Abstract
A study was conducted in the Sabal area, Sarawak, to evaluate the physicochemical properties of sandy-textured soils under smallholder agricultural land uses. Study sites were established under rubber, oil palm, and pepper land uses, in comparison to the adjacent secondary forests. The sandy-textured soils underlain in all agricultural land uses are of Spodosols, based on USDA Soil Taxonomy. The soil properties under secondary forests were strongly acidic with poor nutrient contents. Despite higher bulk density in oil palm farmlands, soil properties in rubber and oil palm land uses showed little variation to those in secondary forests. Conversely, soils under pepper land uses were less acidic with higher nutrient contents at the surface layer, especially P. In addition, soils in the pepper land uses were more compact due to human trampling effects from regular farm works at a localized area. Positive correlations were observed between soil total C and soil total N, soil exchangeable K, soil sum of bases, and soil effective CEC, suggesting that soil total C is the determinant of soil fertility under the agricultural land uses. Meanwhile, insufficient K input in oil palm land uses was observed from the partial nutrient balances estimation. In contrast, P and K did not remain in the soils under pepper land use, although the fertilizers application by the farmers was beyond the crop uptake and removal (harvesting). Because of the siliceous sandy nature (low clay contents) of Spodosols, they are poor in nutrient retention capacity. Hence, maintaining ample supply of organic C is crucial to sustain the productivity and fertility of sandy-textured soils, especially when the litterfall layers covering the E horizon were removed for oil palm and pepper cultivation.
Highlights
In recent decades, the transition of agrarian land uses from traditional shifting cultivation to commercial cash crops systems in Sarawak, Malaysia, has been widely discussed [1,2,3,4,5,6,7]
Study Area and Sampling Sites. is study was conducted at the Sabal upland area (N 01°04′24.6′′, E 110°58′08.6′′), Simunjan, Sarawak, Malaysia (Figure 1), during March 2013 to October 2014. e area has been inhabited by the Iban community for the past century in three adjacent villages, namely, Kampung Sabal Kruin, Kampung Sabal Aping, and Kampung Sabal Tapang. e topography of the northern part of the area is mainly covered by undulating and rolling hills, with the slope degree ranging from 6.2° to 21.0°. e southern part of the study area rises and extended into the steep scarp of the mountainous Klingkang Range [42]. e parent material of the study area is Tertiary Silantek beds of alternating gray shales and sandstone overlain by colluvial boulders [38]
Criteria of site selection were based on the availability of the cash crop farmlands and secondary forests located on sandy-textured soil types (Tanah Pasir or Tanah Kerangas). e age of the secondary forests and cash crop farmlands were determined based on the landowners’ recalling [13]
Summary
The transition of agrarian land uses from traditional shifting cultivation to commercial cash crops systems in Sarawak, Malaysia, has been widely discussed [1,2,3,4,5,6,7]. Little is known on the outcome of sandy-textured soil properties under present agricultural land use practices except for the study on experimental plots of traditional shifting cultivation conducted by Kendawang et al [40]. In their recent study, Hattori et al [41] reported that soil fertility may be difficult to recover on steep slopes under sandy soil condition when the surface layer is destroyed by shifting cultivation. Assessment of the effects of agricultural land use practices on sandy-textured soils deserve genuine priority to obtain baseline information for further improvement of soil management strategies at the study area or elsewhere with similar agro-ecology conditions
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