Stalk Nitrate Results

Click the link below to view the 2010, 2011 & 2012 Results Map and review individual field results (by Township).

Stalk Nitrate Results Map (pdf)

On-Farm Network®

The Stearns County SWCD is partnering with the On-Farm Network® to assist farmers in implementing stalk nitrate evaluations to help them fine tune Nitrogen management in corn production. The On-Farm Network®, a program of the Iowa Soybean Association, focuses on precision agriculture tools and technology to collect information that can increase growers' profits from crop production. This program is available to producers in the upper Sauk River Watershed area through the Mississippi River Basin Initiative. There is an increasing interest in N management because of higher prices for fertilizer N and concerns for environmental quality. While the end-of-season stalk nitrate test can be used to evaluate the availability of N to the corn crop, fields are seldom uniform.

Sampling Information

It's important to consider the location of the sample collection point in context of the entire field. To collect multiple samples that can give a more accurate picture of the entire field, the On-Farm Network uses a technique called guided stalk nitrate sampling. Stalks samples can be collected after the corn plant has reached physiological maturity or prior to silage harvest. Eight inch long sections, cut from 6 to 14 inches above the ground are taken and sent to a lab to determine the nitrate-nitrogen concentration. At least 10 stalks should be combined for a single sample. In a typical field, four different sampling locations are selected. One sampling point is based on a color image taken in late August, trying to locate an area of the field that looks N deficient. The other three sampling locations are guided by the three dominant soil map units in the field. This pre-selection of varying soil map units will help reflect any differences caused by soil variability. A handheld GPS instrument is used to locate the sampling points within the field. Many factors, including overall plant health and the amount of available N in the soil, influence the N status of a corn plant. Factors like rainfall, growing conditions, and the amount of N from fertilizer or manure and other sources (such as organic matter) must also be considered while trying to understand what happened during the growing season that just ended. For an initial review of what happened last season, an interpretation of the stalk values is needed for each sampling point. Table 7.12 above shows the four categories for interpretation.