Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2013
Publication Date: 3/1/2014
Citation: Acosta Martinez, V., Moore-Kucera, J., Cotton, J.E., Wester, D. 2014. Soil enzyme activities during the 2011 Texas record drought/heat wave and implications to biogeochemical cycling and organic matter dynamics. Applied Soil Ecology. 75:43-51. Interpretive Summary: Extreme weather events such as severe droughts and heat waves are anticipated to become more frequent due to climate change. In addition to causing crop losses and larger declines in groundwater supplies, drought may negatively impact soil quality and functioning, which can further limit crop production. In 2011, the Texas High Plains experienced the hottest and driest conditions ever recorded: average daily air temperature was 30.0°C with an average daily maximum of 37.7°C and the Palmer drought severity index (PDSI) during July was -6.13. We conducted samplings in two agricultural soils under different management (rotation vs. monoculture of cotton) during the drought and record heat (July 2011), after precipitation and a reduction in PDSI (-3.32) (March 2012) and after one year (July 2012). Several enzyme activities involved in C, N, P and S nutrient cycling that are important for soil quality were determined. During the drought/heat wave, enzyme activities were higher in the rotations compared to monoculture for both soil types, indicating better soil quality with crop rotation compared to monoculture. In general, enzyme activities were highest during the peak drought/heat wave conditions captured with our July 2011 sampling, then decreased in March 2012 after the drought. In the loam soil, which was also sampled a year after the drought in July 2012, enzyme activities showed a continual decrease over time (July 2011>March 2012>July 2012). Only one enzyme activity (arylsulfatase) increased after the drought/heat wave. In addition, soil total carbon was reduced significantly from July 2011 to March 2012 in the rotation for both soils. The continual decline of enzyme activities and soil carbon over time suggests that the extreme drought and heat wave resulted in adverse effects on soil quality, affecting the long-term sustainability of these low organic matter agricultural soils.
Technical Abstract: Extreme weather events such as severe droughts and heat waves may have permanent consequences on soil quality and functioning in agroecosystems. The Southern High Plains (SHP) region of Texas, U.S., a large cotton producing area, experienced a historically extreme drought and heat wave during 2011, which severely reduced crop production. During the period of November 2010 to August 2011, this region received only 39.6 mm of precipitation (vs. the historical average of 373 mm) and experienced the hottest summer since record keeping began in 1911. This study evaluated several enzyme activities important in biogeochemical cycling at four sites under a loam and a sandy loam soil with a management history of monoculture (continuous cotton) or rotation (cotton and sorghum or millet). These soils were sampled (0-10 cm) when the most extreme drought and heat conditions were experienced (July 2011), after precipitation and a reduction in Palmer drought severity index occurred (March 2012) and after one year (July 2012, loam sites only). During the drought/heat wave, enzyme activities continued to be a fingerprint of the soil management history as all enzymes evaluated were higher in the rotation compared to monoculture for both sites. The management effect on enzyme activities was more pronounced in the loam than in the sandy loam except for phosphatases, which had similar differences in both soil types. In general, enzyme activities were highest during the peak drought/heat wave conditions captured with our July 2011 sampling, with decreased activities in March 2012 when drought conditions were less intense and temperatures were lower. In the loam soil, which was also sampled a year after the drought in July 2012, several enzyme activities (i.e., alkaline phosphatase, urease and aspartase) showed a continual decrease over time (July 2011>March 2012>July 2012). Arylsulfatase was the only enzyme showing an increase in activity after the drought/heat wave, indicating it may be more closely tied to an active microbial community. Total C was reduced significantly from July 2011 to March 2012 in the rotation for both soils. The continual decline of enzyme activities and soil organic matter over time suggests that extreme drought and heat wave may result in adverse effects on soil quality, affecting the long-term sustainability of these low organic matter agricultural soils.