Rapid Changes in Sandy Soils under Intensive Agriculture in Wisconsin

Abstract

We have quantified the effect of land use change by measuring soil physiochemical changes in sandy soils under intensive agriculture, grasslands, and pine forest in the central sands plain of Wisconsin, USA. The soils under agriculture (corn, potato, soybeans, and peas) are irrigated (280 mm yr–1), limed, fertilized, and leveled. Soil observations were made in 82 pedons, and soil horizons, texture, and pH were measured. The soils are all very sandy and somewhat excessively drained. In all pedons, sand percent increases with depth from 88 to 98%; silt content is around 8% until the C horizons where the silt content decreases to 2% on average. Coarse fragments increase at 60 to 100 cm and decrease below 140 cm. Topsoil thickness under agriculture ranged from 20 to 42 cm (mean 28 cm), topsoils under forest ranged from 3 to 27 cm, and topsoils under grassland ranged from 14 to 26 cm. It was found that the soils under agriculture are less acidic, have thicker topsoil horizons, and have slightly more clay, possibly as a result of enhanced mineral weathering. These sandy soils have changed in three decades from Udipsamments and Hapludalfs into Argiudolls and Hapludolls, while some soils have changed from Hapludalfs into Udipsamments. Topsoil depth changes in the Wisconsin Central Sand Plain are the result of intensive agriculture.

Geochemical Fingerprint and Soil Carbon of Sandy Alfisols

“…Kristiansen [36] and Zhang et al [50] found that Fe2O3 was highest in the Bt horizon due to an increase in clay and soil carbon content. Goethite was the only Fe oxide present in the diffractograms for the soil under forest, but other studies have showed that these sandy soils may contain up to 12% feldspars and less than 3% Fe oxides, inosilicates (augite), and silicates (hornblende) [22].…”

“…In these sandy soils, quartz was the dominant mineral, and Si was high throughout the soil profiles (191-297 g Si kg −1 ). Madison and Lee [22] found that up to 96% of these sandy soils are quartz dominant. The Bt horizons had low Si (191-224 g Si kg −1 ), and a slightly higher silt and clay content (100-190 g kg −1 ) than the Ap horizons.…”

“…Much of the soils are intensely cultivated and commonly irrigated, limed, and fertilized. The chemical, physical, and biological components of the soil have changed under agriculture [22]. The carbon stocks are on average 41 Mg carbon ha −1 in the top 30 cm, and this is due to decades nitrogen fertilization and irrigation [23].…”

“…The carbon stocks are on average 41 Mg carbon ha −1 in the top 30 cm, and this is due to decades nitrogen fertilization and irrigation [23]. The soils under agriculture generally have thicker topsoils (28 cm) than soils under grassland (21 cm) and forest (14 cm) [22]. Madison and Lee [24] determined that quartz was the dominant mineral in the sandy soils of Wisconsin (60 to 96%), and feldspars (orthoclase, plagioclase) were the second most dominant mineral (2 to 12%).…”