Fertilize Correctly: It Pays in Many Ways

Robert Hoeft

Robert Hoeft
Professor of Soil Fertility Extension, Department of Crop Sciences

Phone: (217) 333-4424
E-mail: rhoeft@illinois.edu


Report

Following the fertilizer suggestions provided in the Illinois Agronomy Handbook will, over the long term: optimize yield and, consequently, profit; minimize environmental contamination; and now, in some areas of Illinois, result in the public providing assistance in your nutrient management program.

Optimize Yield

The nitrogen recommendation system provided in the Illinois Agronomy Handbook was based on many experiments conducted in the late 1960s and early 1970s. More recent data collected across many environments has affirmed that on the average, the current system works well. These studies clearly demonstrate that the response varies greatly with the year, depending on factors like planting date and conditions, and especially weather. We expect this: Weather, soil moisture, and tillage affect root growth patterns and nitrogen uptake; dry weather that affects yield affects how corn uses the nitrogen it takes up; and weather has a very large influence on how much nitrogen soil microorganisms release from soil organic matter and, in some cases, the amount carried over from the previous year.

A nitrogen rate study conducted at Monmouth, Illinois demonstrates the year-to-year variation in optimum rate. At this location, optimum nitrogen rate varied from 78 in the dry year of 1988 to 240 lb N/acre in the high-yielding year of 1994. Even though it varied that much, use of the overall optimum rate, which was very close to the Agronomy Handbook recommendation, resulted in yields within 5 bushel of the optimum in all but four of the 19 years of the study. The greatest yield loss, 20 bushel per acre, occurred in the very dry and cold year of 1995.

The optimum phosphorus soil test depends upon the subsoil phosphorus level and the crop to be grown. Crops that make a major portion of their growth during the colder part of the year require higher phosphorus test levels. Crops like corn and soybeans will maximize yield at test levels from 20 to 40 lb P/acre, depending on subsoil phosphorus level.

Minimize Environmental Contamination

The mechanisms associated with nitrogen and phosphorus contamination of surface water bodies differ significantly, but some of the techniques that minimize loss are the same. In both cases, use of the recommended rate, time, and method of application will minimize loss. In the case of nitrogen, virtually all of the loss is associated with the movement of nitrate-nitrogen through the soil and into the water body. If tile is present, the movement is faster, but if tile is not present, there will still be nitrogen movement through the soil and into surface water bodies via base flow.

The amount of loss is dependent on the time and rate of nitrogen application and the amount of excess water from precipitation (Table 1). In years of low water flow (2001), there was little loss of N irrespective of when it was applied. However, in years of heavy rainfall (2002), delaying application until near the time of crop need reduced the total amount of N loss. Similarly, applying the rate near the optimum (in this example, optimum would be in the range of 140 to 150 lb N/acre) reduced the amount of N loss per acre by 25 to 30 percent.

Table 1. Effect of time and rate of nitrogen application and the amount of water flowing through tile lines on the amount of nitrogen loss
Treatment 2001 2002 2001 2002
  N loss lb/acre Water, A in.
0 N 7 36 2.8 19.0
140 N fall 14 62 3.6 19.6
140 Spring 10 53 3.2 22.7
210 fall 12 80 2.8 20.9
210 spring 11 66 2.9 27.5

Virtually all phosphorus loss occurs via surface flow of water over the land and into the water body. Loss of soluble phosphorus, that form of phosphorus that is immediately available for use by aquatic plants, is directly related to soil test phosphorus values. Losses of soluble phosphorus are greater with no-till than with conventional tillage systems. The reason for this is that the water is running across soils that have an accumulation of plant residue, and a portion of the phosphorus in the residue is leached into the runoff water.

In contrast to soluble phosphorus runoff, total phosphorus runoff is greater on tilled than on no-tilled fields. This is due to the fact that the majority of the phosphorus in soils is attached to the soil particles. Consequently, reductions in surface residue resulting from an increase in tillage will result in an increase in total phosphorus runoff. While soil test is important in this reaction, the amount of erosion is of the greatest importance.

Public Assistance In Nutrient Management

Three years ago, a pilot project was launched in east central Illinois to provide cost sharing for producers that would develop and follow a nutrient management plan based on recommendations provided in the Illinois Agronomy Handbook. In the initial year, a $5.00 per acre incentive was offered. In subsequent years, the incentive was $5.00 per acre plus $2.00 per acre for the certified planner. In the first two years of the program, plans were implemented on nearly 30 percent of the corn acreage. This program has now been expanded to other areas of the state through a program offered by

the Illinois Department of Agriculture and another by the Illinois EPA.

Both public and private groups are developing software for use in preparing nutrient management plans. This software will be useful to you whether or not you have an opportunity to participate in a government-assisted program. The University of Illinois plan is available online at http://www.aces.uiuc.edu/~longj/nutrient.php. Nutrient recommendations based on the University of Illinois suggestions are available online at http://www.aces.uiuc.edu/~longj/soilplan.php.

 

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