March 7, 2008

With the dramatic increase in nitrogen fertilizer prices over the past year, producers may be wondering if such large investments in fertilizer are worth it. In another CropWatch article, we pointed out that current crop prices make application of recommended rates of N profitable. In fact, recommended N rates may even be slightly higher for 2008 than 2007 due to the increase in value of corn and other grain crops. However, the thought of investing $100 or more per acre in nitrogen fertilizer may cause producers to think about how to protect that investment.

There are several management options producers can consider to protect their investment in nitrogen fertilizer, and insure that as much as possible is used by the crop this season.

• Delay application. The longer N is in the soil, the more likely that some of it will be lost - either by leaching, denitrification, or ammonia volatilization. However, multiple applications will require more trips over the field, and those costs need to be considered against the cost of other options.

   

• Inject fertilizer below the soil surface. Broadcast application of N fertilizers can increase the potential for ammonia volatilization (primarily for fertilizers containing urea) or for runoff. Immobilization of N in decomposing residue is also a concern with broadcast application. Placing N below the soil surface minimizes the potential for volatilization or runoff. If injecting fertilizer is not an option, surface banding fertilizer instead of broadcasting it can help increase efficiency, though not to the degree of injection.

   

• Use a urease inhibitor. Agrotain® is the only product currently on the market labeled as a urease inhibitor, which protects urea-based fertilizer from ammonia volatilization. Agrotain® is applied to fertilizer, so the cost per acre depends on the rate of fertilizer applied. Currently, the cost of using Agrotain® with urea is $0.04 - $0.06/lb N. To protect 150 lb N/acre as urea with Agrotain® the cost will be $6.00 to $9.00/acre.

   

• Use a nitrification inhibitor. N-Serve® is the only product labeled as a nitrification inhibitor. However, dicyandiamide (DCD) is also an effective nitrification inhibitor, and is sold as a slow release fertilizer or fertilizer additive. Both products protect N from leaching and denitrification losses. N-Serve® is applied at the rate of 1 qt/acre, which currently costs $7.18 ($28.73/gal).

   

• Use a slow or controlled release formulation. There are a number of slow or controlled release fertilizer formulations on the market, though they are not available in all areas of Nebraska. These products delay the release of N compared to more traditional fertilizers such as urea or UAN solution, with the intent to match nutrient availability with crop demand. These products can help protect N from loss due to leaching, denitrification, or ammonia volatilization. One controlled release product available in parts of Nebraska is ESN®, a polymer-coated urea fertilizer from Agrium, which costs $0.10 to $0.12 per lb of N. Use of ESN® to protect 150 lb N/acre will cost $15 to $18/acre.

These options should be considered as insurance, rather than yield boosters. If the proper rate of N is applied and climatic conditions are such that the potential for N loss is minimal, there will not be any benefit from using these practices. Normally, there will be some potential for one or more N loss mechanisms to influence fertilizer availability, resulting in some yield protection from the use of these practices. The most appropriate conservation practice, or combination of practices, will depend on your cropping system, soils, fertilizer source, and climatic conditions.

An important consideration is that the cost of most of these practices has changed little over the last couple of years, while the cost of fertilizer has more than doubled. If a practice can help protect against losing 20% of the N applied, for example, that may save $20/acre worth of fertilizer, and perhaps 5-10 bu/ac of yield potential worth $25 to $50/acre, if the applied N fertilizer rate is near the economic optimum rate. With a potential investment of $10,000 to $14,000 for N fertilizer alone for a typical irrigated quarter-section field, adding $800 to $2500 to insure that investment seems worthwhile.

Richard B. Ferguson
Charles A. Shapiro
Extension Soils Specialists