatments at the four locations (P = 0.0001). In the weedy treatments there were no differences between medic species (P=0.31) however, there were differences in yield between locations (P=0.001). At the TREC-1 location yields were reduced by 21 to 46% compared to the medic free check, while Huntley yields were reduced 11 to 59%. At the final two locations there were medic treatments that surpassed the yield of the medic free check (9). Overall the yields were highest at the Lingle location. However, this was most likely due to the fact that when the field was cultivated and ditched for furrow irrigation, approximately six weeks after planting, the weed and medic pressure was reduced. Within the weedy treatments, corn yields were not significantly reduced by any medic species compared to the medic free check for all locations. This shows that the weed competition was excessive and was the main factor in reducing the corn yields in these treatments. Therefore it is believed that the weed pressure should be augmented for this farming approach to be successful.
In weed free treatments, yields were significantly influenced by some medic species at all locations (9). Yields in plots inter-cropped with 'George' medic, sweet clover, and 'Paraponto' medic were similar to those of the weed and medic free check. Plots inter-cropped with alfalfa, 'Sava', 'Caliph', 'Santiago', and 'Orion' medics yielded 11 to 18% less than this check. In this portion of the study the Lingle location had the lowest yields and this may have been due to water stress early in the growing season. The TREC-1 site had the highest overall yields. It had been planted first and also had higher corn populations than did TREC-2.
Light measurements were taken twice during the season and on both occasions the readings were extremely variable and inconsistent. There were no consistent readings between medic treatments or the weed treatments.
Available medic forage production was significantly less (P<0.05) at corn harvest than it was at mid season for all species except black medic (9). Available forage was from 27 to 70% less at corn harvest than at mid season, across locations. 'George' medic, was the exception, producing 10% more forage at corn harvest than it had at mid-season when averaged across locations and weed treatments. Available forage production across medic treatments was 57% higher at corn harvest under weed free conditions compared to weedy conditions when averaged across locations. The fact that 'George' medic produced more forage later in the year makes this species ideally suited to this production system. It did not grow aggressively early in the year when it could reduce corn yield, but it produced more later in the season when build up forage for grazing is desirable. At each harvest time there were differences in forage production between species and locations. At both sampling dates forage production was significantly less (P<0.05), 30 to 90%, in the weedy plots than it was in the weed free plots. There were no differences between species production in the weedy treatments at corn harvest time. This again shows that the weeds, or the combination of weeds and corn, are too competitive for the medics to grow productively. Data for the Lingle location is not reported because the data is not consistent as a result of the cultivation the site received early in the season after the medics were planted.
Medics alone were not able to suppress weeds adequately. Management systems that exploit the competitive abilities of medic in combination with other weed control measures are required. 'George' medic appears to have the greatest potential for this farming system in the central high plains USA. Medic regeneration potential will be monitored. If these species cannot regenerate it will most likely be cost prohibitive to use this farming approach.
Medic stands were lower than desired at all seeding rates (10). Possible explanations for this were inadequate seed-soil contact, poor incorporation with the rotary hoe, variable germination especially with the 'George' medic, plant loss from herbicide treatments as plant counts were not determined until several weeks after herbicide application or spring environmental conditions. The last two weeks of May and the first week of June were extremely cool and wet which may have caused some seeds to rot, or caused seedling diseases of medic which reduced final stands.
Grain Corn Production
Grain yield was significantly different (P = 0.036) in 'George' and 'Orion' medic plots. Further, grain yield was influenced by medic planting date (P = 0.0001), and herbicide treatment (P = 0.001) (10). Since species exhibited differences, each species was analyzed separately to allow for more accurate interpretation of the results. By splitting the data for analysis between species this allowed for selection of the best treatment within a species. In the combined analysis there was no significant difference, in grain yields between medic seeding rate (P = 0.41).
The analysis of the data for 'George' medic showed significant differences (P = 0.0001) in grain yield between medic planting dates. Planting dates PD2 and PD3 affected corn grain yields the least, and were not significantly (P>0.05) different from one another while grain yield in PD1 was significantly reduced. There were no other significant factors affecting grain yield, however the low seeding rate, and the high herbicide input treatment tended to produce the highest grain yield.
The analysis of the 'Orion' data showed that the herbicide treatments had a significant affect on grain yield (P = 0.003). The high herbicide input level yielded 17 bu/acre more than the low input treatment (10). No other factors had a significant impact on grain yield, however, PD3 and the low seeding rate tended to produce the highest yields. In relation to medic species, corn yields were 8.1 bu/acre higher (P=0.019) with 'George' compared to 'Orion'. Therefore, future research with medics in corn will be conducted with 'George' to maximize yield and profit. Within the 'George' medic treatments PD2 produced the highest yield, although grain yield was not significantly different from PD3. Based on these results it appears that it would be best to plant 'George' medic either at the time of corn planting or two weeks after planting. However for ease of planting it would be best to plant the medic at the time of corn planting. The high herbicide input treatment produced the highest grain yield (P=0.001) with yield being increased by 7.9 bu/acre over the low input treatment. This would equate to an increase in income of approximately $20.80 per acre, when corn is $2.80 per bushel. This increase in production would easily cover the ($8.45/acre) cost from the addition of bentazon (Zollinger, 1998) to the herbicide mixture.
Silage Corn Production
The presence of medics regardless of species, seeding rate, seeding date, or herbicide input had no significant (P>0.05) effect on silage corn production (10). However general trends were evident. For example, silage yields were 6% higher in the 'George' medic compared to the 'Orion' treatments. PD3 tended to have the highest forage yields, being 4% better than PD2, and 7% better than PD1. Similarly, the seeding rate of 8 PLS/ft² tended to produce the highest silage yields, being 7% greater than the 16 PLS/ft² rate and 9% greater than the 32 PLS/ft² rate. The high herbicide input treatment produced 9% more silage than the low input treatment because of greater control of common lambsquarters. Based on this information it was concluded that 'George' medic would be a superior species compared to 'Orion' because it tended to allow for more silage production. Further the data indicated the low seeding rate and later medic planting dates also generally increased silage yield. It would also be cost effective to add bentazon to the herbicide mixture to help control weeds and increase yield. The increased yield would result in increased income of $11.40 per acre (silage $9/ton), while the chemical would cost $8.45 per acre to apply (Zollinger, 1998).
Medic production was greater in the silage corn study than the grain corn study (10). In both studies there were significant (P<0.05) differences in forage production between medic harvest dates. In the grain corn study medic production was significantly influenced by medic species (P = 0.0001), seeding rate (P = 0.0001), and seeding date (P = 0.0001). 'George' black medic produced 45% more forage on September 24 and 59% more forage than Orion at grain corn harvest. In the silage corn study, forage production improved 28% from September 24 to October 29. On October 29 'George' medic had an average yield of 1.2 ton/acre which was 49% greater than 'Orion'. The yield of George black medic increased from September to October in both studies however the yield of 'Orion' decreased in the grain corn study. The yield of both species improved 49% in the silage study from September to October. 'George’s production increased 39% between harvest dates in the grain study while 'Orion’s production decreased 35%. Medic dry matter production was significantly (P<0.05) greater in the high herbicide input treatments than the low input treatments because of better common lambsquarters control.
The production data indicates that 'George' medic is better suited to either corn production system than 'Orion'. 'George' medic produced more forage than 'Orion', especially later in the season. There was significantly more forage production in the silage corn than the grain corn crop. From this data it could be concluded that if medic forage production is the main goal of an operation then 'George' medic should be grown in a silage corn production system. If the goal of forage production is only secondary, and grain production is primary then 'George' medic should be grown in grain corn. This would allow for increased forage production over 'Orion' and less reduction in grain yield. To best take advantage of the medic production late in the year, corn either silage or grain, should be removed as soon as possible after maturity. Forage production generally increased with later planting dates and higher seeding rates. Therefore to get optimal forage production medics should be planted as late as possible at the highest rate achieved in this study. The addition of bentazon to the tank mix for increased weed control would be beneficial as medic dry matter production was higher when the herbicide was included in the tank mix.
This study provided further evidence that a corn-medic intercropping system may be a viable option for producers in southeastern Wyoming. The system has been shown to work in both silage and grain corn production. A silage production system would be more suitable if the main objective of the producer is to get good quality fall grazing for livestock. If grain corn production is the goal of the farmer then 'George' medic is the best medic species to incorporate into the intercropping system. 'George' medic allows for increased forage production while having the least effect on corn yields. To allow for optimal corn and medic production 'George' medic should be planted at a seeding rate of 32 PLS/ft² at the time of corn planting, and bentazon should be added to the herbicide tank mixture with imazethapyr, pendimethalin, and NIS.
Year 3 & 4
At TREC 8 plants/ft² medic stands were lower than desired. Possible explanations for this were variable germination, especially with the black medic and plant loss from herbicide treatments as plant counts were not determined until several weeks after herbicide application. Spring environmental conditions may have influenced seed germination. Alfalfa performed the best and had the most plants (15 plants/ft²) but yielded slightly lower in forage production when compared with the medic. Corn stalk forage with medic intercropping was higher than with alfalfa intercropping (11). Corn silage yields were highest with medics when compared to the alfalfa and corn grain yields were the same as the check (no intercropping) and much higher than grain yields with alfalfa. At TREC, medics seem to provide efficient forage and can be beneficial to a grower when intercropped with silage corn. No differences were found at Huntley for silage yields with or without medic intercropping. Medic stands were poorer than expected. The poor establishment may have been due to soil type, pH, or environmental differences at the site. However, two factors are the most probable contributors to the poor stand. The field was managed for corn production from the stand point of sprinkler irrigation. Winter precipitation meant that the corn planted into moisture immerged along with weeds in advance of the shallower seeded medic. This delay in medic emergence meant that the herbicide was applied at a less than ideal time in order to obtain weed control. The result was injury and reduction in medic stand. Also, the drill configuration provided less than ideal seed deep control resulting in highly variable medic stands. The number of medic plants per 95 in² were low and did not produce much forage when intercropped with corn. Broadcast seeded medics were late in establishing and were out competed by the corn making forage measurements marginal. Data could not be obtained from the broadcast medic/silage system. It is not feasible to broadcast seed medics at first cultivation.
Medic regeneration from seed
In order for this system to be practical medic must regenerate itself from the soil seed bank from one season to the next. Regeneration was monitored at TREC. The spring regenerative ability of 'George' medic is encouraging. The year following interseeding populations were 24 plants/ft², 2 years following interseeding seedling populations could be as high as 66 plants/ft². The year 2 results are preliminary. We plan further data collection later this spring. The regeneration is 3 and perhaps 8 times the initial interseeded seedling population.
Silage Corn Production
There was a trend toward lower corn silage production when a legume was present at TREC (11). Corn silage yield was significantly less in the alfalfa/corn plots compared to the corn alone. A similar trend continued with grain production, with alfalfa/corn producing the lowest yield. Only in the case of corn silage were there significant differences. The corn/medic system added from 810 to 950 lb/acre of forage to a fall pasture system following grain corn harvest. No differences were found at the Huntley site.
The final year study provided further evidence that a corn-medic intercropping system may be a viable option for producers in certain areas of central high great plains USA. The system can work in both silage and grain sprinkler irrigated corn production. A silage production system would be more suitable if the main objective of the producer is to get good quality fall grazing for livestock. If grain corn production is the goal of the farmer then 'George' medic is the best medic species to incorporate into the intercropping system. 'George' medic allows for increased forage production while having the least effect on corn yields. The spring regenerative ability of 'George' medic is encouraging.
Medic/corn intercropping has the greatest potential to impact sprinkler irrigated corn. It is estimated that 60% of the corn acreage in Wyoming is under sprinkler irrigation. In Wyoming alone, this practice could provide additional ground cover, improve the pasture resource, and improve soil quality on over 53,000 acres.
Educational & Outreach Activities
Presentations were made at two field days. Conference presentations include the Western Society Weed Science, the Western Crop Science Society, the Western branch meetings of AAAS, Western Alfalfa Improvement Conference, and at the Annual Medic Workshop of North American Alfalfa Improvement Conference. A graduate student thesis was completed. A manuscript is in departmental review with the goal of publication in the Agronomy Journal.
It is still too early to assess the farmer adoption. However, based on the interest expressed by producers at field days there is a strong likelihood that acreage's in southeastern Wyoming may be seeded to the legume/corn. In 1999 a farmer did cooperate on this project as previously described. The results were disappointing. However, it is believed that by altering sowing and irrigation practices medic production can be improved. If an interested farmer cooperator can be identified a field demonstration will be conducted in 2000.
Reaction from Farmers and Ranchers:
Several comments during plot tours were made by farmers expressing interest in the establishment of alfalfa using the corn/legume system. Chuck Jones, now deceased, was enthusiastic and very supportive. He took it upon himself to look at broadcast seeding of medic prior to the first cultivation of corn.
Number of growers/producers in attendance at:
Field Days: 115
Dan Ellis in year 1 and Chuck Jones in year 1 & 4 were important cooperators during on the project. They made suggestions and managed the research on their properties in accordance with their standard farming practices where practical.
Areas needing additional study
Is it possible to develop a corn/medic system that is reliant upon the soil seed bank for medic establishment? If so, is a corn/medic, corn/medic, medic forage 3-year rotation system sustainable?
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