Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/1999
Publication Date: 6/1/2000
Citation: HE, Z.L., CALVERT, D.V., ALVA, A.K., BANKS, D.J., LI, Y.C. NUTRIENT LEACHING POTENTIAL OF MATURE GRAPEFRUIT TREES IN A SANDY SOIL. SOIL SCIENCE, 165:748-758. 2000. Interpretive Summary: Nutrient leaching is a concern in sandy soils under routine agricultural practices. Field and leaching column experiments were conducted to determine leaching of nitrate (NO3), phosphate (PO4), and potassium (K) from a Riviera fine sand (Alfisol), a major soil type used for grapefruit production. Nitrogen (N) and K rates varied from 0 to 168 kg per hectare, while phosphorus (P) rates varied from 0 to 30 kg per hectare. Soil solution samples were collected at 120 and 180 cm depth, which represented above and below the hardpan. There was evidence of nitrate leaching at both sampling depths, however, the concentrations were greater at 120 cm than that at 180 cm depth. All concentrations were below 10 mg per liter, the maximum contaminant level limit for drinking water quality. The concentration of phosphorus in soil solution varied from 0.25 to 0.70 mg per liter at 120 cm depth. Since this depth represents above the hardpan, in a bedded grove the soil solution from this depth can seep into the wate furrows which, in turn, become a part of the return flow. Therefore, management practices aimed to minimize nutrient leaching should be developed to reduce the potential nutrient leaching into surface water.
Technical Abstract: Field and column leaching studies were conducted to examine the leaching of NO3 and PO-4 in a Riviera fine sand (loamy, siliceous, hyperthermic, Arenic Glassaqualf) under grapefruit production that received 0 to 168, 0 to 30, and 0 to 168 kg/ha/yr of N, P., and K, respectively. The concentrations of NO3-N PO4-P and K were measured in soil solution sampled using suction lysimeters installed above (120 cm) and below (180 cm) the hardpan. Colum leaching was conducted using soil collected from 0 to 30, 30 to 60, 60 to 90, 90 to 120, 120 to 150, and 150 to 180 cm of the profile, and the amounts of N, P., and K applied to the leaching column were equivalent to the application rates in the field. The concentrations of NO30N, PO4-P, and K in soil solution at both 120 and 180 cm depths increased with increasing fertilizer rates. The concentrations of NO3-N and PO4-P in soil solution were much higher at the 120 cm depth than at the 180, whereas the reverse was true with respect to K concentrations. The average concentrations of NO3-N in soil solution at both the 120 and 180 cm depths over 3 years were well below 10 mg/L, the U.S. Environmental Protection Agency (U.S.-EPA) drinking water quality standard, even at the highest rate of fertilizer application. Solution K concentrations at the 180 cm depth were close to or slightly higher than 12 mg/L, the maximum level for drinking water. Solution PO4-P concentrations at the 120 cm depth (.25 to 0.70 mg/L) were much higher than the U.S. EPA standard for fresh waters (0.025 to 0.05 mg/L). The argillic horizon in the Riviera fine sand effectively reduced downward movement of PO4-P and K because it had a much greater sorption capacity for phosphate and K, but it had much less effect.