Fertilizer Practices Affecting Soil Nutrient Status of Apple Orchards in Bhutan

Apple (Malus domestica Borkh.) is one of the important fruit crops in Bhutan. However, little information is available on orchard nutrient status. This study aimed to evaluate the soil nutrient status resulting from different fertilizer practices in apple orchards. Three major apple growing districts (Thimphu, Paro and Haa) and three common fertilizer practices (organic, inorganic and mixed) were surveyed. In each district, 10 to 12 orchards were selected and six to seven trees per orchard randomly marked for soil nutrient evaluation. Soil samples were collected in December 2009 (during dormancy) from two depths (0–20 and 21–40 cm). Chemical analyses were carried out in the Soil and Plant Analytical Laboratory, Bhutan for pH, N, P, K, Ca, Mg, organic carbon and cation exchange capacity (CEC). Results showed that the apple orchards had low pH (5.65–5.85) in the inorganic fertilizing practice, low nitrogen (0.05–0.18%) in all fertilizer practices and moderate to high (17.7–86.75 mg kg -1 ) available phosphorous (P) in the inorganic fertilizing practice. The pH level was significantly different between fertilizer practices. No significant difference was observed for P and exchangeable Ca among districts, between fertilizer practices within a district and between soil depths within fertilizer practices. Significant differences were found between districts for N, organic C and CEC. In addition, the results showed significant differences in the nutrient status of N, P, K, Ca, Mg and CEC between the two soil depths; the surface soil (0–20 cm) always contained the higher amount. The results revealed that there was an insufficient level of N in all Bhutanese apple orchards, while the levels of available P and K were in the sufficient range. Fertilizer practices had insignificant results on soil nutrient contents. Orchards under inorganic fertilizer had a lower pH than the optimum range. The study also indicated that collecting soil samples from two depths is necessary to analyze the nutrient content in Bhutanese apple orchards.