Alfalfa producers should plan to use commercial fertilizer to supply nutrients on a consistent basis, according to advice from Dirk Philipp, a forages faculty member at the University of Arkansas System Division of Agriculture. It's needed for high yields and to promote plant health, even though native soil reserves supply some macro- and micronutrients.
"Fertilizer is especially important for forage crops such as alfalfa," Philipp said. "They're perennial crops, so the investment needs to pay off year after year. They need to be harvested on a strict schedule to maintain yields and plant vigor. Also, hay markets set strict requirements for consistent quality."
Alfalfa removes relatively large quantities of phosphorus and potassium. For every ton of dry matter produced, about 15 pounds of phosphate and 60 pounds of potash are being taken up by the plants. However, Philipp said the best plan is to base fertilizer recommendations on soil tests that need to be taken on a regular basis. Nitrogen is supplied by a symbiotic relationship with soil bacteria, so this mineral doesn't have to be imported.
"Phosphorus is important for root development and stand establishment, while potassium is important for maintaining yields, stand survival and disease resistance," Philipp said. A correct pH level of 6.7 to 6.9 is necessary so minerals are available as the plants take up phosphorus.
Phosphorus and potassium fertilizer should be applied after the first cut as a way to stimulate the remaining cuttings. Philipp cautioned against applying fertilizer or allowing traffic over the field when the soil is soft, such as very early in the year, because damage to alfalfa crowns may occur. Because fertilizer can be harsh on plant foliage, He suggested splitting applications if the required amounts exceed a quarter-ton per acre. Leaf damage can result because of fertilizer's ability to "burn" the foliage.
Soil fertility status should be monitored over time; otherwise, fertilizer requirements may add to costs long-term. Philipp said it's not a good idea to apply large amounts at once, but nutrient levels should be kept consistently near optimum. It's also difficult to correct mineral imbalances in the short term or at the beginning of the growing season.
"Try to stay ahead of the game by keeping soil fertility status in check, particularly for management-intensive crops such as alfalfa," Philipp said.