There has been increasing concern over nutrient loss from agricultural practices that may contribute to the accelerated contamination of groundwater and surface waters. This concern is greater in sandy soils, which have minimal nutrient retention capacity. Both field- and column-leaching studies were conducted to examine the leaching of NO - 3 , PO 3- 4 , and K in a Riviera fine sand (loamy, siliceous, hyperthermic, Arenic Glossaqualf) under grapefruit production that received 0 to 168, 0 to 30, and 0 to 168 kg ha -1 yr -1 of N, P, and K, respectively. The concentrations of NO 3 -N, PO 4 -P, and K were measured in soil solution sampled using suction lysimeters installed above (120 cm) and below (180 cm) the hardpan. Column 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 NO 3 -N, PO 4 -P, and K in soil solution at both 120- and 180-cm depths increased with increasing fertilizer rates. Fertigation tended to enhance leaching of NO 3 -N, PO 4 -P, and K compared with dry soluble granular application. The concentrations of NO 3 -N and PO 4 -P in soil solution were much higher at the 120 cm depth than at the 180 cm depth, whereas the reverse was true with respect to K solution concentrations. The average concentrations of NO 3 -N in soil solution at both the 120- and 180-cm depths over 3 years were well below 10 mg L -1 , 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 -1 , the maximum level for drinking water set by the European Community. Solution PO 4 -P concentrations at the 120-cm depth (average 0.25 to 0.70 mg L -1 over 3 years for plots receiving various amounts of fertilizer) were much higher than the U.S. EPA criteria for fresh waters (0.025 mg L -1 in lakes and 0.05 mg L -1 in streams) and may constitute a P source for surface waters as soil solution above this depth is likely to seep into water furrows through lateral movement and be discharged into drainage water. A column leaching study demonstrated that the argillic horizon in the Riviera fine sand effectively reduced downward movement of PO 4 -P and K because it had a much greater sorption capacity for phosphate and K, but it had much less effect on the vertical transport of NO 3 -N along the soil profile. The results indicate that best management practices in this sandy soil region should be directed to minimizing the leaching of PO 4 -P and K in addition to NO 3 -N.
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Mar 1, 2006
D Scott + 1
Open Access