Physical effects of direct drilling equipment on undisturbed soils

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Abstract
A method of measuring soil relative humidity at the seed-soil zone in direct drilled grooves is described. Grooves were formed by several combinations of 3 selected coulter types and seed covering methods. In-groove soil relative humidity was measured at the same time as seeds [wheat] were growing under controlled constant climatic conditions in a soil initially under severe moisture stress. A negative correlation coefficient of r = 0.75 was found between the in-groove relative humidity and combined counts of seedling emergence and subsurface unemerged seedling survival. The ability of seed grooves to retain moisture vapor was described in terms of moisture vapor potential captivity (MVPC). A minimum value of MVPC = 0.4 was suggested for the dry soil of this experiment. A mathematical model relating in-groove relative humidity and seedling emergence plus subsurface seedling survival was developed. Specifications of coulter design and seed covering methods were suggested which might create better soil physical microenvironments suitable for plant establishment.

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