Abstract
Perennial grain crops have been suggested as a more sustainable alternative to annual crops. Yet their water use and how they are impacted by environmental conditions have been seldom compared to those of annual crops and grasslands. Here, we identify the dominant mechanisms driving evapotranspiration (ET), and how they change with environmental conditions in a perennial Kernza crop (US-KLS), an annual crop field (US-ARM), a C4 grassland (US-KON), and a mixed C3/C4 grassland (US-KFS) in the Central US. More specifically, we have utilized the omega (Ω) decoupling factor, which reflects the dominant mechanisms responsible for the evapotranspiration (ET) of the canopy. Our results showed that the US-ARM site was the most coupled with the lowest decoupling values. We also observed differences in coupling mechanism variables, showing more sensitivity to the water fluctuation variables as opposed to the radiative flux variables. All of the sites showed their lowest Ω value in 2012, the year of the severe drought in the Central US. The 2012 results further indicate the dependence on the water fluctuation variables. This was especially true with the perennial Kernza crop, which displayed much higher soil moisture values. In this regard, we believe that the ability of perennial Kernza to resist water stress and retain higher soil moisture values is both a result of its deeper roots, in addition to its higher Ω value. Through the analysis of both the site comparison and the comparison of the differences in years, we conclude that the perennial Kernza crop (US-KLS) is more similar in its microclimate effects to the C4 (US-KON) and mixed C3/C4 (US-KFS) grassland sites as opposed to its annual counterpart (US-ARM). This has implications for the role of perennial agriculture for addressing agricultural resilience under changing climate conditions.
Highlights
The changing climate has led to issues surrounding the sustainability of certain agricultural resources, and has raised concerns about future food security [1]
Research has shown that perennial agroecosystems function more like natural grasslands and the results obtained here seem to coincide with our original hypothesis that US-KLS would be more similar to natural grasslands as opposed to the annual cropland [32,33]
See noticeable differences from site to site in the water fluctuation variables (VPD, soil water content (SWC), and LE). This is especially true when looking at SWC, where US-KLS has much higher soil moisture amounts than the other sites, which is to be expected from the deeper roots associated with the Kernza crop [1C7o].uLpElindgispMlaeycshaansilsigmhst depc-rveaaslueeass wMe mulotvipelferoRm2 coAmdpjulestteeldy Rna2 tural grassland to annual crop.luVxPeDs display
Summary
The changing climate has led to issues surrounding the sustainability of certain agricultural resources, and has raised concerns about future food security [1]. One site located in Oklahoma (US-ARM) (Figure 1) We chose these sites to (1) compare the Ω values and the dominant controlling mechanisms between an annual cropland, perennial cropland, Sustainability 2019, 11, 1640 and two different grasslands and (2) examine certain large-scale regional processes that would be experienced by all of them (i.e., the 2012 drought). Where Γ is psychometric constant [kPa T−1], ∆ is the slope of saturation vapor pressure versus temperature [kPa T−1], and rc and ra are the stomatal and aerodynamic resistance (s m−1), respectively In addition to this equation, we utilized the total transpiration rate (E) equation, from Jarvis and McNaughton [18], to interpret the dominant controlling mechanisms for the land–atmosphere coupling occurring:. This occurred due to the existence of gaps or absence of measurements necessary to calculate Ω according Equations (1) and (2)
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