Characteristics and fertility capability of cassava growing soils under different annual rainfall conditions in Northeast Thailand

บทคัดย่อ

Eight soils from major cassava fields in Ubon Ratchathani (higher rainfall: KL13, KD3, NK9 and NP27 pedons) and Nakhon Ratchasima (lower rainfall: SP3, SP4, SP5 and SP6 pedons) provinces were selected, objectively to investigate their characteristics and evaluate their fertility potential for making a guidance of soil and fertilizer management for cassava crop cultivation.  Soil samples were collected from genetic horizon of each soil for the analyses of soil physico-chemical properties basing on standard methods. Result revealed that the soils were deep soils, derived from alluvial deposit and residuum of sandstone-related rocks. They had loamy sand and sandy loam textures as sand particle dominated throughout their profile and clay increased with depth. All soils were classified as Typic Paleustults. Plough pan was observed in KD3, SP3, SP4 and SP5 pedons of which the layer underneath A horizon had markedly greater bulk density than did overlying and underlying horizons. They were acidic and had low fertility level in both topsoil and subsoil except topsoil of KD3 soil that had medium level. According to Fertility Capability Classification (FCC), these soils similarly shared ‘d’ and ‘e’ modifiers, indicating that they had dry period of >60 consecutive day/yr and intense leaching. The KD3, NK9, NP27 and SP3 soils contained ‘a’ modifier which illustrated a potential of aluminium toxicity problem while KD3, NK9, SP4, SP5 and SP6 pedons were subject to K deficiency as shown by their ‘k’ modifier.  With regard to characteristics and fertility capability of these soils, managing these soils for cassava cultivation must place emphasis on careful nutrient management, especially K, as leaching is the key problem in addition with organic matter augmentation to minimize damage of doughtiness with no exception of the soils in Ubon Ratchathani.