THE LEOPOLD CENTER FOR SUSTAINABLE AGRICULTURE
Priority Area/focus categories Because of the association of phosphorus in runoff with eutrophication of surface freshwater sources, it is likely that the U.S. Environmental Protection Agency will implement regulations to control the Total Maximum Daily Loads (TMDLs) in watersheds within the next five years. To date, phosphorus loads in runoff from agricultural lands in the United States are poorly quantified. This is particularly true for pasturelands in the Midwest. Thus, the database of phosphorus loads that will be used to set TMDLs will likely be developed from models that rely heavily on factors like the slope of the terrain. Unfortunately, these models do not consider the benefits of management practices like rotational or deferred grazing, regulating sward height, or hay harvest that are likely to reduce sediment and/or nutrient losses while increasing forage production and quality. Furthermore, these models do not consider the effects of grazing management on the phosphorus balance and excretion of cows. Thus, grazing could unnecessarily be prohibited on much of the pastureland bordering 8,868 miles of rivers and streams in Iowa alone. Even if grazing were allowed with fencing of buffer strips, it would cost farmers as much as $3,800 per mile or $33.6 million in Iowa alone to provide such fences. Because producers are likely to be unwilling to pay for these alterations, such regulations may actually result in producers converting more pastureland to row crop production with a consequent aggravation of the eutrophication problem.
The objectives of the proposed project are: 1) to quantify sediment and phosphorus losses in run-off and plant phosphorus uptake in pastures managed either with no grazing, continuous grazing at a sward height of 5 cm during summer, rotational grazing to residual sward heights of 5 and 10 cm during summer, or hay harvest during summer and grazing of stockpiled forage during winter; 2) to determine the efficacy of buffer strips to limit sediment and phosphorus losses from pastures; and 3) to relate soil and forage physical properties and cattle grazing management to pasture sediment and phosphorus losses with the objective of developing phosphorus flow models that can be used Comprehensive Nutrient Management Plans to manage sediment and phosphorus pollution of surface water sources. Treatments will be assigned to one of five 1-acre paddocks running to a 30-foot buffer strip within three blocks on hills on the Rhodes Research and Demonstration Farm near Rhodes, Iowa. Summer grazing will be initiated in April of 2001 and will continue through October. Winter stockpiled grazing will occur in November and December. Sediment and nutrient run-off will be measured by collection of water from rainfall simulations conducted in May, July, September, November, and March of each year and from natural rainfall events. Soil and forage physical characteristics will be measured simultaneous to the rainfall simulations. Forage nutrient uptake in pastures and buffer strips will be determined monthly by clipping and analysis of forage proximate to and within grazing exclosures and determination of hay yield and composition. Phosphorus uptake and excretion by cattle will be determined in cows fed indigestible markers. Data will be incorporated into models quantifying P run-off from pastures under different pasture and environmental conditions and integrated with results from a complementary on-farm project evaluating the effects of riparian management on sediment and phosphorus run-off to develop management systems to minimize pollution of surface water sources from pastures.
Significance of the Problem to Agriculture and the Environment in Iowa
Because of the association of phosphorus in runoff with eutrophication of surface freshwater sources, it is likely that the U.S. Environmental Protection Agency will implement regulations to control the Total Maximum Daily Loads (TMDLs) in watersheds within the next five years. To date, phosphorus loads in runoff from agricultural lands in the United States are poorly quantified. This is particularly true for pasturelands in the Midwest. Thus, the database of phosphorus loads that will be used to set TMDLs will likely be developed from models that rely heavily on factors like the slope of the terrain. Unfortunately, these models do not consider the benefits of management practices like rotational or deferred grazing, regulating sward height, or hay harvest that are likely to reduce sediment losses while increasing forage production and quality. Furthermore, these models do not consider the effects of grazing management on the phosphorus balance and excretion of cows. Thus, grazing could unnecessarily be prohibited on much of the pastureland bordering 8,868 miles of rivers and streams in Iowa alone. Even if grazing were allowed with fencing of buffer strips, it would cost farmers approximately $3,800 per mile or $33.6 million in Iowa alone to provide such fences. Because producers are likely to be unwilling to pay for these alterations, such regulations may actually result in producers converting more pastureland to row crop production with a consequent aggravation of the eutrophication problem.
Statement of Expected Results or Benefits The proposed project will benefit Iowa agriculture by quantifying phosphorus transport from paddocks under different grazing management practices. Thus, the results of the project will provide regulatory organizations with data necessary to develop TMDLs that consider the benefits of improved grazing practices on the prevention of nutrient losses in runoff water as well as improved forage yield and quality. Furthermore, determining the relationships of nutrient loss with soil and sward characteristics and modeling plant nutrient uptake, phosphorus intake and excretion by grazing animals, and sediment and nutrient runoff will allow the development of methods of monitoring and, more importantly, managing phosphorus losses from grazed and fallowed pastures. The relationships and models developed from this project will be combined with data obtained in a complementary project in which sediment and phosphorus loads in streams will be determined on 18 farms with different riparian grazing management strategies to develop management practices minimizing sedimentation and phosphorus pollution of surface water sources.
Nature, Scope, and Objectives of Research
Methods, Procedures, Facilities, Interdisciplinary elements of research
Three blocks of approximately 2.75 hectares along hillsides will be located in a smooth bromegrass pasture on the Iowa State University Rhodes Research Farm. A 6-m lane will be placed along the top of each block for movement of cattle between pastures, and a 10-m vegetative buffer strip will be placed between the lane and pastures to prevent nutrient flow onto the experimental plots. To evaluate the efficacy of buffer strips to control nutrient runoff, a 10-m buffer strip (a 10:1 pasture:buffer ratio) will also be located along the bottom of each block. Each block will be divided into five 0.4-hectare paddocks with fence and sandbags to prevent runoff flow between paddocks. To attain equal initial phosphorus concentrations, soils will be sampled at the 0 to 5 cm and 5 to 10 cm depths, analyzed for P by the Bray 1 method, and fertilized with P to an adequate level. Every spring, each paddock will be fertilized with N as ammonium-nitrate at a rate of 67 kg/ha. Waterers for stock will be placed at the top of each paddock.
In each block, 5 forage management treatments will be allotted to the five paddocks. One paddock will not be grazed. To evaluate the effects of grazing systems on sediment and nutrient losses, one paddock in each block will be grazed by 3 non-pregnant cows during summer to a sward height of 5 cm as determined with a rising plate meter (4.8 kg/m2) which will be maintained by a put-and-take stocking system thereafter. This treatment will simulate an intensively grazed continuous stocking system. Two paddocks will be grazed with 3 non-pregnant cows to sward heights of 5 or 10 cm as measured with a rising plate meter. When sward heights decrease below the minimal sward height, cows will be removed from that paddock and placed on an adjacent smooth bromegrass pasture to provide the paddocks with a 35-day rest period. These treatments will simulate rotational grazing systems at an equal and lower number of grazing days per hectare as the continuous stocking treatment. To limit the amount of additional phosphorus added to the pasture as faeces and urine, cows will not be supplemented with phosphorus, either while they are on the experimental paddocks, or while they are grazing the adjacent smooth bromegrass pasture between periods of experimental grazing.
The remaining paddock in each block will be used to evaluate nutrient run-off from pastures used for a management system that integrates summer hay harvest with winter stockpiled grazing. Forage from these paddocks will be harvested as small bales in two cuttings before early August. In early August, residual forage will be allowed to stockpile for late fall grazing. In early December, each stockpiled paddock will be grazed by 3 non-pregnant cows until 70% of the forage is removed.
To evaluate the effects of treatments on sediment and nutrient losses, nine monitoring sites will be located in each paddock. Three of the sites will be immediately above the buffer strip and six of the sites will be on at least two different slopes. Three additional sites will be located immediately below the lower buffer strip. Water infiltration and sediment, phosphorus and nitrogen losses at each monitoring site will be determined by Jim Russell, John Kovar and their assistants in March, May, July, September, and November of each year using 0.5 x 1.0 m drip rainfall simulators (Bowyer-Bower and Burt, 1989) with a precipitation rate of 10 cm/hr for 90 minutes. To validate the use of rainfall simulations to predict nutrient losses from pastures, runoff from natural rainfall events will also be collected by Steve Mickelson and his assistants in the paddocks with no grazing and continuous grazing to 5 cm.. In each of these paddocks, two 3 m x 24.4 m collection plots will be constructed to include both the buffer and the upslope pastures using area ratios of 5:1 and 10:1. All plots will be hydrologically isolated from their surroundings by sheet metal borders driven in the ground. A collector at the bottom of each plot, will direct runoff water to a 2.4 m diameter x 0.6 m deep collection tank. Runoff amounts will be measured volumetrically after each rainfall event. Sediment concentration in runoff water will be determined by oven drying. Subsamples of runoff water will be analyzed for total nitrogen, ammonia-nitrogen, nitrate-nitrogen, total phosphorus, and dissolved reactive phosphate.
To measure the effects of treatments on soil and plant characteristics, soil samples, soil physical measurements and forage samples will be collected adjacent to each monitoring site and within each buffer strip simultaneous to the infiltration experiments by Jim Russell and his assistants. Soil samples will be collected from 0 to 5 and 5 to 10 cm depths and analyzed for texture, bulk density, pH and the contents of moisture, total carbon, total nitrogen, nitrate-nitrogen, total phosphorus and soluble phosphorus. Soil penetration resistance will be measured to a depth of 20 cm. Soil surface roughness will be measured using a 2-m chain. Hill slope will be measured with a digital level. Proportions of bare soil will be measured from image analysis of digital photographs. Forage sward height will be measured with a rising plate meter (4.8 kg/m2). Forage samples will be hand-clipped, weighed, and analyzed for dry matter, in vitro digestible dry matter, total carbon, nitrogen and phosphorus.
The effects of forage treatments on uptake of soil nutrients will be determined using six 1-m2 grazing exclosures in each paddock. At the initiation of each month, grazing exclosures will be moved to a new position within the paddock and a forage sample will be clipped from a .25-m2 area adjacent to the exclosure by Jim Russell and his assistants. At the end of each month, a sample will be clipped from a .25-m2 area within the exclosure. Simultaneously, forage samples will be clipped from within the vegetative buffer strip. Forage harvested as hay will also be sampled at each harvest. Forage samples will be weighed, dried and analyzed for nitrogen and phosphorus to determine nutrient uptake and harvest by the forage plants. Root samples will be collected by John Kovar and his assistants each year to determine the effects of grazing management on below-ground biomass.
Simultaneous to forage sampling, soil samples will be collected and analyzed by John Kovar and his assistants for available phosphorus by the Bray 1 and Mehlich III methods, exchangeable potassium, calcium, magnesium, sodium, total nitrogen and total carbon so that changes in nutrient status with time can be monitored.
To evaluate the impacts of forage management on phosphorus balance within a system and phosphorus losses from a system, phosphorus balance will be determined in cows monthly by Wendy Powers and her assistants. To estimate phosphorus excretion, cows will be dosed with boluses containing an indigestible marker (chromic oxide) daily for 7-day adjustment and 5 day collection periods. During the collection period, fecal samples will be collected and analyzed for chromium and phosphorus to determine total faeces and phosphorus excretion. The concentration of in vitro digestible organic matter and phosphorus in forage consumed by grazing cows and the total fecal excretion will be used to determine phosphorus intake. Phosphorus balance in the cows will be determined as the difference between the amounts of phosphorus consumed and excreted. These values along with the forage phosphorus uptake and phosphorus runoff data will be used to model phosphorus flow within the system which will be used to develop Comprehensive Nutrient Management Plans for farms with grazing enterprises.
Simultaneous to conducting this project, the amounts of stream bank and gully erosion, sheet and rill erosion, phosphorus and nitrogen discharge in streams and in-stream integrity will be monitored by Richard Schultz, Tom Isenhart and their assistants on 18 farms with at least five riparian management strategies including: 1) grazed pastures to varying sward heights, 2) rotationally grazed riparian forest zones, 3) ungrazed filter strips, 4) ungrazed riparian forest buffers, and 5) cropped riparian zones. Models of the results from the controlled studies at the Rhodes Research Farm will be tested using the results of the on-farm projects.
Related Research
Because of its contribution to the eutrophication of surface water, phosphorus in runoff from agricultural lands must be limited through improved management practices. Much of the phosphorus in runoff water is adsorbed to soil and, therefore, management practices that limit soil erosion also limit phosphorus pollution (Sharpley and Menzel, 1987). Because increased leaf cover reduces sediment loss from soils under pasture (Russell et al in press) and associated enhanced plant roots hold soil in place, increased forage production has generally been associated with lower rates of sediment erosion and nutrient runoff than row crop agriculture (USDA, 1982). However, soil compaction, disruption of the soil surface, and loss of plant cover and roots may occur in poorly managed pastures stocked with excessive animal numbers (Betteridge et al., 1999). These changes in sward and soil properties may lead to greater rates of sediment and nutrient runoff, particularly from the highly erodible soils on which most Iowa pastures located. Maintaining adequate forage to reduce surface runoff and associated nutrient flow from pastures (Schepers and Francis, 1982) and maintaining plant integrity and growth to optimize plant nutrient uptake through proper grazing management (Edwards et al., 2000) can be useful in reducing eutrophication of surface water bodies. One technique to manage pasture forage to maintain plant vigor, stabilize sediments, limit streambank trampling, and maintain cattle body weight gains is the maintenace of a minimum stubble height of 7 to 10 cm (Clary and Leiniger, 2000). Placement of vegetative buffer strips between pastures and surface water sources can also reduce nutrient runoff (Dillaha et al., 1989). Furthermore, hay and silage harvest removes nitrogen and phosphorus from pastoral soils, reducing their pollution potential (Russell, 1999). Reducing phosphorus excretion by cattle through nutritional manipulation may also be used to limit phosphorus release into the environment and water sources (Russell, 1999).
Because the effects of these practices on phosphorus losses are poorly quantified, particularly over long periods, current models predicting nutrients in runoff from agricultural lands do not adequately consider the benefits of such management practices in limiting nutrient runoff and, therefore, overestimate phosphorus losses from properly managed pastures. This overestimation may result in excessive reductions in animal stocking rates to meet regulatory requirements. This might then result in poorer economic returns from pastures and reduced incentive for producers to maintain land in forage production. Because 33% of the total length of rivers and streams in Iowa run through pastures, the economic impacts of reduced livestock farming could be considerable.
Graduate Student Training Potential
Because this project is investigating the effects of grazing management on the interface of the water, soil, plant and animal components of the ecosystem, this project provides graduate students with the unique opportunity to become acquainted with methodologies involved in studying all of these components. Amongst the methodologies used will be the measurements of water infiltration, sediment and nutrient losses in run-off water, soil physical and chemical properties, forage yield and composition, and forage intake and digestibility by cattle. In addition to learning a variety of field and laboratory techniques that students in any single discipline would not normally be involved in, graduate students will have the opportunity to develop communication skills by presenting results at field days and professional meetings and preparing papers for extension and refereed journal publications.
Qualifications of Investigators
Professor, Department of Animal Science, 337 Kildee Hall, Iowa State University, Ames IA 50011-3150, 515/294-4631, email jrussell@iastate.edu
Professional Record
Professional Activities
Publication Record Recent pertinent publications
Hitz, A. C. and J. R. Russell. 1998. Potential of stockpiled perennial forages in winter grazing systems for pregnant beef cows. J. Anim. Sci. 76:404.
Betteridge, K., A. D. MacKay, J. R. Russell, D. A. Costall, and P. J. Budding. 1998. Effect of Cattle Treading on the Soil and Pasture Resource and the Wider Environment. pp. 29-34. IN: Animal Production Systems and the Environment. Proceedings Volume I. Des Moines, IA.
Kremer, S. M., J. R. Russell, D. R. Strohbehn, D. G. Morrical, S. K. Barnhart, and A. M. Cowen. 1998. Pasture conditions at the initiation of grazing to optimize forage productivity. Pp. 47-52. IN: Animal Production Systems and the Environment. Proceedings Volume I. Des Moines, IA. Soil Scientist, USDA National Soil Tilth Laboratory, Ames IA 50011, 515/294-3419, email Kovar@iastate.edu Assistant Professor, Department of Animal Science, 109 Kildee Hall, Iowa State University, Ames IA 50011-3150, 515/294-1635, email wpowers@iastate.edu
Van Horn, H.H., A.C. Wilkie, W.J. Powers, and R.A. Nordstedt. 1994. Components of dairy manure management systems. J. Dairy Sci. 77:2008-2030.
Powers, W.J., R.E. Montoya, H.H. Van Horn, R.A. Nordstedt, and R.A. Bucklin. 1995. Separation of manure solids from simulated flushed manures by screening or sedimentation. Appl. Engin. In Agric. 11(3):431-436.
Tomlinson, A.P., W.J. Powers, H.H. Van Horn, R.A. Nordstedt, and C.J. Wilcox. 1996. Dietary protein effects on nitrogen excretion and manure characteristics of lactating cows. Trans. of the ASAE 39(4):1441-1448.
Powers, W.J., A.C. Wilkie, H.H. Van Horn, and R.A. Nordstedt. 1997. Effects of hydraulic retention time on performance and effluent odor of conventional and fixed-film anaerobic digesters fed dairy manure wastewaters. Trans of the ASAE 40(5): 1449- 1455. Powers, W.J., H.H. Van Horn, A.C. Wilkie, C.J. Wilcox and R.A. Nordstedt. 1999. Effects of anaerobic digestion and additives to effluent or cattle feed on odors and odorant concentrations. J Anim. Sci. 77(6):1412-1421.
Powers, W.J. 1999. Odor control for 1ivestock operations. J. Anim. Sci. Vol 77, Suppl. 2/J. Dairy Sci. Vol. 82, Suppl. 2.
Powers, W.J. and H.H. Van Horn. 1999. Nutrient management planning: alternatives that facilitate off-farm nutrient export. Appl. Engng. (accepted).
Select Conference Proceedings Papers Powers, W.J. and H.H. Van Horn. 1998. Whole-farm Nutrient Budgeting: A Nutritional Approach to Manure Management - Proceedings of the 1998 Soil and Water Conservation Society 'Managing Manure in Harmony with the Environment and Society', February 10-12, 1998, Ames, IA.
Powers, W.J. 1999. Impact of state and federal regulations for clean water and air: present and future concerns. In From Feed to Field: Environmental Strategies. March 25, Holiday Inn, Ames, IA. Associate Professor, Department of Agricultural and Biosystems Engineering, 209 Davidson Hall, Iowa State University, Ames IA 50011, 515/294-6524, email estaben@iastate.edu
Professional Record
Lee, Kye-Han, T.M. Isenhart, R.C. Schultz, and S.K. Mickelson. 2000. Multispecies Riparian Buffers Trap Sediment and Nutrients during Rainfall Simulations. J. Environ. Qual. 29:1200-1205.
Lee, K-H., T.M. Isenhart, R.C. Schultz, and S.K. Mickelson. 1999. Nutrient and sediment removal by switchgrass and cool-season grass filter strips in Central Iowa, USA. Agroforestry Systems 44:121-132.
Mickelson, S.K., J.L. Baker, S.W. Melvin, R.S. Fawcett, and D.P. Tierney. 1998. Effects of soil incorporation and setbacks on herbicide runoff loss from a tile-outlet terraced field. J. Soil Water Conserv. 53(1):18-25.
Areas of Expertise
Professor, Department of Forestry, 249 Bessey Hall, Iowa State University, Ames IA 50011, 515/294-7692, email rschultz@iastate.edu
Professional Interests
Professional Experience
Teaching Experience
Publications Marquez, C.O., C.A. Cambardella, T.M. Isenhart, and R.C. Schultz. 1999. Assessing soil quality in a riparian buffer strip system by testing organic matter fractions. Agroforestry Systems 44: 133-140. Lee, K., T.M. Isenhart, R.C. Schultz, and S.K. Mickelson. 1999. Sediment and nutrient trapping abilities of switchgrass and bromegrass buffer strips. Agroforestry Systems 44:121-132.
Tufekcioglu, A., J. W. Raich, T.M. Isenhart, and R. C. Schultz. 1999. Root biomass, soil respiration, and root distribution in crop fields and riparian buffer zones. Agroforestry Systems 44:163-174.
Schultz, R.C., T.M. Isenhart, J.P. Colletti, and O. Marquez. 2000 Integrated riparian management systems to protect water quality. Chapter 7 in B. Rietveld and G. Garrett (eds.) Agroforestry: An integrated Science and Practice pp 189-281.
Isenhart, T.M., R.C. Schultz, and J.P. Colletti. 1997. Watershed restoration and agricultural practices in the midwest: Bear Creek in Iowa. Chapter 15 in J.E. Williams, M.P. Dombeck, and C.A. Woods (Eds.). Watershed Restoration: Principles and Practices. American Fisheries Society.
Schultz, R.C., T.M. Isenhart, and J.P. Colletti. 1994. Riparian buffer systems in crop and rangelands. In: Agroforestry and Sustainable Systems: Symposium Proceedings. USDA For. Ser. Gen Tech Rpt RM-GTR-261. pp13-28.
Schultz, R.C., J.P. Colletti, T.M. Isenhart, W.W. Simpkins, C.W. Mize and M.L. Thompson. 1995. Design and placement of a multi-species riparian buffer strip system. Agroforestry Systems 31:117-132.
Schultz, R.C., T.M. Isenhart, and J.P. Colletti. 1995. Riparian buffer systems in crop and rangeland. Pages 13-27 in Agroforestry and Sustainable Systems: Symposium Proceeding. USDA-Forest Service General Technical Report RM-GTR-261.
Department of Forestry, 251 Bessey Hall, Iowa State University, Ames, IA 50011, 515/294-8056, email isenhart@iastate.edu 1992, Ph.D., Water Resources. Iowa State University, Department of Botany.
Professional Interests
Professional Experience
Teaching Experience
Bharati, L., K. Lee, T.M. Isenhart, and R.C. Schultz. Submitted. Infiltration in riparian buffers and adjacent croplands. Agroforestry Systems.
Tufekcioglu, A., J.W. Raich, T.M. Isenhart, and R.C. Schultz. In Press. Soil respiration in riparian buffers and adjacent croplands. Plant and Soil.
Lee, K., T.M. Isenhart, R.C. Schultz, and S.K. Mickelson. 2000. Multispecies riparian buffers trap sediment and nutrients during rainfall simulation. J. Environ. Qual.29:1200-1205. Schultz, R.C., J.P. Colletti, T.M. Isenhart, C.O. Marquez, W.W. Simpkins and C.J. Ball. 2000. Riparian Forest Buffer Practices. Pages 189-281 In: H.E. Garrett, W.J. Rietveld and R.F. Fisher (Eds.) North American Agroforestry: An integrated Science and Practice. American Society of Agonomy, Madison, WI.
Marquez, C.O., C.A. Cambardella, T.M. Isenhart, and R.C. Schultz. 1999. Assessing soil quality in a riparian buffer strip system by testing organic matter fractions. Agroforestry Systems 44: 133-140.
Lee, K., T.M. Isenhart, R.C. Schultz, and S.K. Mickelson. 1999. Sediment and nutrient trapping abilities of switchgrass and bromegrass buffer strips. Agroforestry Systems 44:121-132.
Tufekcioglu, A., J. W. Raich, T.M. Isenhart, and R. C. Schultz. 1999. Root biomass, soil respiration, and root distribution in crop fields and riparian buffer zones. Agroforestry Systems 44:163-174.
Isenhart, T.M., R.C. Schultz, and J.P. Colletti. 1997. Watershed restoration and agricultural practices in the Midwest: Bear Creek in Iowa. Chapter 15 in J.E. Williams, M.P. Dombeck, and C.A. Woods (Eds.). Watershed Restoration: Principles and Practices. American Fisheries Society.
Isenhart, T.M. 1997. Hypoxia in the Gulf of Mexico. Pages 2:32 - 2:34 in Proceedings of Water Quality, Watersheds and You: Building Local Partnerships Conference. Ames, IA. January, 1997.
Isenhart, T.M., R.C. Schultz, J.P. Colletti and C.A. Rodrigues. 1995. Design, function, and management of integrated riparian management systems. Pages 93-102 in Proceedings of the National Symposium on Using Ecological Restoration to Meet Clean Water Act Goals. USEPA. Chicago, IL. March, 1995.
Schultz, R.C., J.P. Colletti, T.M. Isenhart, W.W. Simpkins, C.W. Mize and M.L. Thompson. 1995. Design and placement of a multi-species riparian buffer strip system. Agroforestry Systems 31:117-132.
Crumpton, W.G., T.M. Isenhart and S.W. Fisher. 1993. Fate of non-point source nitrate loads in freshwater wetlands: results from experimental wetland mesocosms. Pages 283-291 In: G.A. Moshiri, ed. Constructed Wetlands for Water Quality Improvement. Lewis Publishers.
Isenhart, T.M. and W.G. Crumpton. 1989. Transformation and loss of nitrate in an agricultural stream. Journal of Freshwater Ecology 5:123-129.
The Iowa Department of Natural Resources has been involved with this project since its inception. While preparing a proposal that only dealt with the effects of riparian grazing management on stream bank structure in collaboration with the Iowa Cattlemens' Association, the investigators were requested to consider the issue of the relationship of grazing management to phosphorus losses in water run-off from pastures by representatives from the Iowa Department of Natural Resources. After the proposal was revised to consider phosphorus run-off, the Iowa Department of Natural Resources committed $550,000 from the EPA 319 program to the complete project. However, because the budget to complete the entire project over 3 years was $810,000, we are seeking additional support.
The participation of Dr. John Kovar from the USDA-National Soil Tilth Laboratory represents additional governmental involvement in the project.
Information Transfer/Outreach/Plan Results of the project will be made available to the public by publication in the annual Iowa State University Beef Research Report. In addition, annual field days are planned at both the Rhodes Research Farm and at a minimum of one of the collaborating farms in each area of Iowa in which the on-farm demonstrations are being conducted. Furthermore, the Iowa Cattlemens' Association, who helped initiate this endeavor, intends to inform their membership of the results through publications in the Iowa Cattlemen Magazine, presentations at the annual Iowa Cattlemens' Association convention, and videotapes.
THE CONTRIBUTION OF SMALL DIVERSIFIED FARMS TO PHOSPHORUS POLLUTION OF WATER RESOURCES Phosphorus flow within agricultural systems is quite complicated and subject to many factors (Figure 1). Inputs of phosphorus to a system come both in the form of fertilizer and supplemental feeds and can only be removed in the form of marketable commodities such as grain, forage, animal, forest products and, occasionally, manure or even soil. Phosphorus entering the system and not exported as marketable product will preferably be recycled and/or sequestered in the soil, crop or animal components of the
system. Phosphorus that is not captured within the system is likely to enter surface water sources and contribute to the problem of eutrophication. While it is not difficult to hypothesize the direction and factors affecting phosphorus flow, it is imperative that we now determine the actual quantities of phosphorus flowing throughout the system under different management practices so that we can develop Comprehensive Nutrient Balance Plans which meet the Total Maximum Daily Load standards for nutrient pollution while still permitting animal production enterprises. Figure 1. Phosphorus flow on a diversified farm.
In the proposed project, we intend to examine the cycling of phosphorus within the forage component of the system (identified by the full lines in Figure 1). It would be most desirable if the flows of phosphorus to the water and, to a lesser extent, the soil could be minimized. Thus, management systems that would optimize incorporation phosphorus into marketable products or sequester the phosphorus in crops or animals would be desirable.
It is hypothesized that maintaining pasture in a vegetative state through rotational stocking management will reduce phosphorus cycling to water sources directly by increasing incorporation of phosphorus into growing pasture plants and reducing phosphorus release to the soil from senescent plants. Rotational stocking management is also likely to reduce phosphorus flow indirectly by maintaining adequate forage height to trap sediment and prevent soil compaction while increasing phosphorus incorporation in animal tissues. The effects of pasture management on sediment and nutrient loss in run-off are likely related to forage species. However, because of its prevalence in Iowa pastures and its similarities in growth characteristics to other common cool-grass species, smooth bromegrass seems to be an excellent species to use in model development. Furthermore, the physical characteristics of sward height and proportion of ground cover will be included in the models and should carry-over across species.
Harvesting forages will likely will be more effective at phosphorus removal from the system than grazing and, thereby preventing phosphorus recycling back to the soil and water, assuming that the hay is either marketed from the farm and watershed or at least utilized in a less environmentally sensitive area. However, until forage regrowth occurs, hay harvest will usually leave land more denuded and susceptible to erosion than grazing. Winter grazing of forages stockpiled in late summer has been demonstrated to be an effective method of reducing the feed costs of maintaining cows over winter. Winter grazing, however, has the potential to increase phosphorus flow in run-off because soluble phosphorus forms may be leached from stockpiled forage soon after frost damage and urinary and fecal phosphorus are excreted onto frozen ground where they may be subject to run-off with melting snow at a period when there is little forage available to sequester the phosphorus in plant growth or inhibit sediment and nutrient flow. While there may be a potential for phosphorus flow associated with winter grazing of stockpiled forages, it may still be a viable management if combined with summer hay harvest to export excess phosphorus or if conducted in areas of the farm which are less environmentally sensitive.
The use of forage buffer strips around surface water sources have the advantages over grazed pastures because buffer strips provide even greater forage heights to prevent sediment and nutrient flow, protect fragile streambanks and sequester soil nutrients without rapid release of these nutrients in the manure of grazing animals. However, as plants become senescent or a killed by frost, phosphorus within them may be released as in soluble forms similar to stockpiled forages.
The presence of trees in buffer strips provide the advantage over forage plants of sequestering nutrients in plants for decades as opposed to months and requiring infrequent removal if used to export soil nutrients (Identified as dashed lines in Figure 1). While not measured in the proposed project, it will be indirectly measured in the complementary on-farm project conducted by Drs. Schultz and Isenhart. Therefore, this data may be included in the phosphorus flow models and Comprehensive Nutrient Balance Plans developed in this project.
To model phosphorus flow through a total small, diversified farm beyond its forage and agroforestry components, one would need to consider the grain and confinement livestock components as well (identified by dashed lines in Figure 1). While the forage and agroforestry components are certainly complex and funding limitations have limited our abilities to examine all possible management considerations, the proposed project does examine these components with enough breadth to interpret far-reaching implications. In modeling row crop production, one would need to consider at least the types and slopes of soils, the species of crop planted, tillage and cultivation methods, management of fertilizer and manure, crop harvest method (grain or silage), residue management and utilization of the grain as feed or a marketable commodity. In modeling confinement livestock, one would need to consider the species and class of livestock, ration formulation, supplementation, and manipulation (such as the use of phytase), and manure handling, storage, and application. Thus, to develop a project to address this entire system is difficult under budgetary limits. Fortunately, other projects are addressing some of the variables in the row crop and confinement livestock components such that with the inclusion of information as we intend to have at the conclusion of this project, models of phosphorus flow within and from farms with different agricultural enterprises are possible in the future.
Potential for Future Funding from Other Sources: While the proposed project has already received a commitment of funding from the Iowa Department of Natural Resources and the Iowa State Water Resources Research Institute, this funding represents $614,500 of the $810,000 required to complete the entire project in three years. In the future, the investigators to submit proposals to the USDA-National Research Initiative and the USDA-National Needs Program to secure future funding. Because the effects of grazing management on nutrient run-off will most likely be long-term changes, the investigators intend to secure additional funding to monitor these sites well beyond the three years currently proposed. Related References: Betteridge, K., A.D. Mackay, D.J. Barker, T.G. Shepherd, P.J. Budding, B.P. Devantier, and D.A. Costall. 1999. Effect of cattle and sheep treading on surface configuration of a sedimentary hill soil. Australian J. Soil Res. 37:743-760. Bowyer-Bower, T.A.S. and T.P. Burt. 1989. Rainfall simulators for investigating soil response to rainfall. Soil Technology 2:1-16. Clary, W.P., and W.C. Leiniger. 2000. Stubble height as a tool for management of riparian areas. J. Range Manage. 53:562-573. Dillaha, T.A., R.B. Reneau, S. Mostagnimim, and D. Lee. 1989. Vegetation buffer strips for agricultural non-point source pollution control. Trans. ASAE 32:513-519. Edwards, D.R., T.K. Hutchens, R.W. Rhodes, B.T. Larson, and L. Dunn. 2000. Quality of runoff from plots with simulated grazing. J of the Amer. Water Res. Assoc. Gillingham, G., Thorrold, B.S. 2000. A review of New Zealand research measuring phosphorus runoff from pasture. Journal of environmental Quality 29:88-96. Needleman, B.A., Petersen, G.W., Gburek, W.J., Sharpley, A.N. 2000. Site specific environmental management for small fields: modelling the spatial variability structure of soil phosphorus. ASAE, Aug, 2000. Quinn, J.M., Cooper. A.B, Williamson R.B. 1993. Riparian zones as buffer srips in agricultural landscapes - A New Zealand perspective. In: S.E. Bunn et al (Ed.) Ecology and management of riparian zones in Australia, Marcoola, Queensland. LWRRDC. Occasional Series 05/93. Canberra and CCISR, Griffith Univ., Marcoola, Queensland. Roberts, A.H.C., Singleton, P.L., MacKay, A.D. Betteridge, K. 2000. Assuring Customers: The Soil Management Scorecard Concept. Lime and Fertilizer Research Association Conference, February, 2000, Palmerston North. Russell, J. R., Betteridge, K., Costall, D. A., MacKay, A. D. (2001, in press). Impact of Pasture Canopy, Treading Damage by Mature Cattle, and Slope on Sediment Loss, and Water Infiltration on a Hill Soil in New Zealand. J. Range Management. Russelle, M. 1999. Nitrogen and Phosphorus Cycling in Pastures. Proceeding of the Soil, Water, Plant, and Animal Management Workshop. University of Wisconsin-Lancaster Research Farm. Lancaster, WI. Sharpley, A. N. and R. G. Menzel. 1987. The impact of soil and fertilizer phosphorus on the environment. Advances in Agronomy. 41:297-324. USDA-Soil Conservation Service. 1987. Basic Statistics 1982 National Resources Inventory. Statistical Bulletin Number 756. Iowa State University Statistical Laboratory, Ames, IA. Calendar of Activities: Year 1 July-December, 2000: Establish study sites for the specific objectives and requirements of the study. This will include plot survey and flagging and initial sampling of soil. January-April, 2001: Preparation of study sites for experiment. This will include fence construction, isolation of paddocks with sandbags, placement of watering sites and grazing exclosures, initial fertilization of sites, and construction of collection system for natural precipitation. May, 2001: Initiate grazing of summer paddocks, fecal collections in grazed paddocks and rainfall simulations and collection of natural rainfall run-off, soils, and forages of all paddocks. Initiate analysis of all water, soil, and forage samples. June and July, 2001: Bale hay from the paddocks used for hay harvest and continue fecal collections in grazed paddocks July, 2001: Conduct mid-summer rainfall simulations and continue collection and analysis of natural rainfall run-off, soils and forages of all paddocks and fecal collections in grazed paddocks. August, 2001: Initiate stockpiling of forage in the paddock to be used for winter grazing and continue fecal collections in grazed paddocks. September, 2001: Conduct late-summer rainfall simulations and continue collection and analysis of natural rainfall run-off, soils and forages of all paddocks and fecal collections in grazed paddocks. October, 2001: Terminate summer grazing for first year. November, 2001: Conduct autumn rainfall simulations and continue collection and analysis of natural rainfall run-off, soils and forages of all paddocks and initiate winter grazing. December, 2001: Terminate winter grazing. Summarize Year 1 preliminary data for reports for ISWRII and other funding organizations and publication in the ISU Beef Research Report. March, 2002: Conduct early spring rainfall simulations and continue collection and analysis of natural rainfall run-off, soils and forages of all paddocks. Year 2: April, 2002: Fertilize all plots with nitrogen. May, 2002: Initiate grazing of summer paddocks, fecal collections in grazed paddocks and rainfall simulations and collection of natural rainfall run-off, soils, and forages of all paddocks. Initiate analysis of all water, soil, and forage samples. Initiate model development of phosphorus flow within system utilizing Year 1 data. June and July, 2002: Bale hay from the paddocks used for hay harvest and continue fecal collections in grazed paddocks July, 2002: Conduct mid-summer rainfall simulations and continue collection and analysis of natural rainfall run-off, soils and forages of all paddocks and fecal collections in grazed paddocks. Present Year 1 results at the annual Rhodes Research and Demonstration Farm Field Day. August, 2002: Initiate stockpiling of forage in the paddock to be used for winter grazing and continue fecal collections in grazed paddocks. September, 2002: Conduct late-summer rainfall simulations and continue collection and analysis of natural rainfall run-off, soils and forages of all paddocks and fecal collections in grazed paddocks. October, 2002: Terminate summer grazing for Year 2. November, 2002: Conduct autumn rainfall simulations and continue collection and analysis of natural rainfall run-off, soils and forages of all paddocks and initiate winter grazing. December, 2002: Terminate winter grazing. Summarize Year 2 preliminary data for reports for ISWRII and other funding organizations and publication in the ISU Beef Research Report. March, 2003: Conduct early spring rainfall simulations and continue collection and analysis of natural rainfall run-off, soils and forages of all paddocks. Continue model development of phosphorus flow within system by including Year 2 data. Initiate integration of P flow models into Comprehensive Nutrient Management Plans. Year 3: April, 2003: Fertilize all plots with nitrogen. May, 2003: Initiate grazing of summer paddocks, fecal collections in grazed paddocks and rainfall simulations and collection of natural rainfall run-off, soils, and forages of all paddocks. Initiate analysis of all water, soil, and forage samples. June and July, 2003: Bale hay from the paddocks used for hay harvest and continue fecal collections in grazed paddocks July, 2003: Conduct mid-summer rainfall simulations and continue collection and analysis of natural rainfall run-off, soils and forages of all paddocks and fecal collections in grazed paddocks. Present Year 2 results at the annual Rhodes Research and Demonstration Farm Field Day. August, 2003: Initiate stockpiling of forage in the paddock to be used for winter grazing and continue fecal collections in grazed paddocks. September, 2003: Conduct late-summer rainfall simulations and continue collection and analysis of natural rainfall run-off, soils and forages of all paddocks and fecal collections in grazed paddocks. October, 2003: Terminate summer grazing for Year 3. November, 2003: Conduct autumn rainfall simulations and continue collection and analysis of natural rainfall run-off, soils and forages of all paddocks and initiate winter grazing. December, 2003: Terminate winter grazing. Summarize Year 3 preliminary data for reports for ISWRII and other funding organizations and publication in the ISU Beef Research Report and to the Iowa Cattlemens' Association. March, 2004: Conduct early spring rainfall simulations and continue collection and analysis of natural rainfall run-off, soils and forages of all paddocks. April-June, 2004: Summarize laboratory analyses and statistical analyses of data. Integrate data with simultaneous on-farm project evaluating the relationship of grazing management to sediment and nutrients in runoff. Use Year 3 data to test and improve accuracy phosphorus flow model and Comprehensive Nutrient Management Plans. July, 2004: Preparation of final report for ISWRRI and other funding organizations, and presentation at Rhodes Research and Demonstration Farm Field Day. December, 2004: Presentations of final data and models at Iowa Forage Conference and the Iowa Cattlemen's Association Meeting.     |
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