Pedotransfer functions to determine water conducting macroporosity in South African soils

Abstract

Macropores play an important role in the rapid transport of water, solutes and pollutants through the soil. Transport through these pores (>0.5 mm) is dominated by gravitational forces (i.e. matrix forces have low impact) resulting in flow rates orders of magnitude higher than rates that would be predicted, posing problems for modelling and understanding water and solute transport through soils. This study aimed to quantify the water conducting macroporosity (WCM) in a range of soils in South Africa and to develop three pedotransfer functions (PTFs) able to predict WCM. Saturated (K(s)) and unsaturated (K₃₀) conductivities were measured in situ on 120 soil profiles using double ring and tension infiltrometers methods. Differences between K(s) and K₃₀ in conjunction with Poiseuille's law and the capillary rise equation were used to calculate WCM. The first two multiple regression functions made use of all available soil properties influencing WCM using a 'best model' and 'backward' analysis approach respectively. The third model used only easily observable soil properties to predict the WCM. The functions were validated using a double-cross method. Results are encouraging with R² values of 0.78, 0.74 and 0.69 for functions 1, 2 and 3 respectively.

Toprak hidropedolojik özelliklerinin gypsic ustorthent ve typic ustifluent’de faktör analizi ile değerlendirilmesi

“…Pagliai and Vignozzi (2002) reported that water movements in soil depend on the size and type of soil structure and pores. The results are consistent with those reported in many studies, showing positive relations between macropores and Ks (Jarvis 2007;Dexter and Richard, 2009;Van Tol et al 2012). However, soil macropores and voids can increase Ks, which are not completely related to unsaturated hydraulic conductivity K(h) (Libohova et al, 2018).…”

Projected Impacts of Climate Change Scenarios on the Production of Maize in Southern Africa: An Integrated Assessment Case Study of the Bethlehem District, Central Free State, South Africa

“…Soil characteristics needed by the crop models were described for each field individually using the land-type database (ARC, 2006) and pedo-transfer functions (van Tol et al, 2012). Land type in this case is defined as an area with uniform micro-climate, typical terrain morphology, and characteristic soil-distribution pattern in the landscape.…”

Analysing tension infiltrometer data from sloped surface using two-dimensional approximation

“…Field methods in general are more realistic and accurate than laboratory ones because of the larger volume of soil involved and the continuity in the soil profile versus depth and because the soils are also minimal disturbed (Vachaud and Dane, 2002). Tension or double ring infiltrometers are also commonly adopted in the field to measure infiltration rates (Perroux and White, 1988;Timlin et al, 1994;Kechavarzi et al, 2009;Fodor et al, 2011;van Tol et al, 2012). Some advantages of tension infiltrometers, when compared with double rings, include minimal disturbance of soil surface, short testing time and little water requirements (Ankeny et al, 1991).…”