SOIL QUALITY ASSESSMENT AND NUTRIENT MANAGEMENT GUIDELINES FOR DURIAN LONG RAK THAI (DURIO ZIBETHINUS MURR.) ORCHARDS IN PHITSANULOK PROVINCE

Abstract

This study aimed to assess soil quality and propose nutrient management strategies for 'Long Rak Thai' durian orchards in Chomphu Subdistrict, Noen Maprang District, Phitsanulok Province. Soil samples were collected from 11 farmers during two crop periods: the fruit development stage and the harvesting stage. Key soil properties analyzed included pH, organic matter, nitrogen, available phosphorus, and available potassium. The results showed that the average soil pH significantly decreased from 6.22 to 5.72 (P<0.05). In contrast, organic matter, nitrogen, available phosphorus, and available potassium levels showed no statistically significant differences between the two periods. Organic matter averaged 5.01±1.22% and 5.74±0.40%, while nitrogen remained low level at 0.26±0.06% and 0.27±0.15%. Available phosphorus averaged 34.19±20.88 and 27.45±12.94 mg/kg, with only 18.18% of plots falling within the optimal range for durian cultivation. Available potassium levels were markedly higher than recommended levels, averaging 370.91±149.77 and 314.09±171.94 mg/kg. Overall soil fertility was at a moderate level during both periods, with no significant difference (P>0.05). Based on soil nutrient data, a site-specific nutrient management; SSNM approach was proposed. Most plots were recommended to apply nitrogen fertilizer at 720 g/tree, phosphorus (P₂O₅) at 400 g/tree, and potassium (K₂O) at 400 g/tree during both periods. This tailored strategy aims to enhance fertilizer efficiency, reduce costs, and improve durian fruit quality in the long term.