Part 1, Section 2: Soil Fertility Management

Section 2 Table of Contents

Soil cores

Soil Fertility Management

MANURE NUTRIENT MANAGEMENT

Spreader calibration:

Method 2-Best for liquid manure

Equipment required: yardstick or tape measure and a string or rope

  1. Determine the manure spreader capacity using Table 1.2-17.
  2. Tie a string around the tractor tire at the top of the tire. Mark the ground directly below the string where the tire rests on the ground. Pull the tractor forward until the string is again at the top of the tire. Mark the ground again, as before, and measure the distance between the two marks on the ground. This is the distance the tractor moves with one revolution of the tire.
  3. Spread the load of manure, counting the number of times the rope comes to the top of the tire. Multiply the number of revolutions the tire made to spread the load by the number of feet the tractor moved in one revolution (Step 2). This is the distance traveled to spread the load.
  4. Measure the width that the spreader is covering with manure.
  5. Multiply the distance traveled (Step 3) by the width that the spreader is covering with manure (Step 4) and divide by 43,560 (the number of square feet in an acre). This is the number of acres covered by one load
  6. Divide gallons or tons of manure applied (the spreader capacity from Step 1) by the number of acres covered (Step 5). The result is the tons or gallons applied per acre.

Once you have determined the rate at which you are spreading, you may have to make adjustments in either tractor speed or spreader settings to get the desired rate. After making any change, recalibrate the spreader. It may take several tries to get the proper adjustments for the desired rate.

The fertilizer recommendations on Penn State soil test reports do not take into consideration any manure you are applying. You should subtract the amount of available nutrients applied in the manure from the recommendation amounts (see sample calculations). For soil samples taken after manure has been applied, the manure P and K amounts are measured as part of the soil nutrient levels and, therefore, should not be subtracted from the recommendations.

Continued excessive application of manure and/or fertilizer nutrients can create crop, environmental, and economic problems. Environmental problems result from leached N or runoff of manure into surface water. Not only are these nutrients lost to crop use, but their value as fertilizer replacement also is lost. In addition, excessive nutrients in the soil may contribute to excessive vegetative growth, lodging, high nonprotein N levels in crops under stress, delayed maturity or poor storage quality of vegetables, and lower uptake of magnesium and/or zinc.

To conserve manure nutrients and reduce the pollution potential of manure, follow several basic recommendations:

  1. Conserve the liquid portion; this portion contains half the total N and nearly all of the K.
  2. Spread the manure uniformly and at a known rate. General guidelines for application rates suggest 10 to 25 tons per acre for cattle manure, and 3 to 5 tons per acre for poultry. Actual rates should be based on meeting crop nutrient needs.
  3. Do not spread manure on frozen slopes. Spread far enough from streams, lakes, ponds, sinkholes, and wells that runoff does not wash manure into them.
  4. To take better advantage of its nutrients, apply manure just before the growing season, preferably to N-requiring crops. When this is not possible, use cover crops to hold the nutrients against loss.
  5. If possible, incorporate manure soon after application to conserve as much N as possible.

Because of its nutrient content, manure has a dollar value and can be thought of as a commodity. Farmers with manure in excess of needs, rather than using continued heavy applications, should consider some type of arrangement with farmers who could use more. Regardless of the formality of the arrangement, a manure analysis is an absolute first step. Because high water content dilutes the manure- reducing its per-ton value and increasing the transportation required-diverting some of the water that normally would be added is one way to increase manure’s value.

Soil testing is extremely important in manure management. Soil tests provide information that can be used to decide where manure can do the most good in supplying nutrients required by the crop. The lower the soil test level, the higher the probability of a response to adding the nutrient.

Soil tests also help monitor the effect of manure application on soil phosphorus and potassium levels. Consistent use of this tool can be effective in detecting nutrient imbalances or excesses so that corrective action may be taken.

Cropland benefits little from extremely heavy manure application rates. As is the case with other plant nutrient sources, excess phosphorus and potassium accumulations in the soil may occur when manure is applied at excessive rates. Nitrogen also may leach from the plant root zone and adversely affect the environment. In addition, the associated organic matter, which is beneficial at low rates, may become undesirable at excessive levels. Heavy surface applications of manure with no incorporation may inhibit herbicide activity, provide a favorable area for insect pest development, or create an odor problem.

As more farmers store their manure and spread it in the spring all at once, compaction is becoming a more serious consideration in manure management. Compaction is hard to avoid entirely, since there usually is little time in the spring when soil conditions are right for hauling manure without creating compaction and since many other jobs have to be done at this time. Compaction can be reduced, however, by using wide flotation tires on heavy manure-spreading equipment, which might otherwise seriously damage the soil and significantly reduce yield.

Probably the most important factor to be considered in reducing compaction is soil moisture: compaction is much more severe on wet soils than on dry soils. Yield decreases due to compaction usually are related to restrictions in the plant's root system, and these restrictions prevent the plant from getting the nutrients and water it needs.