Four Fall Fertilization Tips

September 23, 2013 12:00 AM
Four Fall Fertilization Tips

As corn and soybean farmers prepare for harvest, it’s not a bad idea to start mapping out a fall fertilizer plan, says Dennis Bowman, Extension educator for commercial agriculture, University of Illinois. For one thing, purchasing nutrients now could save money down the road.

"The wholesale prices of fertilizer have dropped quite a bit," Bowman says. "They’re about the lowest they’ve been in two years."

Before placing an order, review these four steps to make sure the fertilizer you buy will help maximize profitability in the year ahead.

1. Calculate your fertilizer needs

Beyond monetary costs, farmers should avoid yield penalties in 2014 by using a couple of tools to evaluate how much fertilizer they’ll need to apply this fall.

To determine nitrogen needs, Bowman recommends using a state-level Maximum Return to N (MRTN) calculator. The University of Illinois is one of several universities that offer an online calculator farmers can use to tabulate nitrogen requirements based on local nitrogen research data and current prices.

To determine lime, phosphorus and potassium needs, soil tests are key. These should generally be taken right after harvest and in about the same timeframe as soil tests taken in previous years.

"There is a little bit of a cycle in how soils test," Bowman says.

In general, soils within a field fall into one of three categories. Soil below the appropriate nutrient threshold might need a buildup program to restock. Other soil might be at a maintenance level, meaning it needs fertilizer simply to compensate for nutrients removed by crops during the growing season. A third category of soil might need a drawdown program, meaning fertilizing is withheld for one or two years, allowing excess nutrients to be used up.

While many Midwest farmers used to apply 200 lb. per acre of diammonium phosphate (DAP) and an equal volume of potash, the use of calculators and soil tests has become the preferred method for determining needs to maximize efficiency and limit cost.

2. Wait for cool soil temperatures

Most farmers will want to avoid applying nitrogen in October simply because soils probably won’t be cool enough, Bowman says.

"Soil microbes are going to start chewing up that nitrogen and converting it," he says. "They’ll incorporate some of that into their own metabolism, and some of it will be converted from ammonium forms to the nitrate form, which is water-soluble and will leech out."

Instead, it’s generally best to wait until the daily maximum bare soil temperature is below 50 degrees Fahrenheit.

Decisions about when to apply fall fertilizer are also regional. For example, Illinois farmers south of Route 16 generally don’t apply any fall fertilizer because of warmer soil temperatures, whereas those north of the highway wait until later in the year, within a couple of weeks of consistently low soil temperatures.

3. Prepare your applicator

To ensure uniform fall fertilizer application, get your machinery in top working condition. For dry fertilizers such as phosphorus, potassium and lime, that means examining the spreader up close.

"The key thing there is to make sure those are calibrated and adjusted, and to make sure the right overlap is set up for the granules they’re spreading," Bowman says.

On anhydrous applicators, check hoses to verify they are the same length and experiencing the same pressurization. Review manifolds to ensure they are releasing even amount of nitrogen. (This will help prevent the ripple effect sometimes evident in fields, where some rows are greener or taller than others.)

4. Correct in-field mistakes

The good thing about split fertilizer application is that it happens at several points between fall and the next growing season, Bowman says. A program that includes fall-applied DAP, spring-applied ammonia and finally a regimen of side-dressing or starter fertilizer can serve as its own insurance against over- or under-application.

Split application can make up for errors that happen at any one point," Bowman says.


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