Factors Influencing Yield and Quality in Alfalfa

Abstract

Alfalfa is one of the most productive, widely adapted crops in the world, of importance to animal food production systems, to environmental health, as well as the potential for direct human food and industrial uses in the future. However, yield improvements have been painfully slow with this crop. While average farm yields have improved twofold in many environments over a 100-year period, evidence indicates a leveling off of yield improvements over the past 30 years. Disappointing yields are a frequent complaint of growers. However, much higher yields are highly attainable with this crop as evidenced by the ‘yield gap’—the fact that maximum yields are two to threefold greater than the median on-farm yields in a given region. Limitations are largely due to agronomic, not genetic limits, particularly harvest scheduling, the need for quality, and poor stand persistence, but opportunities for cultivar improvement in yield are significant. There are several innate biological and agronomic tradeoffs that limit yield in alfalfa. These constraints include the need for high quality as well as yield, the need for maintenance of stand longevity as well as annual yields, and the requirement for frequent harvests involving farm machinery and wheel traffic. Agronomic strategies are likely to be most important in improving yields, including improved drainage, fertilizer management, harvest efficiency, reduced traffic, improved stand establishment, pest management, and irrigation efficiency. Key genetic characteristics for yield improvement include improved pest resistance, breaking the yield-quality-persistence tradeoff as related to harvest schedules, and improved root resistance to winterkill and wheel traffic. Improving late-season yield (summer slump) is an important goal, since late-season harvests are 40–50% of the yield of early harvests. Delayed flowering and maturity, reduced lignification of the cell wall, disease and insect resistance will be key traits. Other traits, such as the contribution of alfalfa stands to crop rotation and soil health and the environment, should be considered along with yield and quality goals. However, improved yields are the key to the future alfalfa systems that are resilient to the challenges of water supply and increased human populations.