Cool Season Annual Legumes
Still on the fence about planting any winter or spring grazing? Is the cost of fertilizer keeping you from planting? Maybe you should consider a legume. Forage legumes are one of my favorite topics. Everyone is familiar with the legume alfalfa, but there are many other legume species available that can increase or stretch your forage supplies in the spring. Besides producing extremely high quality forage, legumes also produce their own nitrogen. While this is a great asset, many folks misunderstand the nitrogen fixation process. The nitrogen is not being pumped into the soil; it is being used to produce the forage above the ground. So, if you are harvesting the legume forage, you are also removing the nitrogen that was produced, but you were able to grow the plant with free nitrogen. If disked under or allowed to decompose, legumes can add as much as 150lbs of nitrogen to your soil, but that would be on the high side, 40 to 50 lbs. would be more common. It all depends on how much top growth is produced. While legumes are able to fix their own nitrogen, they still require the proper levels of phosphorus and pot ash. The soils pH level is also critical; most legumes require a pH in the 6.5 to 7.5 range.
Comanche county sits on the rainfall border of where you could expect to grow legumes effectively without irrigation. The last few years planting legumes would have been a bust on dryland. However, in a decent rainfall year there are many legumes that will perform very well in this area of Texas. Here is a quick list and description of a few of those that I would recommend for Comanche County. Arrowleaf Clover-Arrowleaf is usually the highest producing of the clover legumes with forage production lasting from March through June. Arrowleaf prefers a well-drained loamy or sandy soil with a pH between 6.5 and 7.0. Use only scarified seed, seeding rate 8-10 lbs. / acre. Arrowleaf has an excellent reseeding capability with about 90% hard seed. If overseeded on warmseason grasses it can competitive with the grass if not kept grazed closely.
Another good clover variety is Crimson Clover it is the earliest maturing variety of the clovers. Forage production will be produced between mid-February to late May. Crimson is one of the larger seeded annual clovers and it has excellent seedling vigor. This good seedling vigor and early maturity make it an ideal clover for overseeding on perennial warm-season grasses. It grows in a wider range of soils from sands to well-drained clay soils with a preferred pH of 6 to 7. Recommended seeding rate is 16 to 20 lbs. per acre. Unfortunately, it is a poor reseeder with only about 10% hard seed. Texas A&M is working on a new Crimson variety that has more hard seed so that you will have more plants come back next year from seed-heads produced this year.
Hairy vetch is perhaps the most valuable and widely used cool season annual legume. At one time vetch was the major provider of nitrogen for crops. A mature crop of vetch can provide up to 150 lbs. of nitrogen/acre. Vetch is adapted to a wider range of soils than other cool-season legumes. It can grow on anything from sandy to clay soils, and it can tolerate a pH from 5.0 to 8.0. Recommended seeding rate is 20 to 25 lbs. /acre at a depth of 1 to 2 inches. Due to the large seed it has excellent seedling vigor. There are many other good coolseason legumes, but these three would probably be the most cost effective for our area.
Legumes offer the opportunity for excellent forage and nitrogen fixation, but they do have some management challenges. Manyfolks worry about bloat with cool-season legumes, the three listed above have low to moderate bloat potential. Cool-season legumes can compete with your warm-season grasses, so you will need to manage them with grazing or mowing to prevent over competition. All legumes need to be inoculated with the proper bacteria to get maximum results for nitrogen fixation. Many varieties now come preinoculated; if not make sure you purchase inoculant when you buy your seed.
One of the biggest issues when growing any legume is weed control. Legumes are broadleaf plants; broadleaf plants are what most all herbicides target. Early summer or late spring herbicide applications will kill your legumes. If possible, be sure to spray after legume has seeded out,usuallyJune. If you have sprayed with Grazon Next, Grazon P+D or Chaparral herbicides you should probably not plant legumes on these fields. While these are excellent weed control products, due to the long residual you would probably not get a stand. Products using 2-4d and dicambia are usually ok as they do not have as long of a residual.
We are starting to get close to the end of the window I would normally recommend planting legumes. However, the forecast calls for a warm and wet fall and winter, so you should be good for another week or two at the very least. There are other legume options, but these are all good ones, and you can usually find the seed for these.