The following 15 tips will help you get the most out of your investment in phosphorus (P) and potassium (K) fertilizers. They come from Dan Kaiser, a nutrient management specialist at the University of Minnesota Extension.
1. Test the soil regularly and follow these recommendations. Although soil tests aren’t perfect, they are your best indicator of nutrient sufficiency.
2. Monitor soil pH, the primary variable that affects nutrient availability. A pH of 6.0 is sufficient for most nutrients to be available. However, lime doesn’t really pay off unless the soil pH approaches 5.0 when growing corn or soybeans.
3. Know that at best, a maize crop takes up 30% or less of the applied P. The rest joins a soil storage pool that is released over time, where it binds to soil ions in a form unavailable to plants. Most of the absorbed phosphorus comes from the soil.
4. Remember that phosphorus binds to calcium, aluminum and iron ions in the soil, becoming less available to plants. The decision to apply liquid in-furrow starter fertilizer (which generally costs more per unit of nutrient than dry fertilizer) depends on where you are on your soil test requirements. If you are applying as a starter, be sure to subtract what is applied from your broadcast or full season application. A 5-gallon-per-acre rate of 10-34-0 is 20 pounds per acre of phosphate (the rate you want for early corn growth response), Kaiser says.
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5. Do not exceed 7.5 to 8 gallons per acre of a starter fertilizer rate of 10-34-0. For clays and silts, 5 gallons per acre is at the high end of the economic recovery range, he says. “Reduce at least half that rate on sandy soils. Placing fertilizer on corn seed is always risky, so keep rates low.
6. Diffuse P if soils are low in P. “Low-input, in-furrow start strategies can work on medium to high P-test soils and can yield a higher yield per unit of nutrient applied,” he says. “It is important to monitor soil testing for P when using low input strategies, to detect low levels that would benefit from broadcast or band application of fertilizer away from the seed row. seeds.”
7. Be aware that starter fertilizer is not cost effective under all circumstances. The in-furrow starter can produce the same corn yield as a higher broadcast P application.
8. Avoid starter fertilizer if broadcast application provides all the P needed by corn. “Beginner’s P needs to be considered to avoid wasting a lot of money,” he says.
9. Do not use an in-furrow starter for soybeans. They are less tolerant of fertilizer placed in the seed.
10. Cover start-up cost with reduced grain moisture at harvest. When grain moisture is 20% to 25% and higher, it’s possible to cover the start-up cost with lower grain moisture at harvest, Kaiser says. (Remember that you should always consider in-furrow starter nutrients when setting your overall P levels.)
11. Apply phosphorus to corn plants early in the season. Choose a starter formulation that can deliver at least 10 pounds per acre of P2O5 economically. There is no difference in the phosphorus sources of fertilizers with respect to their ortho- or polyphosphate content.
12. Use lower cost nutrient formulations. “A simple starter N and P blend like 10-34-0 is more cost effective than a low-salt nutrient formulation,” says Kaiser.
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13. Keep N, K, and S starting rates low to prevent salt burn. Do not exceed 10 pounds per acre N plus K20, and you will avoid too high a salt load.
14. Review chelated micronutrients. “Chelated micronutrients tend to increase costs and likely won’t result in a positive return on investment if your soil test shows sufficient nutrient levels,” says Kaiser.
15. Don’t rely on in-furrow supplies to last the entire season. “Inputs into the groove should be limited to an early season kick,” he says. “You can’t safely apply a full season’s worth of inputs in a furrow in low test soils.”