Leaching and Utilization of Nitrogen During a Spring Wheat Catch Crop Succession

An experiment covering a 2-yr spring wheat (Triticum aestivum L.) catch crop succession was conducted in lysimeters to account for the losses of N due to leaching. We sought to relate these losses to the N uptake of the main crop and to integrate the estimated N loss and uptake into a balance. The non-winter hardy catch crops [yellow mustard (Sinapis alba L.), Phacelia (Phacelia tanacetifolia Benth), and sunflower (Helianthus annuus L.)] as well as bare soil fallow were studied at low and high N input levels of 4 and 29 g N m(-2) yr(-1), respectively. Catch crops allowed for an effective reduction of N leaching of 0.33 to 1.67 g N m(-2) yr(-1) compared to fallow. Reductions in N leaching were achieved mainly by avoiding the fallow period during autumn and winter while the catch crop species grown had little impact. During the spring wheat growing season, N leaching losses were highest after yellow mustard, the most effective catch crop for the entire crop succession. A balance of N indicated that the reductions in N leaching exerted by the catch crops did not result in a higher overall utilization of N by spring wheat. Thus, the efficacy shown by catch crops in reducing N leaching during growth is relatively lower when considering the entire crop succession. In addition, the N saved by growing catch crops does not increase N utilization by succeeding spring wheat.