Wastewater Treatment Plant Upgrades - Potential Reductions:

  • Nitrogen: 35 million pounds at $8.56 per pound
  • Phosphorus: 3 million pounds at $74 per pound
  • Sediment: None

The estimates assume that most, but not all, major wastewater treatment plants in the watershed would control nitrogen concentrations in effluent to 3 milligrams of nitrogen per liter of water as an annual average. The figures include $3.2 billion in construction costs, plus annual operation and maintenance expenses, over a 20-year project period, which works out to an annualized cost of $8.56 per pound of nitrogen. Reducing phosphorus by 3 million pounds would require an additional $1.2 billion, at an annualized cost of $74 per pound. Of all of the practices, wastewater treatment plant upgrades have the greatest degree of confidence for consistent, long-term reductions.

Diet & Feed Adjustments - Potential Reductions:

  • Nitrogen: Figures under development
  • Phosphorus: 0.22 million pounds at no additional cost (poultry only)
  • Sediment: None

Animals only use a certain amount of the nitrogen and phosphorus in their feed, so optimizing nutrients in feed can reduce the amount in the manure they produce. The clearest example is with poultry, where the addition of the enzyme phytase allows birds to absorb more of the phosphorus in feed, reducing the need for supplemental phosphorus in the diet. Phytase has already reduced average phosphorus concentrations in poultry litter by 16 percent, and further diet refinements may achieve a 30–40 percent phosphorus reduction in poultry litter. This analysis assumed a 32 percent reduction from pre-phytase levels with watershed wide use of phytase. In addition, optimizing nutrient levels in feed for other livestock could produce nitrogen reductions of 30–50 percent and phosphorus reductions of 40–60 percent, but the report said that research was too preliminary to incorporate into estimates at this time.

Traditional Nutrient Management - Potential Reductions:

  • Nitrogen: 13.6 million pounds at $1.66 per pound
  • Phosphorus: 0.8 million pounds at $28.26 per pound
  • Sediment: None

Nutrient management plans seek to optimize fertilizer and manure applications to the needs of crops being grown on a particular field, thereby limiting the potential for excess nutrients to run off the field. Through 2002, nutrient management plans had been written for about 85 percent of Maryland croplands, 45 percent of Pennsylvania’s and 40 percent of Virginia’s. Developing nutrient management plans for the remaining croplands would cost about $22.7 million.

Enhanced Nutrient Management - Potential Reductions:

  • Nitrogen: 23.7 million pounds at $4.41 per pound
  • Phosphorus: 0.8 million pounds at $95.79 per pound
  • Sediment: None

Enhanced nutrient management calls for a further 15 percent reduction in nutrient applications beyond those recommended under traditional plans. Traditional nutrient management seeks to maximize production under ideal conditions, which typically are not present, leaving unused nutrients to run off the field. Enhanced nutrient management is based on the fertilizer needs of crops during more typical growing conditions. The costs are $40 an acre to include an incentive for farmers, who are reluctant to risk lower yields, and to provide an insurance “safety net” in the event of reduced production in a given year as well as technical assistance. The report assumes a $255 million expense for the program.

Cover Crops:

Potential Reductions - Late:

  • Nitrogen: 15.2 million pounds at $3.50 per pound
  • Phosphorus: 0.22 million pounds at no additional cost
  • Sediment: 0.11 million tons at no additional cost

Potential Reductions - Early:

[Figures are in addition to benefits of late cover crops]

  • Nitrogen: 8.1 million pounds at $2.33 per pound
  • Phosphorus: 0.22 million pounds at no additional cost
  • Sediment: 0.11 million tons at no addi- tional cost.

Cover crops are small grain crops planted in the fall to absorb excess nutrients left in the field after crops are harvested. Unlike winter grain crops which are grown for harvest, these are not fertilized. “Late” cover crops are sown after the harvest of the row crop and up to 14 days after the average date of the first killing frost. Early cover crops are planted more than seven days before the average date of the first killing frost, and—because they are planted before the row crop is harvested—must be planted through the air or by other means that disperse seeds through existing crops. The report’s estimates were based on planting cover crops on half of all crop acreage, with half of those acres being planted with “early” cover crops. (Under normal crop rotations, fields are planted with a crop every other winter, and therefore not available for cover crop planting.) At an annual cost of $27 per acre for an estimated 2.1 million acres of cropland, the cost would be $56 million a year.

Conservation Tillage - Potential Reductions:

  • Nitrogen: 12 million pounds at $1.57 per pound
  • Phosphorus: 2.59 million pounds at no additional cost
  • Sediment: 1.68 million tons at no addi- tional cost

Conservation tillage covers a set of planting techniques that use minimal soil cultivation to reduce erosion and associated nutrient losses, as well as improve soil quality. The lack of plowing, though, makes it difficult to use manure as it cannot be injected into unplowed land as easily as chemical fertilizers. The reduction figures assume an annual cost of $9 per acre for using conservation tillage on 2.1 million acres not using the practice today. The cost includes a $15 per acre incentive during the first four years to promote the practice, plus an ongoing $3 per acre per year operating cost.

Note: Adding the nutrient reductions from individual agricultural practices overestimates the total amount of nutrient reductions achieved. That’s because some actions, such as nutrient management or enhanced nutrient management, result in less fertilizer being placed on fields, which therefore reduces the benefits of other practices, such as conservation tillage or cover crops. As a result, if the agricultural practices were added individually, they would appear to result in reduction of 72.6 million pounds of nitrogen, and a reduction of 4.85 million pounds of phosphorus. When the cumulative impacts are estimated, though, the reductions are 53.6 million pounds of nitrogen, and 2.93 million pounds of phosphorus. The report uses the cumulative figures to avoid overestimating.