Determination of Application Rates of Nitrogen Fertilizer for ‘Shiranuhi’ Mandarin in Plastic Film Houses Using Soil Electrical Conductivity

Abstract

In this study, we developed an equation to determine nitrogen fertilizer rates for 'Shiranuhi' mandarin [(Citrus unshiu × C. sinensis) × C. reticulata] growing soils in plastic film houses to prevent salt accumulation and maintain optimum nutrient levels. We analyzed the amount of applied fertilizers, soil chemical properties, and yields from 45 farms that vary in salt concentrations on Jeju Island, Korea. The results revealed that the average soil chemical property values, such as electrical conductivity (EC), available P 2 O 5 , and exchangeable cations (K + , Ca 2+ , and Mg 2+ ), were higher than the acceptable range, except for pH and organic matter. The results showed that higher amounts of nitrogen and phosphorus were applied through fertilizer application rates (N 327 kg ha -1 , P 2 O 5 294 kg ha -1 , and K 2 O 236 kg ha -1 ) than the standard amount and rate of fertilizer for the cultivation of 'Shiranuhi' mandarin. The EC values and NO 3 -N concentration in the soils had a close correlation (r = 0.96, p < 0.001). The yields did not differ with the amounts of the applied fertilizers while there was a significant negative correlation with EC values (r = -0.455, p < 0.01) and the concentration of NO 3 -N (r = -0.476, p < 0.01) in the soils. Our results demonstrated that the NO 3 -N concentration in the soil of plastic film houses has a substantial effect on the soil EC value. Soil EC levels may determine the recommended nitrogen fertilizer rates depending on each tree's age.