Monday, October 1, 2018

October 2018 science journal article roundup


Here is a short set of articles on potato cultivation, groundwater, and cattle and rangelands.

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Drakopolous et al. 2016 found that reduced tillage for potatoes led to 13% lower yields (smaller tubers) but also led to higher quality and nitrogen efficiency. The quality boost wasn't enough to offset yield loss and result in net economic benefit from reduced tillage.

Myrick 2016 is a masters thesis investigating adoption (and abandonment) of a potato variety resistant to late blight (C-88) in Yunnan, China. They found smaller farmers and those closer to cities were less likely to grow it, although they noted access to seed is very limited so decisions may largely be driven by which varieties extension agents promote. The appendix has some interesting (and at times, conflicting) data on farmer perceptions.

Jasechko et al. 2017 makes two important points about groundwater. The first is that between 42-85% of groundwater in the upper 1 km of the ground is over 12,000 years old, as is more than half the water pumped from deeper than 250m (highlighting challenges with pumping out "fossil" water which will be very slow to recharge). The other is that while the water is very old,  half of the wells showed contamination with tritium (a radioactive isotope mostly present in the environment from nuclear weapons and testing, showing relatively recent contamination). In other words, groundwater which took millennia to recharge and get clean is being contaminated more rapidly.
You can read a blog about this one:

Reeves and Baggett 2014 developed a relatively simple way to assess rangeland degradation using remote sensing. Essentially they compare rangelands to reference conditions (all rangelands within similar ecological classifications), and found relatively little degradation (with degradation trends almost undetectable). They list several reasons for this in the discussion, but from other work in this space I've read it seems that estimating grassland productivity and degradation remotely is fundamentally challenging and limited (especially without field data to calibrate on), and NDVI is not an ideal tool for grasslands for several reasons. Caution could be taken before assuming relatively simple remote sensing estimates of grassland condition are accurate and actionable.

Reeves et al. 2017 predicts how climate change will affect cattle in the western U.S., considering forage (quantity, interannual variability, and vegetation types) and hear stress. They expect more forage in the north, less woody plants and more grass (in general), more variation in forage quantity year to year, and more heat sress (starting 2020-2030), which taken together means more vulnerability of cattle in most places (especially in the Southwest). In northern areas, the impacts of heat stress are expected to offset the benefits of more forage (with some exceptions). The two top maps in Figure 3 has a good summary of net impacts on cattle by 2060 and 2100, with yellow to red indicating negative effects, and green to blue indicating positive ones.

Drakopoulos, D., Scholberg, J. M. S., Lantinga, E. A., & Tittonell, P. A. (2016). Influence of reduced tillage and fertilization regime on crop performance and nitrogen utilization of organic potato. Organic Agriculture, 6(2), 75–87.

Jasechko, S., Perrone, D., Befus, K. M., Bayani Cardenas, M., Ferguson, G., Gleeson, T., … Kirchner, J. W. (2017). Global aquifers dominated by fossil groundwaters but wells vulnerable to modern contamination. Nature Geoscience, (April), 1–6.

Myrick, S. N. B. (2016). An Economic Impact Assessment of Cooperation-88 Potato Variety in the Yunnan Province of China. Virginia Polytechnic Institute and State University.

Reeves, M. C., & Baggett, L. S. (2014). A remote sensing protocol for identifying rangelands with degraded productive capacity. Ecological Indicators, 43, 172–182.

Reeves, M. C., Bagne, K. E., & Tanaka, J. (2017). Potential Climate Change Impacts on Four Biophysical Indicators of Cattle Production from Western US Rangelands. Rangeland Ecology and Management, 70(5), 529–539.



p.s. as a reminder, you can search all of the science articles written by TNC staff (that we know of) here