Soil health changes following transition from an annual cropping to perennial management‐intensive grazing agroecosystem

Abstract

Management‐intensive grazing (MiG) on irrigated, perennial pastures has steadily increased in the western United States due to pressure for reducing public lands grazing, overall declining land available for pasture, and decreasing commodity prices. However, there are still many unknowns regarding MiG and its environmental impact, especially with regards to soil health. Over a 2‐yr period, a study evaluating the change in soil health under a full‐scale, 82‐ha pivot‐irrigated perennial pasture system grazed with ∼230 animal units (AUs) using MiG. Soil analysis included 11 soil characteristics aggregated into the Soil Management Assessment Framework (SMAF), which outputs results for soil biological, physical, nutrient, chemical, and overall soil health indices (SHIs). Over time, positive impacts were observed in the chemical and biological SHI due to decreases in salt content and increases in microbial and enzymatic activities. Soil organic C (SOC) remained unchanged, yet positive biological SHI changes are potential precursors to future SOC increases. The chemical and nutrient SHI increased in the soil surface due to reductions in salt content in conjunction with increased plant‐available soil P, as a result of salt leaching via irrigation and pre‐study inorganic P fertilizer application in conjunction with manure deposition due to MiG, respectively. Finally, a negative impact was also observed in the physical SHI, driven primarily by increasing bulk density due to hoof pressure from cattle grazing. If managed correctly, compaction issues can be avoided, with MiG systems having potential success in supporting grazing while promoting soil health for environmental and economic sustainability.

Tracking Soil Health Changes in a Management-Intensive Grazing Agroecosystem

“…This study was conducted under an 82 ha center pivot at the Colorado State University Agricultural Research, Development, and Education Center northeast of Fort Collins, CO USA (40 • 39 30.16 N, 104 • 59 09.00 W) at an altitude of 1554 m. Monthly mean temperatures tend to peak in July with an average high of 30 • C and reach a low in December with a minimum average temperature of −10 • C. Total average precipitation is approximately 340 mm, with much of this precipitation occurring between April and August [28]. The region is classified under the Köppen-Geiger classification system as a semi-arid, cold steppe [1,29]. Across this portion of Colorado, many producers graze cattle on unirrigated land, while cropland is dominated by irrigated commodity cropsnamely corn and wheat.…”

“…Between the 2016 and 2017 growing seasons, the field was converted to a cool-season grass-forage mix of multiple bromes, clover species, and other common forages, such as alfalfa. The full details of the grass mix and livestock grazing pattern are available in Shawver et al [1]. In the spring of 2017, the field was split into ~2.6 ha paddocks.…”

“…Soils were sampled in the same location as in the Shawver et al [1] study, focusing sampling on the primary soil series in the pivot: Nunn clay loam (fine, montmorillonitic, mesic Aridic Argiustolls, 26 ha; [30]), Kim loam (fine-loamy, mixed, calcareous, mesic Ustic Torriorthents, 10 ha), and Garrett loam (fine-loamy, mixed, mesic Pachic Argiustolls, 7.5 ha; [30]). In order to maintain continuity between samples from 2017 to 2022, soil was not collected in the northwest quarter of the pivot due to poor initial forage establishment in the spring of 2017.…”

“…Sustainable intensification of agroecosystems has become an important topic for land managers, climate scientists, and numerous stakeholders looking to meet environmental goals while maintaining highly productive farms and ranches. One increasingly popular management strategy for meeting producer on-site goals is Management-intensive Grazing (MiG), which is a management scheme that may increase stocking rates, improve forage quality, and reduce negative environmental impacts from production [1,2].…”

“…The current study builds upon the work by Shawver et al [1], which used SMAF (see Andrews et al [11] for full framework details) to monitor soil health changes during the early transition from irrigated cropland to an irrigated MiG perennial pasture. While the Shawver et al [1] study examined years 1 and 2 following the transition, we present the soil health measurements of years 5 and 6 to reflect upon the continued changes to soil health following cropland to MiG perennial pasture transition.…”