Extension Education: Hard seed affects forage establishment
There is an increasing interest among livestock producers in the West to grow forage legumes such as cicer milkvetch, sainfoin and medic as alternatives to alfalfa, at least in a situation where alfalfa is not a good fit. However, establishment of these legumes is difficult because of low germination, hard seed coat or content, low seedling vigor, high weed competition and disease problems.
One of the major causes for poor establishment is associated with the hard seed of legumes. Hard seed coat or content is a protective outer layer of seed. Many legume seeds are very hard and require artificial scarification to enhance germination and eventual good stand establishment.
There are a few methods or techniques to improve or enhance the stand establishment.
For example, seed scarification, use of companion crops and seed inoculation with the right inoculants may enhance establishment. Seed scarification is one of the easy ways to enhance seedling establishment in the field.
Seed scarification is a process of physically damaging the seed to break the hard seed coat without lowering the quality of seeds. This makes seed soft by scratching hard coat from outer layer of seeds and allows water from the soil to enter easily into the seeds. As a result, seed germination and seedling emergence occur faster with uniform stands across the field.
Hard seed content varies significantly among species and even between varieties within the same species of legumes. Many factors such as weather conditions, or cold and hot temperatures, snow fall, soil moisture, seed storage conditions and, most importantly, seed harvesting and transportation affect hard seed content of legumes.
A recent study in the Plant Sciences Department of the University of Wyoming showed that mechanical scarification, where seeds were rubbed by common sandpapers, greatly reduced hard seed contents and thus enhanced germination of legume seeds in the field. In this study, several varieties of alfalfa, including Ranger, Vernal, Ladak, Falcata yellow flower alfalfa; sainfoin, such as Shoshone, Eski, Remont; cicer milkvetch varieties Monarch, Oxley, Lutana; and the medic variety Laramie were used. Alfalfa and sainfoin did not need any scarification because of their soft seeds. Seeds also may have naturally scarified during seed harvesting and packaging. However, mechanical scarification greatly reduced hard seed content of cicer milkvetch and medic, which ranged from 77 percent hard seed before scarification to four percent hard seed after scarification. The scarified seeds were later planted in the field and successful and uniform stand establishment was achieved.
Hard seed information of forage legumes is provided with the seed-tag of the seed lots. If some seeds appear to have high hard seed content, it is advisable to scarify seeds before planting. Mechanical scarification can easily be done using sandpapers attached to the cement mixer.