December 21, 2005 | By: Laura Skillman

As fertilizer costs escalate, farmers might want to consider what they can do to maximize productivity within their budget. For some that could mean using less nitrogen and focusing on other needed nutrients or perhaps switching nitrogen sources.

“Fertilizer price is one of those issues that isn’t likely to go away,” said Greg Schwab, a soil Extension specialist with the University of Kentucky College of Agriculture.

How will farmers react to fertilizer prices that are likely to remain high for the next few years?

“My prediction is farmers will stay in business and they will figure out a way to do it, and I think it is important for crop advisers who assist farmers to help them decide where their fertilizer money is best spent,” Schwab said.

The first step is figuring out where fertilizer should be applied. As fertilizer prices go up, the value of soil testing goes up. Soil tests allow farmers to see what nutrients are available in their soil and what may be needed to attain maximum yields, as well as “critical levels” of these nutrients needs to be known.

A critical level is a soil test level of a nutrient at which no additional yield response is expected if additional fertilizer is applied. The critical level for phosphorus is about 35 pounds of Mehlich III extractable phosphorus per acre. However, UK recommends fertilizer up to soil test levels of 60 pounds per acre. This is because soil tests are an average value of a field, so pounds are added to fertilize areas within the field that are below the average.

“When we see fields with soil test P below 35 pounds per acre, we know we have a serious problem,” Schwab said.

For potassium, UK recommends potash until the soil test reaches 300 pounds per acre, but the critical level is closer to 225 to 235, he said. Anytime a soil test is below that level, potassium is likely going to be a limiting factor for a large portion of the field.

If fields are showing levels close to or below critical levels, farmers should be advised to back off on their nitrogen fertilizer use somewhat so they can afford the phosphorus and potassium fertilizer that they need, Schwab said.

Phosphorus costs have increased as the result of projected shortfalls this year due to a major plant closing. However, from 2006 and beyond, production is expected to be greater than demand. Foreign competition is coming into the phosphate market from Saudi Arabia and eastern Asia.

The outlook is not as optimistic for potassium, for which prices have more than doubled in the past few years. There are not many potassium deposits in the world, with most coming from Canada or Eastern Europe. Demand has been increasing dramatically, primarily from China, India and Brazil, and it is projected to continue to rise. Supply versus demand looks to be a long-term issue with a shortfall projected through 2009.

Nitrogen prices also are not forecast to get better any time soon. Prices have gone up dramatically due to the increased costs of natural gas, a primary component in the production of nitrogen. Prices for natural gas are expected to remain at relatively high levels through the next few years, meaning nitrogen will also remain costly.

As the price of nitrogen increases, over-use of nitrogen gets more expensive. In UK’s nitrogen recommendations, there is a range of pounds rather than a specific number. An example would be from 100 to 140 pounds per acre. In the past there has not been a real economic disadvantage from over-applying, but with today’s prices additional costs of nitrogen will lower the return per acre.

County agents and crop advisers can be of assistance to farmers as they look at the amount of nitrogen they need and as they factor it in to their overall fertilizer needs. Producers might want to conduct some nitrogen strip trials in their fields to get a better understanding and more confidence in the rates they are using.

Because of the high price of nitrogen fertilizer, producers need to take steps to increase nitrogen efficiency whenever possible through timely applications, use of legume cover crops and accounting for nitrogen in manures used on the field, Schwab said.

Worldwide nitrogen use efficiency is only about 33 percent, so 33 percent actually makes it into the crop. A lot of nitrogen is applied that never gets used by the crop. In the United States, the rate is 50 to 60 percent, but still half the nitrogen never makes it to the crop.

In Kentucky the biggest loss of nitrogen comes from denitrification, when nitrate is converted to nitrogen gas and dissipates into the air. By controlling denitrification, a farmer can potentially reduce the amount of nitrogen needed to produce a crop.

Denitrification occurs when soils are wet. Because of this factor, UK nitrogen rate recommendations are based on soil characteristics. A poorly drained soil has the potential to hold more water, so nitrogen recommendations are higher for these soils. In conservation tillage, the same holds true.

However, if a producer can apply nitrogen closer to when the crop needs it through side-dressing, they can reduce exposure to denitrification. The key thing to remember in poorly drained soils is that side-dressing reduces the amount of time the nitrogen is in the soil, lowering the potential for loss, Schwab said.

Side-dressing is when a second application is made after the crop has emerged from the ground. The nitrogen is applied alongside the row. In the past, the time and expense of side-dressing versus applying additional nitrogen at preplant often could not be justified, he said. But with higher nitrogen prices, it may be worth the time. Producers should weigh the expense of added nitrogen to the expense of going back through the field.


Writer: Laura Skillman 270-365-7541 ext. 278

Contact: Greg Schwab, (859) 257-9780