Uptake of N by Grass from Septic Fields in Three Soils1
- K. W. Brown and
- J. C. Thomas2
The N component of septic tank effluent could increase the concentration of nitrate in the groundwater. This study was conducted to determine the ability of vegetation to take up N from the soil surrounding septic lines, to minimize the movement of N to the groundwater. Six replications of three soils were enclosed in large undisturbed monolith lysimeters each containing a septic line. The soils had percolation rates of 25.4, 3.8, and <0.3 cm per hour and represented the range of those generally used for septic tank effluent disposal. The N content of the effluent was measured weekly and applications of effluent were made daily at rates based on the percolation tests. Common Bermudagrass (Cynodon dactylon L.) was harvested on three occasions representing a period of 1 year. Harvesting was done in strips above and adjacent to the field to determine the horizontal distribution of uptake. Grass uptake was equivalent to 9%, 32%, and 46% of the N applied to the soils which had percolation rates of 25.4, 3.8, and <0.3 cm/hour. Thus, the percent uptake was inversely related to the amount of N applied per unit area. The largest fraction was taken up from the soil which received the least amount of effluent. Uptake decreased rapidly with distance from the septic line, such that at a distance of 60 cm from the edge of the line the uptake approached that from the unfertilized native soil. These results indicate the possibility of utilizing vegetation to remove some of the N applied to septic fields, particularly from large fields which are installed in slowly permeable soils. It is suggested that physical removal of the grass would be necessary to achieve the desired effect.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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