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7 ways to reduce nitrogen limitation

Nitrogen is key to profits, but its variability in soil makes determining optimum rates difficult.

Think Different

Fifth-generation family farmer Steve Killpack has spent the last 15 years trying to identify ways to improve his operation economically without compromising environmental integrity. It led him to create software that uses automated data in a simplified process to help him and other farmers understand what drives profitability on their farms.

When Steve Killpack talked with farmers and farm advisers at a 4R-Plus meeting near Ames at Iowa State University’s FEEL farm last July, he was curious about which inputs were most likely to be applied variable rate. As a farmer and crop consultant on about 200,000 acres near Beebeetown in western Iowa, he had known about 75% of farmers variable rate phosphorus and potassium, and even more variable rate lime. Only about 5% variable rate nitrogen, even though nitrogen has the most variability in the soil.

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Steve Killpack

“Typically farmers would use a soil test to determine P and K rates, and they can see how they save money by not wasting those inputs,” Killpack said. “We use yield data and soil test values to determine the most efficient use of those inputs. But farmers are often afraid to cut back on N. By using their own information, I believe some day we will be able to farm by the foot with variable inputs, including nitrogen. 

So many factors affect nitrogen rates—organic matter (mineralization), soil texture, high risk of N loss in low areas with too much rain, previous crop (four times as much carbon in corn residue as soybean residue), carbon to nitrogen ratio, weather (loss to leaching), soil pH (microbes are greatly influenced by pH) and soil health (microbial action). “Determining nitrogen rates can be challenging, but if we analyze the factors involved, we can come up with solutions. We really need to work on N rates.”

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Detailed corn and soybean profitability maps drive decision-making from both an economic and agronomic perspective for Killpack and his customers. Per acre profits and loss on this field range from $200/acre loss in red, to break-even in white, to $250/acre profits in black. The two maps are among several simplified information reports Killpack’s Acumen Agronomics generates—he provides break-even yield reports and profitability reports to customers at no cost. Other Acumen maps include yield, N mineralization, N rate, and corn ear weights.

Killpack has created software that extracts information from farm input and yield data that simplifies decision-making for farmers to optimize profits and protect resources on the farm. Nitrogen application rates are an important part of the software. Analyzing results on his farm and others for the past few years has led Killpack to take these steps on his farm for more profit:

  • Soil texture (water holding capacity) and pH drove our yields. We’re using electroconductivity to better delineate our soils for this.
  • We will adjust nitrogen rates to maximize yields and profitability, and improve residue decomposition by leaving some N in the stover after harvest to feed soil microbes.
  • We’re going to apply more N with the planter and with multiple in-season applications, and would like to fertigate during grain fill. Our goal is to improve nitrogen efficiency and limit loss to the environment.
  • Our goal is to irrigate 90% of our acres, to provide yield stability. The least profitable acres on the farm will have the highest rate of return with drip irrigation.
  • We’ll optimize nitrogen use by maximizing ear weight according to seeding rates.
  • We get our best soybean yields on our best soils, so we will increase nitrogen rates on our core soils to increase soybean yields.
  • We will continue with no-till, multiple and longer crop rotations, and cover crops.

Killpack’s website is Acumen Agronomics.

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