Impact of the drought on 2013 fertilizer rates
Reduced yields can have implications for fertilizer need in the year after a drought. Intuitively farmers recognize that substantially reduced yield can lead to less removal of nutrients from a field.
When nutrient use is reduced there is an opportunity to estimate a drought nutrient credit from the stricken crop that can be used to reduce fertilizer need in the year following drought.
Farmers have used a range of strategies to deal with drought stricken corn and soybean. How they managed fields this year will directly affect the amount of fertilizer carryover to the next year. This year, corn and soybean fields have been harvested for grain (with substantially reduced yield), mechanically harvested (as green chop, baled forage or silage), grazed as forage, or been abandoned with no removal of any crop material.
Each of these scenarios has implications for how many nutrients applied from this year can be credited to next year’s crop. In some cases these strategies may actually increase fertilizer need next year by removing more nutrients than would have been in the planned grain harvest.
Table 1 summarizes our expectation for the impact of selected strategies on fertilizer need in next year’s crop.
The table assumes that your yield goal for corn was 150 bushel/acre (B/A) and for soybean was 50 B/A. Equations are provided later in the article if you want to calculate drought nutrient credits for different yield goals.
Drought nutrient credits can be important particularly on fields where little or no material was harvested in 2012. Recognize that chopped corn can increase potash requirements for next year’s crop.
Also recognize that there is potential for nitrogen estimated in by the drought nitrogen credit to be lost through leaching or denitrification if we have excessively wet conditions between now and next-year’s crop.
The final section of this article, “Other Considerations”, details strategies to manage this and other risks associated with using drought nutrient credits.
|Table 1. Estimated impact on next year’s fertilizer need (drought nutrient credits) for selected harvest strategies for drought stressed corn or soybean. Assumes fertilizer applied this year was based on 150 B/A yield for corn and 50 B/A yield for soybean. Arrow down means recommended fertilizer rate for next year should decrease by the associated value.|
|- - - - lbs/acre - - - -||- - - - lbs/acre - - - -|
|No crop harvested||↓145||↓50||↓40||0||↓40||↓65|
|Harvested as grain (40% of yield goal)||↓70||↓30||↓25||0||↓24||↓40|
|Chopped and removed¹||0||↓15||↑60||0||↓20||↓25|
|¹Assumes most growth stopped at R1 for corn and R3/4 for soybean.|