Tillage and no-tillage conservation effectiveness in the intermediate precipitation zone of the inland Pacific Northwest, United States

A common cropping system in the intermediate precipitation zone (300 to 450 mm [12 to 18 in]) of the inland Pacific Northwest is the two-year, winter wheat-fallow rotation typically practiced using multiple secondary tillage operations to control weeds and retain seed-zone soil moisture. This crop rotation has proven to be a stable system for producers in this region. However, even conservation tillage (CT) practices such as mulch tillage leave this system prone to substantial erosion where the soil surface is disturbed. Alternatives to this system include no-tillage (NT) practices, increasing the cropping intensity, or a combination of both. Our objective was to evaluate and compare soil and water conservation attributes between NT and a variation on CT, hereafter referred to as tillage practice (TP) under a four-year dryland crop rotation. We established a four-year rotation consisting of winter wheat (Triticum aestivum L.), spring peas (Pisum sativum L.), winter wheat, and fallow. No-tillage consisted of seeding and fertilizing in one pass, two applications of herbicide, and harvest. Conservation tillage consisted of seed bed preparation using a chisel plow, fertilization injection with a disk applicator for spring peas or at time of seeding with a shank drill for wheat, two to three passes with secondary tillage (sweep-rod and rodweeder), applications of herbicide as needed, and harvest. The experimental design was a complete randomized block with four blocks, two tillage treatment main plots per block and four subplots in each main plot for each phase of the four-year rotation. We measured groundcover, infiltration using ring infiltrometers, and runoff and soil erosion from natural weather events. Weather during the four years was relatively mild. Groundcover (81% and 59%) and infiltration rates (41 mm h–1 [1.63 in hr–1] and 14 mm h–1 [0.57 in hr–1]) were significantly greater in the NT treatment than in the TP treatment. Runoff (0.4 mm [0.02 in] and 0.5 mm [0.0.02 in]) and soil erosion (10 kg ha–1 [0.004 tn ac–1] and 21 kg ha–1 [0.009 tn ac–1]] were both significantly less in the NT than the TP. The changes in infiltration, runoff, and soil erosion rates occurred more quickly and to a greater degree than we anticipated. Earlier studies in the inland Pacific Northwest have been ambiguous in their conclusions about the effectiveness of NT to significantly reduce runoff and soil erosion compared to TP. This research found that NT provided a significant improvement in soil and water conservation over TP at this location under mild weather conditions.