AbstractAn attempt was made to evaluate the intrinsic performance of plaster electrical-resistance units, independently of any influence of a surrounding soil. Hydrocal B-11 laboratory-constructed blocks appeared to excel gypsum molding-plaster blocks, including Bouyoucos blocks. This superiority of the Hydrocal B-11 blocks has been evaluated in terms of sensitivity and precision of the units. Platinized nickel-rod electrode blocks seemed to improve somewhat the sensitivity and the precision of the blocks. However, as this type of electrode will make the block more expensive, further investigation on the performance of this block type should be made. Hydrocal B-11 cylindrical blocks with a high water: plaster ratio (0.8) appear to be useful in irrigation scheduling if the data are interpreted in terms of energy relationships, rather than in terms of water-volume considerations.
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