Fall Soil Sampling for Next Year's Fertilizer Decisions
October 14, 2011
Farmers have made excellent progress on this fall's harvest and it's time to think about next year's fertilizer needs. The steady climb in fertilizer prices over the last year, the volatility in grain prices, and the precipitation and flooding extremes across Nebraska this past year make it even more important to do a good job of soil sampling this fall. Recent rains across the state should provide great conditions for sampling after harvest (Figure 1).
This year has produced a range of precipitation across Nebraska. Varying corn yields due to N leaching, disease, or weather damage produce variability in soil residual nitrate-N. Because soil nitrate is mobile, soil sampling is the only reliable way to determine what is left in your soil. Soil samples for nitrate should be taken to at least a three-foot depth for next year's corn crop.
Our NebGuide, Guidelines for Soil Sampling (G1740), covers field division, sample numbers, and sample depths. Another publication, Soil Sampling for Precision Agriculture (EC154) has additional information.
To see the impact of current fertilizer and corn prices on N recommendations, use the Corn Nitrogen Recommendations Calculator, a UNL Excel® spreadsheet. (View other soil management tools at soils.) Changes in UNL N recommendations due to prices are based on the corn:N price ratio ($6/bu of corn and $ 0.60/lb N = 10:1 corn/nitrogen price ratio). Traditionally, this ratio has been in the 8:1 to 10:1 range.
Nitrogen Fertilizer Prices
Nitrogen prices have continued to climb since spring 2010 (Figure 2). Prices for urea in Figure 2 are averaged over several sources calculated weekly, giving equal weight to prices published by major trade publications for granular urea FOB vessel from the Middle East, southeast Asia, the U. S. Gulf, and Latin America.
Retail urea prices are approximately $600/ton plus or minus $25/ton, depending on your area of the state. Prices for spring should be back down around $570/ton which is about $0.60/lb of N. Currently, UAN solution is also as high in cost as urea per pound of N. Ammonia continues to increase, especially on world markets due to production problems in the Caribbean. Prices range from $800/ton to $875/ton depending on when your dealer bought its supply. If production problems are fixed, spring prices should be around $750 or less per ton ($0.45/lb of N).
Information from your soil tests plus fertilizer prices and expected selling price for your corn are used in calculating the recommended nitrogen rate. Current nitrogen fertilizer prices (ammonia lower cost, urea or UAN higher) range from $0.50 to $0.70 per pound of N. Because pricing depends on an individual's marketing plan, a range of fertilizer and corn prices can be used in the spreadsheet to look at the most profitable N recommendations. With corn in the $6 -$7 range and nitrogen in the $0. 50 to $0.70 range, the recommended N rate for 200 bu/ac corn would range from 185 to 240 lb N/acre.
Phosphorus prices for 18-46-0 (DAP) have increased significantly since early 2010 (Figure 3) but have leveled off recently. Next spring this product is expected to be over $700 per ton at the farm level. Ammonium polyphosphate (10-34-0) prices currently are at a premium compared to dry.
High fertilizer prices increase the value of manure. Fall and spring soil sampling are not useful in predicting the nutrients available from recent manure application, due to the extended period when manure releases its nutrients. Nitrogen availability can be estimated based on when the manure was applied, the application rate, the concentrations of organic and ammonium-N, and the application method. For more information on how this is determined, view the UNL webcast, Manure Application and Nutrient Management, at
To take full advantage of manure N, sidedress some or all fertilizer N; use the pre-sidedress nitrate test to determine the rate.
Other manure nutrients such as P and Zn are generally applied in sufficient amounts with a uniform manure application to fully meet crop requirements for two or more years.
- Take soil samples this fall as the first step to producing a profitable crop for 2012.
- The best way to minimize fertilizer expenses and maximize profit is to only put on the nutrients you need.
- Concentrate on the nutrients that have been shown to produce yield increases.
- Products and nutrients that don't have a research-based recommendation should be tested in small areas before being used extensively.
Gary W. Hergert, Charles Shapiro, Charles Wortmann, Richard Ferguson, Tim Shaver
Extension Soils Specialists