Soil Acidification Processes in Agroecosystems of WICST

Soil acidification associated with nitrogen inputs, both as acid-forming fertilizers and biological nitrogen fixation, has been noted in a variety of agroecosystems. Previously reported acidification rates range from 1.1 to 11.4 kmol ha–1 yr–1, largely associated with crop productivity and nitrate leaching losses. The objective of this research was to determine acidification rates at the Arlington site of the Wisconsin Integrated Cropping System Trials (WICST) for several cropping systems that represent major agroecosystems of the Upper MidWest: continuous corn (CS1), corn/soybean rotation (CS2), and corn/alfalfa/alfalfa/alfalfa rotation (CS4). Average annual acidification rates for these rotations at WICST were 0.8, 1.3, and 6.5 kmol ha–1, respectively. The legume phases of CS2 and CS4 were particularly associated with strongly acidifying processes. At WICST, however, ‘best management practices’ reduced annual acidification rates in continuous corn by the use of pre-plant nitrate tests (PPNT) to judiciously apply nitrogen fertilizer by as much as 5.2 kmol ha–1 and by stover return by 3.7 kmol ha–1. The use of manure, which also returns plant alkalinity to soil, in CS4 reduced soil acidification rates by as much as 6.0 kmol ha–1 yr–1.

author: Mauricio Avila, Phil Barak, Josh Posner, David Laird