Lime effects on soil acidity, crop yield, and aluminum chemistry in direct-seeded cropping systems

Our objective was to assess the efficacy of lime to lower soil acidity, alter Al chemistry, and increase crop yield in a direct-seeded system. Treatments of subsurface banded fertilizer (120-168 kg N ha(-1) y(-1)) alone or with subsurface banded lime (224 kg ha(-1) y(-1)), or a one-time broadcast application of lime (7000 kg ha(-1)) or elemental S (1000 kg ha(-1)) were initiated in spring 2002. Grain yield was measured annually from 2002 to 2005 in a spring barley (Hordeum vulgare L.)-spring wheat (Triticum aestivum L.)-winter wheat rotation. Soil was sampled in spring 2004 to assess pH and model Al speciation. Low pH was evident at the depth of fertilizer placement (5-10 cm). Broadcast lime increased pH in the surface 15 cm, although reductions in Al3+ activity [(Al3+)] occurred only in the 0- to 5-cm layer. Relative to banded N, there was no increase in pH at the 5- to 10-cm depth where banded lime was placed. At the 0- to 5-cm depth, lower pHs were observed with broadcast S (4.6) compared with the banded N control (5.1) or banded lime (5.0). There was no effect of treatment on yield. Modeling suggests that soluble Al is dominated by organic matter-Al complexes (fulvic acid, FA; FA(2)Al(+) and FA(2)AlOH(0)). Solid- and solution-phase organic complexes may control (Al3+) at pH <5.5. Although acidification is a concern in the IPNW, the high organic matter content in direct-seeded soils may buffer against Al phytotoxicity.