Fertility and potential of soils under rubber plantation in Pra Yuen district area, Khonkaen province

Abstract

A study on fertility and potential of soils for five-year rubber (RRIM 600 variety) was undertaken at Ban Non Tun, Nong Waeng Subdistrict, Phra Yuen District, Khon Kaen Province. Five soil profiles were collected along toposequence to examine physical properties, chemical properties and limiting factors for plant growth in order to classify their suitability for growing rubber. Result showed that these soils have sand to loamy sand texture in surface layers dominated by sandy particle size with amounts ranging from 841-914 g/kg and rather low to moderate bulk density (1.38-1.54 Mg m-3). Bulk density in subsoils of PY-3 and PY-4 (1.6 Mg m-3) are higher than that of other soils. PY-5, located in the lowest position of the toposequence, is composed of reducing layers within soil profile from 112 cm depth downward. Chemically, they have extreamly acid to neutral soil reaction (pH 4.0-6.7), very low organic matter content (0.06-0.61 g/kg), very low to low available phosphorus (0.7-4.4 mg/kg), very low to very high available potassium (8.8-149.4 mg/kg), very low to rather high cation exchange capacity (1.8-16.0 cmolc/ kg) and low to high base saturation percentage (16.0-77.5%). Fertility level of all soils is low. Pedons 1-4 are classified into suitability class 2 (R-II), indicating these soils poorly suited for growing rubber while Pedon 5 being in class 3 (R-III). Main limiting factors for the growth of rubber are sandy soils (s), low fertility (n) and erosion (e) in addition with poor drainage in subsoils for Pedon 5. The average growth rate of rubber was assessed by the girth (circumference measured at 150 cm height). It was ranged from 16.4 to 17.5 cm which was smaller than that of the lower limit of standard growth at five years old rubber (36 cm) reported by Rubber Research Institute, Department of Agriculture.