Summary
• Phosphorus (P) and potassium (K) recommendations are made based on results of recent and representative soil samples. If you have not soil sampled recently, then your best strategy for dealing with high prices is to first invest in soil sampling and analysis.
• If you find soil test levels of phosphorus and potassium are optimal or above (see Table 1), the most profitable rate of P and K fertilizer is zero pounds per acre regardless of fertilizer cost.
• Apply fertilizer P and K dollars on field areas deficient in P and K (see Table 1), where there is a likelihood of getting a yield increase due to the application of fertilizer. The most profitable rate of P and K is less than the standard build–up (or “feed–the–soil”) recommendation we would normally make, however an official “feed–the–plant” recommendation for how much less to apply is not yet available. Use caution in reducing the recommended rate when soil test P and K levels are deficient.
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