Soil Water Dynamics with Spring Camelina in a Three‐Year Rotation in Washington's Winter Wheat–Fallow Region

Abstract

Core Ideas The soil water dynamics of 3‐yr winter wheat–camelina–summer fallow and 2‐yr winter wheat–summer fallow rotations were measured for 8 yr. At harvest, there was less soil water after camelina than after winter wheat in the 2‐yr rotation. The water deficit persisted through the 13‐mo fallow period and decreased the yield of 3‐yr vs. 2‐yr winter wheat. Increased cropping intensity may increase risk and variability in dry environments. Camelina [Camelina sativa (L.) Crantz] of the Brassicaceae family is a short‐season drought‐ and frost‐tolerant oilseed. Camelina has been promoted as an alternative crop for the low‐precipitation (<350 mm annually) Mediterranean‐like climate region of the US inland Pacific Northwest, where a monoculture 2‐yr winter wheat (Triticum aestivum L.) (WW)–summer fallow (SF) rotation is widely practiced. An 8‐yr experiment was conducted to compare a 3‐yr WW–camelina–SF rotation with the typical 2‐yr WW–SF rotation to analyze the soil water dynamics of these two crop rotations. Growing spring‐planted camelina reduced soil water content at the beginning of the fallow; this reduction resulted in an average of 21 mm less water at WW planting and a 170 kg ha‐1 reduction in grain yield compared with WW–SF. We show that (i) the deep‐rooted broadleaf weed Russian thistle (Salsola tragus L.) present in camelina most years was the most likely reason for greater in‐crop soil water use than with WW–SF, and (ii) the limited camelina residue was probably responsible for greater evaporative loss during the spring to late summer segment of the fallow. We report the first findings from the Pacific Northwest drylands of greater water use by a cool‐season spring crop versus WW and greater evaporative loss during the summer caused by lack of residue in a minimum‐tillage SF comparison. Here, extending the crop rotation to include camelina was costly in terms of water use, surface soil residue cover, soil water storage during the fallow, and WW grain yield.