Surface Soil Nutrient Distribution as Affected by Wheat‐Fallow Tillage Systems

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Abstract
Research was conducted to determine long‐term effects of tillage on soil fertility. Our objective was to determine whether crop residue placement caused by differences in tillage would result in changes in levels of plant available nutrients and other metals in the soil. Two native grassland sites in Western Nebraska were managed under three tillage systems; no‐till, stubble‐mulch, and moldboard plow (bare fallow). The first site was in native sod until 1970 when it was plowed and an alternate wheat‐fallow rotation experiment with no fertilization begun. The second site was farmed from 1930 to 1957, then reseeded to crested wheatgrass (Agropyron desertorum) until 1969 when it was moldboard plowed and an alternate wheat‐fallow experiment with two rates of N‐fertilization (0 and 45 kg N ha−1 every other year) began. After 16 yr of cultivation, soil test values (NH4HCO3‐DTPA extract) were obtained for samples from the 0‐ to 5‐, 5‐ to 10‐, 10‐ to 20‐cm depths. Except at the lower depths, plow tillage, as compared to no‐till or stubble mulch, decreased levels of soil organic matter and extractable K, Zn, Cu, and Pb at both sites, while extractable Ni was decreased at only one site and extractable P, Fe, Mn and Cd were decreased at the other site. Extractable nutrients and metals were generally not affected by tillage in the 10 to 20 cm depths. Fertilization with N decreased soil pH and extractable inorganic P and Zn levels but increased extractable organic‐P, Fe, Mn, Pb, Cd, and Ni in the 0‐ to 5‐ cm depth. Soil organic matter and extractable P, K, Mn, Cu, Pb, and Cd levels decreased with depth. This study shows that the adoption of no‐till, compared to stubble‐mulch or plow‐tillage, maintains fertility status of topsoil nearer to that of native prairie soil. Accumulation of crop residues and maintenance of soil organic matter levels appear to be key factors in sustaining soil fertility status of Great Plains soils.