AGRONOMIC NEWS ITEMS
From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335
Summer 1996, No. 4
MOLYBDENUM SEED TREATMENT FOR SOYBEANS ENHANCES RESPONSE TO PHOSPHORUS AND POTASSIUM
There are excellent opportunities to produce profitable soybeans this year. Many growers will be developing a management plan to ensure that top yields can be achieved to take further advantage of the good prices. Fertilization with adequate amounts of phosphorus and potassium is recognized as essential for top yields and returns by most progressive soybean producers. However, there is an often overlooked nutrient that is just as important as phosphorus and potassium in a grower’s nutrient management plan. That nutrient is molybdenum.
A 55-bushel-per-acre soybean crop may accumulate more than 288 pounds of nitrogen, with about 220 pounds per acre removed at harvest. Soybeans can acquire about 90 percent of their nitrogen through the nitrogen-fixing nodules on their roots,…if molybdenum, phosphorus and potassium are adequate, and nodule bacteria are present and functional.
Molybdenum enables the symbiotic nitrogen-fixing bacteria, which live in nodules on soybean roots, to convert nitrogen gas from the air into a form that plants can use. As the soil becomes more acidic…as soil pH values decline, molybdenum availability decreases. At soil pH values below 7.0, and especially below 6.5, soybean growers should consider treating seed with 0.2 to 0.4 ounces of actual molybdenum per bushel at planting. If soybeans have not been produced on a field within the last three years, seed should also be inoculated with nitrogen-fixing bacteria which are specific to soybeans. This would especially apply to land that is coming out of the Conservation Reserve Program program or any fields with a history of plants with pale-green color, poor nodulation and lower-than-expected yields.
Research has shown that phosphorus and potassium fertilization are important. However, the optimum response, especially to phosphorus, is not possible unless the plant has an adequate supply of molybdenum. For example, scientists at Auburn University observed no yield response to phosphorus unless molybdenum was adequately supplied, even where the soil pH was above 6.0. Yield increases from molybdenum ranged from five bushels per acre on plots which had historical applications of lime plus phosphorus, potassium and some micronutrients…to 15 bushels per acre on plots which had received phosphorus and K but no lime. Increases in leaf nitrogen concentration and 100-seed weight also occurred. Lime alone significantly increased yield by raising the soil pH and increasing soil molybdenum availability.
If lime is needed, it should be applied. If lime is applied this year on soils with a pH below 6.5 to 7.0, molybdenum should also be applied as a seed treatment at, or prior to, planting. If soybean seed is not treated with molybdenum at planting, growers can apply by foliar application about one ounce of sodium or ammonium molybdate per acre, within a couple of weeks after emergence, to prevent or correct molybdenum deficiency.
Make sure that molybdenum does not limit the potential for profitable responses to phosphorus and/or potassium. At a cost of $2.00 to $3.00 per bushel for a molybdenum seed treatment, and with soybeans priced at more than $7.50 per bushel,...balanced phosphorus, potassium, and molybdenum nutrition can result in an excellent return on investment. Failure to provide a balanced supply of these nutrients will limit nitrogen fixation, reduce yields, and lead to disappointment and lost profits.
High yields don’t just happen...they require planning. Plan now for high yields in 1996 with phosphorus, potassium and adequate molybdenum.
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