Abstract
Effects of overhead liquid fertilizer application on soil property, tree nutrition, yield and fruit quality of satsuma mandarin (Citrus unshiu Marc.) were investigated. Liquid fertilizer was prepared by dissolving solid fertilizer containing 15% nitrogen, 15% phosphorus and 10% potassium in water at 300-fold dilution. Eleven-year-old ‘Nichinan No. 1’ trees top-grafted on ‘Nankan No. 20’ (interstock)/trifoliate orange rootstocks were used. The soluble fertilizer was applied three times in March and five times from early October to early November at weekly or ten-day intervals. As controls, pellet-shaped solid fertilizer containing 50–60% organic materials, 8–10% nitrogen, 7% phosphorus and 7–8% potassium was applied on soil surfaces at a rate of 7 kg (early March), 8 kg (early October) and 5 kg (early November) per 10 a as nitrogen equivalents. In addition, plots in which nitrogen content was reduced by 30% in both liquid and solid fertilizer were allocated. The soil EC was slightly lower in the liquid than solid fertilizer application. The soil and leaf nitrogen content were also lower in the liquid fertilizer plots. These facts were further evidenced by leaf SPAD values representing chlorophyll concentrations. There were no significant differences in yield, fruit weight, Brix or titratable acidity of fruit juice among the treatments. Thus, liquid fertilizer application using sprinkler systems can be recommended since this method can greatly save labor cost compared with solid fertilizer application by hand.
