EFFECTS OF MOIST STORAGE AND DIFFERENT DRYING TEMPERATURES ON THE EXTRACTABILITY OF IRON, COPPER, MANGANESE, AND ZINC IN SOIL SAMPLES

The objective of this study was to investigate the effect of different pretreatments on the extraction of cationic micronutrients [iron (Fe) , copper (Cu), manganese (Mn), and zinc (Zn)] from four different soil s. Samples were either stored in the field-moist state for seven days before drying or dried immediately. Three drying treatments were used: air-dried (72 hours), oven-dried at 40 degrees C (48 hours), or oven- dried at 105 degrees C (24 hours). Micronutrients were then extracted with 0.1N HCl or diethenetriamine-pentacetic acid (DTPA). Storage, dry ing temperature, extractant, and soil type all influenced micronutrien t extractability. In general, a higher temperature increased the level of micronutrient extracted. However, the reverse effect was also obse rved. The effect of storage was variable and probably depended on the sample moisture content. We conclude that the results from routine ana lysis and experimentally determined indices can only be compared if so il samples are subjected to the same pretreatments. Hence, rigorous st andardization of the sample preparations is imperative for accurate de termination of-plant-available micronutrients.