Type O inoculant is recommended for Yuchi Clover Seed
and Apache Arrowleaf Clover Seed
One package inoculates up to 50 lbs. of seed.
Legumes can be categorized by their inoculant groups, however, these are only general guidelines. Most inoculant companies mix different inoculums to give a broader range of effectiveness.
Nodulation is a highly specific process that is extremely complex. The first step in the establishment of symbiotic N2-fixation is the attachment of host-specific Rhizobia bacteria to the root hair tips. Legume roots exude flavenoids (specific phenolic compounds) which attract and stimulate bacteria growth around the rhizosphere. The Rhizobia use flavenoids to stimulate the nod gene (symplasmid gene) to stimulate this process known as nodulation. Rhizobia bacteria secrete Indole acetic acid (IAA), which acts like an auxin stimulating cell division in the root causing root hair curling and deformation called a nodule.
Legume roots secrete sugar-binding proteins (lectins), which facilitate the binding of bacteria to the root hairs. An infection thread, which is an internal tubular extension of the plasma membrane grows from the infection site to other cells and fuses with the host cell plasma membrane by degrading the cell wall. This allows for the exchange and essentially allows the bacteria and root to act as one unit.
Poor nodulation may occur even if good seed inoculation practices were used. Rhizobia bacteria begin dying as soon as the inoculated seed are planted. The longer the seed lies in the soil before germination, the fewer viable rhizobia are present. If regular inoculant is just applied to the seed with water, buttermilk, or Coke as a sticker, the bacteria may only survive in the soil for about a week. Inoculant containing a sticker or that is coated on the seed provides more protection for the bacteria, which improves its survival to about 3 weeks. It is difficult to introduce a new legume species into a pasture that has had a native, naturalized, or different legume species growing on it for several years. The rhizobia strain infecting the previously grown legume species will have built up a large soil population over the years. Just because of greater numbers, the resident rhizobia strain may occupy most of the infection sites on the new seeded legume and prevent infection by the introduced rhizobia strain.
Nitrogen fixation is the conversion of atmospheric nitrogen to ammonium nitrogen in the presence energy (ATP) and the nitrogenase enzyme complex. The bacteria encode an enzyme complex called nitrogenase (Mo-Fe, Fe-S protein), which is made up of Molybdenum, Iron, and Sulfur. This enzyme complex is actually responsible for N2-fixation.
N2 + 8e- + 8H+ +16Mg-ATP Nitrogenase 2NH3 + 16 ADP + 16 Pi +H2
Rate of N2-fixation is directly related to legume plant growth rate. Anything that reduces plant growth such as drought, low temperature, limited plant nutrients, or disease will also reduce N2-fixation. Maintaining sufficient leaf area in a legume stand to intercept most of the sunlight is also critical to maintaining a high growth rate to support N2-fixation. When the legume plant matures and dies, nodules on the root system decompose and release the rhizobia into the soil. If the same legume species is planted again the following year or volunteers from seed produced the previous year, sufficient numbers of rhizobia are usually present to provide good nodulation.
The ammonium form of nitrogen is incorporated into organic acids in the root. These compounds (amides temperate legumes and ureides in tropical legumes) are transported via the xylem to the plant. The primary pathways for nitrogen transfer from the legume to the soil are through grazing livestock and decomposition of dead legume plant material. The root system and unused leaves and stems of annual legumes die at plant maturity and are decomposed by soil microbes over time. Nitrogen contained in this plant material is released over time and is available to other plants. However, because this nitrogen is not available until after the legume dies only grasses that follow the legume growing season can use it.
When legume forage is consumed by grazing livestock most of the nitrogen in that forage passes through the animal and is excreted in the urine and feces. Unfortunately about 50% of the nitrogen in the urine is lost through volatilization. Another problem is the distribution of feces and urine on the pasture. With continuous grazing at low stocking rates, much of the animal excreta is concentrated around local areas. Animal excreta distribution is improved with rotational grazing systems where stock density is higher.
The quantity of nitrogen fixed by legumes can range from none to over 200 kg ha-1. Factors that influence the quantity of nitrogen fixed are the level of soil nitrogen, the rhizobia strain infecting the legume, amount of legume plant growth, how the legume is managed, and length of growing season. If given a choice, a legume plant will remove nitrogen from the soil before obtaining nitrogen from the air through N2-fixation. A legume growing on a sandy soil very low in nitrogen will get most of its nitrogen from the air while a legume growing on a fertile river bottom soil will get most of its nitrogen from the soil. General estimates of the amount of nitrogen fixed in the eastern half of Texas range from 50 to 100 lb N/acre for annuals and about 150 lb N/acre for alfalfa.