N.C. STATE UNIVERSITY

College of Agriculture and Life Sciences
N.C. Agricultural Research Service
N.C. Cooperative Extension Service

Maximum non-hazardous soil phosphorus concentrations from applications of poultry house litter.

Prepared by: F. R. Cox

Objectives:

1. Determine the effect of poultry litter on soil test P concentration,

2. Determine the changes in soil test P with time,

3. Determine the importance of clay content and tillage practices on the P status of the soil, and

4. Determine the amount of P eroded, both sorbed on clay and in runoff waters, from soils that differ in P content and with rainfall of varying intensity.

Accomplishments:

1. Applications of poultry litter cause marked increases in soil test P that are similar to that of inorganic fertilizer per unit of P applied.

2. Soil test P is increased more on a sandy soil than a clayey one.

3. Soil test levels did not decrease in time as expected due to crop removal and soil fixation when poultry litter was applied.

4. Soluble runoff P was much greater initially on the sandier soil than the clayey ones, but soluble P also decreased more markedly with time on the sandy site.

5. Soluble P was somewhat more on the no-till than the conventionally tilled site.

6. Total runoff P was increased considerably by poultry litter applications when the soil was conventionally tilled, but was much less with no-till.

7. Total runoff P appears to decrease with time, possibly with the change in soil test P.

Significance of accomplishments:

The application of poultry litter markedly increases the extractable soil P level. This increase compares with that from the inorganic P fertilizer on both the immediate extent and overall length of the effect. The increase in soil P is less in the Piedmont than in the Coastal Plain due to the greater P buffering capacity of the Piedmont soil. Using no-till markedly reduces erosion compared to conventional tillage, thus keeping much of the P in the sediment on the land. The amount of P eroded from conventionally tilled land seems to increase with an increase in soil P and with rainfall. This last point needs to be evaluated critically to determine the threat of over-fertilizing with poultry litter to the point that our soils become a source of P pollution to our streams and lakes.

Future plans:

1. Determine the change in soil test P with time.

2. Relate soil test P concentration and runoff amount to P losses.