IANA: Time for late-season nutrient analysis, scouting 

By Ben Wicker 

Now that summer has officially arrived, analysis of remaining nutrients for cash crops can occur. As the crop approaches its reproductive stages, nutrient uptake increases exponentially, so a ready supply of nutrients in the soil is necessary to achieve optimal efficiency through grain fill. 

Excessive rainfall in several areas of Indiana has led some to question if their applied nitrogen is still available and what options they may have to identify and address late season deficiencies. Some tools exist to help us estimate any remaining needs with the knowledge that machinery exists to provide rescue treatments. 

Nitrogen in corn 

Corn nitrogen uptake curves have been around for years with few updates needed. By the R3 (milk growth stage), 80 percent of the crop’s nitrogen has been taken up and partitioned within the plant. By R5 (dent), that number is almost 100 percent. Around 60 percent of the crop’s nitrogen needs occur in vegetative stages of growth. 

However, by the time of black layer (full maturity), 60 percent of the full nitrogen need has been partitioned into the grain on the cob. Nitrogen can be a mobile nutrient – in the plant, soil and water – so timing its application with uptake in the plant can help avoid yield-robbing deficiencies. 

Once the sidedress rig is parked, weather becomes the predominant driver in how much nitrogen remains plant available. The Pre-Sidedress Nitrate Test (PSNT) can provide snapshot of nitrate availability in the soil. Admittedly, only knowing nitrate values later in the season is a snapshot that may or may not have any action items that can come with it, but pulling at multiple depths may give some indication of how your nitrogen in moving through the soil profile. 

Plant tissue testing is a great way to assess nutrient availability in leaves and can be done any time in the season. Consult the testing laboratory’s sampling guide for proper procedure. Corn stalk testing at plant maturity can provide some information on any nitrogen left in the stalk. 

Very high or very low values of N left in the stalk will point toward overuse or underuse of nitrogen fertility and may be cause for considering management changes in future years. Crop and nutrient models may also provide insights to nitrogen availability and loss through the growing season. 

Importance of scouting 

Scouting for nutrient deficiencies is equally as important, however, especially now that high clearance equipment and drones are available for rescue treatments if economically justified. In many years, deficiencies can show toward the end of the season and cause early maturity of field crops. Even if a rescue treatment is not possible, it can inform management decisions for the next growing season. 

More producers today are also looking at the 4Rs: right rate, right source, right time, right place, as a way to fine tune nutrient rates more often throughout the growing season with the benefit of likely losing less to heavier rains or inaccessibility for soil access to nutrients in droughts. With more precision nutrient management, the importance of scouting and soil/tissue testing increases. 

Volatility in fertilizer prices and weather can add layers of difficulty in managing our nutrients. Taking actions and utilizing tools at our disposal to keep our crops and pocketbooks healthy through sound 4R management. Visit nagnutrients.org for more information and resources.