TILLAGE AND WATER-CONTENT EFFECTS ON SURFACE SOIL HYDRAULIC-PROPERTIES AND SHORTWAVE ALBEDO

The modification of surface soil structure affects soil-water processes important in crop production and soil conservation. Effects of pretillage soil water content (PTSW) with multiple-pass tillage operations were determined on soil hydraulic properties and shortwave albedo on freshly tilled soil. Objectives included determination of whether PTSW can be used to improve management of seedbed hydraulic properties and whether tillage-induced soil surface conditions significantly affect albedo. Of the three tillage sequences (minimum, intermediate, and excess tillage) applied to a Templeton silt loam soil (mixed, mesic Udic Ustochrept), the excess tillage sequence resulted in the lowest macropore volume, mainly through a decrease in the volume of aeration pores (pores >300-mum diam.). The slope of the water characteristic between -1.0 and -1500 kPa matric potential was unaffected by tillage treatments. The excess tillage sequence resulted in a mean hydraulic conductivity (matric potential = -0.4 kPa) of 11.1 cm h-1, compared with 14.9 cm h-1 following minimum tillage. Different PTSW did not cause significant differences in hydraulic properties of freshly tilled soil. The range of tillage-induced soil structures produced did affect shortwave albedo, but to a smaller extent than shown in some previous studies. Bare soil shortwave albedo variation with zenith angle appears soil specific; here a small decrease in albedo was observed as zenith angle increased. In this soil, with commonly practiced tillage sequences and a range of PTSW representative of field conditions, information about PTSW will not help manipulation of hydraulic properties and shortwave albedo in the fresh seedbed.