THE INFLUENCE OF CROP ROTATION AND TILLAGE METHODS ON DTPA-EXTRACTABLE COPPER, IRON, MANGANESE, AND ZINC IN NORTHERN IDAHO SOILS

Abstract

The objective of this study was to determine the influence of crop rotation and tillage management on the levels and distribution of DTPA-extractable Cu, Fe, Mn, and Zn in northern Idaho agricultural soils. Field plots were established north of Moscow, Idaho, in 1974 using no-till, minimum tillage, and conventional tillage treatments with three cropping rotations. Rotations included: (1) a 2-year winter wheat (Triticum aestivum L. cv. Nugaines)-spring pea (Pisum sativum cv. Alaska) rotation (1:1 cereal: legume ratio), (2) a 3-year winter wheat-spring wheat (Triticum aestivum L. cv. Fieldwin)-spring pea rotation (2:1 cereal:legume ratio), and (3) a 3-year winter wheat-alfalfa (Medicago sativa L. cv. Ladak), red clover (Trifolium pratense cv. Kenland), pea-alfalfa, red clover rotation (1:2 cereal:legume ratio). Soil samples were collected by 7.5-cm depth intervals in all plots, and Cu, Fe, Mn, and Zn were determined on an inductively coupled argon plasma spectrophotometer in DTPA extracts. Micronutrient distribution differences as a consequence of 10 years continuous management were observed for Cu, Fe, Mn, and Zn in many instances. Tillage-by-depth interactions were observed for all four micronutrients. When parameters (rotation, tillage, depth) were considered individually, extractable Cu, Fe, Mn, and Zn levels in the sampled soils decreased with increasing depth. As a single factor, tillage affected DTPA-extractable Fe and Mn levels in the northern Idaho soils, as the surface 30 cm of conventional and minimum tillage plots contained greater amounts than no-till plots. DTPA-extractable Zn was affected by crop rotation. Zinc was greatest in the winter wheat-spring pea rotation. Conversely, as a single factor, rotation did not affect available levels of Cu, Mn, and Fe in the soils of the Palouse region in northern Idaho. This report contains the first documentation of the long-term effects (10 years) of tillage, crop rotation, and depth on the distribution of DTPA-extractable Cu, Fe, Mn, and Zn in an agricultural soil. This new information about the relationship of tillage and crop rotation to the distribution and availability of Cu, Fe, Mn, and Zn in soils may result in modification of fertilizer recommendations or placement under certain cultural practices.