BASIS FOR A PROCEDURE TO SPECIFY SOIL PHYSICAL-PROPERTIES OF A SEED BED FOR WHEAT

The rationale of characterizing seed beds prepared for wheat by describing the environment at a distance from the plant/soil interface by a selected number of measurements on a bulk basis in the horizontal plane at small increments of depth is discussed. A field procedure is described of in situ measurements to specify the soil conditions of biological consequence to germination and emergence. Measurements at small increments of depth are made to determine: (i) moisture status by moisture content and by moisture potential; (ii) aeration status by air-filled porosity; (iii) temperature regime by monitoring the soil temperature profile with depth; (iv) soil strength by the bulk shear strength of the soil under in situ stress conditions. Field results suggest that the described field procedure is suitable for the routine study of soils involving a wide range of moisture contents, of moisture potentials and of structure. The results show that, within the top 15 cm of a prepared seed bed, soil physical properties change markedly with depth. In particular, tenfold increases of bulk shear strength were measured. Results also showed that bulk shear strength could not be predicted from penetrometer readings and that the mean aerial temperature at 1.2 m is not sufficient to define the mean temperature regime of the developing seedling. The field procedure described is recommended for the characterization of seed beds. © 1979 CSIRO.