The fall of 2018 and so far in 2019, there have been limited opportunities to apply nitrogen fertilizer. Average rainfall through the first 25 days of March ranged from a little less than normal in the northern half of Illinois to an inch or more above normal in south-central Illinois. But temperatures have averaged 3 to 4 degrees below normal, which slowed drying. There were several days in the first week of March when it was frozen on the surface and a considerable amount of P and K went on. This was followed by an inch or more of rain (which had been forecast) in many areas, and it’s likely that some of the nutrients—those in MAP/DAP and potash are soluble—moved from higher to lower parts of fields, or off of fields altogether. While it’s good to get P and K applied before spring work starts, we really should consider holding off the next time soils are frozen and substantial rainfall is forecast before a thaw.

 

N Rate

 

Results from the on-farm trials coordinated by Dan Schaefer of the IFCA and funded in part by the Illinois Nutrient Research & Education Council (NREC) showed that at about two-thirds of Illinois sites in 2018, the N rate needed to maximize the dollar return to N was higher than we have typically seen. We think that the slow start to mineralization during the cool weather in April 2018 might have meant more dependence on fertilizer N. Yields were also higher than we’ve usually found, which meant that the crop took up more N than usual.

 

Adding the 2018 data to the database used by the N rate calculator to calculate best (MRTN) rates for N in Illinois, and taking out some older data, resulted in an increase in the MRTN values compared to the previous (2018) version for corn following soybean. With N priced at $615 per ton of anhydrous ammonia ($0.375 per lb of N) and corn at $3.75 per bushel, the calculator gives MRTN rates for corn following soybean of 166, 180, and 192 lb N per acre for northern, central, and southern Illinois. These rates are 11 lb higher than the 2018 rates in northern and southern Illinois, and 5 lb higher in central Illinois. Those are modest changes because the 2018 data is added to a lot of existing data, but they illustrate how generating and adding new data keeps the guideline N rates responsive to research-based changes.

 

MRTN values for corn following corn did not change very much, in part because there weren’t as many trials in 2018, and in part because trials over the over the past several years have shown that corn following corn has required less fertilizer N than we found in many previous trials. It’s not clear why that is the case, but as we found with corn following corn, rates are responding to research findings to stay linked to what today’s corn crop needs.

 

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