THE INFLUENCE OF CROP ROTATION AND TILLAGE METHODS ON THE DISTRIBUTION OF EXTRACTABLE BORON IN NORTHERN IDAHO SOILS1

Abstract

The objective of this study was to determine the influence of crop rotation and tillage methods on the level and distribution of extractable boron in northern Idaho soils. Plots were established north of Moscow, Idaho, in 1974 using no-till, minimum tillage, and conventional tillage treatments with three crop 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 depth in all plots, and boron was determined by hot water extraction. Tillage × depth and rotation × depth interactions characterized extractable boron distribution in the northern Idaho soil studied. When parameters were considered individually, extractable boron levels in the sampled soils decreased with increasing depth. Extractable boron in the surface 30 cm of the soil profile was greater in conventional than in minimum and no-till treatments. Lower extractable boron levels found in soils with no-till and minimum tillage treatments may be attributed to greater B leaching potential, or greater B tie-up by organic matter, or both. The crop rotation with the greatest cereal/legume ratio (2:1) had highest levels of extractable soil B. It is probable that the greater demand of B by legumes, more specifically alfalfa, peas, and red clover in this study, resulted in lower extractable soil B levels in rotations with smaller cereal/legume ratios.