​Introduction

The advent of Maryland's Water Quality Improvement Act of 1998 will present challenges as farmers producing poultry and livestock are required to develop and implement nutrient management plans using phosphorus as the limiting factor. In addition to mandating nutrient management plans, the law also provided resources to conduct research, develop alternative uses for manure, and assist with manure transport from farms unable to utilize it. The purpose of this paper is to inform agricultural agency staff and other resource managers around the state about a number of nutrient management techniques some currently in use, others under development that may be used to help farmers with animals implement phosphorus based nutrient management plans.

Present Management Practices

Many of the practices currently used in Maryland can continue to be effective tools in managing manure and nutrients on farms. Proper management is the single most important factor controlling the fate and transport of agricultural nutrients. Cover crops, crop rotation changes, vegetative filter strips, and vegetated/riparian buffers may all be used to reduce the risk of nutrient movement. Waste management system components such as manure storage may be recommended for an operation to reduce labor, improve the timing of nutrient application, and increase flexibility. Diversion of clean surface water and roof runoff will reduce the amount of waste needing management.

Pilot Poultry Litter Transport Project

This program is currently available to assist poultry farmers who have excess poultry litter or excessive phosphorus levels in their soil. Cost-share to transport the litter to farms or other facilities where it can be used may offer the best solution for some farmers. Eligibility for this program will be expanded to include manure transport from other types of animal operations in the fall of 2000. A Manure Matching Service is also available for all animal operations that cannot fully utilize their manure resources

Phosphorus Site Index

Phosphorus can occur in either dissolved or particulate forms. Recent research indicates that when soil phosphorus levels build up in soils and exceed optimum levels for crop production, dissolved phosphorus can be transported in runoff. Although sediment control continues to be important in the control of phosphorus, which adheres to soil particles, new methods to control this dissolved fraction need to be developed and utilized. Using soil tests to indicate when problems may exist from phosphorus buildup in the soil incorrectly equates levels above agronomic optimums to environmental impacts.

The Phosphorus Site Index takes into consideration a number of site-specific factors, including slope, runoff potential, proximity to surface water, soil P levels, and fertilizer/manure application rates and methods to determine the risk of phosphorus movement. The level of risk low, medium, high, or very high governs how phosphorus may be managed. Changes in management such as incorporation of manure or implementation of best management practices (BMPs) such as vegetated buffers may reduce the risk rating. Additionally, field testing indicates that phosphorus management options can often be expanded by subdividing an existing field into smaller management units. The high risk area, for example, a steeply sloped section, could be put into permanent cover so the balance of the field could have a lower risk and manure could continue to be used as a nutrient source.

Research is continuing to evaluate, modify and verify the reliability of the P Site Index. P Site Index calibration data is being collected from farm fields in Maryland. Software using the P Index to assess P loading risk is under development. It will be incorporated into a Windows-based nutrient management planning software update of UMD's current FERTREC Program. In the interim, soil properties used in the P Index such as runoff class, erosion factor, drainage class, and leaching potential are now available on a CD for ease of use.

Conclusions Implementation of nutrient management requirements will require ongoing attention in the development of short and long-term solutions to problems associated with managing phosphorus. New laws and regulations have accelerated the need for proper management of nutrients. Developing new and cost-effective tools for nutrient management on farms is vital because of increasing livestock densities, greater reliance on purchased feeds, fewer cases of soil nutrient deficiency, and increased public concern over air and water quality. Much research on phosphorus in agriculture and animal waste management is being conducted in Maryland and throughout the world. In the short run, significant progress is being made in understanding the risks associated with excessive soil-P levels, refining animal diets, treatment of litter, soil remediation, horticultural operations and alternative uses. It will take time to develop and integrate new, cost-effective strategies into production systems. In support of these initiatives, public agencies are funding very focused and applied research in order to implement the Water Quality Improvement Act of 1998. Many research needs, however, are long term. The technologies that are developed as a result of this research are needed to achieve our environmental goals while maintaining a viable agricultural industry.

Emerging Technologies

Cost-effective and innovative solutions are needed to expand the range of acceptable options in the management of agricultural nutrients, especially manure. A number of environmentally-sound nutrient management alternatives are being studied for feasibility and implementation both on farms and as separate business enterprises. Here is a look at the current research and technological advances in the field of nutrient management in Maryland.

Dietary Changes/Feed Amendments/Enzyme Additives

In Maryland, adherence to nutrient management requirements will limit the application of excess P to the soil. Research is therefore being conducted on improving feed and feed crops for more efficient utilization of phosphorus by poultry and livestock. Phosphorus in manure can be reduced by feeding the animals less P or treating feed to improve phosphorus utilization efficiency by the animal while maintaining overall animal health and a given level of growth or production. These dietary changes hold promise in reducing the phosphorus content of manure. Researchers in Maryland are studying how various nutritional factors such as feeding methods, dietary supply of calcium and vitamin D, and enzymes such as phytase interact and affect P availability and retention.

By December 31, 2000, all contract feed produced in Maryland for chickens must include phytase or some other enzyme or additive that reduces phosphorus to the maximum extent that is commercially and biologically feasible. Maryland's Animal Waste Technology Fund offers a cost- share program to feed companies with mills in the state to cover a percentage of the eligible costs associated with equipment purchased and used in the production of feed with phytase or other similar enzymes.

Poultry On the Eastern Shore, where the greatest concentration of poultry production exists in Maryland today, litter application is limited by land and environmental constraints. Related feed and management strategies that reduce P in poultry litter are being investigated by researchers. The first of these strategies formulates feeds closer to the birds' actual P requirements. Using a four-phase production system, P and calcium dietary requirements will be established, and the nutrient content and variability of feed ingredients considered. A second feeding strategy being tested is to use phytase, an enzyme which enhances the efficiency of P recovery from phytin in grains fed to poultry. Broiler diets contain plant P, a high proportion of which is bound to phytic acid in the form of phytate P (PP). Phytase breaks down the P-phytate bonds making the P available for absorption by the bird. This will allow for reductions in dietary P. A combination of these two strategies is expected to result in a reduction in excreta P (Angel et al, 1999).

Dairy Like poultry, dairy farms in Maryland produce more P than can be used on available crop- land. As a result, many of the soils in Western and Central Maryland are high in available P. Current feeding recommendations may overestimate the amount of P required in dairy cattle diets. They use the assumption that only 50% of dietary P is digested and absorbed from the gut of mature dairy cows. Researchers are investigating ways to reduce the amount of P in manure by reducing the amount of P fed for a given level of production. A major objective of this research is to determine the amount of P in manure, P digestibility, and P retention in lactating cows fed diets with different levels of P. Results from this research could reduce mineral P supplements in dairy cattle diets, decrease total farm input of P, and decrease manure P (Kohn et al, 1999). Research using a whole-farm nutrient budgeting (nutrient inputs minus outputs) approach will identify ways to reduce phosphorus and nitrogen losses and accumulation in soils by examining different ways to improve farm management, including animal nutrition, crop management, manure handling, and soil management. Software will be developed to calculate farm nutrient balances, thereby enabling decisions related to the many other aspects of farm management that reduce environmental risk (Kohn and Steinhilber, 1999). In another research study, the impact of somatotropin, milking frequency and photoperiod on dairy farm nutrient flows was investigated. It was found that N and P reductions in manure per unit of milk produced were achieved by extending photoperiod with artificial light, using bovine somatotropin, and milking three times daily (Dunlap et al, 2000).

Soil Remediation

Soil remediation involves either chemically fixing a compound so it is biologically inactive or using some process to remove the compound from the soil. One innovative approach being investigated is a soil amendment which, in part, combines poultry litter with dredged material. Research on chemical fixation of phosphorus in poultry litter, however, has focused on the addition of compounds that "fix" or render the P in manure unavailable to the environment, i.e. to amend the animal waste with a high P affinity material. The three fixatives most often discussed in the literature are alum (aluminum sulfate), iron sulfate, and gypsum (calcium sulfate). Research is being conducted to investigate the affinity for phosphorus from agricultural waste under field conditions using gypsum and iron oxide filter cake (industrial by-products produced by a Maryland company) as a soil and manure amendment (Felton and Hughes, 1999). Chemical fixation makes P unavailable for the long term. It does not remove phosphorus from the system. Though research indicates significant reductions in soluble P are possible as compared to unamended poultry litter, the secondary effects of fixatives on the environment remain a concern

Phytoremediation

Phytoremediation is the growing of crops that are hyper accumulators of target compounds. Hyper accumulators have the ability to concentrate high levels of target elements in plant tissue. This technique has been successful in removing heavy metals from contaminated soils. With respect to nutrients, research is being conducted to identify alternative cover crops and cultivars with high P uptake potentials (Dzantor and Vough, 2000). In another study, six different cropping systems composed of alfalfa and other cool-season forage grasses will be compared over a three-year period. An expected result of this project will be to quantify soil P reduction that can be attained annually using crops that are known to take up large amounts of P from phosphorus-enriched soils and which have high market value (Vough and Dzantor, 2000). Use of constructed wetlands to study the growth and nutrient uptake response of five different wetland plant species is also being investigated (Baldwin and Clarke, 1999).

Nursery Industry

The "green industry," the second largest agricultural industry in Maryland, offers unique challenges as growers use a variety of fertilizers, types of irrigation, and runoff containment systems. Risk assessment profiles are being developed for these operations. Irrigation, nutrient application, and nutrient runoff are currently being researched to quantify potential environmental impacts and to develop nutrient reduction strategies for container-nursery and greenhouse operations (Lea-Cox et al, 1999). The data collected in this study will be used to calculate complete N and P budgets and associated risk assessment for applying soluble fertilizers to containerized growing systems for conditions on Maryland's Eastern Shore.

Composting for Horticultural Uses

Composting is the natural, biological process of decomposition of solid material in a predominantly aerobic environment. During composting, water content decreases and handling characteristics improve. After the compost is cured, it can be used as a soil amendment or can be further enhanced with either organic or inorganic nutrients to develop a value-added compost of known and marketable fertilizer value. Current research is being conducted to identify potential uses of poultry litter and cattle manure compost in horticultural potting mixes. This study is examining compost preparations, potting mix formulations, and fertilizer regimes appropriate to the compost based media for these high value markets (Bouwkamp and Carr, 1999). Preliminary results show a great deal of promise but longer term evidence of product consistency and homogeneity is required before widespread industry adoption is likely.

Pelletizing

Processed manure can be pelletized and used in fertilizer and feed production. Pellets can be handled using conventional equipment and easily stored and transported. Because manure is compacted during pelleting, the post-processing costs of transportation and handling are less. Poultry manure pellets can be applied on farms using conventional, accurately calibrated fertilizer spreaders and planting equipment. Perdue AgriRecycle is developing a multipurpose facility which will include numerous technologies (pelleting, composting, etc.) for the production of products from poultry waste.

Energy Generation

The use of poultry litter as fuel for generation of off-farm electricity is currently being examined for technical and economic viability. The combustion of poultry litter at power stations in Great Britain produce gases which are low in major pollutants and after electrostatic treatment, are suitable for discharge to the atmosphere. The process also produces a nitrate-free, sterile ash which is high in phosphate and potash and can be used as a base in the manufacture of fertilizers. The residue is 10% of the original weight and can be easily transported. Great Britain currently has two facilities of this type on line, however, the technology is heavily subsidized by the government and requires a guaranteed source and quantity of litter. Similar facilities are also being considered in Minnesota and Australia.

In Maryland, this technology was considered at an existing wood chip burning cogeneration facility in Somerset County. A feasibility study was conducted and in November 1999, and a test burn was performed using poultry litter as the primary fuel source. It was determined from this test that extensive boiler modifications would be required and that it was not economically feasible for this plant to convert to litter. Maryland Environmental Service continues to operate this cogeneration plant for the Department of Corrections using wood chips for fuel. Private enterprise is continuing to pursue the use of poultry litter as the source of fuel at a gasification plant also located in Somerset County and granulated fertilizer will be produced for the custom blend market.

Implementation of nutrient management requirements will require ongoing attention in the development of short and long-term solutions to problems associated with managing phosphorus. New laws and regulations have accelerated the need for proper management of nutrients. Developing new and cost-effective tools for nutrient management on farms is vital because of increasing livestock densities, greater reliance on purchased feeds, fewer cases of soil nutrient deficiency, and increased public concern over air and water quality.

Much research on phosphorus in agriculture and animal waste management is being conducted in Maryland and throughout the world. In the short run, significant progress is being made in understanding the risks associated with excessive soil-P levels, refining animal diets, treatment of litter, soil remediation, horticultural operations and alternative uses. It will take time to develop and integrate new, cost-effective strategies into production systems. In support of these initiatives, public agencies are funding very focused and applied research in order to implement the Water Quality Improvement Act of 1998.

Many research needs, however, are long term. The technologies that are developed as a result of this research are needed to achieve our environmental goals while maintaining a viable agricultural industry.

References

Kohn, R.A., B.P. Glenn, R. Angel and R.A. Erdman. 1999. Feeding to Reduce Phosphorus Excretion by Lactating Dairy Cattle. Maryland Nutrient Reduction Research Proposal.

Kohn, R.A. and P.M. Steinhilber. 1999. Quantifying the Phosphorus and Nitrogen Flows in Animal Production Systems. Maryland Nutrient Reduction Research Proposal.

Dunlap, T.F., R.A. Kohn, G.E. Dahl, M. Varner, and R.A. Erdman. 2000. The Impact of Sumatotropin, Milking Frequency, and Photoperiod on Dairy Farm Nutrient Flows. J. Dairy Sci. 83:968-976.

Felton, G. and K. Hughes. 1999. Immobilization of Soluble Phosphorus in Agricultural Waste Using Secondary Waste Acid Neutralization (SWAN) Gypsum and Iron Oxide Filter Cake By-Products. The State of the Science of Phosphorus in Agriculture: The Second Annual Report of the University System of Maryland (12/99).

Angle, J.S., R.L. Chaney and A. Baker. 1995. Soil Remediation Using Hyper accumulator Plant Species. Internal MAES Project. www.agnr.umd.edu/maes_exe/research/facsearch.cfm

Dzantor, E.K. and L.R. Vough. 2000. Feasibility of Developing New Plant Species and Management Practices for Phytoremediation of Phosphorus Enriched Soils. Maryland Nutrient Reduction Research Proposal.