Nitrogen best management practice for citrus trees. II. Nitrogen fate, transport, and components of N budget

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Scientia Horticulturae


Soils in central Florida citrus production region are very sandy, hence are vulnerable to leaching of soluble nutrients and chemicals. The objective of this study was to develop nitrogen (N) and irrigation best management practices for citrus in sandy soils to maintain optimal crop yield and quality, and to minimize N leaching below the rootzone. A replicated plot experiment was conducted in a highly productive 20+ year-old 'Hamlin' orange [Citrus sinensis (L.) Osbeck] trees on 'Cleopatra mandarin' [(Citrus reticulata Blanco)] rootstock grove located on a well drained Tavares fine sand (hyperthermic, uncoated, Typic Quartzipsamments) in Highland County, FL. Nitrogen rates (112-280 kg ha-1 year-1) were applied as fertigation (FRT), water soluble granular (WSG), a combination of 50% FRT and 50% WSG, and controlled release fertilizer (CRF). Tensiometers were used to monitor the soil moisture content at various depths in the soil profile as basis to optimize irrigation scheduling. Fruit yield and quality and nutritional status of the trees were reported in a companion paper. Soil solution was sampled at 60, 120, and 240 cm depths under the tree canopy using suction lysimeters. Concentrations of NO3-N in the soil solution at 240 cm deep, which is an indicator of NO3-N leaching below the tree rootzone, generally remained below the maximum contaminant limit (MCL) for drinking water quality (10 mg L-1) in most samples across all N sources and rates, but for few exceptions. Total N in the fruit was strongly correlated with fruit load, thus, at a given N rate N removal by the fruit was lower during years of low fruit yield as compared to that during the years of high fruit yield. Furthermore, there was a strong linear relation between N and K in the fruit. This supports the need to maintain 1:1 ratio between the rates of N and K applications. In a high fruit production condition, the N in the fruit accounted for about 45% of the total N input on an annual basis. Fifteen percent of the total N input at 280 kg N ha-1 year-1 was not accounted for in the citrus N budget, which could be due to leaching loss. This estimate of potential leaching was very close to that predicted by LEACHM simulation model. The improved N and irrigation management practices developed in this study contributed to an improved N uptake efficiency and a reduction in N losses. © 2006 Elsevier B.V. All rights reserved.

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