A comparative study of MAF (Ruakura) and DSIR Land Resources soil analysis results

摘要

New Zealand topsoil samples from 108 soils were analysed for pH, phosphate retention, exchangeable cations (calcium (Ca), magnesium (Mg), potassium (K), and phosphate-extractable sulphur (S) at MAF Technology, Ruakura Agricultural Centre, Hamilton, New Zealand and DSIR Land Resources (DLR), Lower Hutt, New Zealand and results compared. Ruakura determinations followed their standard soil test procedures for fertiliser advice, which meant that extraction times were significantly less than those ofDLR for the determination of phosphate-extractable S and particularly for the cations Ca, Mg, and K. There were other specific method differences also. However, the methods used by both laboratories for pH and phosphate retention were closely comparable. Linear regressions (significant at 0.1%) best described the relationships between Ruakura and DLR values, for all determinations except phosphate-extractable S where an exponential curve (also significant at 0.1%) best described the relationship. The poorest relationships were obtained for Ca and phosphate-extractable S. The results obtained for pH and phosphate retention were closely comparable. Converting quick test values for Ca, Mg, and K to a mass basis, using bulk density values, improved the relationships with DLR values, particularly for Ca, although quick test values for these cations were usually markedly lower than equivalent DLR values. Ruakura S values were generally higher than DLR values at lower absolute levels, with the reverse the situation at higher levels. These differences could largely be explained in terms of differences in analytical methods. Although all significant at 0.1 %, 95% confidence limits indicated that the Ca, Mg, K, and S relationships were of little use for predictive purposes.