Agrochemophysica - Volume 5, Issue 1, January 1973

In a pot study with Eragrostis curvula exchangeable ? (using neutral ? NH4OAc) and several quantity-intensity (Q/I) parameters were correlated with cumulative yield, cumulative ? uptake, and ? content of plant tissue. All the parameters used provided essentially similar indices of ? availability when soil was not dried prior to analysis. Air drying, however, markedly reduced the prognostic value of ? NH4OAc exchangeable ? and ? index A (given by - ? ? � X PBCK). In a field study with maize (Zea mays L.) the various indices of ? availability were correlated with ? content of the stover at four stages during the growing season. Although all soil analyses were conducted on air dry samples, ? NH4OAc exchangeable ? provided at least as good an index of ? availability as any of the other measures used and proved superior to equilibrium activity ratio (AR^) or indices involving PBCK measurements. Data from both the field and pot studies suggested that the form of the Q/I relationship was affected by air drying and ? fertilization.

An economical and sensitive lysimeter for evaluating hourly water usage of crops has been designed, constructed and tested. A cylindrical steel lysimeter of surface area 2,5457 m2 and soil depth of 0,4 m rests on a mechanical balance system, having a resolution of 1 in 10 000. A precision strain gauge load beam of 0,1% accuracy and 20 kg capacity is incorporated in the balance lever system and its output is recorded on a galvanometric strip chart recorder. The complete system provides measurement of evapotranspiration to within 0,1 mm of water.

The determination of half-lives for a number of nuclides in a well-type scintillation counter is descriptionbed.