Soil Profile Transformation after 50 Years of Agricultural Land Use

Abstract

Despite a large body of scientific research that shows that soils change on relatively short time scales under different management regimes, classical pedological theory states that we should expect these changes to occur only in the surface few centimeters and that they are not of adequate magnitude to suggest fundamental changes in pedon character over short periods of time. In fact, rarely, do the scientists that make these comparisons report on any properties deeper than 30 to 45 cm in the soil profile. With this study, we evaluate soil transformation to a depth of 150 cm after 50 yr of intensive row-crop agricultural land use in a temperate, humid, continental climate (Iowa, United States), by resampling sites that were initially described by the United States soil survey between 1943 and 1963. We find that, through agricultural land use, humans are accelerating soil formation and transformation to a depth of 100 cm or more by accelerating erosion, sedimentation, acidification, and mineral weathering, and degrading soil structure, while deepening dark-colored, organic-matter rich surface horizons, translocating and accumulating organic matter deeper in the soil profile and lowering the water table. Some of these changes can be considered positive improvements, but many of these changes may have negative effects on the soils' future productive capacity.Abbreviations: SOC, soil organic carbon.

Use of the USDA National Cooperative Soil Survey Soil Characterization Data to Detect Soil Change: A Cautionary Tale

“…2) had an R 2 of 0.982 and RMSE of 0.185% SOC (n = 478), and was similar to a result reported by Veenstra and Burras (2015) for selected Iowa soils. The slope (0.957) had an SE of 0.006 and the intercept (0.0478) had a SE of 0.012.…”

“…Re-sampling studies Veenstra and Burras, 2015) were utilized by Van Meter et al (2016); these studies documented changes in both SOC and TN since the 1950s, while accounting for changes in methodology. Both these studies resampled profiles that were initially sampled through cooperative soil survey efforts in a single state, and both documented increases in soil TN in the lower profile (50-100 cm).…”

A deeper look at the relationship between root carbon pools and the vertical distribution of the soil carbon pool

“…Initial soil organic C measurements in that study were made ∼ 50 years after these soils had already been converted to annual systems, preventing comparison to soil organic C levels at depth under native vegetation. The results from Veenstra et al (2015) still show that Mollisols can and do gain soil organic C at deeper depths under maize and soybean systems. Similarly, David et al (2009) andFollett et al (2009) found cultivated sites that gained deep soil organic C relative to remnant prairies and grasslands.…”

“…The loss of C in the soil surface after cultivation is well known and attributed to mass loss through soil erosion, increased mineralization of organic matter through tillage, and decreased belowground organic matter inputs (Davidson and Ackerman, 1993;Huggins et al, 1998). The change in soil carbon below 30 cm is less documented, but using a robust dataset, Veenstra et al (2015) found soil organic C to increase be- low 35 cm after 50 years in maize and soybean cropping systems in Iowa, USA. Initial soil organic C measurements in that study were made ∼ 50 years after these soils had already been converted to annual systems, preventing comparison to soil organic C levels at depth under native vegetation.…”

Leveraging agroecology for solutions in food, energy, and water

“…Such biologically simplified farming systems have been connected to water-related issues such as pollution and toxic algal blooms (Porter et al, 2015;Smith et al, 2015), and depletion of groundwater (Richey et al 2015). At the same time, many of these systems are also prone to soil erosion and degradation (Montgomery, 2007;Veenstra and Burras, 2015), loss of pollinator species (Kremen et al, 2002), and the decline of rural communities (Francis et al, 2014), all of which could contribute to additional problems, such as a loss of system resiliency. One recent study supported this hypothesis regarding resilience, finding that higher-income countries that are more heavily reliant on large-scale monocultures had a greater yield deficit following extreme weather as compared to lower-income countries that likely include more diverse crops and management (Lesk et al 2016).…”