Phosphorus application improved the yield of citrus plants grown for three years in an acid soil in the Three Gorges Reservoir Area

The objectives of the current study were to investigate the effects of nitrogen (N), phosphorus (P), and potassium (K) application rates on yield and quality of citrus fruits, and soil nutrient availability. The experiment was carried out using 8-year-old 'Navelina' navel orange (Citrus sinensis L. Osbeck) trees in an acid yellow sandy soil over three consecutive growing years in Zigui County in the Three Gorges Reservoir Area. This experiment consisted of 14 treatments with three factors (N, P, and K) and four levels of each factor. N application doses were 0, 66, 132, and 198 kg hm-2; P application doses were 0, 16.5, 33.0, and 49.5 kg hm(-2); K application doses were 0, 27, 54, and 81 kg hm(-2). P application at 49.5 kg hm(-2) increased the yield of citrus by 32.6 % attributed to the increase in fruit number rather than mean fruit weight. P application did not affect total soluble solids of fruits when compared with the treatment without P application. Soil receiving 198 kg hm(-2) of N rate revealed the lowest soil pH, which likely increased the toxicity of aluminum and then reduced citrus yield compared with the treatment without N fertilization. N and P application did not affect available N and available P in soils compared with treatments without N and P applications, respectively. We speculate that the increased fruit yield response of citrus trees by P fertilization is possibly due to aluminum detoxification as a result of phosphate complex with aluminum ions.