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Extension > Local Extension Offices > Dakota > County Agriculture Educator > Articles > New N Recs for Irrigated Sands, Based on Local Research

New N Recs for Irrigated Sands, Based on Local Research

Example MRTN graph, courtesy of John Lamb

New nitrogen guidelines for corn on irrigated sands

4/22/15

Revised fertilizer guidelines for corn grown on irrigated sandy soils have been published by University of Minnesota Extension. You can read the bulletin by clicking here: “Fertilizing Corn Grown on Irrigated Sands” (AG-NM-1501).

These new recommendations are locally important for several reasons:

  • Irrigated sands are relatively common in the eastern part of Dakota County. If you are unsure of your soil’s texture, you can look it up on the USDA-NRCS Web Soil Survey. Or you’re welcome to give me a call (651-480-7223).
  • Irrigated sands require careful management to control nutrient loss. Because coarse soils have low water holding capacity, nitrate nitrogen can be easily lost to leaching, wasting your investment in fertilizer and contaminating water.
  • Dakota County farmers played an important role in developing these new recommendations. Many of the studies that the new guidelines are based on were conducted on farms in Dakota County. To learn how to be part of this project moving forward, click here.

The new guidelines include new nitrogen rates for corn grown after corn on irrigated sandy soils, nitrogen credits for corn grown after other crops, results of trials of different nitrogen application timings and sources, and Best Management Practices to reduce economic risk and risk of environmental degradation.

Nitrogen rate: The recommended nitrogen rate is based on the Maximum Return to Nitrogen (MRTN), or the amount of nitrogen that will pay for itself in increased yield. The MRTN rate is calculated using a database of nitrogen rate experiments and the ratio of the price of nitrogen fertilizer divided by the sale price of the crop (see example graph, courtesy of John Lamb). A calculator for the MRTN rate is available online here. This calculator does not yet include the new recommendations for irrigated sands. Until it is updated, you can use the tables in the new bulletin to find the MRTN and account for nitrogen credits for previous crops.

Nitrogen application timing: On irrigated sandy soils, split nitrogen applications are superior to a single application. Previous studies had led to that conclusion, and recent Extension studies on Minnesota’s irrigated sands have confirmed that modern corn production systems benefit from split nitrogen applications.

Split nitrogen applications are beneficial because in wet years nitrogen applied pre-plant is at risk of being leached by spring rains before the crop takes it up. In recent Extension studies, in dry years split applications achieved yields that were as good as those in plots that received all the nitrogen as urea pre-plant, and in wet years split applications provided higher yields than nitrogen applied pre-plant.

Because of these findings, the new Extension guidelines do not recommend pre-plant nitrogen application on irrigated sands. The total nitrogen rate can be split among starter, side-dress, injection into irrigation water (fertigation), or UAN used as a carrier for pre-emergent herbicides. The last application of nitrogen should be done before corn silks turn brown.

Nitrogen sources and additives: Many products are available to reduce nitrogen loss, such as slow-release nitrogen sources and nitrification inhibitors. A recent study reported in the bulletin found that several such products did provide greater corn yield than untreated urea applied pre-plant. However, the products tested were not superior to split urea applications.

Best Management Practices: The BMPs recommended in the bulletin include:

  • Do not over-apply nitrogen: Use the MRTN rate and subtract credits for nitrogen supplied by previous crops, manure, irrigation water, starter fertilizer, and the nitrogen included in your P fertilizer application.
  • Apply nitrogen fertilizer split between planting and at least one in-season application. Do not apply nitrogen to irrigated sands in the fall or pre-plant. Extension research has shown that on irrigated sands, split nitrogen applications provide superior yields, net returns, and environmental benefits.
  • Protect against nitrogen losses by taking steps to reduce volatilization and avoid overwatering. 

Extension research has shown that, because of the high risk of nitrogen loss on these sandy soils, it is important to both your bottom line and your environmental stewardship to use the above BMPs.


This article is based on “Fertilizing Corn Grown on Irrigated Sands” (AG-NM-1501), by John Lamb, Carl Rosen, Phyllis Bongard, Daniel Kaiser, Fabián Fernández, and Brian Barber. 
 

We need your help: Click here to learn how to be part of this research going forward. 

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