Phosphorus

Phosphorus (P) is referred to as P₂O₅ for the purposes of soil testing, fertilizer grades and recommendations. We don't apply P in this form, but it has become the standard over many years. Table 6 lists the amounts of certain nutrient elements that are removed by vegetable crops. It shows that most vegetable crops use relatively little P compared to nitrogen (N) or potassium (K). For example, sweet corn takes up about 155 lb/A of N and about 105 lb/A of K, but only about 20 lb/A of P. However, growers commonly apply about 100 lb/A of P. This is justified if P soil test levels are low, because most of the applied P becomes fixed in the soil and unavailable to plants. However, if soil test levels for P are high and the pH is adequate, there is little if any crop response to additional applications. Plant uptake of P is very slow in cold soils. For this reason, when planting early, it is advisable to apply a starter fertilizer high in P in a band about 2" below and 2" to the side of the seed when planting, or as a liquid around transplants.

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