EFFECTS OF IRRIGATION AMOUNT AND TIMING ON ALFALFA NUTRITIVE VALUE

Most hay producers in southwest Kansas irrigate their alfalfa (Medicago sativa L.) because precipitation is insufficient for profitable rainfed production. However, water supplies in the central Great Plains are dwindling, particularly in the central and southern Ogallala Aquifer region. Irrigating many field crops in this region, including alfalfa, is therefore becoming a challenge. We determined the effects of irrigation quantity and timing on alfalfa forage nutritive value during a five-year field study of alfalfa in southwest Kansas. Nutritive value was quantified in the form of crude protein, acid detergent fiber, neutral detergent fiber, total digestible nutrients, and relative feed value. In general, applying the highest amount of irrigation (610 mm during the growing season) resulted in the lowest forage nutritive value compared to lower amounts of irrigation (0, 200, and 380 mm irrigation). Nutritive value concentrations (g kg(-1)) under full irrigation averaged 211 for crude protein, 316 for acid detergent fiber, and 422 for neutral detergent fiber, while concentrations (g kg(-1)) in rainfed production averaged 225 for crude protein, 247 for acid detergent fiber, and 370 for neutral detergent fiber. Alfalfa nutritive value was not affected whether the same amount of irrigation water was applied either before green-up and between each cutting, or before green-up and between all cuttings except between cuttings 2 and 3. However, there was a tendency for lower forage nutritive value at the fourth cutting when irrigation was withheld between cuttings 2 and 3, and that saved water was added to the amount of irrigation applied to the fourth cutting. When averaged over irrigation treatments, alfalfa nutritive value was lower from the first and second cuttings than from the third and fourth cuttings. Annual yields, averaged over years, declined from 1.53 kg m(-2) with 610 mm of irrigation to 0.43 kg m(-2) for rainfed production. Annual yields were the same when irrigation was distributed over the growing season or withheld between the second and third cuttings. Irrigation amounts less than full crop requirement resulted in a 13% higher dollar value product based on relative feed value, but decreasing irrigation from 610 to 380 mm reduced yield by 19%.