Fine-Tuning Manure Application

How will nutrient management plans be enforced? How will we assure neighbours that the plan is being followed as diligently as possible?

Record keeping is an important component of nutrient management planning. How often is manure applied to a field, and how many loads? What is the capacity of the tanker or the spreader? What application rate was applied - and just as important - how uniformly was the manure applied?

The amount of manure a field should receive depends on inherent soil fertility, the nutrient requirements of the crop and the nutrient value of the manure itself. Farmers often underestimate how much is being applied, especially in solid manure systems and with liquid irrigation systems. Variation in the uniformity of the manure applied is often surprising. In one extreme case, the variation in spread pattern ranged from 500 to 22,500 gallons per acre. This resulted in an application range from 15 to 675 lbs of nitrogen per acre.

Solid manure spread patterns show considerable variation between spreaders, but the spread pattern is relatively constant. For older style box spreaders, the most uniform spread pattern is obtained by driving wheel to wheel, since half the manure is distributed directly behind the spreader, and 25% is applied to either side.

Liquid manure application uniformity is influenced by equipment set-up, consistency of manure (ie well-agitated manure is best), wind speed and direction. Wind speed and direction is the largest culprit in non-uniform application from traditional irrigation gun systems.

Irrigation systems cover a large area quickly with much less weight and tire traffic to cause compaction. Irrigation systems have, and must, move to a "low trajectory" application - manure is applied less than 4 feet from the soil surface. Advantages of decreased droplet size, less wind movement, less odour and more uniform manure coverage are realized, at the expense of decreased application width. This is being done with both drag hose systems, and boom systems mounted on tankers. Irrigation systems are being modified for manure application.

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Overlap is an issue with irrigation systems and tankers. Overlap of 6 to 15% of spread width is adequate to maintain consistent coverage. 10% overlap gives the best uniformity. However, the width of application (with an irrigation/dragline reel) often narrows from the beginning to the end of an irrigation run. The application width also often narrows with liquid tankers from the beginning to the end of the load.

Liquid tankers with splash plates need to be properly set for best uniformity. With the splash plate too close to the outlet, the volume will be higher on the edges of the spread pattern (ie finger too close to a garden hose). Where the splash plate is too far from the outlet, the volume is higher in the middle of the application run.

Liquid tankers with injection units for immediate incorporation result in less volatilization of nitrogen and reduced odour. However, point application rates are increased. For example, rather than 5000 gallons applied uniformly across the soil surface, a point application rate equivalent to 20,000 gallons is applied in a 6-inch band, 6 inches closer to tile drains. Injection units must have proper distribution and chopping ability to avoid plugs the lines. When a plug-up occurs, the volume significantly increases in the other units. Injection units must disturb macropores (manure can't get to the tiles) and allow for maximum distribution through the soil profile.

Manure application equipment is constantly improving, with advances in technology to address needs. As nutrient management plans become a requirement for all farms, the calibration of equipment to accurately and uniformly apply the manure will become increasingly important. Accuracy, along with good application records, will go a long way to assuring society that we are following our nutrient management plans!

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