There seems to be an increased interest in legumes in the area and forage legumes are one of my favorite topics. Everyone is familiar with the legume alfalfa, which we can grow very well in central Texas under irrigation.
However, 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.
During a decent rainfall year there are several legumes that will perform very well in this area of Texas. Here is a 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 welldrained loamy or sandy soil with a pH between6.5 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 warm-season grasses it can competitive with the grass stand 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.
Here is one other legume variety that is not a clover, that in county trials has shown the most potential: 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 coolseason 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. Many folks worry about bloat with cool-season legumes, the three listed above have low to moderate bloat potential. As mentioned in the descriptions coolseason legumes can compete with your warmseason 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 you are hoping for some natural reseeding, be sure to spray after legume has seeded out, usually June. Never use products with longlasting soil residues (Grazon Next, Grazon P+D, Tordon) over clover stands or where you plan to plant legumes. While these are some of the better weed control products they have long lasting residuals in the soil, up to one year, and may prevent reseeding next year. Products using 2-4d and dicambia are usually ok after June. 2-4D would be the least harmful, although dicambia may have up to 120-day soil residual.
Finally, when should you plant legumes? While every year is different typically mid-October is the prime time to overseed cool-season annual legumes. Like all crops moisture is going to be key for legume production. Legume seed is expensive so if not planting under irrigation, be sure to look at the long-range forecast. Despite all the benefits of planting a legume, I have to be honest with this year’s dry outlook and the cost of seed, I would not recommend anyone plant very many acres of dryland legumes, but certainly try them on limited acres.