Browsing by Author "Mdemu, Makarius Victor Chogimembe"

Now showing 1 - 1 of 1
  • No Thumbnail Available
    Item
    Evaluation of pedo-transfer functions for the estimation of hydraulic properties in some Morogoro soils, Tanzania
    (Sokoine University of Agriculture, 2002) Mdemu, Makarius Victor Chogimembe
    A study was conducted to evaluate some selected pedotransfer functions (PTFs) for soil water retention (SWR) and saturated hydraulic conductivity (Ks) using soils from Sokoine University of Agriculture (SUA) farm. Laboratory methods were used in analysis of collected samples for soil texture, organic carbon (OC), bulk density (BD), total porosity (p) and SWR characteristics (soil WRC). The Ks values were determined using the double ring and tension infiltrometer methods. Existing PTFs for soil WRC and Ks were selected from the literature for evaluation depending on their usability from the obtained soil data, easiness to apply them and their predictive capacity. Representative soil physical properties (RSPPs) for each soil profile studied were calculated using the ratios of individual soil profile horizons depths divided by the total depth of the soil profile. The RSPPs were used in evaluating PTFs for Ks estimation based on field measured Ks. The pedotransfer functions of Tomasella and Hodnett (1998), and PTFs of Ahuja et al. (1984), Campbell (1985), Vereecken, et al. (1990) and Jabro (1992) for SWR and or Ks were evaluated using obtained soil physical properties. Good estimates of SWR were obtained by Tomasella and Hodnett (1998) PTFs. Estimates of Ks proved unreliable by the evaluated PTFs. Simple linear multiple regression models were developed for SWR and Ks using determined soil physical properties following similar procedures to the evaluated PTFs. This was done for SWR so as to include important soil physical properties such as BD and OC, which were not included in evaluated PTFs. Soil texture, BD and OC contributed significantly (p < 0.05) to the developed regression equations for SWR characteristics at different matric potentials. Retained soil water contents significantly (p < 0.05) correlated to percentage clay, OC and BD in most developed regression equations. Estimates of AWC by the developed regression equation were not good enough compared to other estimated soil WRC. Only representative percentage clay had a significant (p < 0.05) contribution to the developed regression equation for Ks estimation. The correlation coefficient for the developed regression equation was high (r = 0.94). Generally, the Ks values estimated using the developed models matched measured values well with mean differences not significantly different from zero. The root of mean squared differences between measured and estimated SWR and Ks were 0.055 cm3cm'3 and 0.198 mm/h respectively. The developed PTFs for soil WRC and Ks gave good estimates compared to evaluated PTFs. It is recommended that more PTFs for soil hydraulic properties be developed using large soil samples under variable soil conditions for reliable estimations of the properties.