Proc. 56th Southern Pasture and Forage Crop Improvement Conference, Springdale, AR April 21-22, 2001
Developing annual medics for Texas
William R. Ocumpaugh
ocumpaug@fnbnet.net
Regents Fellow and Professor
Texas A&M University Agricultural Research Station, Beeville, TX
The history of development of winter annual legumes in Texas goes back several decades. In fact, there was research on annual medics that dates back to the middle of the last century (Harvey, et al., 1950; True, 1956; Davis, 1957). However, no annual medic (Medicago spp.) seed had been available from these locally adapted cultivars for most of the last half of the century. When I began my research program at Beeville in the early 1980’s, most of the effort in Texas was directed toward the true clovers. Furthermore, most researchers and ranchers alike told me that planting winter legumes in warm season perennial grass pastures was counter productive. They believed that the winter legumes would use up all the moisture in the soil so that the summer grass production would be decreased. To test that hypothesis, I conducted a 4-year grazing trial with subclover (Trifolium subterraneum) and arrowleaf clover (T. vesiculosum) , sod seeded into ‘Coastal’ bermudagrass (Cynodon dactylon) (Ocumpaugh, 1990). These two clovers were planted in replicated treatments with a third treatment receiving two 50 lb/ac N-fertilizer applications per year. With proper management, we were able to demonstrate no detrimental effects on the carrying capacity or average daily gain of heifers grazing the bermudagrass during the summer months (except one summer in one arrowleaf pasture). This negative effect was the result of the excessive growth in a wet spring shading out the Coastal, it was not a moisture issue. We were able to document some short term depressions in carrying capacity just as the clover phased out in the spring, but typically these depressions could only be seen for about two weeks. These findings gave us the incentive to pursue a better adapted legume, as both clovers that we used in the above trial had to be reseeded all but one season.
The next serious issue for us was Iron-deficiency Chlorosis in nearly every clover we evaluated. We spent several years searching for resistance in otherwise well adapted species (Ocumpaugh, 1987b; Ocumpaugh et al., 1989), and following two Ph.D. dissertations (Gildersleeve, 1987 and Wei, 1995), uncovered the mechanism for resistance to Iron-Deficiency Chlorosis. Fe, Zn, and P have very low solubility at pH’s approaching 8, which are prevalent in the lower rainfall regions of the world, including much of the central and western regions of Texas. We determined that the mechanism for resistance was an Iron-Deficiency induced response. When iron was left out of nutrient solutions, the roots would pump out H+ ions, reducing the pH in the rhizosphere (Wei, et al., 1997). All legumes we tested had the capacity to do this, but the legumes that were well adapted could respond very rapidly under almost any soil temperature conditions (Wei, et al., 1994). Legumes that were classified as susceptible were very temperature sensitive, and were only able to give near normal growth under nearly ideal growing conditions. Once we discovered this, it allowed us to focus our research on species that were resistant to Fe-Deficiency Chlorosis. From the early years, we had looked at Australian cultivars of annual medics, but most were of limited use in Texas, because they lacked sufficient winter hardiness to grow north of Beeville (Ocumpaugh, 1986 and 1987a). The one exception was ‘Jemalong’ barrel medic (M. truncatula), and the Australians I worked with kept telling me that it was an old variety and that someday they were going to quit producing seed on it. Well, that someday has now arrived, seed of Jemalong was not available from Australia in 2000. The good news for those that found Jemalong to be well adapted to their farm, is that a local seed company in Texas is starting to produce Jemalong seed.
Developing ‘Armadillo’: During this world wide search for a well adapted legume, we were constantly battling a naturalized legume on the Research Station and generally in the region. This legume was burr medic (M. polymorpha), so in about 1993 we decided it was time to work with this naturalized legume instead of fighting it. Our approach was to collect seed from naturalized stands all over the region where it was observed and to evaluate it at Beeville in South Texas and College Station in East Central Texas to determine how much variation there was within and among these collections. We grew out spaced plants at both locations and quantified a number of traits including flowering date, and plant size. Several other traits were documented, but most were not that different among collections. The main factor we documented was that collections from East Central Texas area flowered later than those collected in South Texas. We knew that the stands found in South Texas had persisted (and spread) for nearly a century in spite of what managers had done to discourage them. The judicial use of herbicides, particularly those with high levels of residue would nearly eliminate legumes from most pastures, but periodically good stands of burr medic would be present in spite of the herbicide regiment. We did not consider the later flowering trait as a real asset, as we were targeting South Texas for our cultivar release. We were concerned that if we selected the later flowering types that we would not get consistent reseeding in South Texas. And one of our criteria for a winter annual legume was that it had to reliably reseed. The potential cost of having to annually purchase the seed, inoculum, and the annual planting cost were too high to make a legume cost-effective in the low and variable rainfall region of South Texas. Hence we decided to stay away from the later flowering collections. All other traits, except plant size were rather uniform, but we had one collection from the Research Station at Beeville that had very few small plant types. Hence we decided to use the seed collected from Pasture 18 at the Research Station as the basis for a cultivar development. We had harvested seed from each of the spaced plants at both locations. Once the data was all analyzed we discarded the seed from the small plant types that originated from Pasture 18 and went trough two additional cycles of growing out spaced plants and discarding the smaller plant types. In 1996 we planted two major seed increase blocks, to produce enough seed to plant a Foundation Seed block in the fall of 1997. The Foundation Seed block consisted of 15 acres planted under a center pivot. That winter we also acquired a used Horwood-Bagshaw suction harvester from a seed company in Oregon that had been used for harvesting subclover seed. We had no idea as to how much seed we could produce. We thought that we would have adequate seed for extensive testing in 1998, and to plant the needed acreage for Certified Seed production that fall of 1998. Much to our surprise, we harvested over 13,000 lb of clean seed from 15 acres. At that point, we knew that we had more seed than we needed for any future Certified Seed production, more that we wanted to give away for testing, and more than we could store in our limited cold storage facility at Beeville. Hence, accelerated the potential release documentation. To make a long story short, we got approval to release it as ‘Armadillo’ burr medic AND signed an exclusive release document with Pogue Seed Company, of Kenedy, TX (the company that had allowed us to plant our Foundation Block on their irrigated farm) in time to sell a limited quantity of seed in the fall of 1998.
Nearly 2000 lb of Seed was distributed in 1998 for extensive testing by Research and Extension personnel at various locations in the Southeastern USA and County Agents in Texas (Ocumpaugh, 1999a & b). The seed production area was increased to 65 acres in the winter of 1998-99, but only about 24,000 lb of seed were produced. In the fall of 1999, Pogue Seed Company sold all of the seed that was carried over from 1998 and all that was produced in 1999. In the fall of 1999, additional acres were planted to bring the total up to nearly 120 acres, and over 50,000 lbs of seed were produced in 2000. About 35,000 lbs of seed were sold in the fall of 2000.
Since Armadillo has only been on the market for about 3 years, and seed was very difficult to harvest before we acquired the suction harvester in 1998, we are still uncertain of the limits of adaptation of Armadillo. We think the northern limit is somewhere near I-20 (Ocumpaugh, et al., 1997a & b; 1998) . It is limited on the west by rainfall, but we are not certain exactly where that line is either. The eastern limit appears to be soil type limited. Armadillo is not well adapted to the sandy soils of East Texas.
Other Medics for Texas
Once it became obvious to us that Armadillo burr medic was so prolific and well adapted we started looking for other medics that would extend the area of adaptation beyond where Armadillo burr medic was well adapted. We have started evaluation of several species of medics that have become naturalized in Texas. These are described below.
Other burr medics: M. polymorpha. In addition to Armadillo burr medic, we have also increased other collections of burr medic that may have the potential to expand the area of adaptation of the species. We have one collection that Darrell Ueckert from TAES-San Angelo collected from the roadside north of Abilene, TX. This collection is considerably latter flowering than Armadillo, and does not grow off nearly as quickly in South Texas, but is quite impressive later in the spring. We think this collection may have utility for more northern and perhaps western areas than we can currently grow Armadillo.
Little burr medic: M. minima. We have collected little burr medic from several places in Texas, including one collection north of Lubbock. However, the one we are currently testing was collected from a pasture near Devine, TX. We are evaluating little burr medic for the colder and drier regions of Texas and perhaps into Oklahoma. We also think that little burr medic may fit in some of the poorer soils of South Texas where the water holding capacity will limit Armadillo’s ability to persist.
Black medic: M. lupulina. We are evaluating several collections of black medic for the potential use with Armadillo, and to extend the northern limits of annual medics into Oklahoma. We are currently concentrating our efforts on two collections, one we call “BEBLK”, that was collected at TAES-Beeville, and one we call “NT-Blend”, which is a composite of some of the best plants from several collections made in the Dallas area by James Read. Black medic may also prove to uniquely useful for those that do not want the “velcro-like” characteristics of the seed pod of both little burr and burr medic. Black medic bears it’s seed in a slick round black pod containing mostly one seed per pod. Hence we think that birds may be able to consume the seed of black medic better than many of the other medics.
Button medic: M. obicularis. During the time we were evaluating button medic, Turner Seed Co. of Breckenridge, TX harvested a field of button medic in Fisher County Texas that was originally planted in the 1950’s to an un-named cultivar that was released by the Texas Research Foundation, at Renner (near Dallas, TX) (Davis, et al., 1957). They have started marketing this seed as ‘Estes’ button medic. It seems to be fairly well adapted to North Central Texas. The seed of button medic is a large smooth coil, and one weakness we have noted to this trait is that the pods are consumed by deer and other wildlife (Ocumpaugh, et al., 2000). This seed foraging can dramatically reduce the plants ability to reseed itself.
Spotted burr medic: M. arabica. The final naturalized medic we are working with is spotted burr medic. This medic is naturalized in the sandy soils of East Texas. We have located a field of naturalized spotted burr medic in East Texas and have made arrangements to harvest it this year. That was the approach we used with little burr, and so far that approach has worked out well. Time will tell if we can just evaluate and release this “wild collection”, or if we will have to go through the process of screening for superior plants from this collections like we did with Armadillo.
Cultivar Development Approach:
We like the approach of harvesting seed from naturalized stands and NOT going through a lot of screening for superior traits. We think one of the real values we obtain from this approach is that we know that the plants are adapted to the region and to grazing, as they have persisted for years in spite of what managers have done to them. Furthermore, when you start selecting for or against a particular trait, you may throw away some traits you would be better off keeping, as it gives you more diversity in the population. In fact we may have lost something when we developed Armadillo. As several of my cooperators who have evaluated what we call “BECOM” burr medic, which is “field run seed” harvested from areas on the Beeville Station, have found BECOM to be somewhat adapted to the North Texas and even into Arkansas where Armadillo will not persist (Cassida, et al., 2000). I think what we did when we selected Armadillo, is that when we took out all the plants that had slow growth in the mid-winter period in South Texas, we also took out the part of the population that had better winter hardiness. Therefore, we will likely take less of a purist approach as we develop future cultivars.
References
Cassida, K.A., D. Malinowski, W.E. Pinchak, W.R. Ocumpaugh, and G.R. Smith. 2000. Annual legumes as reseeding components of pastures in north central Texas. p. 115-119. In: Proc. American Forage and Grassland Council.
Davis, J. H., E.O. Gandstad, and H.L. Hackerott. 1957. Botton Clover: A reseeding winter annual legume for North Central Texas. Bulletin 6. Hoblitzelle Agricultural Laboratory, Texas Research Foundation, Renner, TX.
Gildersleeve, R. R. 1987. Screening Trifolium species for susceptibility to iron-deficiency chlorosis. Ph.D. Dissertation. Texas A&M University, Soil and Crop Science Dept.
Harvey, Clark, V.E. Schember and R.C. Potts. 1950. Burr-clover and relates species at the Brazos River Valley Laboratory. Progress Report 1278. Texas Agric. Experiment Station, College Station, TX.
Ocumpaugh, W. R. 1986. Annual medic evaluation. Field Day Report, TAES-Beeville, p. 5-6.
Ocumpaugh, W. R. 1987a. Annual medics for South Texas pastures. Forage Research in Texas. CPR-4537, p. 39-40.
Ocumpaugh, W. R. 1987b. Evaluation of subclover Plant Introductions on calcareous soils in South Texas. Clovers and Special Purpose Legumes Research, Progress Report, Vol. 20:52-55.
Ocumpaugh, W. R., G. R. Smith, D. F. Bryn, and R. R. Gildersleeve. 1989. Breeding for resistance to iron-deficiency chlorosis in arrowleaf clover. Forage Research in Texas. CPR-4731, p. 16-17.
Ocumpaugh, W. R. 1990. Coastal bermudagrass-legume mixtures vs nitrogen fertilizer for grazing in a semiarid environment. J. Prod. Agric. 3:371-376.
Ocumpaugh, W. R., J. N. Rahmes, W. J. Grichar, D. C. Sestak, and M. A. Hussey. 1997a. Evaluation of reseeding winter annual medics for South Texas. p. 45-48. In Forage Research in Texas 1996.
Ocumpaugh, W. R., M. A. Hussey, J. H. Rahmes, W. J. Grichar, Jr., D. C. Sestak, and Ray Smith. 1997b. Burr medic—A persistent cool-season legume for Texas. p. 59-63. In: Proc. American Forage and Grassland Council.
Ocumpaugh, W. R., D. H. Bade, K. A. Cassida, S. W. Coleman, W. J. Grichar, M. A. Hussey, R. A. Lane, W. E. Pinchak, W. D. Pitman, J. N. Rahmes, J. C. Read, R. L. Reed, D. C. Sestak, and G. R. Smith. 1998. Limits of adaptation of a burr medic selection naturalized in South Texas. p. 148-152. In: Proc. American Forage and Grassland Council.
Ocumpaugh, W. R. 1999a. Armadillo burr medic: A new legume variety for Central and South Texas. TFGC Advances. Vol. 12, No. 1. p. 1-3.
Ocumpaugh, W. R. 1999b. Armadillo burr medic: 1998-99 update. TFGC Advances. Vol. 12, No. 3. p. 3-4.
Ocumpaugh, W. R., Tim Ginnett, Fred Bryant, and Daniel Kunz. 2000. Report on deer food plot research at West Wind Ranch for 1999. Submitted to Caesar Kleberg Wildlife Research Institute and TAMU-Kingsville, and Larry Martin, Houston, TX. January 2000. 5 pages.
Trew, E.M. (1956). Burclover. L-306 Texas Agric. Extension Service, College Station, TX.
Wei, L. C., W. R. Ocumpaugh, and R. H. Loeppert. 1994. Differential effect of soil temperature on Fe-deficiency chlorosis in susceptible and resistant subclovers. Crop Sci. 34:715-721.
Wei, Liangchou. 1995. Mechanisms of Fe-deficiency resistance in subclover. Ph.D. Dissertation. Texas A&M University, Soil and Crop Science Department.
Wei, L. C., R. H. Loeppert, and W. R. Ocumpaugh. 1997. Fe-deficiency stress response in Fe-deficiency resistant and susceptible subterranean clover: Importance of induced H+ release. J. Exp. Botany. 48:239-246.