Linking geospatial information and effects of land management to edaphic properties

Abstract

This study combines geospatial data and a classification scheme that uses landform elements to derive landform complexes that codify the collection of soils data at variable scale within a single field site. Our experiment was initiated in 2018 on three, 1.6 ha self-contained watersheds representing a southern tall grass prairie (STGP), a system of continuous winter wheat (<i>Triticum aestivum</i>) tilled via offset disking and chisel plow (WWCT), and a minimally disturbed winter wheat system that was periodically planted to a warm season forage, typically sorghum-sudangrass (<i>Sorghum bicolor</i> L.) (WWMT) from 1978 to 2018. A class I soil survey was conducted in 2018 by grid sampling the landscape of all watershed systems at the site. The survey indicated four distinct catena were present across all watersheds, which enabled us to utilize a split block design. This statistical approach allowed for testing of interactions among management practices, landscape position, and soil depth to obtain means and standard errors for different edaphic properties. Using a hydraulic probe, 144 random soil cores were collected to a 30 cm depth at each of the four 4.6 m by 3.8 m replicated blocks per landscape position (tread, riser, and toe) within the three watersheds. Cores were further divided into three depths (0 to 5, 5 to 15, and 15 to 30 cm). Baseline analyses included Mehlich-3, soil sulfate (SO₄) and DTPA-sorbitol extractions, soil texture, bulk density, pH, total soil organic carbon (TSOC) and total soil nitrogen (TSN), particulate organic matter (POM), and non-hydrolysable C (RCAH), the resistant fraction of soil organic C. The majority of edaphic properties associated with soil classification varied with landscape position and depth. These included clay content, base saturation (calcium [Ca], magnesium [Mg], and potassium [K]), pH, and sulfur in the form of sulfate (SO₄-S) and phosphorus (P). Carbon and N fractions varied with land use, conservation practices, and/or depth. The establishment of replicate sampling stations that account for and limit the spatial variability of edaphic properties within defined landform complexes enables researchers to more accurately quantify the effects of conservation practices and land management.