Effect of land use systems on soil resources in Northern Thailand SFB 564 – The Uplands Program Sustainable Land Use and Rural Development in Mountainous Regions of Southeast Asia Effect of land use systems on soil resources in Northern Thailand Suwimon Wicharuck, Petra Erbe, Ulrich Schuler, Jiraporn Inthasan, Ludger Herrmann, Karl Stahr and Mattiga Panomtaranichagul Introduction Results 1. Soil Translocation Conversions of hilly-natural forest to shifting cultivation, swiddening and annual intensive mono-cropping in northern Thailand, have caused severe soil erosion for several decades due to the increased land pressure and socio-economic problems, consequently leading to decreased soil bio-physico-chemical fertility and crop productivity, including ecological and environmental problems. Different land-used types has different effects on soil translocation rates significantly. Negative and positive values of soil sediments presented in figure 3 indicated the amounts of soil deposition and soil loss respectively. The low translocation rates were given under the growing trees and shrub, SF, MO and FL, whilst agricultural fields, MF and RF gave rather high translocation rates, particularly the highest rate was found under RF. In general, the highest soil translocation rates were obtained during the early rainy season, due to the loosen soil caused by soil preparation for seed bed and high rainfall intensity. Objectives (i) Investigating the effects of several land use types on seasonal changes of soil chemical, physical and hydrological properties. (ii) Identifying the details of soil translocation (soil deposition and soil loss) at various locations down the sloping land under different land- used types. (a) (b) (c) Materials and Methods Five land use types were selected in Pang Ma Pha district, Mae Hong Son Province, northern Thailand: (i) secondary forest (SF), (ii) mixed orchard (MO), (iii) maize fields in three different locations (MF-A, MF-B and MF-C) (iv) upland rice in two places (RF-A and RF-B) and (v) fallow land (FL) (Fig. 1a,b). Soil translocation was measured using modified Gerlach troughs (Fig. 2). Soil composite sampling (0 – 200 mm depth) were conducted at different locations down the sloping land under different types of land usages, during wet and dry seasons in 2007-2009. (a) The measured soil properties were soil acidity (pH), organic matter content (OM), extractable phosphorus (Ext. P) and potassium (Ext. K), bulk density (BD) and total stored water (TSW) within 1 m soil depth. Figure 3. Cumulative values of soil translocation (t/ha) under different types of land use from May 2007 to October 2009 (a) 2007, (b) 2008 and (c) 2009. 2. Soil Chemical Properties Soil pH and OM were not significantly varied along the different studied periods, whilst seasonal variations of Ext. P and Ext. K were found under every studied land - used types. Ext. P was increased while Ext. K was decreased from 2007 to 2009. The highest values of Ext. P and Ext. K were found under MF-B and MF-A respectively (Fig. 4a-b). These variations might be caused by reduction and oxidation of Phosphate minerals, increased P-consumption of crop, from the deep soil layer and accumulation of plant residues, leading to increased Ext. P in the top soil. (b) The decreased Ext. K might be due to removal of soluble K with runoff and the exchangeable K with soil erosion. Figure 4. Average values of soil chemical properties within 200 mm soil depth, (R) = rainy season, (D) = dry season, (a) ext. P and (d) ext. K from June 2007 to December 2009. 3. Soil Physical and Hydrological Properties Figure 1. (a) Locations and topography of study areas and (b) overview of five types of land use systems. Fig. 5a shows that the highest and lowest BD values were found under RF-A and SF respectively, compared to the other land-used types. These might be due to accumulation of plant residues, surface soil cover and disturbance including rainfall distribution and intensity during the study period. The highest TSW was obtained under SF in 2007, while RF-B and MF-C tended to give the highest and 2nd highest TSW in 2008 and 2009 almost through out the studied periods. These results might be due to the higher clay content, lower interception loss, lower water consumption and higher accession of rainfall during low intensity in MF-C and RF-B field, compared to the others land use (Fig. 5b). Figure 2. The locations of Gerlach trough along the slope at each slope positions under different types of land use systems. Figure 5. Variations of soil physical and hydrological properties in 0 – 200 mm soil depth, R = rainy season and D = dry season, (a) bulk density and (b) seasonal variation of TSW from 2007 to 2009. Conclusions and outlook The results indicated that different land-used types had different effect on soil properties and soil translocation significantly. In general, annual cropping on sloping land must be carried out under soil conservation practices. Soil and water conservation may maintain soil bio-physico-chemical fertility and increase crop productivity substataneously. Furthermore, TSW values indicated that there was sufficient stored soil water for multiple crop production under rainfall cropping system through out the studied periods. The results will be used in future studies to calibrate/validate and predict soil erosion, using EPIC (Erosion Productivity Impact Calculator) and WEPP (Water Erosion Prediction Project). Furthermore, the TSW and climatic data will be used to estimate the possibility of cropping systems under rainfed condition. Finally, the main objective of the project is to assist decision making of the researcher extensioners and stakeholders for selecting the sustainable cropping system on the highland rainfed agricultural area.