The effects of intensified rainfall patterns on the distribution of nitrate in deep soil profiles of conventional and no-till agriculture

Hess LJT, Robertson GP, Matson PA
Department of Earth System Science, Stanford University; Kellogg Biological Station; Department of Plant, Soil, and Microbial Sciences, Michigan State University

Presented at the All Scientists Meeting (2015-04-15 to 2015-04-16 )

In the coming century, the proportion of total rainfall that falls in very heavy rainfall events is likely to increase in many areas. In fact, climate observations show that heavy rainfall events have already been increasing in North America over the second half of the 20th century, particularly in the US Midwest. These changes may have important consequences for rain-fed agriculture, including for the loss of nitrogen. We explored the extent to which intensified rainfall patterns (specifically, large rainfall events with long intervening dry periods) affect the downward movement of nitrate in agricultural soils. We also explored the extent to which these effects interact with cropping system management. From July-November 2014, ambient and intensified rainfall patterns were simulated over 5m x 5m plots using rainout shelters in the conventional and no-till treatments of the Kellogg Biological Station Long Term Ecological Research site. Soil cores to 1.2m depth were taken in November 2014 and analyzed for inorganic N concentrations, bulk density, and water content. In conventional agriculture, soils exposed to intensified rainfall patterns had more nitrate at depth than soils exposed to ambient rainfall patterns, consistent with the hypothesis that intensified rainfall patterns may augment nitrate leaching. In no-till agriculture, soils exposed to intensified rainfall patterns had less nitrate at all depths than soils exposed to ambient rainfall patterns, suggesting that these rainfall patterns had already leached considerable nitrate out of the soil profile. These results suggest that intensified rainfall patterns may increase nitrate leaching in agricultural soils. They also suggest that cropping system management may play an important role in mediating the extent of this increase, possibly through effects on soil structure.

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