Soil management system effects on soil water movement under non-saturated conditions.

VILLARREAL, RAFAEL; LOZANO, LUIS ALBERTO; SORACCO C.G.; SARLI, GUILLERMO OLIVERIO

Curitiba

Encuentro; 3rd Brazilian Soil Physics Meeting; 2015

Soil hydraulic properties determination is crucial in order to assess water entry, accumulation and transport into the soil profile. Diffusivity (D) and sorptivity (S) are important in order to characterize the ability of the soil to transport water under non-saturated conditions. These conditions are the most frequent in agricultural soils. However, there are few studies comparing the effects of different management systems on these properties, because the determination is difficult and time consuming. The study of horizontal infiltration, where the gradient of gravitational component of soil water can be neglected, allows the determination of non-saturated soil water properties. The aim of this study was to determine the effect of different soil management systems on D and S estimated from laboratory horizontal infiltration experiments. Additionally, two methodologies to obtain S from horizontal infiltration were compared. The experiment was carried out near the city of La Plata, in the Research Field ?Don Joaquin? belonging to the Faculty of Agricultural and Forestry Sciences, National University of La Plata (37º11? S, 57º50? W). The soil was classified as typic paleudol and the texture of the upper layer was silty clay loam. The soil A-horizon under three management systems (T1: Natural grassland, T2: direct drilling mayze, and T3: Polyphitic Pasture) was sampled. The samples were sieved through 2 mm sieve, and then the soil was packed into horizontal columns with 10 cm diameter and 70 cm large. Water content and time was measured using 5 moisture sensors placed at 10, 20, 30, 40 and 55 cm from water source. Cumulative horizontal infiltration was measured directly from a graduated reservoir. D was estimated following the method of Whisler et al. (1968). Two methodologies derived from the traditional method of Phillip (1957) were used and compared to determine S. The first one (M1) estimates S from the cumulative infiltration, and the second one (M2) estimates S using initial and final water contents at all measured points, throw Boltzmann transformation. The values of S obtained by the two methodologies were not significantly different. The dependence of D with water content was exponential (R2=0.7053; 0.8049 and 0.8699 for treatments 1, 2 and 3, respectively). The soil management system affected significantly both S and D values. They were significantly greater for T2 as compared to T1 and T3. Overall, mean values of S estimated with M1 were 0.0972, 0.1571, and 0.1027 cm.s-0,5, for T1, T2 and T3, respectively. The mean values of S estimated by M2 were 0.0991, 0.1615, and 0.1023 cm.s-0,5, for T1, T2 and T3, respectively. Finally, mean values of D at 20 % of water content were 0.00209, 0.00208, and 0.0037 cm2.s-1, for T1, T2 and T3, respectively. These results show that this soil under T2 has the ability to transmit water faster under non saturated conditions.