Abstract
Abstract. Adequate water management is required to improve the efficiency and sustainability of agricultural systems when water is scarce or over-abundant, especially in the case of land use changes. In order to quantify, to predict and eventually to control water and solute transport into soil, soil hydraulic properties need to be determined precisely. As their determination is often tedious, expensive and time-consuming, many alternative field and laboratory techniques are now available. The aim of this study was to determine unsaturated soil hydraulic properties under different land uses and to compare the results obtained with different measurement methods (Beerkan, disc infiltrometer, evaporation, pedotransfer function). The study has been realized on a tropical sandy soil in a mini-watershed in northeastern Thailand. The experimental plots were positioned in a rubber tree plantation in different positions along a slope, in ruzi grass pasture and in an original forest site. Non-parametric statistics demonstrated that van Genuchten unsaturated soil parameters (Ks, α and n) were significantly different according to the measurement methods employed, whereas the land use was not a significant discriminating factor when all methods were considered together. However, within each method, parameters n and α were statistically different according to the sites. These parameters were used with Hydrus1D for a 1-year simulation and computed pressure head did not show noticeable differences for the various sets of parameters, highlighting the fact that for modeling, any of these measurement methods could be employed. The choice of the measurement method would therefore be motivated by the simplicity, robustness and its low cost.
Highlights
The rubber tree (Hevea brasiliensis) has become a crop of high economic interest in the northeast of Thailand since the rise in price of natural rubber on the international market and the policy of the Thai government to extend rubber tree plantation
The higher dispersion for hydraulic conductivity values derived from the disc infiltrometer could be explained by the fact that measurements are very dependent on the quality of the contact between the disc and the soil surface
The presence of macro-pores related to biological activity could partly explain the differences between the Beerkan method and the disc infiltrometer, as with this latter method, water can only infiltrate into the soil matrix
Summary
The rubber tree (Hevea brasiliensis) has become a crop of high economic interest in the northeast of Thailand since the rise in price of natural rubber on the international market and the policy of the Thai government to extend rubber tree plantation. The introduction of the rubber tree in the northeast of Thailand may contribute to important land use changes affecting soil and water resources. In this area, the average annual rainfall (1.1–1.2 m) does not completely meet the minimal requirements for rubber trees (1.3 m), and it is necessary to design a wise water management to be able to ensure sustainable rubber tree farming. In order to achieve accurate quantification of these changes with modeling, it is necessary to estimate precisely the hydrodynamical properties of the vadose zone
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