Soil Fertility on an Agricultural Frontier: The US Great Plains, 1880–2000

In contrast to most long-settled agricultural landscapes, the US Great Plains presents a rare example of well-documented agricultural colonization of new land. The Census of Agriculture provides detailed information about evolving grassland farm systems from the beginning of agricultural expansion and then at some two dozen time points between 1880 and the present. From early sod-busting, through drought and depression, and into late-twentieth-century modernization, it is possible to track how farmers used their land in any county. Treating farmland as an agroecosystem, a hybrid human-natural landscape, this article asks how farmers captured, altered, and replenished soil fertility. Did they extract more soil nitrogen than they returned, or did they maintain a balance? The article assesses land use from a soil nutrients perspective in several plains environments to capture variation in climate (especially rainfall), native soil quality, and availability of irrigation water. It traces farm management strategies through time to understand agricultural crises, growth periods, and technological transitions in the context of soil fertility. Soil management on an agricultural frontier was markedly different from that in places that had been farmed for centuries. A shortage of people and livestock and an abundance of deep, rich soils in the plains informed farmers’ calculations as they juggled labor, capital, and market forces against family and financial strategies. Uniform methods of estimating and representing soil nutrient processes make possible a direct comparison of the relative sustainability of historical agroecosystems.

The Role of Soil Texture in Local Land Surface–Atmosphere Coupling and Regional Climate

Soil hydraulic properties are critical in estimating surface and sub-surface processes, including surface fluxes, the distribution of soil moisture, and the extraction of water by root systems. In most numerical weather and climate models, those properties are assigned using maps of soil texture complemented by look-up tables. Comparison of two widely-used soil texture databases, the USDA State Soil Geographic database (STATSGO) and Beijing Normal University’s soil texture database (GSDE), reveals that differences are widespread and can be spatially coherent over large areas that can eventually lead to regional climate differences. For instance, over the US Great Plains, GSDE stipulates finer soil grains than STATSGO, while the opposite is true over Central Mexico.In this study, we employ the WRF/CLM4 modeling suite to investigate the sensitivity of the simulated regional climate to changes in the prescribed soil maps. Wherever GSDE has finer grains than STATSGO (e.g., over the US Great Plains), the soil retainswater more strongly as evidenced by smaller latent heat flux (–20 W m−2), larger sensible heat flux (+20 W m−2), and correspondingly, a decrease in the 2-m humidity (–1 g kg−1) and an increase in 2-m temperature (+1.5 K). The opposite behavior is found over areas of coarser grains in GSDE (e.g., over Central Mexico). Further, the changes in surface fluxes via soil texture lead to differences in the thermodynamic structure of the PBL. Results suggest that neither soil hydraulic properties nor soil moisture solely dictate the strength of surface fluxes, but in combination they alter the land–atmosphere coupling in non-trivial ways.

Herbicide programs to manage glyphosate/dicamba-resistant kochia (Bassia scoparia) in glyphosate/dicamba-resistant soybean

Evolution of kochia resistance to glyphosate and dicamba is a concern for growers in the US Great Plains. An increasing use of glyphosate and dicamba with the widespread adoption of glyphosate/dicamba-resistant (GDR) soybean in recent years may warrant greater attention. Long-term stewardship of this new stacked-trait technology will require the implementation of diverse weed control strategies, such as the use of soil-residual herbicides (PRE) aimed at effective control of GDR kochia. Field experiments were conducted in Huntley, MT, in 2017 and 2018, and Hays, KS, in 2018 to determine the effectiveness of various PRE herbicides applied alone or followed by (fb) a POST treatment of glyphosate plus dicamba for controlling GDR kochia in GDR soybean. Among PRE herbicides tested, sulfentrazone provided complete (100%), season-long control of GDR kochia at both sites. In addition, PRE fb POST programs tested in this study brought 71% to 100% control of GDR kochia throughout the season at both sites. Pyroxasulfone applied PRE resulted in 57% to 70% control across sites at 9 to 10 wk after PRE (WAPRE). However, mixing dicamba with pyroxasulfone improved control up to 25% at both sites. Kochia plants surviving pyroxasulfone applied PRE alone produced 2,530 seeds m−2 compared with pyroxasulfone + dicamba (230 seeds m−2) at the Montana site. No differences in soybean grain yields were observed with PRE alone or PRE fb POST treatments at the Montana site; however, dicamba, pyroxasulfone, and pendimethalin + dimethenamid-P applied PRE brought lower grain yield (1,150 kg ha−1) compared to all other tested programs at the Kansas site. In conclusion, effective PRE or PRE fb POST (two-pass) programs tested in this research should be proactively utilized by the growers to manage GDR kochia in GDR soybean.