TSSH Part 624
Developing Comprehensive Nutrient Management Plans
The role of the resource soil scientist in developing comprehensive nutrient management plans (624.00)
Resource soil scientists are uniquely qualified to assist conservation planners and engineers in the design of animal waste application rates. While application rates are specified in tables in the NRCS Agricultural Waste Management Field Handbook, obtaining accurate data, sampled properly from representative locations, can maximize the impacts of implementing a comprehensive nutrient management plan (CNMP). An understanding of nutrient forms and soil and effluent/manure test methods and results requires a knowledge of chemistry, microbiology, soil fertility, and soil chemistry and is important for making the most accurate recommendations. An understanding of soil conditions at the site can facilitate the detection of undesirable conditions that might occur in areas of a minor component within an otherwise suitable map unit.
The National Planning Procedures Handbook, Subpart B, Parts 600.50-54, “Comprehensive Nutrient Management Planning Technical Guidance,” provides considerations for CNMP. The degree to which each CNMP element is addressed is determined by the General Criteria (Section 600.53).
Sampling waste lagoons and manure (624.01)
In order to determine the most accurate assessment of nutrient concentrations, it must be known whether effluent is to be applied after treatment in a lagoon, at what depth the effluent will be extracted from the lagoon (pump intake depth), the method of application, and to what vegetation or land use the effluent will be applied.
If solids are to be applied, it must be recognized that solids from the bottom of the lagoon have very different forms and concentrations of nitrogen and phosphorus than solids from the solids separator. Have the solids subsequently been or are they to be composted? Was the stockpiling an aerobic composting or in an anaerobic mound where the surface has crusted over?
Timing and location of solids and effluent sampling are important because of the dynamic and volatile nature of nitrogen. If solids are to be applied, analysis of nitrogen can be performed as total nitrogen, but nitrate N would not be included in total N. Nitrate N is normally a low proportion of total N and can be ignored in manure analysis. Some N will be in the ammonium form and may be converted readily to ammonia and lost from manure composting. This process is continuous, and so the sampling N data should be as close to the time of application as possible. Samples should not be taken from the surface of the compost pile but rather should be taken from a representative depth in three or four locations; they should be mixed, and a subsample should be bagged for analysis. Preferably, this sample should be frozen with dry ice in the field. Alternatively, chilling the sample on ice in an ice chest and then freezing it upon arrival back in the office is acceptable. If a sample is mailed to a lab, it should be packed in dry ice. If the sample is to be hand delivered to the lab, placing a frozen sample in an ice chest with ice is acceptable. Make sure the lab freezes the sample immediately.
If fresh solids are to be composted, wait until the compost is nearly ready for field application before sampling. Take into account the turnaround time for the lab analysis.
If the “compost pile” is not managed (turned regularly), there is actually an anaerobic digestion process occurring.
Effluent should be sampled from the discharge end of the lagoon at the depth of the intake pipe to the pump that will deliver the effluent to the irrigation system. Sampling should never be from the inlet side where material is entering the lagoon from the animal waste source. In many lagoons, the effluent has been in storage for some months or even longer. Solids (that passed the solids separator) have long since decomposed or become a surface mat or have sunk to the bottom. Much of the solution N will be in the ammonium form if the lagoon is not vigorously aerated. Analysis requested should be for total N, which will include organic and ammonium N. Again, freezing of the sample is critical if accurate results are to be achieved. Three replicates are recommended. These should be in separate containers, unmixed. Take care not to agitate the sample; any agitation introduces air to the sample and encourages ammonia losses.
Soil sampling: In well drained fields, total and nitrate N should be analyzed. Freezing is not as important as it is with effluent and manure since the ammonium content is relatively small because it is continuously being converted to nitrate. However, it is highly recommended that the sample be kept chilled and be delivered to the lab as soon as possible. Are the soils uniform in terms of nutrient status, or should they be sampled separately?
Sample contrasting areas separately. Sampling the upper 20 cm may be suitable for nitrogen analysis or for both N and P in tilled fields, but fields with perennial grass cover should be sampled from 0 to 5 cm to capture the zone of greatest P concentration. Another sample taken from the 5-to-20-cm zone is required. Homogeneous fields can be subsampled and mixed, but submitting three or four separate noncombined samples can provide information on field variability.
In arid areas and for fields that have had effluent or manure applied for several years, soil analysis should include salts (EC) and exchangeable sodium (ESP). Also request analyses for arsenic, selenium, cadmium, molybdenum, and zinc. NRCS Agricultural Waste Management Field Handbook, Sections 651.1103 and 651.0604(b), deal with the salt content of agricultural waste. USEP A Title 40 Part 503, Standards for the Use or Disposal of Sewage Sludge, Section 503.13, contains pollutant limits for biosolids heavy metal content and cumulative loading rates but does not address resident levels of metals in the soil. NRCS Agricultural Waste Management Field Handbook, Sections 651.0603(g) and 651.0605(a and b), deal with the heavy metal content of agricultural waste.
Soil suitability: After downloading soil interpretive ratings for onsite waste disposal for the field(s), an onsite investigation may be needed noting soil depth, texture, depth to water table, drainage class, slope, estimated or measured infiltration rate, compaction, leaching and runoff potential, presence of carbonates, and pH. Generate N and P Index ratings and verify that the soils are as mapped. In some areas, salinity, sodicity, or acidity also may be of concern.
If adverse conditions exist, plants growing on the site may be impaired and less able to remove nutrients from the site or provide optimum forage biomass. This information should be included in the customer’s plan folder and a copy provided to the State Soil Scientist or MLRA SSO Leader as appropriate.
Soils have such a wide ability to sorb P that, for a given available P level per a given extraction method, a newly farmed sandy soil might require 20-40 pounds/Ac P2O5, a clayey soil 60-80 pounds, a clayey oxidic soil 200-400 pounds, and a fine, weathered Andisol 1000+ pounds to provide enough P in solution for plant growth. Soils that have had P fertilizers applied for several years may have had any P fixation capacity satisfied, and application rates can be greatly reduced. Many fields that have a long history of fertilization have high or very high available P levels and can accept no further P applications safely. Local university and other testing labs have P release curves for the local soils, which are used to make P application recommendations. When soil samples are submitted for testing for N and P, it is important to note the soil phase and crop and yield expectation on the submission form.
Applying effluent when soil moisture is low can maximize infiltration and the sequestering of nutrients within the soil. The resource soil scientist can assess soil moisture immediately prior to the planned application and advise accordingly regarding the timing of the application.
The resource soil scientist can assist the conservation planner and engineer in developing a nutrient budget for nitrogen, phosphorus, and potassium that includes all potential sources of nutrients.
Air quality issues: These include ammonia (NH3) odors, aerial N enrichment to water bodies, and NOx evolution. Odors and N drift are addressed in practice standards. Ammonia loss is well known to occur from dry soils and leaves of vegetation, such as in a pasture situation. Ammonia losses can be large in dry, windy areas; this issue is addressed in the engineering guides. Also, effluent and manure applications contain significant amounts of N as ammonium. Sprinkler gun applications volatilize a significant amount of ammonium. If the surface soil contains free carbonates, ammonium is readily converted to ammonia gas and is volatilized even in moist soils. If N fertilization is a goal of the waste application, subsequent soil testing may be needed to ensure adequate N supply.
NOx evolution can readily occur if applied effluent or manure contains nitrates and the soil is saturated or nearly so as a result of denitrification. Mainly, ammonium that is nitrified in a well drained soil will denitrify if the soil remains saturated for any reason for as little as a day in warm conditions. NOx is approximately 310 times more effective as a greenhouse gas than CO2 and, wherever possible, should not be allowed to form. If the pasture is grazed when too moist and compacted, an otherwise well drained surface layer may easily become anaerobic.
For additional information, refer to the NRCS Nutrient Management Planning Web site.