Influence of pastoral fallow on plant root growth and soil physical and chemical characteristics in a hill pasture

Pastoral fallowing over a growing season (October-May) has a profound effect on standing biomass and sward structure, and should have an impact on below ground plant growth and soil biological activities. Two field studies were conducted to compare the effects of pastoral fallow with rotational grazing on root growth and soil physical and chemical properties. Root growth and distribution was altered by pastoral fallowing and there was significantly (P < 0.01) less root biomass at 0-50 mm depth of soil in the fallowed sward than the grazed sward. Compared with the grazed treatment, pastoral fallow increased soil air permeability at 500 mm tension by 38%, saturated hydraulic conductivity by 26%, unsaturated hydraulic conductivity at 20 mm tension by 67% and soil moisture by 10-15%, and reduced soil bulk density by 11%. Fallowing had little effect on soil nutrients both at the end of fallowing, except for small reductions in K and Mineral N levels at 0-75 mm soil depth, and two to three years after fallowing.