Site‐specific effects of winter cover crops on soil water storage

Addition of an overwintering cereal rye (Secale cereale L.) cover crop (CC) to midwestern maize (Zea mays L.)-based systems offers several environmental benefits, but the long-term effects of this practice on soil hydrological properties are not well understood. We utilized four long-term (10+ yr) trials (two commercial fields, two research plots) in Iowa that included a replicated winter rye CC and no-cover treatment in no-till maize/soybean [Glycine max (L.) Merr.] systems. We took intact 7.62-cm diam. soil samples from a 10-to-18-cm depth shortly after cash crop planting in the spring. We measured the soil water retention curve using matric potentials ranging from saturation to -500 cmH(2)O. In addition, we measured organic matter, textural composition, and bulk densities of the soil samples. At the depth sampled, CCs did not meaningfully affect bulk density, water contents at saturation, or air-entry potentials at any trial, nor increase the percentage of macropores. At two trials, soil water content at field capacity (-100 cmH(2)O) in the CC treatments was 2.5 vol% (SE: 1.2%; commercial field) and 2.4 vol% (SE: 1.3%; research plot) higher compared with the no-cover treatments. This increase could meaningfully reduce the amount of water drained from a field after a saturating rain and should be considered when assessing CC impacts on landscape hydrology. The presence or absence of a CC effect on field capacity was not related to CC aboveground biomass production, previous cash crop, or soil texture at the trial sites. Based on our results, a causal model, and previous literature we hypothesize CC root characteristics are key to understanding variable effects of CCs on soil water storage. Our results indicate it is possible for CCs to meaningfully affect soil water storage, but more research is needed on the mechanisms by which these changes occur.