The first few fields in the central Corn Belt that began to turn pale green instead of the dark green of healthy corn about three weeks ago certainly looked like they were nitrogen deficient. There was firing on leaves in many fields, particularly on hills and the side of hills in areas where rain has been scarce over the past 30 days. But at first it was difficult to believe that these fields could be short on nitrogen. Many had been sidedresssed with nitrogen after the rainy May period.
Agronomists are now confirming that indeed, nitrogen shortage may well be one of the factors that caused corn to begin to shut down early in many areas. However, it's not the only factor. It's coupled with diseases, such as Diplodia stalk and ear rot, and gray leaf spot, a foliar disease, and even northern corn leaf blight, another foliar corn disease, that has shown up in some northern areas of the Corn Belt, running as far south as into northern Illinois and Indiana counties in some cases.
Underlying it all is a very warm, now hot season that kept pushing corn to develop faster and faster as the season progressed. The number of days above 90 degrees F in the central part of he Corn Belt are now approaching 50% more than normal. Humidity has been another hallmark of this 2010 growing season. Those kinds of temperatures and humidity levels promote disease development. They are especially conducive to the development and spread of the two diseases already mentioned- gray leaf spot and Diplodia.
Also becoming a factor is suspicion of shallow rooting. In some cases it's soil compaction, especially on heavy-traveled end rows. In other cases, it's just shallow rooting because moisture was so easily available in most areas in May and even June.
So is the nitrogen shortage and signs of it real? Yes, says Mark Lawson, a Syngenta agronomist based in Danville, Indiana. On a company learning plot he maintains near his home, liquid N was applied on the surface. He figures as the season turned out, some if not quite a bit of N was lost. Corn is firing, although ears were developed and there's still potential for a reasonably good yield.
Others are noting that even sidedressing may not have been the silver bullet this year. Coupled with the underlying problems, heavy rains after sidedressing in some areas may still have caused enough N loss that symptoms began to show as conditions changed later in the season.