Effects of stand density on alfalfa (Medicago sativa L.) morphology, yield, and quality

The dehydrated alfalfa industry requires high quality plant material. To achieve this, dehydrated products are produced from alfalfa that is cut in the late bud to early flowering stage. The stands are often seeded at higher than normal rates and they may remain productive for only two to three years. The short stand life may be partly attributable to the high initial seeding rates which will reduce individual plant size and hence may reduce the plant's ability to survive the winter. The objectives of this study were: (1) to determine the optimum population density for a higher yield, better quality and longer persistence of alfalfa stands; (2) to compare gross morphology, forage quality, and winter survival of cultivars Algonquin and Vernal grown at a range of stand density; (3) to investigate the relationship among stand densities, individual plant size, carbohydrate storage, and winter survival of alfalfa.;To determine the optimum population density, alfalfa seedlings were transplanted at spacings of 6, 10, 15, 20 25 and 30 cm. Plants grown at the 4.5 cm plant spacing were directly seeded. Alfalfa stand density of alfalfa influenced shoot number per plant, yield per shoot and winter survival, and a combination of these three factors determined yield. The large alfalfa plants from low stand densities survived winter better than the small alfalfa plants from high stand densities under Edmonton environmental conditions. The amount of total nonstructural carbohydrates (TNC) per root increased and total etiolated growth (TEG) decreased as the stand density decreased. As stand density declined, the lethal temperature at which 50% of the plants were killed (LT 50) got lowered. Gross plant morphology was affected by plant spacing. Shoots per plant and yield per shoot increased linearly with increased plant spacing at all harvests. However, other morphological characteristics such as stem diameter, stem length, number of nodes per stem, leaf area per m;High stand density appeared to be of little economic advantage in terms of winter survival, yield, persistence and forage quality.;It will be necessary to continue this study to ascertain the long-term effects of stand density on productivity, stand persistence, and forage quality.