Extension by Anowar IslamWritten by Anowar Islam
Companion Crop and Seed Scarification Enhance Forage Legumes Establishment
By Anowar Islam, UW Extension Forage Agroecologist
There is an increasing interest among producers in the Central West regions and High Plains to grow forage legumes, such as cicer milkvetch, sainfoin and medic as alternatives to alfalfa. However, establishment of these legumes is difficult because of low germination, hard seed coat, low seedling vigor, high weed competition and disease problems.
Seed scarification (a physical damage to break the hard seed coat without lowering the quality of seeds), use of companion crops and seed inoculation with the right inoculants may enhance the establishment. Using companion crops (e.g., oat) in establishing alfalfa is a common practice in the region, but information is lacking on whether the same technique can be utilized in other forage legume establishment.
Researchers in the Department of Plant Sciences at the University of Wyoming are trying to find appropriate techniques for seed scarification, apply the best technique(s) of scarification to increase seedling emergence in the field and to use a companion crop to enhance seedling establishment.
Seed scarification studies were initiated in early spring 2009 at the greenhouse complex of the Laramie Research and Extension Center (LREC). Treatments included in this study were heat, freeze-thaw, mechanical and acid scarification; each of the treatments was replicated five times. A number of varieties from four legume species were used. These included ‘Ranger,’ ‘Vernal,’ ‘Ladak,’ and ‘Falcata yellow flower’ from alfalfa; ‘Shoshone,’ ‘Eski,’ and ‘Remont’ from sainfoin; ‘Monarch,’ ‘Oxley’ and ‘Lutana’ from cicer milkvetch; and ‘Laramie medic’ from medic.
The field study is being conducted at LREC and the James C. Hageman Sustainable Agriculture Research and Extension Center (SAREC) near Lingle. In May 2009, legumes were planted in four replicated plots perpendicular to oats at both locations in such a way that half of the plots had oat, whereas the rest had none.
Three years of data from this study are in the process of final analyses and compilation, however, initial data suggest that acid and mechanical scarifications greatly reduced hard seed contents, thus enhanced germination, of some of the varieties used in the study.
For example, the hard seed of Monarch cicer milkvetch reduced from 77 percent to 33 percent with five minutes of mechanical scarification (sandpaper scarification) while hard seed of Laramie medic reduced from 23 percent to one percent with acid scarification treatment. None of the varieties of alfalfa and sainfoin used in this study required any seed scarification, as they had soft seeds (hard seed contents range from zero to six percent).
On the other hand, oats as a companion crop showed potential to suppress weed infestation and enhance establishment of different forage legumes during the study period.
Forage legumes are highly valuable crops because of their ability to fix atmospheric nitrogen and reduce fertilizer input cost while producing high quality forage. Hard seed in many of the forage legumes is one of the major constraints, however, for successful stand establishment. The hard seeds’ lower germination rate creates less competitive stands against weeds over resources (e.g., water, light and nutrients) in the establishment year.
Scarification methods such as heat, freeze-thaw, mechanical, and acid scarification are useful tools to soften hard seeds, improve germination and enhance seedling establishment. However, effectiveness of the methods varies, depending on the duration of imposed treatments and species or varieties to be used. Over-treatment or longer time scarification may impose negative impacts on or injury to the seeds. The study suggests that there is no single method of scarification that can be recommended for all legume species in general. The effectiveness of scarification methods varies among species and even varieties within the same species. A companion crop, such as oats, can further enhance the forage legume establishment, however, seeding rates of companion crops need to be optimum to reduce initial competition with legume seedlings.