Impact of deep plowing on groundwater recharge in a semiarid region: Case study, High Plains, Texas

Abstract

[1] Groundwater recharge is critical in semiarid regions where aquifers are currently being mined for intensive irrigation. Land use management related to agriculture can be used to control partitioning of water near the land surface and to potentially manage water resources. The purpose of this study was to quantify impacts of deep plowing in rainfed (nonirrigated) agriculture in a semiarid region on groundwater recharge, which had not been previously evaluated. Deep (0.7 m) plowing was conducted once in 1971 to remove low-permeability soil layers (0.15-0.70 m deep) in Pullman clay loam (20,000 km 2 area) in a bench terrace system in the semiarid High Plains in Texas (USA). Deep plowing was followed by conventional tillage. Boreholes were drilled in deep plowed cropland (three boreholes) and also beneath conventionally tilled cropland (four) and natural ecosystems (three) to provide baseline controls. Soil samples were analyzed for water content, chloride concentrations, and matric potentials to quantify subsurface water movement. Bulges of chloride that accumulated beneath natural ecosystems during the past 9,000-14,000 years (Holocene period) provided a marker to quantify timeintegrated response of subsurface drainage to hydrologic forcing in deep-plowed cropland. Displacement of chloride bulges to depths of 10.7, 12.3, and 13.7 m beneath deep-plowed cropland indicate minimum drainage rates of 58, 60, and 81 mm/a, whereas drainage beneath conventionally tilled cropland ranged from 0 (nonterraced) to 9 and 14 mm/a (bench terraced). Deep plowing slightly increased crop yield during wet years by reducing waterlogging. If deep plowing were applied to 10% of the Pullman soils, it could increase regional volumetric recharge by 0.1 km 3 /a, which is similar to the current regional volumetric recharge. Low-permeability soil layers are widespread in cropland areas globally, and deep plowing could greatly enhance groundwater recharge in such areas, which is critical in semiarid regions where recharge is negligible.

Effects of irrigated agroecosystems: 1. Quantity of soil water and groundwater in the southern High Plains, Texas

“…Relationship between depth‐weighted mean matric potential (MP), chloride (Cl), and nitrate‐N (NO 3 ‐N) in unsaturated zone profiles beneath natural ecosystems (4 profiles), rain‐fed agroecosystems (19 profiles), and irrigated agroecosystems (13 profiles, Table 1). Data for natural and rain‐fed profiles are from Scanlon et al [2008a, 2008b]. Black symbols represent median values of profile means below the root zone (Natural: MP = −200 m, Cl = 780 mg/L, NO 3 ‐N = 8.1 mg/L; Rain‐fed: MP = −6.6 m, Cl = 8.4 mg/L, NO 3 ‐N = 30 mg/L; Irrigated: MP = −40 m, Cl = 720 mg/L, NO 3 ‐N = 71 mg/L) (Table 1).…”

“…Percolation rates in these profiles are 22 and 36 mm/a (). These percolation estimates are attributed entirely to percolation during irrigated periods because previous studies show no percolation or displacement of natural Cl bulges beneath rain‐fed systems in these clay‐loam soils [ Scanlon et al , 2008a]. Calculated percolation rates represent time‐integrated estimates that may be appropriate for profile 1, which was irrigated with a sprinkler system throughout and irrigation water quality may not have changed over time.…”

“…In the area of fine‐grained soils in the SHP‐N region, there is no recharge under rain‐fed or irrigated agroecosystems. Recharge in areas of natural ecosystems is restricted to ephemeral lakes or playas, and regional recharge estimates in this region based on groundwater Cl data range from 6 mm/a, using long‐term Cl concentrations in bulk precipitation [ Scanlon et al , 2008a], to 11 mm/a, using Cl precipitation data from 1 year [ Wood and Sanford , 1995]. A regional recharge rate of 6 mm/a cannot sustainably support irrigation.…”

Effects of irrigated agroecosystems: 2. Quality of soil water and groundwater in the southern High Plains, Texas

“…Recharge beneath natural ecosystems is focused beneath ephemeral lakes or playas and averages ∼6 to 11 mm/year, on the basis of groundwater Cl data in the SHP‐N region [ Wood and Sanford , 1995; Scanlon et al , 2008a]. Salt loading from playas is negligible.…”

Coastal Lagoons in Europe: Integrated Water Resource Strategies

“…So far, the attention of researchers has mostly been focused on investigating land use change scenarios, which partly considered also agricultural practices, for example ploughing methods (Scanlon et al 2008) and their impacts on water resources. There are many published studies, which have explored the impacts of land use change separately, (e.g., Schilling et al (2008), Farley et al (2008) …”