|Plant Part and Time:||Top 4 to 6 inches of plant taken prior to or at 1/10 bloom stage.|
|Element and Sufficiency Range||Interpretation and Recommendations|
Low leaf N is due primarily to poor nodulation or ineffective nodules. If N is low, apply a foliar application of molybdenum in late winter or early spring before new shoots reach 2 inches in height. Apply at the rate of 3 oz. of Mo (8. oz. of sodium molybdate) in 25 gallons of water per acre. Low soil pH and low soil P levels can also result in low leaf N; therefore, it is important to maintain the proper soil fertility for optimum N fixation. Alfalfa does not respond favorably to topdress N; in fact, such treatment may inhibit Rhizobia bacteria and stimulate weed growth. Nitrogen content will decrease as the season progresses; therefore, low N may indicate late harvested forage.
Low P due to low soil test P and/or inadequate P fertilization. If P is low in the tissue apply 75-100 pounds P2O5 per acre. For succeeding years soil test and follow soil test recommendations. Maintain soil pH at recommended level.
Low K due to low soil test K and/or inadequate K fertilization. If K is low in the tissue apply 100-200 pounds K2O per acre, adjusting the rate based on the number of harvests remaining for the current growing season. Low K in the tissue may indicate late harvested forage. The K content of alfalfa will tend to decrease as the season progresses particularly the last cutting. High K levels indicate luxury consumption due to excessive fertilization. For succeeding years, soil test and follow soil test recommendations.
Low Ca due to low soil pH and/or low soil Ca. Also Ca content of the forage may be depressed following large K applications. Maintain soil pH at recommended level and split K application if more than 200 pounds K2O per acre is recommended.
Low Mg due to low soil Mg, low soil pH and/or heavy applications of K fertilizers. Low Mg can be prevented by maintaining soil pH at recommended level using dolomitic limestone. Also split K applications when more than 200 pounds K2O per acre is recommended. If Mg is low in the forage, apply 25 pounds Mg per acre.
Low S may occur on sandy soils, on soils under intensive management and where S-free containing fertilizers have been used for an extended period. Low S can normally be corrected by including 25 pounds S per acre in the fertilizer program. Maintain the N:S ratio between 10:1 to 15:1 for ruminant nutrition.
Low Mn may occur on some sandy Coastal Plain soils when the pH is near or above pH 7.0. When low Mn levels are detected, include Mn in the succeeding fertilizer program at the rate of 10-15 pounds Mn per acre. For the current season, apply a foliar application of Mn using 1 pound Mn per acre as manganese sulfate or 1/2 pound Mn per acre as chelated Mn in 20-25 gallons of water per acre. Apply after each harvest when the alfalfa is about 4-6 inches high.
Deficiency not likely to occur. High Fe levels normally indicate soil or dust contamination.
Low B due to low soil B and/or inadequate B fertilizer. Boron deficiency can be corrected during the current season by applying 2 to 3 pounds B per acre with the next split application of fertilizer and/or by applying a foliar application of B using 1/2 pound B in 25 to 30 gallons of water per acre. Apply the foliar spray after each harvest when plants are about 4 to 6 inches high. To prevent B deficiency in succeeding years include 3 pounds B per acre annually in the fertilizer program.
Deficiency not likely to occur.
Zinc deficiency is not a common occurrence in alfalfa, but low Zn may occur on coarse-textured Coastal Plain soils when soil Zn is low and soil pH is near 7.0 or above. Zinc deficiency symptoms are usually evident at concentrations of approximately 10 ppm. If leaf Zn is 10 ppm or less, deficiency may be corrected in the current crop by applying a foliar application of Zn using 1/2 pound Zn per acre as zinc sulfate or zinc chelate in 25-30 gallons of water. Apply after each harvest when plants are about 4-6 inches high. For succeeding years include 3 to 5 pounds Zn per acre in the fertilizer program until the Zn level in the tissue is within the sufficiency range. If the Zn level is between 11-19 ppm include 3 to 5 pounds Zn per acre in the fertilizer program until the Zn level in the tissue is within the sufficiency range.
Element not a factor in plant nutrition. High levels are generally due to soil or dust contamination.
Molybdenum is required for nodulation and nitrogen fixation and is recommended as a seed and foliar treatment. Low Mo in the plant is generally accompanied by low N. If low Mo is detected in the tissue, apply Mo as described in the nitrogen section above.