Ahb 506 - Animal Waste Production and Management Week – 8 – Land application of Manure

Land application of animal manure is an efficient utilization alternative because of usually lower costs compared to treatment and the nutrient benefits derived by crops from the manure. Manure nutrients help build and maintain soil fertility. Manure can also improve soil tilth, increase water-holding capacity, lessen wind and water erosion, improve aeration, and promote beneficial organisms.

There are two principal objectives in applying animal manure to land: 1) ensuring maximum utilization of the manure nutrients by crops; 2) minimizing water pollution hazard.

There are two of the most common land- application methods. Surface spreading and subsurface injection

Surface spreading and subsurface injection are two of the most common land-application methods. Several guidelines should be followed to achieve maximum nutrient use with minimal environmental hazard: Test soil to establish existing soil-fertility levels. Test manure and wastewater to determine nutrient content. Select an application rate that does not exceed crop nutrient requirements and avoids soil contamination, crop damage, and runoff and contaminated tile flow. Check soil moisture before applying liquid wastes, and adjust application rates to avoid runoff. Estimate soil moisture based on soil feel and appearance. " Limit the volume of water applied to an amount that brings the soil to field moisture capacity. Calibrate application equipment to obtain the desired application rate. Incorporate raw or untreated manure to reduce odors and nitrogen losses.

Techniques in Manure Application Restrict manure spreading on the land to the growing season of the crop, do not apply manure on the land when there is no crop. Balance the quantity of manure with the nutrient requirements of the crop. The quantity of manure which can be applied per ha depends on the soil type and should be limited to not more than the equivalent of 150 kg N per hectare. Evaporation of ammonia and greenhouse gases will be reduced when manure is not or only for a short time exposed to fresh air. The manure should be covered with soil (e.g. by harrowing) immediately after spreading or should be injected into the soil directly.

Manure application techniques to reduce the emissions of ammonia include machinery for decreasing the surface area of slurries and burying slurry or solid manure through incorporation into the soil. The techniques included are: 1. Band-spreading. 2. Trailing shoe or ‘sleigh-foot’ machines. 3. Injection - open slot. 4. Injection - closed slot. 5. Incorporation of surface applied manure and/or slurry into soil.

Band-spreading.  Band-spreaders discharge slurry at or just above ground level through a series of hanging or trailing pipes. The width is typically 12 m with about 30 cm between bands. The technique is applicable to grass and arable land e.g. for applying slurry between rows of growing crops. Because of the width of the machine, the technique is not suitable for small, irregularly shaped fields or steeply sloping land. The hoses may also become clogged if the straw content of the slurry is too high.

Trailing shoe. This technique is mainly applicable to grassland Trailing shoe.  This technique is mainly applicable to grassland. Grass leaves and stems are parted by trailing a narrow shoe or foot over the soil surface and slurry is placed in narrow bands on the soil surface at 20 - 30 cm spacings. The slurry bands should be covered by the grass canopy so the grass height should be a minimum of 8 cm. The machines are available in a range of widths up to 7 - 8 m. Applicability is limited by size, shape and slope of the field and by the presence of stones on the soil surface.

Injection - open slot. This technique is mainly for use on grassland Injection - open slot.  This technique is mainly for use on grassland. Different shaped knives or disc coulters are used to cut vertical slots in the soil up to 5 - 6 cm deep into which slurry is placed. Spacing between slots is typically 20 - 40 cm and working width 6m. Application rate must be adjusted so that excessive amounts of slurry do not spill out of the open slots onto the surface. The technique is not applicable on very stony soil nor on very shallow or compacted soils where is impossible to achieve uniform penetration of the knives or disc coulters to the required working depth.

Injection - closed slot Injection - closed slot.  This technique can be shallow (5 - 10 cm depth) or deep (15 - 20 cm). Slurry is fully covered after injection by closing the slots with press wheels or rollers fitted behind the injection tines. Shallow closed-slot injection is more efficient than open-slot in decreasing ammonia emission. To obtain this added benefit, soil type and conditions must allow effective closure of the slot. The technique is, therefore, less widely applicable than open-slot injection. Deep injectors usually comprise a series of tines fitted with lateral wings or ‘goose feet’ to aid lateral dispersion of slurry in the soil so that relatively high application rates can be achieved. Tine spacing is typically 25 -50 cm and working width 2 - 3 m. Although ammonia abatement efficiency is high, the applicability of the technique is severely limited. The use of deep injection is restricted mainly to arable land because mechanical damage may decrease herbage yields on grassland. Other limitations include soil depth and clay and stone content, slope and a high draught force requiring a large tractor. There is also a greater risk of nitrogen losses as nitrous oxide and nitrates, in some circumstances.

Incorporation.  Incorporating manure spread on the surface by ploughing is an efficient means of decreasing ammonia emissions. The manure must be completely buried under the soil to achieve the efficiencies. Lower efficiencies are obtained with other types of cultivation machinery. Ploughing is mainly applicable to solid manures on arable soils. The technique may also be used for slurries where injection techniques are not possible or unavailable. Similarly, it is applicable to grassland when changing to arable land (e.g. in a rotation) or when reseeding. Ammonia loss is rapid following spreading manures on the surface so greater reductions in emissions are achieved when incorporation takes place immediately after spreading. This requires that a second tractor be used for the incorporation machinery which must follow close behind the manure spreader. A more practical option might be incorporation within the same working day as spreading the manure, but this is less efficient in reducing emissions.

Factors Controlling Application Rate The factors that most often limit the amount of manure that should be applied to cropland are: existing soil-fertility levels, manure nutrient content, crop nutrient needs, site limitations, slope, runoff potential, and leaching potential.

Factors Controlling Application Rate Nitrogen and/or phosphorus is usually the limiting nutrient for manure application. All manure contains measurable amounts of both. Applying levels that exceed crop nutrient requirements may lead to nutrients entering surface waters or leaching into ground water.

The amount of nutrients available in raw manure varies with the type and size of animal. The nutrient composition of waste is affected by housing and the waste-handling system. Bedding and additional water can dilute manure, resulting in less nutrient value per pound. Nutrient losses from storage and handling reduce the amount of nutrient available for land application. Phosphorus and potassium losses are usually negligible, but nitrogen losses can be significant. Table 1 provide average nutrient values.

TABLE 1. Annual Raw Manure Production per 1,000 lb Animal Weight. Animal Type Manure Tons/yr Prod Gal/yr Percent Solids Nutrient Content N P2O5 K2O (lb/ton) (lb/1,000 gal) Dairy 15.0 3614 12.7 10.0 4.1 7.9 41.5 17.0 32.8 Beef 11.0 2738 11.6 11.3 8.4 9.5 45.4 33.7 38.2 Veal 11.5 8.7 2.1 9.0 36.5 8.8 37.8 Swine   Growing pig 11.9 3008 9.2 13.8 10.8 54.6 42.7 Mature hog 5.9 1425 13.9 57.5 44.7 Sow & litter 15.9 3894 14.2 10.7 11.1 58.0 43.7 45.3 Sheep 7.3 1679 25.0 22.5 7.6 19.5 97.8 33.0 83.5 Goat 7.0 1789 31.7 22.0 5.4 15.1 86.1 21.1 59.1 Poultry Layers 9.7 2464 27.3 23.5 13.2 107.5 92.5 52.0 Broilers 13.1 3285 33.4 16.7 12.5 133.2 66.6 49.8 Turkey 2044 23.7 20.8 16.9 97.4 85.5 69.5 Horse 8.2 2048 21.0 12.1 4.6 48.4 18.4 36.0

TABLE 2. Nitrogen Losses During Storage and Handling (a) System % Nitrogen Lost Solid   Dairy scrape and haul 15-35 Manure pack 20-40 Open lot 40-60 Deep pit (poultry) Liquid Below-ground storage tank 15-30 Above-ground storage tank 10-30 Earth storage Anaerobic lagoon 70-80 (a) Typical losses due to storage and handling between excretion and land application. Values adjusted for dilution. These values are in addition to any losses that occur during land application.

Recommended Maximum Manure Application Rates at Different Soil Test Levels. Level ppm (lb/Acre) Surface Applied on High Runoff Potential Sites (2) Incorporated or Low Runoff Potential Sites (3) 0-30 (0-60) N needs of non-legume crops N removal rate of legume crops 30-1254 (60-250) N needs or P removal rate for non-legume crops, whichever is less N or P removal rate for legume crops, whichever is less N needs of non-legume crops N removal rate for legume crops 125-1504 (250-300) Manure application for crop production purposes not recommended >1504 (300) Application of manure crop production purposes not recommended. If application is necessary, apply no more manure than supplies N or P removal for the next crop, whichever is less. A site plan which controls erosion and runoff is recommended. (1) Surface Application is any application at a depth which would be disturbed by tillage within the next three years. High runoff potential refers to sites where surface movements of manure and/or phosphorus are likely to occur from the field of application. (2) Incorporation is any application at a depth which would NOT be disturbed by tillage within the next three years. Low runoff potential refers to sites where surface movement of manure and/or phosphorus from the field of application is not likely to occur under normal weather conditions. (3) Yearly plant tissue and soil analysis recommended.

Adding high levels of manure may increase salts in soils and reduce plant stands. When manure is applied to a field, annual soil tests are strongly recommended to more accurately monitor soil nutrient levels and determine appropriate manure application rates. Manure applications should not provide more available nitrogen (N) than what is needed by the succeeding crop. The determination of total available nitrogen should include credits for any contributions of the present or preceding crop, any nitrogen fertilizer added, and available nitrogen provided by previous manure applications.

Factors Affecting Runoff Potential Naturally occurring factors that affect runoff potential include: 1. Location of receiving stream. Runoff to streams is much more likely when the field selected for manure application is bordered by a stream or other surface water rather than separated from surface water by another field, pasture, wooded area, or other suitable buffer strip. 2. Slope steepness and complexity. Runoff is more likely from fields sloping steeply and evenly toward a stream than fields with a gentle or no slope. Fields with depressional areas between the area of manure application and the stream have a lower potential for stream contamination. 3. Soil and weather conditions. Runoff is more likely when applied on saturated, or compacted soils, especially during months when rainfall exceeds evapotranspiration. 4. Soil type. Soils with low infiltration rates and/or soils with limited water-holding capacity are more likely to promote runoff than soil types that absorb and retain large quantities of water.