Soil Nitrate and Crop Yield In Response to Subsoil Loosening by Paraplow.

The paraplow is a deep tillage implement produced by Howard Rotavator in England. A study was conducted to determine if paraplowing of soils under long-term pivot irrigation in south-central Saskatchewan would alter the soil physical and chemical properties and benefit crop production. Paraplow treatments of 45 cm depth and 45 cm width were imposed in October 2009 and April 2010 at three sites.  Soil samples were collected in spring prior to seeding (0 - 30 cm and 30 – 60 cm) and after harvest for nitrate-N measurement and yields were taken from each plot.

The sites received approximately 250 mm of precipitation in May and June. Large nitrogen losses were anticipated from denitrification, leaching and run-off. At the solonetzic site, soil nitrate was generally higher in paraplow treatments than in the undisturbed control, while at the chernozemic site, nitrate was lower. At the vertisolic site, there was little difference among the treaments. Paraplowing may have reduced losses of the fall applied N in the solonetzic site by increasing aeration and reducing denitrification.  For the chernozemic site, at which the N was spring applied, the paraplowing treatments may have increased N leaching and/or denitrification losses. Wheat grain yield at the chernozemic site was slightly higher than the control in some treatments. At the vertisolic site, canola yields were similar among all treatments, consistent with lack of differences in soil available nitrate content.  In fall after harvest, soil nitrate levels were variable, with fall paraplow resulting in significantly higher soil nitrate in the chernozemic soil, and significantly lower nitrate in the vertisol.