Impact of long-term no till and plow till on soil properties and soil nutrient cycling.

摘要

The Triplett - van Doren plots are experimental sites in northwest Ohio (Hoytville site) and northeast Ohio (Wooster site). These sites are part of the OARDC (Ohio Agricultural Research Development Center) and provide a unique opportunity to investigate the long term impact of tillage (plow tillage, PT; chisel tillage, ChT; and no tillage, NT) combined with crop sequences (continuous corn, CC; corn-soybean, CS; and corn-oats-meadow, COM) on soil properties and in the cycling of major nutrients in soils of contrasting properties. The climate at both experimental sites is similar but dominant soils differ in texture, clay mineralogy and drainage class. A poorly drained, Hoytville silty clay loam soil (fine, illitic, mesic Mollic Epiaqualf) is present at the Hoytville site, and a well drained Wooster silt loam soil (mixed, mesic, Typic Fragiudalf) dominates at the Wooster sites. One phase of this study involved pedon description and sampling conducted in the summer of 2005 at both experimental sites in order to compare the impacts of agricultural management (tillage-rotation) on soil properties and nutrient cycling with respect to less intensive land uses (wooded and grassed areas). The sampling included one pedon each under forest cover, grass cover, and CC (one PT plot and one NT plot) at both locations. Standard laboratory characterization, mineralogical analysis and micromorphological study of thin sections were conducted in order to identify changes in morphological, physical and chemical properties, and total carbon (C) and nitrogen (N) pools in the four land uses. At both sites, strong structure and more bioturbation were found in the Ap horizons of the NT plot, leading to lower bulk density values and increased highly connective macroporosity. The soil C pool (volumetric C content in the upper 31 cm) was essentially the same in the forest and NT soils at the Wooster site, and somewhat more in the grass soil whereas PT had the lowest values. At the Hoytville site, the forest and the grassed pedons had the highest C pool values with slight differences between NT and PT. According to the original C levels, both the grass and NT soil sequestered C during the period of analysis at Wooster but all sites under cultivation lost C at Hoytville.; Two other studies were conducted analyzing soil samples from the last two decadal soil samplings of the long term plots (1996 and 2005 at Hoytville and 1993 and 2003 at Wooster) in order to track the evolution of soil C and N concentration and pools, and available P, pH and exchangeable bases as affected by tillage (NT and PT) and crop rotations (CC, CS and COM). A split plot model by time considering rotation, tillage, and depth in a complete randomized block arrangement was used to analyze the information of each site. At both sites, C and N concentration and C and N pools were higher under CC and COM than CS due to the easily decomposable and reduced amount of residues with soybean as compared to corn or oats residues. No tillage had higher C and N concentrations and C and N pool values than PT, but C and N pool values under NT were rather stable at Wooster and decreased at Hoytville from the 1990's to the 2000's whereas C pool values under PT increased in the same period of time. This pattern indicates that C content and C pool under NT is stabilizing in both sites but more time is needed for PT to reach a new equilibrium condition.; The soil under CS and COM rotations had a higher pH value than CC at both sites, and higher extractable base concentration that can be attributed to lower N fertilizer rates and greater cation recycling by roots and residues. No tillage had, in general, lower pH values than PT at the soil surface, although cation retention was greater overall for NT considering the whole sampling depth (0-45cm). Soil available P was heavily stratified under NT in both soils, which increases concerns of environmental degradation due to high soluble P in water that can reach