Submitted to: International Society of Citriculture Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/1999
Publication Date: 6/1/2000
Citation: ALVA, A.K., PARAMASIVAM, S., WHEATON, T.A., SYVERTSEN, J.P., TUCKER, D.H. OPTIMAL CITRUS PRODUCTION AND WATER QUALITY IN SANDY ENTISOLS. INTERNATIONAL SOCIETY OF CITRICULTURE PROCEEDINGS, Orlando, FL, p. 338. 2000. Interpretive Summary: The EPA standards for drinking water specify that nitrate_nitrogen concentration must be less than 10 mg/L. Nitrate is a final breakdown product of nitrogen fertilizers, i.e. both organic and inorganic sources. In sandy soils with low organic matter content, nitrate is not retained. Therefore, excess nitrate in these sandy soils can be transported downwards sbelow the rootzone and subsequently into groundwater along with waterfront Evidence of this potential problem was apparent in the Central Florida sandy soils under citrus production. This study summarizes six years field experiments to develop best management practices of nutrients and irrigation delivery to minimize leaching losses, while maintaining optimal production and net returns. Under careful irrigation management to replenish the deficit in the top 90 cm depth soil for 25+ year old Hamlin orange trees, the optimum fruit yield was obtained at 250 kg/ha nitrogen. Fruit yield was greater with fertigation as compared to that with similar nitrogen rate as broadcast application of water soluble granular form. The concentration of nitrate_nitrogen in the leachate below the rootzone was maintained less than 10 mg/L.
Technical Abstract: Groundwater nitrate-N (NO3-N) levels above10 mg L-1 have been found in some parts of the central Florida citrus production region where soils with >95% sand have no confining soil horizons (Entisols). We sought 6 years of data to support best management practices (BMP) for economically feasible management practices to maintain citrus yield and quality while minimizing potential leaching of nitrate into groundwater. Mature Hamlin orange tree on Cleopatra Mandarin rootstock were growing on a well drained Tavares fine sand (hyperthermic, uncoated Typic Quartzipsamments) in Highland County, Florida. Nitrogen rates from 112 to 280 kg ha-1 yr-1 were applied as eithe fertigation (FRT; 15 appl yr-1), water soluble granular (WSG; 4 appl yr-1), a combination of 50% FRT and 50% WSG (2 + 15 appl yr-1), or controlled- release fertilizer (CRF; 1 appl yr-1). Tensiometers (15 and 30 cm depth) were used to schedule irrigation to minimize leaching. Leaching was estimated from tensiometers located below the rooting depth where leached NO3-N was sampled using suction lysimeters. Within an N rate, mean fruit yield, over 6 years, was greater with FRT or WSG forms of N than that with either WSG+FRT or CRF sources. Optimum fruit yield was obtained at about 250 kg N ha-1 where the spring flush N concentration was within the range of 2.5 to 2.7%. Most of the water and nutrient leaching occurred during May through September. Using careful scheduling of irrigation and nutrient application, leaching of NO3-N accounted 22 to 34 kg ha-1 yr-1 and the NO3- concentration in the leachate remained below the 10 mg L-1 limit.