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MANURE IS A NATURAL ORGANIC FERTILIZER

Manure is an excellent natural fertilizer containing nitrogen, phosphorus, potassium and other nutrients. It also adds organic matter to the soil which may improve soil structure, aeration, soil moisture-holding capacity, and water infiltration.

To determine how much manure is needed for a specific application, the nutrient content and the rate nitrogen becomes available for plant uptake needs to be estimated. Nutrient content of manure varies depending on source, moisture content, storage, and handling methods.

Nitrogen content in manure varies with the type of animal and feed ration, amount of litter, bedding or soil included, and amount of urine concentrated with the manure. Moisture content is also a major consideration. For example: The moisture content of fresh manure is around 70% to 85%. The moisture content of air-dried manure is around 9% to 15%. As manure dries, the nutrients not only concentrate on a weight basis, but also on a volume basis due to structural changes (settling) of the manure. Volatilization of urine nitrogen can result in considerable loss of nitrogen - up to 50% or more of the total nitrogen.

Manure Handling

Handling can affect the fertilizer value of manure, particularly its nitrogen content. Nitrogen is present in manure in a variety of forms, most of which gradually converts to ammonium and nitrate nitrogen.

The ammonium form can be lost to the air and the nitrates leached by rainfall. Ammonium losses can be minimized by not stockpiling manure while it is moist, minimizing its handling, and working it under immediately after spreading. Ammonia can be lost to the air each time manure is moved or hauled. Much of the loss is from hydrolysis of the NH₂ groups (enzymatic) and then volatilization of N₂0 and NH₃. This loss can be very high when spreading manure, especially during warm, dry weather. Here, at least 50% of the ammonium nitrogen can be lost within 12 hours. Studies have also shown that, by one week after spreading, almost 100% of the ammonium nitrogen can be lost. This loss can represent up to 50% of the total nitrogen available in stockpiled manure. Therefore, the importance of simultaneously spreading and working in manure is obvious.

Nutrient Availability and Manure Application

Manure is a source of many nutrients including: nitrogen, phosphorus, potassium and many others. However, nitrogen is often the main nutrient of concern for most crops. Potassium deficiency is usually quite localized within a field and would not be corrected with common rates of manure. However, some improvement might be expected with high rates above 10 tons per acre. The high rates needed to correct a potassium (K) deficiency would supply an excess amount of nitrogen for many crops, and this should be avoided. (See Table 1)

Table 1. (Typical)

Rates of Manure for Nitrogen Needs

The nitrogen compounds in manure are eventually converted to the available nitrate form. Nitrate is soluble and is moved into the root zone with water. It is the same form ultimately available to plants from commercial nitrogen fertilizers.

However, the release of available nitrogen from the complete organic compounds during manure decomposition is very gradual. This slow release of nitrogen is manure's most important asset. It extends nitrogen availability and reduces leaching. This is of particular importance in sandy soils.

The idea is to first apply enough manure to meet the first year's need of available nitrogen. Decreasing amounts are then applied in following years because of the carry-over organic nitrogen that will be released from previous applications. If the same rate of manure is applied each year, it is possible for a field originally low in nitrogen to accumulate unnecessarily high levels in successive years.

The nitrogen in poultry manure is in released fastest, as most is the urea or uric acid form, with 90% of nitrogen released in the first year.

Fresh manure which contains both the urine and solid portions and has a large amount of urea or uric acid provides a somewhat slower release rate, with approximately 75% of the total nitrogen released the first year.

An even more gradual nitrogen release can be expected from dry feedlot steer manure, with only 35% of the total nitrogen released the first year.

Other Benefits of Manure

The use of manure helps to maintain the organic matter content of the soil which can improve soil structure and water infiltration. However, manure is quickly decomposed under warm, moist soil conditions. With the manure rates used for most crops, organic matter content in soil is only temporarily increased.

Possible Disadvantages

Weed seeds are common in some manure. They may enter the animal with its feed and then pass through the digestive tract, still viable, or they may have come with the litter, or they may have simply blown into the feed yard.

Poultry droppings typically have fewer weed seeds surviving the digestive processes. However, other animal manure may contain numerous viable weed seeds if the original feeds were contaminated. Composting and stockpiling manure can reduce the number of viable weed seeds.

Manure commonly contain 4 to 5% soluble salts (dry weight basis) and may run as high as 10%. To illustrate, an application of 5 tons of manure containing 5% salt would add 500 lbs. of salt.

Normally, irrigation and rain water will sufficiently leach well-drained soils to prevent damaging salt accumulations. However, one should be cautious with poorly drained soils, soils with existing salinity problems, or unusually high application rates, especially when concentrated near young plants.

Zinc deficiency can be induced or increased with repeated high rates of manure, especially on sandy soils.

Moderate or infrequent applications do not normally present a zinc problem. However, growers should be aware of the potential problem, especially with soils and varieties or crops of known susceptibility to zinc deficiency.

Summary

The principal value of manure is its extended availability of nitrogen and its ability to improve soil fertility in cut areas from land leveling.

Nutrient content and rate of availability varies widely, depending mostly on manure source, handling methods, and water content. Fresh manure which includes both liquid and solid fractions will retain the most nitrogen when work in immediately after spreading. A laboratory analysis of the manure for nitrogen content is useful. An accurate sample of the manure requires a composite of many samples throughout the pile or lagoon.

Generally, poultry manure is highest in nitrogen content, followed by hog, steer, sheep, dairy, and horse manure. Feedlot, steer manure requires fairly high rates to meet first-year nitrogen requirements because of its lower nitrogen percent and gradual nitrogen release characteristics.

However, this feature provides for more continued nitrogen availability in succeeding years, allowing for progressively lower annual application rates to meet plant requirements.

Faster nitrogen-release sources, such as poultry manure, require more constant and lower annual rates to maintain nitrogen availability.

The possible advantages of organic matter content and disadvantages of weed seed and salt content should be considered in using manure.