Nutrient Management Strategies
Nutrient Management Strategies
J. M. HART, E. S. MARX, N. W. CHRISTENSEN,
and J. A. MOORE
Department of Crop and Soil Science,
Oregon State University,
3017 Agricultural and Life Sciences Building,
Corvallis 97331-7306
ABSTRACT
Large dairies on relatively small land bases are rich in nutrients, which sometimes accumulate in excess of crop use. Twenty-six silage corn fields in the Willamette Valley, Oregon were sampled over a 2-yr period. Soils at approximately 40% of the sites contained NO3 N in excess of crop need. Excess amounts of P and K were measured from the same fields. Unused plant nutrients can be potential pollutants or animal health risks.
Nutrient accumulation on dairy farms can be reduced by eliminating or reducing commercial fertilizer and reducing the net accumulation of on-farm nutrients from purchased feed. Each dairy should produce as much of its feed as possible to reduce the importation of nutrients in feed and the cost of purchased feed. Dairy producers must match plant nutrient need and uptake with crop growth and distribute nutrients on land as needed. A program of monitoring nutrient need and sufficiency through analysis of manure, soil, and plant tissue allows nutrient distribution to be matched to crop need. ( Key words: nutrient loading, soil testing, soil nitrate nitrogen, monitoring system)
Abbreviation key: PSNT = pre-sidedress soil nitrate test.
INTRODUCTION
In the five decades since the end of World War II, agricultural production in the US has become specialized. One result of specialization is large livestock units on a small land base. In addition, the production of feed grain and animals is concentrated in disparate areas. One factor that has allowed the segregation of production to occur has been an inexpensive and reliable source of commercial N fertilizer (6).
Commercial fertilizer, primarily N, is fixed ortransformed from atmospheric N2 gas to a form thatis available to plants via the Haber-Bosch process(10). Nitrogen is the nutrient that is most likely tolimit feed grain production. When an alternative Nsupply was made available, feed grain productioncould be uncoupled from the traditional N source,animal manure, but this specialized production concentratednutrients on animal production sites withno mechanism for the return of the unused nutrientsin manure to the site of feed grain production (6).
The central components of Figure 1 illustrate thesituation before World War II. A cow consumedforage, utilized some of the nutrients in forages, andexcreted the remaining nutrients in manure. The manurewas applied to the soil, which in turn producedadditional forage. Small amounts of nutrients left thefarm in milk and meat. After the introduction ofcommercial fertilizers, additional nutrients were utilizedin production on the dairy and brought to thefarm as feed. As more nutrients were added, the soilacted as a buffer, holding the nutrients in place. Onmany dairies, enough nutrients have been added sothat the soil can no longer hold them.
Examples of N, P, and K loading from dairies inwestern Oregon are shown in Figures 2 to 4 (8).Figure 2 compares soil NO3 N in fields from a smalldairy (800 cows). In addition, the smalldairy used a clear water source for irrigation, and thelarge dairy used a wastewater lagoon as an irrigationwater source. The soil profile from both dairies containedapproximately the same amount of NO3 N atplanting. The primary difference between the twosites is the amount of N remaining at the end of thegrowing season. After harvest, the soil profile at thesmall dairy contained 193 kg/ha (172 lb/a) NO3 N,which is approximately 65 kg/ha (60 lb/a) less thanat planting, compared with approximately 400 kg/ha(350 lb/a) more at harvest than at planting for thelarge dairy. Approximately 40% of 26 fields sampledover a 2-yr period contained similar amounts of NO3 N in their profile as the large dairy used in thisexample (8).
At planting, the soil profile from the large dairyshows an increase in NO3 N concentration beginningat 90 cm (3 ft). Lower NO3 N concentrations in thesurface 60 cm of soil are most likely from leaching of NO3 N from the surface to <90 cm (3 ft) in the soilprofile during rainy winter months. Christensen andBrett (1), and Kjelgren ( 5 ) showed that the N from aspring fertilizer application that remained in the soilprofile at the end of the summer growing season waslost by January or February and presumed to accumulatein groundwater.
The accumulation of extractable P as a result ofcontinual application of manure and commercial fertilizeris illustrated in Figure 3. Two adjacent fields ofthe same soil type are compared. Extractable P concentrationsare higher in the surface 30 cm (12 in)than the remainder of the soil profile, indicating littlemobility for P in soil. Subsurface concentrations of Pare similar in both fields, which provides additionalevidence that P has not moved appreciably in thissoil. The comparable amounts of P measured at plantingand harvest indicate that the application rate isthe same or greater than crop utilization or that thesoil-buffering capacity produces an equilibrium betweencrop use and P application. Lower utilization ofP by crops than the application rate is another reasonthat the surface P concentration in a field spread withmanure is more than three times the P concentrationin a field without manure. Most dairy producers andagronomists have been applying manure to meet cropN demands. In doing so with dry stacked manure, anequal amount of N and P2O5 are applied. Corn silagewill use most of the N but only < 25% of the applied P.The high concentration of extractable P in the surfaceof the soil is an indication of an excess application ofmanure for many years.
Figure 1. Nutrient flow, cycling, and sources on dairies after World War II.
Soil profile K characteristics, which are similar to those for P, of the same two fields are presented in Figure 4. Surface soil concentrations of K are higher than subsurface measurements. Subsurface K concentrations are similar <90 cm (3 ft). The amount of K in the soil at planting and at harvest is the same, and the field that was spread with manure contains 10-fold the K in the surface as does the field on which no manure was spread.
The accumulated nutrients have economic and environmental implications. The excess nutrients in the soils that have been spread with manure can be discharged into the environment as pollutants or cycled through forage at elevated concentrations. Elevated amounts of each nutrient pose different risks. Examples of concern about elevated nutrient concentrations in groundwater, surface water, and animal nutrition follow.
The standards of the Environmental Protection Agency (14) require nitrate concentrations in drinking water to be < 10 mg of NO3 N/L. Drinking water containing NO3 in excess of this amount is associated with methemoglobinemia, a restriction of oxygen renewal in the bloodstream. Infants are especially sensitive to NO3 in drinking water, which causes “blue baby syndrome” (2). The Oregon Department of Environmental Quality rates agricultural activities fourth in a ranking of 12 major sources of groundwater contamination. Nitrate N and some pesticides are the potential agricultural contaminants of greatest concern (11).
Phosphate contamination of surface water is a problem in areas where a large livestock population is located. Phosphates move to surface waters by overland flow and erosion. The P concentration in surface water is one of two nutrients controlling growth of freshwater phytoplankton and is often considered to be the leading indicator of water quality in regard to eutrophication (13).
In contrast to NO3 and PO4, K poses little or no contamination threat to ground and surface water but presents the dairy producer with a concern. Animal nutritionists recommend that dietary K not exceed 3% of a dairy cow ration. Dry cows are especially susceptible to problems induced by excessive K, which include milk fever, hypocalcemia, downer cow syndrome, and, in severe cases, death. Hypocalcemia affects the smooth muscle contraction of the rumen, abomasum, and uterus, increasing the risk of retained placenta and displaced abomasum (17). Perennial grasses accumulate K in excess of growth requirements, especially on soil to which manure has been added. Adequately fertilized orchardgrass forage consumed by animals on pasture or as silage rarely contains < 2.5% K and generally contains ?3% K (4). In an effort to utilize the maximum amounts of manure N from large herds on an inadequate land area, dairy producers grow perennial grasses and fertilize with 560 to 675 kg of N/ha per yr (500 to 600 lb N/a per yr). Manure from a reception tank or storage lagoon contains equal amounts of N and K. Less than one-half of the K is needed by the plant for growth, but excess K is taken up, producing high K forage. An increase in forage K concentrations was documented in British Columbia where grass forage K increased from 2.7% in 1983 to 3.6% in 1992 (12).
Excess nutrients and the continued increase in nutrient concentration in soil and plants can be reduced by planning nutrient flow and crop utilization, monitoring nutrient flow on a dairy, and reducing nutrient inputs.
TABLE 1. Nutrient content of dry matter for selected forages.
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MANAGEMENT THEORY
Plan
Feed and forage needs should be planned for the next 5 to 10 yr, and needs should be examined to determine whether feed can be produced on the farm to replace purchased feed. A plan should be developed for each field that maximizes the use of nutrients in manure while producing feed for the dairy. The goal is to reduce nutrient input from sources off the farm such as commercial fertilizer and purchased feed while distributing manure based on crop requirements. Each field should have a nutrient management plan through several rotations that can be adjusted using soil test results. The goal should be to match manure nutrients with crop need. Manure storage needs should be computed based on nutrient needs and appropriate timing of manure applications.
Matching manure application to cropping conditions requires an understanding of nutrient removal by crops. Table 1 shows that the relative amounts of N and K are approximately equal in the three forages listed, but the amount of N removed per ton of dry matter in silage corn is approximately half the amount of N contained in alfalfa or orchardgrass chopped for silage. In the Pacific Northwest, where 18 to 22 Mg/ha (8 to 10 t/a) of dry matter from grass can be produced annually, substantially more N can be removed with grass than in a silage corn crop of 16 Mg/ha (7 t/a) of dry matter [67 Mg/ha (30 t/a)].
Fields with a history of manure application typically have high soil test P and K. These fields could be planted to alfalfa to use the P and K. No manure would be needed because alfalfa will fix N. Soil test K can be lowered by several years of alfalfa production, but the same cropping plan would not be expected to have a measurable impact on soil test P.
Matching crop need and manure application is termed application at an agronomic rate. Agronomic rates are amounts of a nutrient that produce optimum growth or yield without detrimental economic or environmental consequences. An agronomic nutrient rate is a combination of soil science, plant growth, philosophy, and politics.
One approach to determining the agronomic rate is to apply the amount of nutrient that has been removed by a crop. This approach assumes that the soil does not supply nutrients to the crop and that 100% of the added material is taken up by the crop. Neither assumption is valid. The soil can supply a range of nutrients, from very little to the entire amount needed by a crop. Plant absorption of added nutrients under the best of growing conditions may be as low as 5 to 20% for P and as much as 50 to 60% for N.
Most agronomists contend that manure or commercial fertilizer applications are site specific. Recommendations for manure or any nutrient application are based on general guidelines. A nutrient application from manure or commercial fertilizer, based on the general guidelines, is an appropriate starting point. After the application of commercial fertilizer or manure, soil and tissue levels should be monitored to determine whether an appropriate amount of nutrients has been applied.
In contrast, water quality regulators from state and federal agencies would like a plan that would fit all situations and does not vary yearly.
Monitor
Soil should be monitored in relation to manure nutrient content, forage nutrient content, and end of season corn stalk and soil NO3 N. Manure application rates should be altered, or distribution of your manure nutrient should be revised, based on results of nutrient monitoring. The manure application rate can be reduced by increasing the farm acreage base or by hauling manure to neighboring land. Standard soil tests for pH, P, and K should be used.
Soil testing differs from mineral nutrient analyses of animal feeds, expressed on a total elemental basis. In contrast, P and K analyses of soil samples extract a portion of each nutrient that is correlated with plant growth. A parallel analysis performed by animal scientists is analysis of feed for digestible nutrients or a fraction of the feed instead of a total carbohydrate analysis.
Soil test results are generally expressed in parts per million of extractable PO4 or K and can be considered an index of nutrient availability. For example, a P soil test of 100 ppm is considered to be very high and indicates that no fertilizer P is needed. Simple conversion of the soil test for P to a rate (pounds per acre) is not an appropriate method for making a fertilizer recommendation because soil test P is correlated with plant growth rather than being a measure of P amount in the soil.
Fertilizer concentration of P and K are traditionally expressed as P2O5 or K2O. A fertilizer with a grade of 10-20-5 contains 10% N, 20% P2O5, and 5% K2O. Local extension offices provide information on analyses and interpretation of a standard soil test.
Reduce
Excess nutrients added to cropland should be reduced by reducing or eliminating the purchase and use of commercial fertilizer, which will reduce nutrient loading and save money. For example, amounts and nutrient contents of manure produced by a cow vary. For our purposes, a high figure will be used to ensure that sufficient manure storage and land are available for manure application. Following this logic, each year a 640-kg (1400-lb) lactating cow producing 32 kg (70 lb) of milk/d excretes the following nutrients in manure: 110 to 135 kg (250 to 300 lb) of N, 20 kg (45 lb) of P, and 75 kg (165 lb) of K (15). The manure from one cow is sufficient to supply all of the N needed for 0.6 ha (1.5 a) of silage corn or 0.25 ha (0.66 a) of grass forage cut five to six times. Using the nutrient excretion information for a cow, a ratio of 3.75 to 5 cows/ha (1.5 to 2.0 cows/a) provides a sufficient amount of nutrients to grow most crops with no addition of commercial fertilizer. If the dairy producer has sufficient amounts of nutrients in manure and is purchasing commercial fertilizer, use of manure only would result in a savings of $150 to $250/ha ($60 to $100/a) for the production of corn for silage.
IMPLEMENTATION
The remainder of this paper presents methods for monitoring N on dairies with the production goal of agronomic, environmental, and economic crops. The examples used monitor N in corn production for silage.
Nutrient management can be addressed by answering three questions:
Application Rate
To determine how much N should be applied, the N requirement of the corn plant and the N that is available for those needs must be determined. A 65-Mg/ha (30-t/a) silage crop requires approximately 220 kg/ha (195 lb/a) of N (8). When corn is at the five- to six-leaf stage and is 30 cm (12 in) tall, the crop has taken up approximately 5% of the total requirement, or 11 kg/ha (10 lb/a) of N. From the sixleaf stage until silking, about two-thirds of the total N is taken up by the corn plant. This period is characterized by rapid growth and N demand (Figure 5a).
An adequate supply of N from the soil after the sixleaf stage is critical for optimal yield of silage corn. The interpretation of available soil N, primarily as NO3 N, has been relatively unsuccessful in humid climates until the last decade. The reason for the inability of soil tests to predict N availability in humid climates is illustrated in Figure 5b. Nitrogen mineralization, the conversion of organic to available inorganic N, is a biological process governed by organic N supply, temperature, soil pH, and soil moisture. Mineralization proceeds at various rates, some of which supply sufficient N for the crop (Figure 5b, A or B), or a rate (C) that is insufficient to meet crop demand. Soil sampling and analyses early in the season could not differentiate among the mineralization rates (Figure 5b), or adequately predict the amount or sufficiency of NO3 N for a corn crop.
Pre-sidedress soil nitrate test. Magdoff et al. ( 7 ) proposed an in-season soil test to solve this problem. The pre-sidedress soil nitrate test (PSNT) measures soil NO3 N when corn is 30 cm (12 in) tall. By the time corn is 30 cm tall or has five to six leaves, the soil should have warmed sufficiently to allow N mineralization to occur and a supply of NO3 N to accumulate in soils that have routinely received manure. The test is taken before the period of intensive N uptake by the crop and in time for supplemental N to be supplied if such supplementation is necessary.
TABLE 2. Suggested N fertilization rates for silage corn in western
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Oregon based on pre-sidedress soil nitrate test (PSNT) values.
The PSNT was not designed to answer the question of how much N to apply, but to determine whether the amount of N at the five- to six-leaf stage is sufficient; soils are sorted into two categories: responsive to additional N or not responsive. The point separating the two categories is termed the critical value. The PSNT critical value of 25 ppm of NO3 N in the surface 30 cm (12 inches) of soil when the corn is 30 cm (12 in) tall is a remarkably universal value. The critical values for PSNT in 17 eastern and midwestern states range from 19 to 30 ppm NO3 N; 10 states report a critical value of 25 ppm of NO3 N (16). Instructions for the PSNT follows:
If the NO3 N is ?20 to 25 ppm, no additional N from manure or commercial fertilizer is required. Many extension publications provide N recommendations based on PSNT values (Table 2) (9).
Time of Nutrient Application
As shown in Figure 5 and the preceding text, a minimal supply of N is needed before the corn reaches a height of 30 cm. The PSNT allows producers several options. Manure can be applied before planting, and N sufficiency can be measured with the PSNT. If additional N is needed, it can be applied as commercial fertilizer. In addition, producers who irrigate corn with wastewater from a storage lagoon can use the irrigation water as a supplemental N source. However, producers who choose to supply corn with N should apply N at or before the corn begins rapid growth and N uptake.
Source of Nutrients
Source of nutrients requires careful consideration; manure may or may not be the best choice. Nutrient content of manure varies with handling (Table 3). If a producer is concerned about P levels in soil, application of separated solids is preferred to a reception tank or storage pond wastewater.
Manure analysis for nutrient contents is necessary to allocate nutrients adequately in the manure to fields where they will be best utilized. A standard table of nutrient contents, such as Table 3, is useful when no manure analysis has been made, but use of this table should not replace on-farm manure analysis because manure nutrient content can vary greatly among dairies. The manure nutrient content of dairies in Willamette Valley in Oregon was relatively constant for individual dairies throughout the year but varied greatly among producers (3). Gangwer and Graham ( 3 ) attributed the difference among dairies to differences in rations, and those results suggest that manure samples should be taken whenever rations are changed.
Ensuring Sufficient Nutrients
Producers of all crops want to ensure that the crop is adequately supplied with nutrients. Dairy producers are no different, especially when faced with reducing inputs such as manure or commercial fertilizer. Two end-of-season tests can be used to ease concerns and to aid in planning for the next crop.
Corn stalk NO3 test. If excess N is supplied to a corn plant, accumulates in the lower portion of NO3 the stalk. The concentration of in the stalk can NO3 be used at harvest to evaluate N management.
TABLE 3. Typical nutrient composition of dairy manure in Pacific Northwest.1
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| Dry stack, | |||
| lb/t of wet manure | 10 | 4.0 | 13 |
| kg/tonne of wet manure | 4 | 1.5 | 5 |
| Separated solids | |||
| lb/t of wet solids | 5 | 1.0 | 2 |
| kg/tonne wet solids | 2 | 0.4 | 1 |
| Reception tank | |||
| lb/1000 gal | 20 | 3 | 16 |
| mg/L | 2400 | 48 | 240 |
| Storage pond, | |||
| lb/acre-inch | 135 | 13 | 120 |
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| 1. Sources of data: storage pond and separated solids, Willamette Valley, Oregon; dry stacks, Yakima area, Washington; and reception tank, Whatcom County, Washington. | |||
TABLE 4. Concentrations of NO3N in the corn stalk at harvest used to determine N supply during the growing season.
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| <3500 | The N may have limited yield |
| 3500-5000 | The N is sufficient for maximum yield |
| >5000 | The N supply is in excess of crop need1 |
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| 1. The NO3 N concentrations of >10,000 ppm in the corn stalk are an indication that silage should be analyzed for NO3 N concentration as a determination of feed suitability. | |
Ten to 15 stalks should be collected, cutting a 20-cm (8-in) section of stalk beginning just above the brace roots. The outer leaves should then be removed, and the stalk should be split lengthwise to aid in drying. Then the plant can be analyzed for NO3 N. Interpretation of stalk NO3 N concentration can be made using Table 4.
Report card soil test. After harvest, the soil in a corn field can be sampled in the same manner as described for the PSNT. If > 15 ppm NO3 N remain in the surface 30 cm (12 in) of soil, N was supplied in excess of crop need. The elevated residual NO3 N indicates that excess N was supplied to the corn crop early in the season, N was mineralized from manure late in the growing season, or manure was applied late in the season.
CONCLUSIONS
The cycle of nutrients through crop and livestock systems has been disrupted. Large dairies on relatively small land bases often accumulate nutrients in excess of crop use. Unused nutrients can be pollutants or animal health risks.
Nutrient accumulation can be reduced by eliminating or reducing commercial fertilizer and nutrient inputs from feed. The next step is to match nutrient need with crop growth and to distribute nutrients on land where they are needed. A program of monitoring nutrient need and sufficiency through manure, soil, and tissue testing is necessary.
Nutrients should be applied judiciously on cropland. No more nutrients should be applied than the crop will use and less than the crop will use if soil tests show that high amounts of nutrients are already present in the soil. Nitrogen should be applied to grain and silage corn only when the PSNT is < 25 ppm NO3 N. Future N applications should be reduced when the end of season silage corn stalk NO3 N concentration is >5000 ppm.
REFERENCES
1 Christensen, N. W., and M. A. Brett. 1988. Wheat yield and N uptake as influenced by treating crop residue with urea-sulfuric acid. J. Fert. Issues 5:50.
2 Fan, A. M., and V. E. Steinberg. 1996. Health implications of nitrate and nitrite in drinking water: an update on methemoglobinemia occurrence and reproductive and developmental toxicity. Regul. Toxicol. Pharmacol. 23(1, Part 1):35.
3 Gangwer, M., and M. Graham. 1995. Analysis of separated manure solids from selected manure separators in Willamette Valley, Oregon, dairy facilities. Oregon State Univ. Ext. Serv. Spec. Rep. 945, Oregon State Univ., Corvallis.
4 Hart, J. 1996. Soil and forage potassium—“How did it get so high?” Page 8 in Proc. Oregon State Univ. Dry Cow Management Workshop and Open House. Oregon State Univ., Dep. Anim. Sci., Corvallis.
5 Kjelgren, R. K. 1984. Fertilizer nitrogen use efficiency by winter wheat in the Willamette Valley. M. S. Thesis, Oregon State Univ., Corvallis.
6 Lanyon, L. E. 1995. Does nitrogen cycle?: Changes in the spatial dynamics of nitrogen with industrial nitrogen fixation. J. Prod. Agric. 8:70.
7 Magdoff, F. R., D. Ross, and J. Amadon. 1984. A soil test for nitrogen availability to corn. Soil Sci. Soc. Am. J. 48:1301.
8 Marx, E. S. 1995. Evaluation of soil and plant analyses as components of a nitrogen monitoring program for silage corn. M.S. Thesis, Oregon State Univ., Corvallis.
9 Marx, E. S., N. W. Christensen, J. Hart, M. Gangwer, C. G. Cogger, and A. I. Bary. 1996. The pre-sidedress soil nitrate test (PSNT) for western Oregon and western Washington. Ext. Serv. EM 8650. Oregon State Univ., Corvallis.
10 McVickar, M. H., W. P. Martin, I. E. Miles, and H. H. Tucker, ed. 1966. Symp. Proc.: Agricultural Anhydrous Ammonia— Technology and Use, St. Louis, MO. Agric. Ammonia Inst., Am. Soc. Agronomy, Soil Sci. Soc. Am., Madison, WI. 11 Oregon Department of Environmental Quality. 1992. Page 4 in Oregon’s 1992 Water Quality Assessment Report 305(b). Oregon Dep. Environ. Qual., Portland.
12 Schmidt, O. 1994. The news spreader. Dairy Producers’ Conserv. Group Newslett. 4:1.
13 Stewart, S. R., and G. F. Kling. 1991. Phosphorus loading of a western Oregon watershed. Page 37 in Proc. Forty-Second Annu. Reg. Fertilizer Conf., Coeur d’Alene, Idaho, July 7–9. Far West Fertilizer and Agrichemical Assoc. Spokane, WA.
14 United States Environmental Protection Agency. 1991. Drinking water regulations and health advisories. Office of Water, US Environ. Protection Agency, Washington, DC.
15 Van Horn, H. H., A. C. Wilkie, W. J. Powers, and R. A. Nordstedt. 1994. Components of dairy anure management systems. J. Dairy Sci. 77:2008.
16 Woodward, M. D., V. A. Bandel, and B. R. Bock. 1993. Soil nitrate tests for corn; 1993 state surveys. USDA Ext. Serv., Washington, DC.
17 Wustenberg, J., and B. Biedenbach. 1996. Forage sources used in dry cow rations. Page 4 in Proc. Oregon State Univ. Dry Cow Manage. Workshop Open House. Oregon State Univ., Dep. Anim. Sci., Corvallis.
Source: Oregon State University
Author: Hart, Marx, Christiansen