Producers often ask questions about tissue testing to decide emergency in-season phosphorus (P) and potassium (K) fertilization for corn and soybean. Previous articles(June 2010 and July 2008) have discussed the viability of post-emergence application of P and K fertilizers. A large application of granulated P or K fertilizer to soil during the very early crop growth stages may result in some grain yield increase although an economic benefit for the current crop is not likely. The probability of an economic response to foliar fertilization is likely with insufficient preplant fertilization or when soil and climate factors (other than drought) limit nutrient uptake. Traditionally, farmers and crop consultants have used soil sampling and testing of visually affected and seemingly unaffected field areas to determine if there is a nutrient deficiency. This is an effective practice when crop growth is limited by low soil nutrient supply, but will not be effective when soil or climatic factors other than low soil nutrient levels limit early nutrient uptake
