Soil physical properties and root density under zero and conventional tillage in three Manitoba soils
Martino, Daniel L.
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The trend toward reduced or zero tillage systems may bring about changes in the physical environment for crop roots. 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 these effects to wheat or barley response. The zero (ZT) and conventional (CT) tillage treatments had been established between 3 and 10 years prior to the initiation of the study. Penetrometer resistance, bulk density, soil moisture, pore size distribution and oxygen diffusion rate were measured at various depths and times during two growing seasons. The effects of the tillage systems were generally low, particularly in the poorly structured Souris loamy sand. Penetration resistance in the top 10 cm of soil tended to be higher under ZT than CT. ZT also tended to produce a higher proportion of macropores (>100 um in diameter) near the soil surface, suggesting a better preservation of biopores under this system. The aeration status of the roots may have been impaired at the beginning of the growing seasons at the finer-textured soils, but there was no evidence of a negative effect of aeration on the final root density profiles of wheat. The cone index varied markedly in time, and was related to changes in the soil water content. The proportion of roots penetrating the soil was negatively related to the resistance to cone penetration. The relationship obtained suggested that no roots penetrated the soil when the cone index was over 2 MPa. However, in most situations, roots were able to grow in soil with high mechanical impedance, probably by making use of spatial and temporal heterogeneity in the soil structure.