Productivity, economic performance, and soil quality of conventional, mixed, and organic dryland farming systems in eastern Washington State

摘要

The global trends of shortening crop rotations, simplifying cropping systems, and segregating livestock from cropping enterprises have generated high yields while creating high environmental costs. Diversification, including integrated crop/livestock systems and the use of cover, forage, and perennial crops, can be used to improve soil health, reduce financial risk, increase yields, and reduce many negative environmental externalities. With such diversification in mind, we conducted a 5-year study examining four contrasting farming systems in dryland eastern Washington State in terms of their impacts on total productivity, economic performance, and soil quality. The four systems were a conventional (CONV) winter wheat/spring wheat/spring pea rotation, typical for the area; a mixed crop-livestock (MIX) winter wheat/spring wheat/grazed winter pea forage rotation; an organic mixed crop-livestock (ORGcrop) rotation of 3 yr perennial alfalfa and grass/grazed pea forage/winter wheat; and an organic hay (ORGhay) continuous perennial alfalfa and grass system. Soft white winter wheat (SWWW) yields were higher following grazed pea forage in MIX (6.2 Mg ha(-1)) than following harvested pea crop in CONV (5.9 Mg ha(-1)) despite lower N fertilizer rates in MIX. Following 3 yr of alfalfa and grass hay and no N fertilizer, SWWW yields in ORGcrop (6.2 Mg ha(-1)) were similar to CONV and MIX yields but averaged 15.5% lower protein concentration. Over the 5-yr rotation, average net returns were ORGhay ($616 yr(-1))> ORGcrop (216 yr(-1))> MIX (-1 yr(-1)) = CONV (-13 yr(-1)), in part due to high hay prices and average grain prices during this period compared to long-term averages. Over the course of the study, total soil profile SOC showed significant negative trends in CONV (-3.1 Mg C ha(-1) yr(-1)) and MIX (-4.1 Mg C ha(-1) yr(-1)) but not in ORGcrop and ORGhay. In surface (0-15 cm) soil, microbial biomass carbon and nitrogen and beta-glucosidase activity were greater in ORGcrop and ORGhay than in CONV and MIX. The landscape position of this study site is of relatively poorer soil quality and results may differ across the heterogeneity of a whole farm field. Overall, ORGhay, ORGcrop, MIX, and CONV in this order produced a gradation of forage production relative to cereal production from greatest to least, and also a gradation of economic and soil sustainability metrics from greatest to least. This study found that integrating perennial crops, such as alfalfa and forage grasses, into organic farming systems can build soil quality, be profitable, and supply nitrogen to succeeding grain crops.