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Agronomy Talk

NW Illinois & Iowa - Craig Kilby, CCA

Fall Fertility Decisions

Published on Tuesday, October 20, 2015

Fall fertility decisions in northwest Illinois have traditionally been based on crop removal and recent soil test levels. That may remain unchanged for some in 2015, while others may find the need to adjust levels lower due to economics. The cost to apply major nutrients like P and K have not dropped at the same rate as grain prices, resulting in heightened interest of economical use of these nutrients. Referring to soil test information, P and K can be allocated to only those areas most likely to respond to applications. Be sure to review critical levels of nutrients for corn, soybean, wheat, and alfalfa. The probability and magnitude of return to P and K fertilizer will increase when applied to soil test levels below the critical level.

Soil test levels above the critical levels are referred to “maintenance” levels where P and K should be maintained by replacing crop removal amounts. Above some soil test P and K level, a low probability of yield response is expected which is referred to as “maintenance limit”. Above these levels, fertilizer may be omitted without reducing yield. For more information on fertility removal rates by crop and soil test draw-down rates when no P and K fertilizer is applied, go to:

Author: Craig Kilby