Deep percolation under center pivots with no-till

Percolation of water beneath the plant root zone and subsequent flow in the intermediate vadose zone are important processes that affect not only the efficiency of center-pivot irrigation systems but also the transport of contaminants and return flow to the groundwater. No-till planting potentially influences percolation because its impacts on other key hydrologic processes such as evapotranspiration and infiltration. In 2009, investigation of the potential impacts of no-till planting systems on percolation took place at two locations in central Nebraska. At both locations, two center pivot fields were paired, one that has been no-till planted and one that uses two to three field operations annually for seedbed preparation and cultivation. All fields have maintained the tillage practices for at least seven years. Samples of the sediments were collected in the intermediate vadose zone to a depth of 7.5 m. Using the hydraulic properties that were measured and those estimated with pedo-transfer functions along with the water content profiles, percolation rate in zones that have approximate unit hydraulic gradients were estimated. At the first site, tilled volumetric water contents measured between the root zone and the bottom depth of water movement since the practices first began were significantly higher than no-till. Average volumetric water contents were 0.39 and 0.38 m³/m³ for tilled and no-till, respectively. The second site showed a similar trend, although not significant, with 0.30 m ³/m³ found for the tilled field and 0.28 m ³/m³ for no-till. Mean pore water velocity was 0.43 m yr-1 and 0.97 m yr-1 for tilled fields and 0.53 and 0.58 in no-till fields.