Abstract
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.
Highlights
Ecological instability, high demand for inputs, and low resource use efficiencies are concerns for the long-term productivity of conventional cereal monoculture systems (Matson et al, 1997; Tilman, 1999)
We found that winter wheat (WW) yields varied considerably across and within the 11 locations (Figure 1A) with annual precipitation ranging from 220 to 650 mm yr−1, with an overall mean of WW in traditional rotations of ∼6,000 kg ha−1 and a coefficient of variation (CV) of 31% (Figure 1B, Table 2)
We observed that WW yields increased with increasing annual precipitation before maximizing at 520 mm yr−1 and subsequently declining
Summary
Ecological instability, high demand for inputs, and low resource use efficiencies are concerns for the long-term productivity of conventional cereal monoculture systems (Matson et al, 1997; Tilman, 1999). Diversification, reduced tillage, and variable N management are among the strategies proposed to mitigate and adapt monocultures to projected climate shifts (Burney et al, 2010; Smith and Olesen, 2010; Tilman et al, 2011; Powlson et al, 2014; Ponisio et al, 2015). In the summer-dominate precipitation region of the North American Great Plains, soil conservation practices have enabled crop intensification through fallow replacement (Lafond et al, 1992; Anderson et al, 2003), which has increased opportunities to diversify crops (Halvorson et al, 1999; Zentner et al, 2002b; Tanaka et al, 2005; Roberts and Johnston, 2007), enhance N and water use efficiencies (Pikul et al, 2012). A combination of these alternative cropping system strategies may increase productivity and economic returns (Tanaka et al, 2002; Alam et al, 2015; Babu et al, 2016), and multiple strategies may be needed (Kirkegaard and Hunt, 2010; Snapp et al, 2010)
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