Productivity and Water Use Efficiency of Intensified Dryland Cropping Systems under Low Precipitation in Pacific Northwest, USA

A lack of plant available water limits the ability to intensify the summer fallow-winter wheat (SF-WW) rotation in low precipitation (<350 mm) areas of the inland Pacific Northwest (PNW). The objective of this study was to compare crop yield, water use efficiency, precipitation capture, and soil water storage between conventional-tillage SF and reduced tillage fallow (RTF) and among different 2-yr and 3-yr cropping sequences. After full initiation of the experiment, eight sequences were evaluated over a 3-yr period (2016-18) including SF-WW, RTF-WW, RTF-WW-spring barley (SB), RTF-winter napus canola (WN)-spring wheat (SW), RTF-spring carinata (SC)-SW, RTF-WN-spring forage triticale (ST), and RTF-winter forage triticale (WT)-SC. Growing season precipitation was near average (269 mm) each year. Ponded infiltration rates were significantly higher (P <= 0.05) in 2-yr rotations managed with RTF (77.68 +/- 24.56 mm h(-1)) than SF (37.08 +/- 13.03 mm h(-1)). Water use efficiency and yields of WW were generally greater following RTF than for WW after SF. Water use and yield of winter cereals WW and WT after fallow were greater than for oilseeds WN and SC that also followed fallow. Pre-plant soil water contents were significantly lower following a primary crop than after fallow. Consequently, water use and yield of secondary crops were <50 % of primary crops. Of 3-yr cropping sequences, RTF-WW-SB and RTF-WW-SC had the highest water use efficiencies with annualized yields generally approaching that of RTF-WW and SF-WW. These results support integration of spring barley and spring carinata under low precipitation dryland conditions in the PNW to increase diversification and improve conservation of water.