Changes in Soil Water Retention Curves Due to Tillage and Natural Reconsolidation

Abstract

Changes in soil water retention of the surface soil brought about by tillage can significantly alter the amount of rain water that infiltrates into the root zone and is available for plant growth. Soil tillage generally increases porosity and changes the pore‐size distribution, leading to changes in the soil water retention curve and hydraulic conductivities. The objective of this study was to investigate some simple ways of estimating the soil water retention curve of a tilled soil from that of an untilled soil, knowing the change in soil porosity or bulk density due to tillage. The study of literature and empirical analysis of the available data indicated: (i) under field conditions the tillage did not significantly change the air‐entry value of the soil; (ii) tillage increased the absolute value of the slope of the log‐log relationship below the air‐entry value; and (iii) the changes due to tillage in the retention curve occurred only in the larger pore‐size range, approximately between the air‐entry pressure head value and 10 times the air‐entry value. Assuming these observations hold in general, two simple methods of estimating the water retention curve of a tilled soil from that of its untilled condition are proposed. The first method is a simple imposition of the Brooks and Corey function between the air‐entry value and 10 times this value. The second method assumes that the change in soil water content at a given pressure head in the above range of pressure heads was inversely proportional to the value of the pressure head. The tests on four pairs of measured water retention curves on three different soils showed that these methods provided good approximations.

Soil physical attributes in forms of sowing the annual winter pasture and intervals between grazing

“…The reduction in bulk density between years when the grazing period had higher (2009 and 2011) and lower rainfall (2010 and 2012) can be explained by the rearrangement of particles promoted by cycles of soil expansion (wetting) and contraction (drying) during the cycle of the summer crop, which occurs in greater magnitude in the topsoil M. Veiga et al Table 4 -Soil bulk density and porosity in four layers of a Hapludox in four years of evaluation of two forms of sowing and four intervals between grazing of annual winter pasture DS: direct seeding; S+H: seeding + harrowing; 7D, 14D and 28D: grazing in intervals of 7, 14 and 28 days, respectively; UG: ungrazed. Means followed by different letters within each attribute and source of variation differ significantly (Tukey test, P<0.05); NS : no significant differences Attributes/ Treataments (AHUJA et al, 1998;VEIGA et al, 2008), without recompaction of the soil during the subsequent grazing cycle with lower volume of rainfall.…”

“…This system results in the intensification of land use for the production of annual crops and increased and diversified the income in properties, improving the ecological and economic system (BALBINOT JUNIOR et al, 2009a;BARTH NETO et al, 2014;SALTON et al, 2013). However, the CLIS requires proper management, since the use of crop area under grazing can cause surface soil compaction due to animal trampling and reduction of soil cover by straw before the sowing of summer crop in areas managed with no-till system (NICOLOSO; LANZANOVA; LOVATO, 2006;VEIGA et al, 2012).…”

Stochastic model for posttillage soil pore space evolution

“…Consequently, our fundamental working hypothesis is that posttillage changes in pore space and hydraulic properties concern primarily the "effective pore space" within the 0-33 kPa water retention range [Ahuja et al, 1998]. …”

“…The soil pore system is divided into textural and structural components, the latter being far more susceptible to changes due to either wetting and drying processes or external loading [Ahuja et al, 1998]. We illustrate the use of the FPE in evolution of bimodal PSD by considering an evolving interaggregate porosity (structural) and a stationary intra-aggregate porosity (textural).…”

Determining Soil Hydraulic Properties

“…The sampling process itself often causes the most severe disturbance, when an "undisturbed" soil sample is isolated from the natural embedding. (ii) Soils exhibit considerable temporal variability (Mapa et al, 1986;Ahuja et al, 1998;Leij et al, 2002). Thus, measurements at the same site may yield different results if applied at different times (van Es et al, 1999).…”