Tai Maaz

Canola integration into semi-arid wheat cropping systems of the inland Pacific Northwestern USA

Abstract. The inland Pacific Northwestern USA (iPNW) wheat-producing region has a diversity of environments and soils, yet it lacks crop diversity and is one of the few semi-arid wheat-growing regions without significant integration of oilseeds. Four major agroecological zones, primarily characterised by water availability, feature distinctly different fallowed and annually cropped systems, each presenting different challenges and opportunities to integrate winter and spring canola. Although major interests in regional energy crops and rotational diversification spurred feasibility research on iPNW canola food, feed and fuel production in the 1970s, commercial canola adaptation has lagged behind other semi-arid wheat regions for various socioeconomic, ecophysiological and agronomic reasons. New federal crop insurance policies will reduce economic risks in new crop adaptation, and oilseed processing facilities are creating new local markets. Although canola management largely relies on wheat farm equipment, agronomic approaches require strategic adjustments to account for physiological differences between canola and cereals including seed size, seedling morphology and responses to temperature extremes. Climate change predictions for the region threaten to exacerbate current hot and dry summers and research aims to develop and adapt flexible winter and spring canola-based systems to regional water and temperature stressors in each zone. Adaptation will require novel planting, fertilisation and weed control strategies to successfully establish improved winter canola cultivars in hot dry summers that survive cold winters, and spring canola cultivars direct-seeded in cool wet springs. The adaptation of winter and spring canola will somewhat mirror the rotational placement of winter and spring cereals within each zone. Economic analysis of oilseed break crop benefits such as weed and disease control will help to demonstrate the medium-term economic benefits of crop diversification to support the growth of a regional canola industry in the iPNW.

Impact of Climate Change Adaptation Strategies on Winter Wheat and Cropping System Performance across Precipitation Gradients in the Inland Pacific Northwest, USA

Ecological instability and low resource use efficiencies are concerns for the long-term productivity of conventional cereal monoculture systems, particularly those threatened by projected climate change. Crop intensification, diversification, reduced tillage, and variable N management are among strategies proposed to mitigate and adapt to climate shifts in the inland Pacific Northwest (iPNW). Our objectives were to assess these strategies across iPNW agroecological zones and time for their impacts on 1) winter wheat (Triticum aestivum L.) productivity, 2) crop sequence productivity and 3) N fertilizer use efficiency. Region-wide analysis indicated that WW yields increased with increasing annual precipitation, prior to maximizing at 520 mm yr-1 and subsequently declining when annual precipitation was not adjusted for available soil water holding capacity. While fallow periods were effective at mitigating low nitrogen (N) fertilization efficiencies under low precipitation, efficiencies declined as annual precipitation exceeded 500 mm yr-1. Variability in the response of WW yields to annual precipitation and N fertilization among locations and within sites supports precision N management implementation across the region. In years receiving less than 350 mm precipitation yr-1, WW yields declined when preceded by crops rather than summer fallow. Nevertheless, WW yields were greater when preceded by pulses and oilseeds rather than wheat across a range of yield potentials, and when under conservation tillage practices at low yield potentials. Despite the yield penalty associated with eliminating fallow prior to WW, cropping system level productivity was not affected by intensification, diversification, or conservation tillage. However, increased fertilizer N inputs, lower fertilizer N use efficiencies, and more yield variance may offset and limit the economic feasibility of intensified and diversified cropping systems.

Integrating Historic Agronomic and Policy Lessons with New Technologies to Drive Farmer Decisions for Farm and Climate: The Case of Inland Pacific Northwestern U.S.

Climate-friendly best management practices for mitigating and adapting to climate change (cfBMPs) include changes in crop rotation, soil management and resource use. Determined largely by precipitation gradients, specific agroecological systems in the inland Pacific Northwestern U.S. (iPNW) feature different practices across the region. Historically, these farming systems have been economically productive, but at the cost of high soil erosion rates and organic matter depletion, making them win-lose situations. Agronomic, sociological, political and economic drivers all influence cropping system innovations. Integrated, holistic conservation systems also need to be identified to address climate change by integrating cfBMPs that provide win-win benefits for farmer and environment. We conclude that systems featuring short-term improvements in farm economics, market diversification, resource efficiency and soil health will be most readily adopted by farmers, thereby simultaneously addressing longer term challenges including climate change. Specific ‘win-win scenarios’ are designed for different iPNW production zones delineated by water availability. The cfBMPs include reduced tillage and residue management, organic carbon (C) recycling, precision nitrogen (N) management and crop rotation diversification and intensification. Current plant breeding technologies have provided new cultivars of canola and pea that can diversify system agronomics and markets. These agronomic improvements require associated shifts in prescriptive, precision N and weed management. The integrated cfBMP systems we describe have the potential for reducing system-wide greenhouse gas (GHG) emissions by increasing soil C storage, N use efficiency (NUE) and by production of biofuels. Novel systems, even if they are economically competitive, can come with increased financial risk to producers, necessitating government support (e.g., subsidized crop insurance) to promote adoption. Other conservation- and climate change-targeted farm policies can also improve adoption. Ultimately, farmers must meet their economic and legacy goals to assure longer-term adoption of mature cfBMP for iPNW production systems.

Water and Temperature Stresses Impact Canola (Brassica napus L.) Fatty Acid, Protein, and Yield over Nitrogen and Sulfur

Interactive effects of weather and soil nutrient status often control crop productivity. An experiment was conducted to determine effects of nitrogen (N) and sulfur (S) fertilizer rate, soil water, and atmospheric temperature on canola (Brassica napus L.) fatty acid (FA), total oil, protein, and grain yield. Nitrogen and sulfur were assessed in a 4-yr study with two locations, five N rates (0, 45, 90, 135, and 180 kg ha-1), and two S rates (0 and 17 kg ha-1). Water and temperature were assessed using variability across 12 site-years of dryland canola production. Effects of N and S were inconsistent. Unsaturated FA, oleic acid, grain oil, protein, and theoretical maximum grain yield were highly related to water and temperature variability across the site-years. A nonlinear model identified water and temperature conditions that enabled production of maximum unsaturated FA content, oleic acid content, total oil, protein, and theoretical maximum grain yield. Water and temperature variability played a larger role than soil nutrient status on canola grain constituents and yield.

Nitrogen Affects Wheat and Canola Silica Accumulation, Soil Silica Forms, and Crusting

Raindrop-induced crusting of mineral soils supporting wheat ( L.) in the semiarid US Pacific Northwest reduces seedling establishment of late summer-seeded winter crops during dry, hot conditions. Canola ( L.) integration is diversifying regional food, feed and fuel global markets. Subsequent shifts in recycled crop residue characteristics, including Si and crop fiber, may shift soil characteristics of traditional wheat-dominated systems, potentially affecting their propensity to form soil crusts. In a greenhouse study, wheat and canola were fertilized with varying N rates. Increased N supply increased transpiration, shoot weight, and hemicellulose and cellulose yields, but with only minor increases in shoot Si and lignin yields. Both crops had similar increases in root Si with greater N-stimulated transpiration. Two subsequent soil incubations were conducted to determine how Si, N fertilization, and crop residues from wheat and canola affected soil properties. In the first incubation, Si was applied as aqueous HSiO, which increased soil amorphous and water-soluble Si (Si and Si), physical resistance, and crust thickness. Electron micrographs showed increased amorphous material, presumably a Si precipitate, on soil particles with increased Si application. Second, two Ritzville soils were treated with the canola or wheat shoot residues with and without N fertilizer. Nitrogen lowered soil pH, Si, Si, surface resistance, and crust thickness; however, first-time application of crop residue types had no short-term effect on these parameters. Any impacts of lower Si returned by lower Si crop residues on soil physical properties likely require several rotational cycles of Si crop uptake and residue returns.