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Nutrient management for water quality protection: Integrating research into environmental policy
~ Pergamon
War. Sci
T~ch.
Vol. 39, No. 12, pp. 291-298, 1999 <01999
Published by Elsevier Science Ud on behalf ofthe IAWQ Printed m Great Bntam. All nghts reserved 0273-1223199$20.00 + 0.00
PIT: S0273-1223(99)00346-7
NUTRIENT MANAGEMENT FOR WATER QUALITY PROTECTION: INTEGRATING RESEARCH INTO ENVIRONMENTAL POLICY J. T. Sims*, N. Goggin** and J. McDennott** • Department ofPlant and Soil Sciences. College ofAgriculture and Natural Resources, University ofDelaware. Newark. DE 19717-/303. USA "Division ofSoil and Water Conservation. Delaware Department ofNatural Resources and Environmental Control. 89 Kings Highway, Dover , Delaware, USA
ABSTRACT Agriculture's impacts on water quality have been the focus of bas ic and applied research in Delaware for more than 2S years. Research has examined nutrient cycling in soils, nutrient transport from soils to water , and the environmental consequences of ground water contamination and surface water eutrophication by nutrients. Much of the research has specifically been oriented towards the development of agricultural management practices to prevent the degradation of water quality by nutrients . Other research has focused on increasing our understanding of the chemical , physical, and biological processes that control nutrient cycling and transport and improving the monitoring techniques needed to document how changing management practices affects water quality . Agencies respons ible for water quality protection have sought to integrate t1us research into environmental policy, but have often been frustrated by the fragmented and sometimes contradictory nature of the information provided to them. This paper reviews key advances in research on nutrient management and water quality in Delaware and discusses the obstacles faced in translating research into widely accepted management practices and environmental policies . iC 1999 Published by Elsevier SCience Ltd on behalf of the lAWQ. All rights reserved
KEYWORDS Agricultural research; environmental policy; water quality. INTRODUCTION Environmental issues in Delaware : agricultural nutrients and water quality The quality of Delaware's ground and surface waters has been impaired by nutrients from point and nonpoint sources. Agriculture is the major nonpoint source of nutrients to waters for several reasons. First, crop land is the greatest percentage of the land area in most watersheds . Second, the soils, climate, and hydrology (sandy, highly leachable and/or ditch-drained soils, abundant rainfall, and shallow aquifers interconnected with surface waters) combine to create situations conducive to nutrient movement from land to water. And third, Delaware's agriculture is nutrient intensive, dominated by one of the most highly concentrated poultry industries in the U.S. 291
292
J. T. SIMS et al.
Developing nutrient management practices that sustain agriculture and protect water quality has been an ongoing effort in Delaware since the 1970·s. The major water quality concerns in Delaware today are (i) nitrate-nitrogen (N03-N) contamination of ground water aquifers that are used as drinking water supplies; (ii) eutrophication of surface waters (fresh waters and coastal estuaries) by nitrogen (N) and phosphorus (P), which has both ecological and economic impacts; (iii) the fact that investments in municipal and industrial wastewater treatment infrastructures in the 1970s and 1980s, done to reduce point source discharges of nutrients into surface waters, have not been sufficient to restore water quality to acceptable levels, causing increased interest and efforts at reducing nonpoint source pollution; (iv) the complex scientific, social, economic, and political challenges faced in preventing nonpoint source pollution of ground and surface waters by N and P from agricultural lands. Pressures to find solutions to agricultural nonpoint source pollution of ground and surface waters are greater today than ever before. For example, in 1998 the state of Maryland in the U.S., located with Delaware and Virginia on the Delmarva Peninsula, because of concerns about the role of nutrients in eutrophication of coastal rivers and estuaries and the role of eutrophication in the stimulation of toxic algal/dinoflagellate blooms (e.g, Pfiesteria spp.), passed legislation requiring that N and P based management plans be developed for farmers and for large-scale non-agricultural nutrient users (e.g. commercial lawn care companies). Those only using inorganic fertilizer must have plans implemented by 2002 and those using animal wastes and municipal biosolids by 2005. In Delaware, as a result of a lawsuit by environmental groups, a Total Maximum Daily Load (TMDL) agreement was signed in 1997 between the state and the U.S. Environmental Protection Agency (USEPA). This agreement requires the state to establish maximum limits for pollutants (nutrients, sediments, pathogens, organics) that can be discharged into waters by point and nonpoint sources and calls for the development of pollution control strategies to reduce pollutant levels below the TMDL. For example, reductions in N loading of 85% and P loading of 65% (from point and nonpoint sources) have been proposed to meet the TMDL for Delaware's Inland Bays. Achieving reductions of this magnitude will necessitate wider implementation of current best management practices (BMPS) and the development and testing of new BMPS. Both will require more interaction between the agricultural community, those setting environmental policy, and the researchers and advisors that develop and promote practices to minimize nutrient loss to waters. Environmental Policy and Scientific Research A fundamental premise of U.S. environmenul policy is that laws, regulations, and guidelines should be based on the best scientific information available. Envirorunental regulatory agencies (e.g. USEPA) invest millions of dollars each year into research and technology designed to prevent or remediate environmental pollution, as do other state and federal agencies, and many industries. All seek to find a common ground whereby the environment can be protected or improved and a profitable economy can be sustained or expanded. The research needed for environmental policy is conducted by scientists from universities, government agencies, private research institutes, and industry, either individually or in collaboration with colleagues in other disciplines. Depending upon the source of funding, research results may be quickly in the hands of those charged with developing environmental policy or they may be received more slowly, over the course of several years, as individual components are completed and new avenues are identified and explored. However, even if the research is received in a most timely manner, the results may not be quickly translated into "pollution control strategies". The most common reason given for failure to adopt practices identified by researchers as being effective at reducing nonpoint source pollution is that they are not economically viable that is the costs sufficiently outweigh the benefits to make them unprofitable. This is a common feature of most agricultural pollution prevention or remediation practices since the question of who bears the environmental costs offood production has never been clearly answered in the U.S. Other reasons are: (i) the cause of the environmental problem has not been conclusively identified by research or is not well understood by policymakers, hence there is reluctance to adopt practices that may not be effective in reducing the impacts of the nutrients; (ii) more than one source of nutrients is present and debate exists as to which should be controlled first; (iii) there is disagreement about the practicality of the solution; and (iv) the infrastructure needed for widespread adoption of a practice is not in place; (v) the solution may have other environmental effects that are difficult to predict. In Delaware, a number of agencies and organizations have worked collaboratively for »
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293
years to reduce agricultural nonpoint source pollution (Goggin and McDennott, 1998). Research on these issues has primarily been conducted by the University of Delaware, while technical advice and/or cost-share funds have been provided to farmers by the U.S. Department of Agriculture Natural Resources Conservation Service (USDA-NRCS), the Cooperative Extension System (CES) , local conservation districts, and the Delaware Department of Agriculture (DDA) . Regulatory program originate and are implemented by the Delaware Department of Natural Resources and Environmental Control (DNREC) alone or in cooperation with USEPA. DNREC also provides funds to support applied research, and the evaluation and adoption of (BMPs) to reduce nonpoint source pollution. For the past 25 years, and particularly since the early 1980s DNREC and its state, federal, and university partners have sought the advice and recommendations of researchers from universities and federal research institutions (e.g. the USDA Agricultural Research Service [USDA-ARS)) in their efforts to institute environmental policies that protect water quality in Delaware. The primary focus of most nutrient management research in Delaware has, until recently, been on the effects of animal wastes and fertilizers on N03-N contamination of ground and surface waters. These concerns were justified by studies documenting large N surpluses in the state (Sims and Wolf, 1994), low N use efficiency by agricultural crops and N03-N leaching in soils (Bitzer and Sims, 1988), and high N0 3-N concentrations in ground waters (Ritter and Chimside, 1984). However, in the past few years the mounting scientific evidence worldwide about the possible transport of P to surface waters via runoff (surface and subsurface) has resulted in more emphasis being placed on environmental policies and management practices that address both N and P. Examples of the research conducted as part of this collaborative effort to reduce N and Ploss to waters follow, emphasizing how and why the results have, or have not, been widely adopted. It is important to note that, since the state of Delaware currently follows a strictly voluntary approach with regard to nutrient management, this research has been incorporated into environmental policy only as guidelines and recommendations and not as regulations. As noted by Goggin and McDennott (1998) other states and national agencies are moving in a more regulatory direction with regard to nutrient management, often without fully resolving some of the uncertainties mentioned above. Nitrogen management practices for agriculture: research, development. and implementation Nitrogen management has always been problematic in Delaware because of the well-drained nature of the soils (loamy sands and sandy loams), the plentiful rainfall (- 100 cm/yr), the shallowness of the groundwater aquifers, and the type of agriculture practiced in the state (intensive animal agriculture, large areas of arable, non-leguminous crops needing annual inputs ofN, such as com, sorghum, and wheat). A major contributing factor to the N management problems in Delaware has been the rapid growth of the poultry industry since the mid 1960s which has resulted in the widespread use of poultry litter (a dry mixture of manure and the wood shavings used as a bedding material) as a fertilizer for agronomic crops. While poultry litter is an excellent N source, it is also heterogeneous, bulky, and difficult to apply uniformly, hence the exact application rates of plant available N can only be estimated. Further, the litter must often most be applied well in advance ofplanting because of the time required to move it from the site of generation (farmstead) to the site of use (crop land). Despite the growth and intensification of this industry and the large amounts ofN generated as litter, fertilizer N sales have not declined, thus resulting in a large, statewide surplus of N each year (Table 1). Consequently, while a considerable amount of research has been directed at the efficient use of poultry litter and commercial fertilizers as N sources for crops, more recent efforts have focused on identifying alternatives to land application of manures (e.g. for bioenergy or re-distribution as value-added products such as composts and pelletized organic fertilizers). Using environmental policy to significantly reduce sales of commercial N fertilizers as a means to achieve a statewide N balance has, to date, never been seriously considered. Two examples illustrate how N management research has been used as the basis for recommended nutrient management practices in Delaware.
Predicting availabilityofnitrogen in poultry litters. The application rate of poultry litter, as with most other organic wastes, has historically been based on the amount of plant available N (pAN, not total N) required to attain an economically optimum crop yield. Field and laboratory research in Delaware (Bitzer and Sims, 1988; Sims, 1987), showed that, for poultry litters : PAN (%)
=
[e-x
N,l + [kmx Nol
J. T. SIMS et al.
294
where N, and Noare the percentages of inorganic N (mainly ammonium-N) and organic N in poultry litter, er is an efficiency factor related to loss of arnmonia-N during application and km is the percentage of No mineralized during the growing season. Values for er range from 20-80% as a function of time of application, tillage, and rainfall and values of km range from 50·75% as a function of soil temperature and moisture. This research provided a quantitative basis for the preplant poultry litter rates needed to provide an optimum amount of plant available N in Delaware and is used in the Delaware Guidelines for Animal. Agriculture (DNREC, 1997). Table 1. Statewide mass balance for Nand P in Delaware (from Sims et 01., 1998) Nutrients Available and Crop Nutrient Requirements
Nutrient Available or Required' Nitrogen
Phosphorus
-·------·.--····-·-MglStateNear---·----·-····-Nutdents Sold or Ayailable; Sources Commercial fertilizers'
22,800
3,900
Poultry litter/manure Total Available (N @ 75%, P @ 80%)
13,000 9,750
6,500 5,200
Dairy Manure Total Available (N @50%, P@ 75%)
860 430
100 75
Beef Manure Total Available (N @ 60%, P @75%)
ISO 90
40 30
Swine manure Total Available (N @ 65%, P @ 75%)
185 120
60 45
36,995 33,190
10,600 9,250
Total N orP Available N or P Nutdents Required by Crops Corn (62,750 hal
8,785
690
0
980
Wheat (32,500 ha)
3,900
360
Barley (10,000 hal
1,200
110
Soybeans (89,000 hal
Vegetables, Hay (35,000 hal
4,200
385
Total required by all crops
18,085
2,520
Annual Nutdent Balance Statewide Based on total Based on available
+18,910 +15,105
+8,080 +6,730
+82 +66
+35 +29
Per hectare of Crop Land Based on total Based on available
"See Sims et al., (1998) for assumptions and references used to calculate statewide budget. *StatewideNand P fertilizer sales have averaged 22,200 and 3,500 Mglyr, respectively, from 1983-1997.
Soil and plant nitrogen tests. The PAN approach was based on applying all poultry litter N needed for a crop shortly before planting. This is less efficient than the multiple applications ofN recommended for inorganic fertilizers (starter, sidedressing, fertigation). Further, the logistics of litter storage and handling, the time
Nutrient management for water quality protection
295
required to apply a bulky material over large areas ofland, and, until recently (Glancey and Adains, 1996), the lack of equipment that can sidedress poultry litter, often means that applications are made from one to four months prior to planting . Since this can result in unpredictable mineralization of organic N in the litter and weather-related leaching and volatilization losses of initially available and subsequently mineralized inorganic N, a more efficient approach was needed. Magdoff et al. (1984) developed the pre-sidedress soil nitrate test (PSNT) for com based on the premise that a soil nitrate test taken to a depth of 30 em early in the growing season (four to six weeks after planting) could accurately measure soil N supplying capacity. Any supplemental N required would be sidedressed during the growing season, more efficiently than preplant fertilization . The PSNT was evaluated in a three-year, on-farm study in Delaware (56 locations) and accurately predicted sidedress fertilizer N requirements of com when poultry litter was applied at or shortly in advance of planting (Sims et al., 1995). This test has been accepted by Delaware farmers as an accurate means to measure available N in poultry litter and as a basis for purchasing and applying fertilizer N for sidedressing com. A typical recommendation today would be to apply 4 to 6 Mg/ha of poultry litter shortly before planting, use a starter fertilizer, take a PSNT sample, and, if necessary, sidedress with fertilizer N. The value of the PSNT is illustrated in Figure 1, based on the results of 366 samples collected in Sussex County, Delaware by advisory agency staff as part of a cost-sharing program to promote use of this test. About 55% of the PSNT samples had values> 20 mg/kg, where no additional sidedress fertilizer N would be required and, where sidedress N was needed, recommendations by advisors were consistently lower than those planned by farmers. Some aspects of the PSNT, however, have precluded its widespread use in Delaware . The PSNT sample must be collected in late May to mid-June, to a deeper depth than standard soil samples (30 em), and must be dried immediately to prevent mineralization of inorganic N during sample storage. While field kits are available to measure soil nitrate immediately after drying, the time required to collect and analyze the soil samples, during a time of year when farmers are very busy with other operations (e.g. sidedressing com, has seriously limited the number of hectares sampled each year. Cost-share funds provided by DNREC through local conservation districts have alIowed advisory personnel to collect, analyze, and interpret PSNT samples at little or no cost to farmers, but staff limitations still preclude sampling enough land to impact the amount of fertilizer N purchased and applied in Delaware each year. For example, the 366 PSNT samples mentioned above represent 1,400,2,020, and 1,875 ha for 1996, 1997, and 1998, respectively, in a county with -100,000 ha of crop land. Private consultants and commercial fertilizer dealers have assisted in PSNT sampling somewhat by offering the service for a fee, but again not to the level required. Thus, although research has identified a valuable BMP, the infrastructure currently available cannot fully implement the test, thereby precluding its more widespread use and reducing its effectiveness in water quality protection.
In addition to soil N tests, there has been increased interest in the use of plant testing to predict N availability and the need for fertilizer N after manuring. Diagnosing N sufficiency based on analysis of whole plants and leaves for N has been an accepted practice foridecades. More recently, however, there has been increased interest in other approaches to plant N testing including: (i) in-situ N testing methods such as the leaf chlorophyll meter (LCM) used both to identify the need for sidedress N and to continuously monitor the need for fertigation with N for irrigated crops and, (ii) a late season stalk nitrate test developed to determine if excess N was present in the field during the growing season . Research in Delaware (Sims et al., 1995) and other states (Blackmer et al., 1992) has shown that these tests can improve N management and critical values or ranges have been proposed for both. Both tests are easier to conduct than the PSNT because they do not involve collection and analysis of a soil sample, but neither has received widespread use in Delaware to date. The most likely reason for this is that they are still regarded as experimental tests - that is not enough "on-farm" demonstration of the research has occurred to provide farmers with the confidence they have in the PSNT.
J T. SIMS vt ill.
296
40
(a)
Respon sive: 45%
30 on-responsive: 55% Vl
OJ
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20
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lO ?:::::~~ :. ~~~: :~ >
0
10-20
0-10
20-30
30-40
40-50
>50
- --
-
PS T Range (mglkg)
200 r--
-
----:----::-:---:-:--:- --
Average Fertilizer N (kg/h al Planned 67 Recomm ended 32
160 120
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••
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•• 120
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(h)
200
Fertilizer N Planned (kg/ha) Figure 1. Use and value of the PSNT III Delaware: (a) percentage of samples collected by advisory agency staff in Sussex County, Delaware where response, or non-response, of com to sidedress fertilizer N would be expected; (b l comparison of fertilizer N applications planned by farmers WIth those recommended by advisory agency staff based on the PSNT.
Phosphorus management practices for agriculture: research, development, and implementation Phosphorus is well-known to he a major contributing factor to the eutrophication of surface waters which in tum promotes increased growth of algae and undesirable aquatic weeds, depletion in dissolved oxygen and fish kills, foul odors, sedimentation and restriction of navigation, and surface scums that impair recreational uses, In Delaware two of the major recent issues related to nonpoint source pollution of surface waters by P have been nuisance blooms of seaweed in the Inland Bays (a national estuary heavily used for recreational purposes) and concerns that P contributes to the conditions associated with blooms of Pfiesteria spp. A 65% reduction in P loads to these bays (point and nonpoint) has been suggested as being needed to restore water quality. Research on the environmental implications of high P soils began in Delaware in the late I980s as part of an effort to demonstrate "on-farm" BMPs for poultry litter management. These studies found very high P soils on most cooperating farms, as did subsequent studies focusing on P leaching in the Inland Bays watershed (Mozaffari and Sims, 1994), Detailed analysis of soil test summaries also showed, as in most areas with intensive animal agriculture, widespread distribution of soils that needed little or no P, as fertilizers or manures, for optimum crop production. For example in Sussex County, Delaware (site of the poultry industry) > 85% of the soils tested in 1992-1997 were rated as "optimum" (30%) or "excessive" (55%) in P (Sims, I997a). Mass balance calculations first conducted on a statewide basis (Sims and Wolf, 1994; see
Nutrient management for water quality protection
297
Table 1) and later in more detail at farm and watershed scales (Sims, 1998) showed annual P surpluses ranging from 45 to 90 kg Plha on many poultry farms, A major contributing factor to these high P soils has been the long-term application of poultry litters to crop land based on crop N requirements which typically adds -100-150 kg Plha, relative to crop removal of 20-30 kg Plha (Mozaffari and Sims, 1994). While the relatively flat topography of most of Delaware creates fewer risks for P movement to surface waters by soil erosion and surface runoff than in many areas, the long-term buildup ofP to increasingly higher levels is not viewed as an agriculturally sustainable practice. Further, an extensive ditch drainage system exists in some poultry-grain areas with ditch waters discharging into streams and the Inland Bays. Although P losses in leaching and drainage have usually been assumed to be a minor issue, studies in Western Europe (Breeuswma et al., 1995) have shown that as soil profiles become progressively "saturated" with P the downward movement and lateral flow of soluble P into drainage waters can occur. Recent research in Delaware has focused on the movement of P via these drainage ditches to surface waters and the BMPs needed to prevent P loss (Sims et al., 1998). Examples include: (i) the development of a "P Index" system that integrates soil P with hydrology and management to better identify the areas on a farm or in a watershed where the risk ofP loss to Water is greatest. This will enhance targeting of resources to control P loss to the areas where they will have the greatest impact; (ii) dietary manipulation to reduce P excretions by poultry, such as inclusion of phytase enzymes and low phytic acid com in poultry diets; (iii) chemical amendment of poultry litter in the poultry house with acidic amendments such as alum (aluminum sulfate) to decrease P solubility and ammonia loss, which not only reduces the environmental impacts of poultry production but increases profitability because poultry health is improved when ammonia concentrations are lower; and (iv) using soil amendments, such as the residuals from drinking water treatment plants to reduce P solubility and increase P sorption in hydrologically active areas in a watershed (e.g. buffer zones near drainage ditches). To date, little of this research on P has been integrated into environmental policies in Delaware, although the importance of managing P for water quality protection has clearly been recognized. The lack of economically viable alternatives to land application for poultry litters and other organic wastes (dairy and swine manures, municipal biosolids) has frustrated most efforts to base nutrient management on P as well as N. Research-based solutions are emerging, however, and P- based nutrient management plans are likely to become more widespread in the next five to ten years, not only in Delaware, but in many U.S. states. CONCLUSIONS Managing agricultural nutrients to protect water quality remains a major challenge in Delaware, despite more than 20 years of research and concerted efforts to develop management practices and environmental policies based on this research. The increasing national and regional emphasis on regulatory actions in the U.S., rather than voluntary practices, likely means that more restrictive agricultural policies will emerge in the next decade to protect air, soil, and water quality. A solid research base exists to support improved nutrient management practices and ongoing research is identifying more innovative solutions. However, the infrastructure to implement the BMPs identified in the past decade, let alone new practices, is not well established, nor is the allocation of the economic costs of more intensive management by farmers to protect environmental quality. Developing environmental policies that can sustain agricultural productivity in such a changing climate will require a collaborative approach between the scientific community and a consortium of farmers, agribusiness, state and federal advisory and regulatory agencies, and public interest/environmental groups. A key aspect of this will be the willingness of scientists to not only conduct research but to work with others with more diverse backgrounds and varying agendas to integrate research into sound and defensible environmental policies. LITERATURE CITED Bitzer, C. C. and Sims, J. T. (1988). Estimating nitrogen availability in poultry manure through laboratory and field studies. J. Environ. Qual., 17, 47-54. Blackmer, A. M., Morris, T. F. and Binford, G. D. (1992). Predicting N fertilizer needs for com in humid regions: advances in Iowa. In: Predicting N Fertiltzer Needs for Corn, K. Kelley and B. Bock (eds), Bulletin Y-226, pp. 57-73. Natl. Fert. Environ. Res. Ctr., Tennessee Valley Authority, Muscle Shoals, AL. Breeuwsma, A., Reijerink, J. G. A. and Schoumans, O. F. (1995). Impact of manure on accumulation and leaching of phosphate in areas of intensive livestock fanmng.ln: Animal Wastes and the Land-Water Interface, K. Steele (ed), pp. 239-251. Lewis Publishers-CRC Press, NY.
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Glancey, J. L. and Adains, R. K. (1996). An applicator for side-dressing row crops with solid wastes. Trans. ASAE, 39, 829-835. Goggin, N. and McDermott, J. (1998). Developing and implementing research-based environmental policy for water quality protection: The Delaware experience. Proceedings of 31 International Conference on Diffuse Pollution, Edinburgh, Scotland. Magdoff, F. R., Ross, D. and Amadon, J. (1984). A soil test for nitrogen availability to com. Soil Sci. Soc. Am. J., 48, \301-\304. Mozaffari, P. M. and Sims, J. T. (1994). Phosphorus availability and sorption in an Atlantic Coastal Plain watershed dominated by intensive, animal-based agriculture. Soil sa; IS7, 97-107. Ritter, W. F. and Clumside, A. E. M. (1984). Impact ofland use on groundwater quality in southern Delaware. Groundwater, 22, 39-47. Sims, J. T. (1997a). Phosphorus soil testing: Innovations for water quality protection. Proceedings of the 5th International Symposium on Soil and Plant Analysis, pp. 47-63. Minneapolis, NN. Sims, J. T. (l997b). Agricultural and environmental issues in the management of poultry wastes: Recent innovations and longterm challenges. In: Uses of By-Products and Wastes in Agriculture, J. Rechcigl (ed), pp. 12-90. Am. Chern. Soc., Washington, D. C. Sims, J. T. (1998). The role of soil testing in Environmental risk assessment for phosphorus in the Chesapeake Bay watershed. In: Proc. Conf. Agric. Phosphorus Chesapeake Bay Watershed, A. N. Sharpley (ed), University Park, PA, April 4-6, 1998 (in press). Sims, J. T. and Wolf, D. C. (1994). Poultry waste management: Agricultural and environmental issues. Adv. Agron., 52,1-83. Sims, 1. T., Andres, A. S., Denver, J. M., Gangloff, W. J., Vadas, P. A. and Ware, D. R. (1998). Assessing the impact of agricultural drainage on ground and surface water quality in Delaware: Development of best management practices for water quality protection. Final Project Rep. Delaware Dep. Nat. Res. Environ. Control, Dover, DE. Suns, J. T., Vasilas, B. L., Gartley, K. L., Milliken, B. and Green, V. (1995). Evaluation of soil and plant nitrogen tests for maize on manured soils of the Atlantic Coastal Plain. Agron. J., 87, 213-222.
War. Sci
T~ch.
Vol. 39, No. 12, pp. 291-298, 1999 <01999
Published by Elsevier Science Ud on behalf ofthe IAWQ Printed m Great Bntam. All nghts reserved 0273-1223199$20.00 + 0.00
PIT: S0273-1223(99)00346-7
NUTRIENT MANAGEMENT FOR WATER QUALITY PROTECTION: INTEGRATING RESEARCH INTO ENVIRONMENTAL POLICY J. T. Sims*, N. Goggin** and J. McDennott** • Department ofPlant and Soil Sciences. College ofAgriculture and Natural Resources, University ofDelaware. Newark. DE 19717-/303. USA "Division ofSoil and Water Conservation. Delaware Department ofNatural Resources and Environmental Control. 89 Kings Highway, Dover , Delaware, USA
ABSTRACT Agriculture's impacts on water quality have been the focus of bas ic and applied research in Delaware for more than 2S years. Research has examined nutrient cycling in soils, nutrient transport from soils to water , and the environmental consequences of ground water contamination and surface water eutrophication by nutrients. Much of the research has specifically been oriented towards the development of agricultural management practices to prevent the degradation of water quality by nutrients . Other research has focused on increasing our understanding of the chemical , physical, and biological processes that control nutrient cycling and transport and improving the monitoring techniques needed to document how changing management practices affects water quality . Agencies respons ible for water quality protection have sought to integrate t1us research into environmental policy, but have often been frustrated by the fragmented and sometimes contradictory nature of the information provided to them. This paper reviews key advances in research on nutrient management and water quality in Delaware and discusses the obstacles faced in translating research into widely accepted management practices and environmental policies . iC 1999 Published by Elsevier SCience Ltd on behalf of the lAWQ. All rights reserved
KEYWORDS Agricultural research; environmental policy; water quality. INTRODUCTION Environmental issues in Delaware : agricultural nutrients and water quality The quality of Delaware's ground and surface waters has been impaired by nutrients from point and nonpoint sources. Agriculture is the major nonpoint source of nutrients to waters for several reasons. First, crop land is the greatest percentage of the land area in most watersheds . Second, the soils, climate, and hydrology (sandy, highly leachable and/or ditch-drained soils, abundant rainfall, and shallow aquifers interconnected with surface waters) combine to create situations conducive to nutrient movement from land to water. And third, Delaware's agriculture is nutrient intensive, dominated by one of the most highly concentrated poultry industries in the U.S. 291
292
J. T. SIMS et al.
Developing nutrient management practices that sustain agriculture and protect water quality has been an ongoing effort in Delaware since the 1970·s. The major water quality concerns in Delaware today are (i) nitrate-nitrogen (N03-N) contamination of ground water aquifers that are used as drinking water supplies; (ii) eutrophication of surface waters (fresh waters and coastal estuaries) by nitrogen (N) and phosphorus (P), which has both ecological and economic impacts; (iii) the fact that investments in municipal and industrial wastewater treatment infrastructures in the 1970s and 1980s, done to reduce point source discharges of nutrients into surface waters, have not been sufficient to restore water quality to acceptable levels, causing increased interest and efforts at reducing nonpoint source pollution; (iv) the complex scientific, social, economic, and political challenges faced in preventing nonpoint source pollution of ground and surface waters by N and P from agricultural lands. Pressures to find solutions to agricultural nonpoint source pollution of ground and surface waters are greater today than ever before. For example, in 1998 the state of Maryland in the U.S., located with Delaware and Virginia on the Delmarva Peninsula, because of concerns about the role of nutrients in eutrophication of coastal rivers and estuaries and the role of eutrophication in the stimulation of toxic algal/dinoflagellate blooms (e.g, Pfiesteria spp.), passed legislation requiring that N and P based management plans be developed for farmers and for large-scale non-agricultural nutrient users (e.g. commercial lawn care companies). Those only using inorganic fertilizer must have plans implemented by 2002 and those using animal wastes and municipal biosolids by 2005. In Delaware, as a result of a lawsuit by environmental groups, a Total Maximum Daily Load (TMDL) agreement was signed in 1997 between the state and the U.S. Environmental Protection Agency (USEPA). This agreement requires the state to establish maximum limits for pollutants (nutrients, sediments, pathogens, organics) that can be discharged into waters by point and nonpoint sources and calls for the development of pollution control strategies to reduce pollutant levels below the TMDL. For example, reductions in N loading of 85% and P loading of 65% (from point and nonpoint sources) have been proposed to meet the TMDL for Delaware's Inland Bays. Achieving reductions of this magnitude will necessitate wider implementation of current best management practices (BMPS) and the development and testing of new BMPS. Both will require more interaction between the agricultural community, those setting environmental policy, and the researchers and advisors that develop and promote practices to minimize nutrient loss to waters. Environmental Policy and Scientific Research A fundamental premise of U.S. environmenul policy is that laws, regulations, and guidelines should be based on the best scientific information available. Envirorunental regulatory agencies (e.g. USEPA) invest millions of dollars each year into research and technology designed to prevent or remediate environmental pollution, as do other state and federal agencies, and many industries. All seek to find a common ground whereby the environment can be protected or improved and a profitable economy can be sustained or expanded. The research needed for environmental policy is conducted by scientists from universities, government agencies, private research institutes, and industry, either individually or in collaboration with colleagues in other disciplines. Depending upon the source of funding, research results may be quickly in the hands of those charged with developing environmental policy or they may be received more slowly, over the course of several years, as individual components are completed and new avenues are identified and explored. However, even if the research is received in a most timely manner, the results may not be quickly translated into "pollution control strategies". The most common reason given for failure to adopt practices identified by researchers as being effective at reducing nonpoint source pollution is that they are not economically viable that is the costs sufficiently outweigh the benefits to make them unprofitable. This is a common feature of most agricultural pollution prevention or remediation practices since the question of who bears the environmental costs offood production has never been clearly answered in the U.S. Other reasons are: (i) the cause of the environmental problem has not been conclusively identified by research or is not well understood by policymakers, hence there is reluctance to adopt practices that may not be effective in reducing the impacts of the nutrients; (ii) more than one source of nutrients is present and debate exists as to which should be controlled first; (iii) there is disagreement about the practicality of the solution; and (iv) the infrastructure needed for widespread adoption of a practice is not in place; (v) the solution may have other environmental effects that are difficult to predict. In Delaware, a number of agencies and organizations have worked collaboratively for »
Nument management for water quality protection
293
years to reduce agricultural nonpoint source pollution (Goggin and McDennott, 1998). Research on these issues has primarily been conducted by the University of Delaware, while technical advice and/or cost-share funds have been provided to farmers by the U.S. Department of Agriculture Natural Resources Conservation Service (USDA-NRCS), the Cooperative Extension System (CES) , local conservation districts, and the Delaware Department of Agriculture (DDA) . Regulatory program originate and are implemented by the Delaware Department of Natural Resources and Environmental Control (DNREC) alone or in cooperation with USEPA. DNREC also provides funds to support applied research, and the evaluation and adoption of (BMPs) to reduce nonpoint source pollution. For the past 25 years, and particularly since the early 1980s DNREC and its state, federal, and university partners have sought the advice and recommendations of researchers from universities and federal research institutions (e.g. the USDA Agricultural Research Service [USDA-ARS)) in their efforts to institute environmental policies that protect water quality in Delaware. The primary focus of most nutrient management research in Delaware has, until recently, been on the effects of animal wastes and fertilizers on N03-N contamination of ground and surface waters. These concerns were justified by studies documenting large N surpluses in the state (Sims and Wolf, 1994), low N use efficiency by agricultural crops and N03-N leaching in soils (Bitzer and Sims, 1988), and high N0 3-N concentrations in ground waters (Ritter and Chimside, 1984). However, in the past few years the mounting scientific evidence worldwide about the possible transport of P to surface waters via runoff (surface and subsurface) has resulted in more emphasis being placed on environmental policies and management practices that address both N and P. Examples of the research conducted as part of this collaborative effort to reduce N and Ploss to waters follow, emphasizing how and why the results have, or have not, been widely adopted. It is important to note that, since the state of Delaware currently follows a strictly voluntary approach with regard to nutrient management, this research has been incorporated into environmental policy only as guidelines and recommendations and not as regulations. As noted by Goggin and McDennott (1998) other states and national agencies are moving in a more regulatory direction with regard to nutrient management, often without fully resolving some of the uncertainties mentioned above. Nitrogen management practices for agriculture: research, development. and implementation Nitrogen management has always been problematic in Delaware because of the well-drained nature of the soils (loamy sands and sandy loams), the plentiful rainfall (- 100 cm/yr), the shallowness of the groundwater aquifers, and the type of agriculture practiced in the state (intensive animal agriculture, large areas of arable, non-leguminous crops needing annual inputs ofN, such as com, sorghum, and wheat). A major contributing factor to the N management problems in Delaware has been the rapid growth of the poultry industry since the mid 1960s which has resulted in the widespread use of poultry litter (a dry mixture of manure and the wood shavings used as a bedding material) as a fertilizer for agronomic crops. While poultry litter is an excellent N source, it is also heterogeneous, bulky, and difficult to apply uniformly, hence the exact application rates of plant available N can only be estimated. Further, the litter must often most be applied well in advance ofplanting because of the time required to move it from the site of generation (farmstead) to the site of use (crop land). Despite the growth and intensification of this industry and the large amounts ofN generated as litter, fertilizer N sales have not declined, thus resulting in a large, statewide surplus of N each year (Table 1). Consequently, while a considerable amount of research has been directed at the efficient use of poultry litter and commercial fertilizers as N sources for crops, more recent efforts have focused on identifying alternatives to land application of manures (e.g. for bioenergy or re-distribution as value-added products such as composts and pelletized organic fertilizers). Using environmental policy to significantly reduce sales of commercial N fertilizers as a means to achieve a statewide N balance has, to date, never been seriously considered. Two examples illustrate how N management research has been used as the basis for recommended nutrient management practices in Delaware.
Predicting availabilityofnitrogen in poultry litters. The application rate of poultry litter, as with most other organic wastes, has historically been based on the amount of plant available N (pAN, not total N) required to attain an economically optimum crop yield. Field and laboratory research in Delaware (Bitzer and Sims, 1988; Sims, 1987), showed that, for poultry litters : PAN (%)
=
[e-x
N,l + [kmx Nol
J. T. SIMS et al.
294
where N, and Noare the percentages of inorganic N (mainly ammonium-N) and organic N in poultry litter, er is an efficiency factor related to loss of arnmonia-N during application and km is the percentage of No mineralized during the growing season. Values for er range from 20-80% as a function of time of application, tillage, and rainfall and values of km range from 50·75% as a function of soil temperature and moisture. This research provided a quantitative basis for the preplant poultry litter rates needed to provide an optimum amount of plant available N in Delaware and is used in the Delaware Guidelines for Animal. Agriculture (DNREC, 1997). Table 1. Statewide mass balance for Nand P in Delaware (from Sims et 01., 1998) Nutrients Available and Crop Nutrient Requirements
Nutrient Available or Required' Nitrogen
Phosphorus
-·------·.--····-·-MglStateNear---·----·-····-Nutdents Sold or Ayailable; Sources Commercial fertilizers'
22,800
3,900
Poultry litter/manure Total Available (N @ 75%, P @ 80%)
13,000 9,750
6,500 5,200
Dairy Manure Total Available (N @50%, P@ 75%)
860 430
100 75
Beef Manure Total Available (N @ 60%, P @75%)
ISO 90
40 30
Swine manure Total Available (N @ 65%, P @ 75%)
185 120
60 45
36,995 33,190
10,600 9,250
Total N orP Available N or P Nutdents Required by Crops Corn (62,750 hal
8,785
690
0
980
Wheat (32,500 ha)
3,900
360
Barley (10,000 hal
1,200
110
Soybeans (89,000 hal
Vegetables, Hay (35,000 hal
4,200
385
Total required by all crops
18,085
2,520
Annual Nutdent Balance Statewide Based on total Based on available
+18,910 +15,105
+8,080 +6,730
+82 +66
+35 +29
Per hectare of Crop Land Based on total Based on available
"See Sims et al., (1998) for assumptions and references used to calculate statewide budget. *StatewideNand P fertilizer sales have averaged 22,200 and 3,500 Mglyr, respectively, from 1983-1997.
Soil and plant nitrogen tests. The PAN approach was based on applying all poultry litter N needed for a crop shortly before planting. This is less efficient than the multiple applications ofN recommended for inorganic fertilizers (starter, sidedressing, fertigation). Further, the logistics of litter storage and handling, the time
Nutrient management for water quality protection
295
required to apply a bulky material over large areas ofland, and, until recently (Glancey and Adains, 1996), the lack of equipment that can sidedress poultry litter, often means that applications are made from one to four months prior to planting . Since this can result in unpredictable mineralization of organic N in the litter and weather-related leaching and volatilization losses of initially available and subsequently mineralized inorganic N, a more efficient approach was needed. Magdoff et al. (1984) developed the pre-sidedress soil nitrate test (PSNT) for com based on the premise that a soil nitrate test taken to a depth of 30 em early in the growing season (four to six weeks after planting) could accurately measure soil N supplying capacity. Any supplemental N required would be sidedressed during the growing season, more efficiently than preplant fertilization . The PSNT was evaluated in a three-year, on-farm study in Delaware (56 locations) and accurately predicted sidedress fertilizer N requirements of com when poultry litter was applied at or shortly in advance of planting (Sims et al., 1995). This test has been accepted by Delaware farmers as an accurate means to measure available N in poultry litter and as a basis for purchasing and applying fertilizer N for sidedressing com. A typical recommendation today would be to apply 4 to 6 Mg/ha of poultry litter shortly before planting, use a starter fertilizer, take a PSNT sample, and, if necessary, sidedress with fertilizer N. The value of the PSNT is illustrated in Figure 1, based on the results of 366 samples collected in Sussex County, Delaware by advisory agency staff as part of a cost-sharing program to promote use of this test. About 55% of the PSNT samples had values> 20 mg/kg, where no additional sidedress fertilizer N would be required and, where sidedress N was needed, recommendations by advisors were consistently lower than those planned by farmers. Some aspects of the PSNT, however, have precluded its widespread use in Delaware . The PSNT sample must be collected in late May to mid-June, to a deeper depth than standard soil samples (30 em), and must be dried immediately to prevent mineralization of inorganic N during sample storage. While field kits are available to measure soil nitrate immediately after drying, the time required to collect and analyze the soil samples, during a time of year when farmers are very busy with other operations (e.g. sidedressing com, has seriously limited the number of hectares sampled each year. Cost-share funds provided by DNREC through local conservation districts have alIowed advisory personnel to collect, analyze, and interpret PSNT samples at little or no cost to farmers, but staff limitations still preclude sampling enough land to impact the amount of fertilizer N purchased and applied in Delaware each year. For example, the 366 PSNT samples mentioned above represent 1,400,2,020, and 1,875 ha for 1996, 1997, and 1998, respectively, in a county with -100,000 ha of crop land. Private consultants and commercial fertilizer dealers have assisted in PSNT sampling somewhat by offering the service for a fee, but again not to the level required. Thus, although research has identified a valuable BMP, the infrastructure currently available cannot fully implement the test, thereby precluding its more widespread use and reducing its effectiveness in water quality protection.
In addition to soil N tests, there has been increased interest in the use of plant testing to predict N availability and the need for fertilizer N after manuring. Diagnosing N sufficiency based on analysis of whole plants and leaves for N has been an accepted practice foridecades. More recently, however, there has been increased interest in other approaches to plant N testing including: (i) in-situ N testing methods such as the leaf chlorophyll meter (LCM) used both to identify the need for sidedress N and to continuously monitor the need for fertigation with N for irrigated crops and, (ii) a late season stalk nitrate test developed to determine if excess N was present in the field during the growing season . Research in Delaware (Sims et al., 1995) and other states (Blackmer et al., 1992) has shown that these tests can improve N management and critical values or ranges have been proposed for both. Both tests are easier to conduct than the PSNT because they do not involve collection and analysis of a soil sample, but neither has received widespread use in Delaware to date. The most likely reason for this is that they are still regarded as experimental tests - that is not enough "on-farm" demonstration of the research has occurred to provide farmers with the confidence they have in the PSNT.
J T. SIMS vt ill.
296
40
(a)
Respon sive: 45%
30 on-responsive: 55% Vl
OJ
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20
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lO ?:::::~~ :. ~~~: :~ >
0
10-20
0-10
20-30
30-40
40-50
>50
- --
-
PS T Range (mglkg)
200 r--
-
----:----::-:---:-:--:- --
Average Fertilizer N (kg/h al Planned 67 Recomm ended 32
160 120
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Fertilizer N Planned (kg/ha) Figure 1. Use and value of the PSNT III Delaware: (a) percentage of samples collected by advisory agency staff in Sussex County, Delaware where response, or non-response, of com to sidedress fertilizer N would be expected; (b l comparison of fertilizer N applications planned by farmers WIth those recommended by advisory agency staff based on the PSNT.
Phosphorus management practices for agriculture: research, development, and implementation Phosphorus is well-known to he a major contributing factor to the eutrophication of surface waters which in tum promotes increased growth of algae and undesirable aquatic weeds, depletion in dissolved oxygen and fish kills, foul odors, sedimentation and restriction of navigation, and surface scums that impair recreational uses, In Delaware two of the major recent issues related to nonpoint source pollution of surface waters by P have been nuisance blooms of seaweed in the Inland Bays (a national estuary heavily used for recreational purposes) and concerns that P contributes to the conditions associated with blooms of Pfiesteria spp. A 65% reduction in P loads to these bays (point and nonpoint) has been suggested as being needed to restore water quality. Research on the environmental implications of high P soils began in Delaware in the late I980s as part of an effort to demonstrate "on-farm" BMPs for poultry litter management. These studies found very high P soils on most cooperating farms, as did subsequent studies focusing on P leaching in the Inland Bays watershed (Mozaffari and Sims, 1994), Detailed analysis of soil test summaries also showed, as in most areas with intensive animal agriculture, widespread distribution of soils that needed little or no P, as fertilizers or manures, for optimum crop production. For example in Sussex County, Delaware (site of the poultry industry) > 85% of the soils tested in 1992-1997 were rated as "optimum" (30%) or "excessive" (55%) in P (Sims, I997a). Mass balance calculations first conducted on a statewide basis (Sims and Wolf, 1994; see
Nutrient management for water quality protection
297
Table 1) and later in more detail at farm and watershed scales (Sims, 1998) showed annual P surpluses ranging from 45 to 90 kg Plha on many poultry farms, A major contributing factor to these high P soils has been the long-term application of poultry litters to crop land based on crop N requirements which typically adds -100-150 kg Plha, relative to crop removal of 20-30 kg Plha (Mozaffari and Sims, 1994). While the relatively flat topography of most of Delaware creates fewer risks for P movement to surface waters by soil erosion and surface runoff than in many areas, the long-term buildup ofP to increasingly higher levels is not viewed as an agriculturally sustainable practice. Further, an extensive ditch drainage system exists in some poultry-grain areas with ditch waters discharging into streams and the Inland Bays. Although P losses in leaching and drainage have usually been assumed to be a minor issue, studies in Western Europe (Breeuswma et al., 1995) have shown that as soil profiles become progressively "saturated" with P the downward movement and lateral flow of soluble P into drainage waters can occur. Recent research in Delaware has focused on the movement of P via these drainage ditches to surface waters and the BMPs needed to prevent P loss (Sims et al., 1998). Examples include: (i) the development of a "P Index" system that integrates soil P with hydrology and management to better identify the areas on a farm or in a watershed where the risk ofP loss to Water is greatest. This will enhance targeting of resources to control P loss to the areas where they will have the greatest impact; (ii) dietary manipulation to reduce P excretions by poultry, such as inclusion of phytase enzymes and low phytic acid com in poultry diets; (iii) chemical amendment of poultry litter in the poultry house with acidic amendments such as alum (aluminum sulfate) to decrease P solubility and ammonia loss, which not only reduces the environmental impacts of poultry production but increases profitability because poultry health is improved when ammonia concentrations are lower; and (iv) using soil amendments, such as the residuals from drinking water treatment plants to reduce P solubility and increase P sorption in hydrologically active areas in a watershed (e.g. buffer zones near drainage ditches). To date, little of this research on P has been integrated into environmental policies in Delaware, although the importance of managing P for water quality protection has clearly been recognized. The lack of economically viable alternatives to land application for poultry litters and other organic wastes (dairy and swine manures, municipal biosolids) has frustrated most efforts to base nutrient management on P as well as N. Research-based solutions are emerging, however, and P- based nutrient management plans are likely to become more widespread in the next five to ten years, not only in Delaware, but in many U.S. states. CONCLUSIONS Managing agricultural nutrients to protect water quality remains a major challenge in Delaware, despite more than 20 years of research and concerted efforts to develop management practices and environmental policies based on this research. The increasing national and regional emphasis on regulatory actions in the U.S., rather than voluntary practices, likely means that more restrictive agricultural policies will emerge in the next decade to protect air, soil, and water quality. A solid research base exists to support improved nutrient management practices and ongoing research is identifying more innovative solutions. However, the infrastructure to implement the BMPs identified in the past decade, let alone new practices, is not well established, nor is the allocation of the economic costs of more intensive management by farmers to protect environmental quality. Developing environmental policies that can sustain agricultural productivity in such a changing climate will require a collaborative approach between the scientific community and a consortium of farmers, agribusiness, state and federal advisory and regulatory agencies, and public interest/environmental groups. A key aspect of this will be the willingness of scientists to not only conduct research but to work with others with more diverse backgrounds and varying agendas to integrate research into sound and defensible environmental policies. LITERATURE CITED Bitzer, C. C. and Sims, J. T. (1988). Estimating nitrogen availability in poultry manure through laboratory and field studies. J. Environ. Qual., 17, 47-54. Blackmer, A. M., Morris, T. F. and Binford, G. D. (1992). Predicting N fertilizer needs for com in humid regions: advances in Iowa. In: Predicting N Fertiltzer Needs for Corn, K. Kelley and B. Bock (eds), Bulletin Y-226, pp. 57-73. Natl. Fert. Environ. Res. Ctr., Tennessee Valley Authority, Muscle Shoals, AL. Breeuwsma, A., Reijerink, J. G. A. and Schoumans, O. F. (1995). Impact of manure on accumulation and leaching of phosphate in areas of intensive livestock fanmng.ln: Animal Wastes and the Land-Water Interface, K. Steele (ed), pp. 239-251. Lewis Publishers-CRC Press, NY.
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Glancey, J. L. and Adains, R. K. (1996). An applicator for side-dressing row crops with solid wastes. Trans. ASAE, 39, 829-835. Goggin, N. and McDermott, J. (1998). Developing and implementing research-based environmental policy for water quality protection: The Delaware experience. Proceedings of 31 International Conference on Diffuse Pollution, Edinburgh, Scotland. Magdoff, F. R., Ross, D. and Amadon, J. (1984). A soil test for nitrogen availability to com. Soil Sci. Soc. Am. J., 48, \301-\304. Mozaffari, P. M. and Sims, J. T. (1994). Phosphorus availability and sorption in an Atlantic Coastal Plain watershed dominated by intensive, animal-based agriculture. Soil sa; IS7, 97-107. Ritter, W. F. and Clumside, A. E. M. (1984). Impact ofland use on groundwater quality in southern Delaware. Groundwater, 22, 39-47. Sims, J. T. (1997a). Phosphorus soil testing: Innovations for water quality protection. Proceedings of the 5th International Symposium on Soil and Plant Analysis, pp. 47-63. Minneapolis, NN. Sims, J. T. (l997b). Agricultural and environmental issues in the management of poultry wastes: Recent innovations and longterm challenges. In: Uses of By-Products and Wastes in Agriculture, J. Rechcigl (ed), pp. 12-90. Am. Chern. Soc., Washington, D. C. Sims, J. T. (1998). The role of soil testing in Environmental risk assessment for phosphorus in the Chesapeake Bay watershed. In: Proc. Conf. Agric. Phosphorus Chesapeake Bay Watershed, A. N. Sharpley (ed), University Park, PA, April 4-6, 1998 (in press). Sims, J. T. and Wolf, D. C. (1994). Poultry waste management: Agricultural and environmental issues. Adv. Agron., 52,1-83. Sims, 1. T., Andres, A. S., Denver, J. M., Gangloff, W. J., Vadas, P. A. and Ware, D. R. (1998). Assessing the impact of agricultural drainage on ground and surface water quality in Delaware: Development of best management practices for water quality protection. Final Project Rep. Delaware Dep. Nat. Res. Environ. Control, Dover, DE. Suns, J. T., Vasilas, B. L., Gartley, K. L., Milliken, B. and Green, V. (1995). Evaluation of soil and plant nitrogen tests for maize on manured soils of the Atlantic Coastal Plain. Agron. J., 87, 213-222.