Zone-subsoiling effects on infiltration, runoff, erosion, and yields of furrow-irrigated potatoes

Soil compaction is a problem in many Pacific Northwest fields. We hypothesized that zone subsoiling would improve potato (Solanum tuberosum L., cv. ‘Russet Burbank’) yield or grade, increase infiltration, and decrease bulk density, runoff, and erosion of furrow-irrigated fields, while maintaining trafficability and irrigability of furrows. A 2 year study was established on a Portneuf silt loam (coarse-silty, mixed, mesic Durixerollic Calciorthids). In the fall, plots were in wheat stubble (1988) or bean stover (1989), and were either disked (10–12 cm), chiselled (25–30 cm), or moldboard plowed (20–25 cm). Fall tillages were split in spring, half of each plot receiving in-row zone subsoiling (46 cm) after planting potatoes. The effect of zone subsoiling on infiltration in 1989 was small because of variation across fall tillages. In 1990, zone subsoiling increased infiltration by 10% across fall tillages. Erosion decreased up to 278% with zone subsoiling. Zone subsoiling reduced erosion more effectively than it increased infiltration, shown by a two- to three-fold decrease in the sediment loss to water infiltrated ratio. Zone subsoiling increased infiltration and reduced erosion more in 1990 when the study was conducted on a slightly steeper slope with higher water application rates than in 1989. In 1989, zone subsoiling increased the yield of grade 1 tubers by 3.8 t ha⁻¹ (4.6%), but the total yield was not significantly increased. In 1990, zone subsoiling increased the total yield by 4.2 t ha⁻¹, and the yield of grade 1 tubers by 5.6 t ha⁻¹ (7.7%). With zone subsoiling, the percentage of large grade 1 market-grade tubers increased by 3.3% in 1989 and 5.7% in 1990. Zone subsoiling requires some extra attention by the irrigator early in the season to insure uniform furrow irrigation, but it can potentially conserve both soil and water while improving grade and yield.