Let’s start thinking about water!

Woody Plant Encroachment Enhances Soil Infiltrability of a Semiarid Karst Savanna

Schematic of the hypothesized effect of woody plant encroachment on infiltration and deep percolation in shallow karst soils in the Edwards Plateau.

Brad Wilcox has made quite the career of employing scientific rigor to answer the questions on brush management and water resources, especially with respect to the dearly despised Ashe juniper, AKA cedar. In this paper, he and his co-authors investigate how Ashe juniper affects infiltration of water into the subsurface. They note the dogma that Ashe juniper decreases recharge but also note that encroachment of woody species like Ashe juniper have resulted in dramatic increases in stream baseflow in the Edwards Plateau Region.

They tested the hypothesis that Ashe juniper was the cause of these increases by measuring infiltration at Ashe juniper sites of different ages. They found that in soils underlying shrubs, infiltration ability quintupled, and percolation depth almost tripled compared with soils without junipers. As might be expected, infiltration increased as measurements approached the trunk. Surprisingly, infiltration improvements didn’t appear to depend on the age of the juniper. There may be other reasons to chop down your cedars — Omicron-like symptoms perhaps being one, but adversely affecting groundwater recharge does not appear to be one of them. Makes me wonder if some of the decrease in runoff to the Colorado River might be due to woody plant encroachment.

Dryland Irrigation Increases Accumulation Rates of Pedogenic Carbonate and Releases Soil Abiotic CO2

Soils can release biogenic carbon — carbon derived from biological activity — and they can release abiogenic carbon, which is derived from the formation of minerals in soil. In this study, the authors investigated pedogenesis in the irrigated soils of the Rio Grande Valley in the El Paso area. Specifically, they looked at how calcium- and bicarbonate-rich water used for irrigation can accelerate the formation of calcite while releasing abiotic carbon dioxide to the atmosphere. Using isotopes, they found that about 20 to 50% of soil carbon dioxide in irrigated soils is calcite-derived abiotic carbon dioxide instead of soil-respired or from the atmosphere. Furthermore, they found that agricultural soils in the Valley have accumulated up to 10% of calcite by weight after just about 100 years of irrigation. That’s a lot of calcite! And it’s slowly clogging up the soils. The large amount of carbon dioxide released from irrigation may have consequences for the global carbon cycle.

The Synergy Between Water Conservation and Economic Profitability of Adopting Alternative Irrigation Systems for Cotton Production in the Texas High Plains

Paradoxically, the installation of more efficient irrigation techniques in the Southern High Plains has not resulted in less water use. The big reason for this is that many irrigators are irrigating at a deficit — they can’t economically produce enough water from the Ogallala Aquifer to overcome the deficit between evapotranspiration and rainfall. More efficiency means more water to decrease the deficit. This study evaluated water conservation and economic profitability of agricultural production of cotton in the High Plains of Texas. Results showed that more irrigation water consistently increased average net return of cotton production for all irrigation systems except for subsurface drip irrigation, which produced a similar net return at 75% and 100% of evapotranspiration replacement levels. Economic risk analysis showed that low-energy precision application (LEPA) had a higher net return than other irrigation systems and that it would be preferred by risk-neutral, somewhat risk averse, and rather risk-averse cotton producers. Indeed, LEPA is what many (most?) irrigators use in the Texas High Plains. The authors conclude that subsurface drip would result in water savings without a reduction in crop yields but would require incentives for irrigators to adopt it.