Submitted to: Soil Science Society of America Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/1/2000
Publication Date: 6/1/2001
Citation: PARAMASIVAM, S., ALVA, A.K., FARES, A., SAJWAN, K.A. ESTIMATION OF NITRATE LEACHING IN AN ENTISOL UNDER OPTIMUM CITRUS PRODUCTION. SOIL SCIENCE SOCIETY OF AMERICA JOURNAL, 65:914-921. 2001. Interpretive Summary: Sandy Entisols with sand content > 95 %, low organic matter content, and lack of confining soil horizon provide favorable conditions for leaching of water as well as soluble nutrients and chemicals applied as a part of routine crop production practices. Nitrate leaching potential was evaluated in a sandy soil with 21 year old Hamlin orange trees on Cleopatra mandarin rootstock. Nitrogen was applied at either 112, 168, 224, or 280 kg N per hectare using either water soluble granular form(4 appl/yr), fertigation (15 appl/yr), or controlled release form (1 app/yr). Soil solution was sampled at 60, 120, and 240 cm depth using suction lysimeters for analysis of nitrate concentrations. The nitrate levels in soil solutions sampled at 240 cm depth was considered as that with potential for contamination of groundwater, since this depth represents well below the rootzone. Careful scheduling of irrigation was done using tensiometer to minimize excess leaching of water below the rootzone The nitrate concentrations in the 240 cm soil solution were generally below the 10 mg/liter limit of drinking water quality standards. This is attributable to improved irrigation scheduling and nutrient management.
Technical Abstract: Leaching of fertilizer nutrients and widespread NO3-N contamination of drinking water wells in proximity to citrus growing regions of central Florida are a serious concern. We evaluated NO3-N distribution in soil solution at various depths in the vadose zone, and N leaching below the root zone for two cropping seasons under the canopy of 21-yr-old Hamlin orange (Citrus sinensis (L.) Osbeck) trees on Cleopatra mandarin (Citrus reticulata Blanco) rootstock, on an Entisol of central Florida. The treatments included 112, 168, 224, and 280 kg N/ha/yr as either dry granular fertilizer (DGF; broadcast, in 4 equal doses) or fertigation (FRT; 15 applications/yr), and 56, 112, and 168 N kg/ha/yr as controlled- release fertilizer (CFR; single application/yr). Irrigation was scheduled using recommended tensiometer set points as guidelines, with a target wetting depth of 90 cm. The NO3-N was measured in soil solutions bi- weekly at 60-, 120-, 240- cm depths using suction lysimeters (SLs) installed under the tree canopy. The 240- cm depth sample represented soil solution below the rooting depth of the trees, and the NO3-N at this depth could contaminate groundwater. At 60- or 120- cm depths, the NO3-N concentrations occasionally peaked at 12 to 100 mg/L, but at 240 cm NO3-N concentrations mostly remained below 10 mg/L. The careful irrigation management, split fertilizer application and timing of application contributed to low leaching of NO3-N below the roots zone. Calculated NO3-N leaching losses below the rooting depth increased with increasing rate on N application and the amount of water drained, and accounted for 1 to 16 percent of applied fertilizer N.