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NC State Soil Science: SSC 341, Soil Fertility and Fertilizers

Fundamentals of Nutrient Management: Organic Waste Utilization
Assignments
Reading: Chapter 10, pages 400-414
Homework: 51 Problems for entire chapter.
Notes

Topic Outline

1. Overview

2. Learning Objectives

3. Discussion

4. Summary

5. Homework




Organic Waste Utilization

RESIDUAL FERTILIZER AVAILABILITY
  • Because crops do not recover all the nutrients applied, a portion remains in the soil after harvest. The quantity remaining depends on application rate, yield (amount removed by the crop), proportion of crop harvested, and the soil.
  • Long-term residual N benefits (except in arid environments) are not as large as immobile nutrients (P and K). Residual availability of fertilizer N are related to buildup of soil OM with intensively managed cropping systems (Chapter 13). The residual availability of large P applications can be observed for many years, depending on P rate and the soil P fixation potential (text Figure 10-51). Residual S availability is demonstrated in text Figure 10-50.
  • As fertilizer rate increases, residual value increases. Although the cost of fertilization is usually charged to the treated crop, residual fertilizer availability should be included in evaluation of fertilizer economics.
UTILIZATION OF NUTRIENTS FROM THE SUBSOIL
  • Crop utilization of nutrients from the subsoil depends on many soil factors (soil structure, aeration, pH, drainage) that influence root distribution and nutrient availability.
  • Many humid-region subsoils are acidic and low in fertility, contributing little to nutrient availability (text Figure 10-52). Deep-rooted crops (alfalfa, sweet clover, etc.) contribute to higher surface soil available P by transfer from the subsoil as nutrient rich residues are decomposed. For example, the surface soils in forests are commonly higher in nutrients than subsoil because of upward nutrient transfer and accumulation.
  • Loess or alluvial soils can be high in K and P throughout the profile and can be utilized by deep-rooted plants. In these cases, correlating surface soil tests may not be as acurate if subsoil availability is ignored. When subsoil P or K the content is considered, the relation between extractable P or K and crop response is improved. Some states have established subsoil contribution to nutrient availability (text Figure 10-53), improving accuracy of fertilizer recommendations.
  • In calcareous soil, soil test K is usually high in both surface soil and subsoil, but most subsoils are low in plant available P. Subsoil pH is usually high, reducing micronutrients (Zn and Fe) availability. However, P and micronutrient fertilization of the surface soil is generally adequate to increase P and micronutrient availability.
  • Subsoil nutrient application can greatly enhance deep root development. Lime added to an acidic subsoil will not only supply Ca but also reduces Al and Mn toxicity.
  • Subsoiling alone may increase crop yields, although subsoil incorporation of fertilizers can further increase yields (text Table 10-13). Deep tillage (24 to 36 in.) without subsoil fertilization can improve root growth and crop yield by more efficient subsoil water use. Under some conditions, turning up heavy clay subsoil material may cause the surface soil to seal off more rapidly and decrease water intake. Deep tillage to break up plowpans and improved management practices to encourage deeper rooting and improve productivity.
FERTILIZATION WITH MANURE
  • Animal wastes are a valuable source of plant nutrients and OM. Manures have always been used in crop production systems; however, compared to fertilizer their use is still relatively small. Over the last decade manure use is increasing because:
    • increased use of large confined animal feeding operations
    • increased interest in organic production systems
  • Beneficial effects of manure use include:
    • Increased soil OM, moisture retention, and buffer capacity (BC)
    • Improved soil structure, with a corresponding increase in infiltration rate and a decrease in soil bulk density
    • Increased supply of NH4+
    • Greater movement and availability of P and micronutrients due to OM complexation
    • Complexation of Al3+ in acid soils
Animal Manure Composition (text Table 10-15)
  • Manure composition varies with:
    • animal type and age
    • feed type and composition
    • bedding type and composition
    • waste handling system
  • dry matter is highest in the solid wastes
  • N, P, and K are highest in liquid manure
Manure Handling Effects on Nutrient Composition (text Tables 10-15 & 10-16)
  • Historically, the common method of disposal was collection of manure with bedding and spread it on fields.
  • Newer liquid waste systems dilute waste with water by storage in open or closed pits or lagoons.
  • N losses during storage various greatly (15-80%) with storage system (text Tables 10-16 and 10-17)
  • P and K losses range from 5 to 15%, but are about 50% in open pit and lagoon systems because P and K settles out.
Waste Application Method
  • Four principal methods used for field application of manure are:
    • Field spreading of solid waste when weather, soil, and crop permit.
    • Injecting the slurry (water and manure) below soil surface or sprayed on soil surface.
    • Injection of slurry into a sprinkler irrigation system.
    • Surface band applied under crop canopy.
  • N loss is greatly affected by application method (text Table 10-17).
  • incorporation immediately after application will minimize NH3 volatilization.
  • N availability with injected liquid manure can be improved by adding nitrification inhibitors (maintaining NH4+ form longer).
  • In large animal feedlot operations, solid manure or lagoon effluent that is dried and bagged for horticultural is a valuable byproduct.
  • manure N availability depends on the length of time the material remains on the soil surface before incorporation (text Figure 10-54). Minimal N is available if waste is incorporated 5 to 8 days after application. Subsurface waste application maximizes manure N availability.
  • Nutrient management programs on large livestock farms include manure; however, soil fertility may still gradually decline in some nutrients.
  • Comparisons between manure and fertilizers on crop production have generally showed equal response behavior (text Figure 10-56).
  • Producers interested in manure as a nutrient source to crops should consider:
    • high transportation costs may encourage manure application close to the source, where overapplication may increase N and P loss to surface and groundwater.
    • nutrient content is highly variable, which makes it difficult to accurately supply required quantities for crop yield potential.
    • variability of manure N mineralization can limit available N at periods of high N demand.
    • Increased soil compaction can occur with manure application equipment.
    • Possible nutrient imbalances (e.g. S supplementation can be beneficial with lagoon-stored hog waste.

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APPLICATION OF SLUDGE AND SEWAGE EFFLUENT
  • Disposal of processed sewage from municipal treatment plants is increasingly important because of expanding human populations increasingly concentrated in urban and suburban communities.
  • Agricultural use of sludge has both benefits and problems.
    • Sludge is a source of OM containing macro and micronutrients
    • Agricultural use is a cost effective alternative to more costly burning or burying disposal methods.
    • Like animal waste, sludge contains inorganic and organic N (text Table 10-20).
    • NH3 volatilization losses of 20 to 50% can occur with surface application of sludge. Incorporation of sludge reduces N volatilization.
    • Variability in N mineralization rates (20 to 30% of total organic N) results in inaccurate estimates of sludge rates needed for crop N requirements. Generally, 20% of the organic N is mineralized in year of application, with about 3% of the remaining N mineralized in each of the next 2 years.
    • N and P added with a single sludge application can be as high as 800 Ib total N/acre (~50% as NH4+) and 1,000 lb P2O5/acre.
    • Additional fertilizer N and P on sludge-applied land is generally not required for at least 2 years following sludge application. However, imbalances of other nutrients may have to be corrected.
  • It is essential that appropriate application and soil management techniques be used to protect the environment and the health of humans and animals. Because of the possibility of applying excessive N and subsequent movement of N03 into surface and groundwater, careful monitoring is necessary.
  • Because of potential soil buildup of heavy metals (Cd, Hg, Zn, Co, Pb, Cu, etc.) from frequent sludge application, rate limits have been established by the EPA (text Table 10-23).
  • Continued sludge application on a site is determined by the cumulative addition of metals. Guidelines for heavy metals buildup are summarized in text Table 10.23.
  • On non-agricultural soils, higher heavy metal levels are permitted.
  • Soil testing and fertilizer recommendations are used in conjunction with sewage sludge characteristics to determine application rates. Annual sludge rates are based on either the lowest tonnage that will satisfy crop N requirements or the maximum quantity that can be used without exceeding permissible limits for Cd.
  • Some regulations limit sludge application to forages, oilseed crops, small grains, commercial sod, and trees. Sludge may not be used on edible root crops, vegetables and fruit, tobacco, and dairy pastures. Direct grazing of sludge-treated forage is not recommended for 3 years immediately following application.
  • Crop response to sewage sludge is at least equal to that of commercial fertilizer in the year of application, but may be greater in subsequent years because of residual nutrient availability.
  • Sewage effluent can be either a valuable water and nutrient resource for crops or a pollutant to land and waters. Large quantities of water are generally applied requiring internally well drained and medium textured soil, having a pH of between 6.5 and 8.2, and (2) be supporting a dense stand of trees, shrubs, or grasses. The groundwater should be monitored periodically for N03-.
  • Forage crops are commonly used for effluent application because of their long growing season and high evapotranspiration and nutrient uptake rates (text Table 10.24)
SUMMARY
  1. Plant growth is a function of time, genetic makeup of the plant, environmental, and management. The importance of selecting crops that are genetically capable of making maximum use of the supply of available plant nutrients was pointed out.
  2. Growth of annual plants follows a well-defined pattern. Plant responses to environmental conditions, including the supply of plant nutrients, also follow a set pattern. When growth is plotted as a function of increasing amounts of applied nutrients, successive increments of fertilizer give successively smaller increases in plant growth.
  3. Although nutrient uptake by crops cannot be used as an accurate guide for fertilizer recommendations, it does indicate differences among crops and provides insight into the rate at which the nutrient reserves in the soil are being depleted.
  4. Root development helps to indicate the most effective placement of fertilizer. For example, potato roots are much less extensive than corn roots; hence, potatoes can utilize nutrients closer to soil surface.
  5. Soil characteristics influence depth of rooting, and yields may be directly proportional to the water available to the roots.
  6. Proper fertilizer placement is important in efficient nutrient use, prevention of salt injury, enhancement of deeper rooting to compensate for dry conditions at the soil surface, and convenience to the growers.
  7. Movement of some fertilizer salts in soils is appreciable. Nitrates move most freely, but NH4+ is adsorbed by the soil colloids and moves very little until converted to NO3-. K is also adsorbed and moves little except in sandy soils. P movement is generally limited but can be appreciable on sandy irrigated soils, in the presence of large quantities of organic residues, and when heavy batch applications are made.
  8. More concentrated materials have a lower salt index per unit of plant nutrient and, when placed close to the roots, have less salt effect on young plants.
  9. Band application at planting is important for early seedling vigor. Under cool conditions, N, P, K, and Zn are generally less available to the young plants, and band placement will enhance their absorption.
  10. Broadcast application will provide large quantities of nutrients that cannot be conveniently preplant applied.
  11. With reduced tillage, nutrients tend to accumulate in the top 1 to 2 in. of soil. This may necessitate subsurface band applications or plowing every 4 or 5 years if conditions permit.
  12. Because of the limited mobility of P, it should be band applied near roots. Band applications are generally most efficient when soil test P is low and when low rates are applied. For high yields of many crops, however, it is essential to build up soil test P to critical levels or above.
  13. In no-till crop production where planting is done in killed sod or plant residues, surface applications of P and K are generally available to the crop in humid regions. The soil is moist under the residues, and the roots develop near the surface. If the soil is low in these elements, building the soil fertility of the plow layer is desirable before beginning no-till. In drier regions, surface applications may not be as effective due to lower soil moisture.
  14. Small amounts of N in the fertilizer at planting encourage absorption of P. Because N is mobile or becomes mobile after nitrification, application of the major portion before planting or side-dress applications after planting are both effective. In general, the nearer the time of application to peak N demand, the more efficient the utilization. The amount and distribution of rainfall must be considered.
  15. Leaching losses of K are insignificant except on sandy or organic soils under heavy rainfall. Hence band applications at planting and broadcast applications before planting or at some point in the rotation are effective. Starter responses from K similar to those from N and P are obtained on low K soils.
  16. In determining the method and time of application, convenience to the grower must be considered, along with efficiency and safety.
  17. Significant yield losses can occur when fertilizers are spread unevenly.
  18. As higher rates of fertilizer are used in conjunction with excellent management, more attention is given to fertilization for the entire rotation. Bulk applications of P and K may be used once or twice in a 4-year rotation in addition to starter applications at planting for the more responsive crops. N is applied annually to nonlegume crops.
  19. Year-round fertilization implies fertilization any time the soil, crop, or weather permits and is becoming a must with increased volumes of fertilizer declining transportation facilities, and the need to save labor. As soil fertility levels increase, the place and time of application of P and K decline in importance. The point is to apply adequate quantities for maximum profit.
  20. Application of nutrients for the most profitable yield will result in a portion remaining in the soil. In many cases, the cost of fertilization is charged to the crop treated. However, if a critical evaluation of fertilizer use is made, the carryover value must be considered.
  21. Subsoil fertilization promotes deeper rooting, greater root penetration, and more efficient use of water. Field results from fertilization with a subsoiler have been variable.
  22. With problems of soil fixation of nutrients, foliar fertilization may constitute the most effective application method, particularly for certain micronutrients.
  23. Fertigation, application of plant nutrients in irrigation water, is an effective method of applying N. Fertigation of other nutrients are not as common (P, S, K, Zn, and Fe).
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