OBJECTIVES:

1. Determine potential nitrogen transformations and loss pathways following applications of swine lagoon effluent on grazed and ungrazed pastures.

2. Determine potential phosphorus transformations and loss pathways from applications of swine lagoon effluent on grazed and ungrazed pastures.

3. Determine the impact of swine lagoon effluent on ground and surface water surrounding application fields.

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ACCOMPLISHMENTS:

1. Nitrogen removal from pastures with grazing cattle is much less than from fields where grass is removed as hay. Nitrogen not removed from the application site has potential to move offsite and contaminate ground or surface water.

2. A nitrogen budget has been constructed to predict the environmental fate of nitrogen in grazed and ungrazed pastures receiving swine lagoon effluent.

3. Denitrification may result in potentially significant losses of nitrogen from poorly drained soils. This gaseous loss from the soil may reflect emissions from the swine lagoon effluent or from the cattle manure and urine.

4. Ammonia volatilization from application of swine lagoon effluent can result in significant losses of nitrogen applied to bermudagrass pastures. Ammonia emissions can also be significant from the cattle manure and urine.

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SIGNIFICANCE:

Swine lagoon effluent is typically applied to crops based on the plant requirement for nitrogen. Bermudagrass hay can assimilate as much as 300-400 kg N/ha/yr from the applied effluent. Historically, the bermudagrass was cut and removed from the field as hay, carrying with it the nutrients from the applied effluent. However, there has been a rapid shift towards using the bermudagrass fields for grazing cattle instead of hay. Since cattle only assimilate 10-15' of the N ingested, there is concern that a nitrogen buildup may occur in the grazed pastures. The potential build up of nitrogen could be a threat to ground and surface water. This study is investigating the transformations and transport of nitrogen and phosphorus in grazed and ungrazed bermudagrass fields receiving regular applications of swine lagoon effluent.

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FUTURE PLANS:

Most of the current work has concentrated on nitrogen accumulation and loss mechanisms. Future efforts will include the rapid buildup of other nutrients that are concurrently applied to the soil in the effluent. In particular, phosphorus buildup has been rapid in soils receiving large applications of effluent. Similarly, the soil concentrations of zinc and copper have also been rapidly increasing. Phosphorus leaving the receiving fields may have a direct impact on water quality. Accumulation of zinc and copper may pose a threat to the future productivity of the soil for subsequent crops.

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