EFFECTS OF SOIL TEMPERATURE, MOISTURE, AND AIR-DRYING ON EXTRACTABLE MANGANESE, IRON, COPPER, AND ZINC

Abstract

Soil samples for microelement extraction are often taken with little regard to field moisture content and stored under a variety of conditions. In order to study the effects of these practices on extractable microelements, we incubated three soils for 2 weeks at various temperatures and moisture contents. The temperatures were 10, 25, and 40°C, and the moisture levels were 5, 1/3, and 0 bars tension. The soils were extracted for diethylenetriamine pentaacetic acid manganese, iron, copper, and zinc after air-drying, as well as in the moist state.Extractable Mn, Fe, and Cu increased with increased temperatures when the soils were incubated at the 0-bar moisture level. Temperature had no effect on these elements at the dryer moisture levels. Increased temperatures decreased Zn extractability in many cases for samples air-dried prior to extraction. Large increases in extractable Mn and smaller increases in Fe and Cu resulted when soils were incubated at 0-bar moisture. Changes in the extractable Mn, Fe, and Cu between the two drier moisture levels were mostly nonsignificant. Extractable Zn decreased with increasing moisture levels. Air-drying the soils prior to extraction caused increased extractable Mn and Fe, when compared with moist extraction at the lower two incubation moisture levels, but at the 0-bar level this pattern was reversed. Extractable Cu and Zn increased upon air-drying the samples prior to extraction, as compared with moist extraction, in nearly every case.Varying temperature and moisture caused significant changes in the extractability of all the microelements studied. The effect of air-drying increasing extractability at low incubation moisture and decreasing extractability at high moisture is particularly important. The conditions of soil moisture prior to air-drying may influence the effects of air-drying on extractable soil microelements. Soil samples for microelement extraction are often taken with little regard to field moisture content and stored under a variety of conditions. In order to study the effects of these practices on extractable microelements, we incubated three soils for 2 weeks at various temperatures and moisture contents. The temperatures were 10, 25, and 40°C, and the moisture levels were 5, 1/3, and 0 bars tension. The soils were extracted for diethylenetriamine pentaacetic acid manganese, iron, copper, and zinc after air-drying, as well as in the moist state. Extractable Mn, Fe, and Cu increased with increased temperatures when the soils were incubated at the 0-bar moisture level. Temperature had no effect on these elements at the dryer moisture levels. Increased temperatures decreased Zn extractability in many cases for samples air-dried prior to extraction. Large increases in extractable Mn and smaller increases in Fe and Cu resulted when soils were incubated at 0-bar moisture. Changes in the extractable Mn, Fe, and Cu between the two drier moisture levels were mostly nonsignificant. Extractable Zn decreased with increasing moisture levels. Air-drying the soils prior to extraction caused increased extractable Mn and Fe, when compared with moist extraction at the lower two incubation moisture levels, but at the 0-bar level this pattern was reversed. Extractable Cu and Zn increased upon air-drying the samples prior to extraction, as compared with moist extraction, in nearly every case. Varying temperature and moisture caused significant changes in the extractability of all the microelements studied. The effect of air-drying increasing extractability at low incubation moisture and decreasing extractability at high moisture is particularly important. The conditions of soil moisture prior to air-drying may influence the effects of air-drying on extractable soil microelements. © Williams & Wilkins 1980. All Rights Reserved.