Root penetration profiles of wheat and barley as affected by soil penetration resistance in field conditions

Abstract

A study was conducted on three Manitoba soils (Marquette heavy clay, Fortier silty clay loam, and Souris loamy sand) with the objectives of: (a) assessing the effects of contrasting tillage systems on various soil physical properties; and (b) relating root penetration of cereals to these properties. The zero tillage (ZT) and conventional tillage (CT) treatments had been established between 3 (Marquette and Souris) and 10 (Fortier) years prior to the initiation of the study. Penetrometer resistance (PR), bulk density (BD) and pore size distribution (PSD) were measured at various depths and times during two growing seasons. The effects of tillage systems on soil properties were generally small, particularly in the poorly structured Souris loamy sand. PR in the top 10 cm of soil tended to be higher under ZT than under CT. PR varied markedly with time and was closely related to changes in soil water content. The proportion of macropores (> 100 μm in diameter) near the soil surface tended to be higher under ZT than under CT. There was no evidence of any detrimental effect of poor aeration on the final root penetration profiles of wheat. The proportion of roots penetrating the soil was inversely related to PR. Soil strength critical for root penetration was determined to be 2 MPa and was independent of soil type. In most situations, however, roots were able to grow into soil with mechanical impedance greater than 2 MPa, possibly by making use of biochannels and spatial and temporal heterogeneity in the soil structure. Key words: Wheat, barley, zero tillage, conventional tillage, root penetration, penetration resistance