Perennial legume forages drive soil acidification and nitrogen availability to subsequent crops in a cereal-forage rotation

Historically, soil acidification has not been a widespread concern in Western Canadian cropping systems, although pH declines have been documented and may be accelerated in current systems because of significant increases in fertilizer applications over the last 20 years. This study quantified the long-term liming effects and nutrient management on soil acidification (pH), N stocks, marketable yields, and crop uptake of N, P, and cations in alfalfa-brome forage, wheat, and oats in a cereal-forage rotation at the University of Alberta Breton Plots. Grain protein content and N surplus were also evaluated for wheat and oats. Nutrient treatments included 1) Check (no fertilizer), 2) Manure, 3) NPKS, and 4) PKS fertilizers, where S denotes sulfur, each with and without lime applications. Alfalfa-brome yields, N, P, and cation uptake increased significantly with liming under NPKS and PKS treatments and were linked to higher N uptake in subsequent wheat and oat crops. In the Check and Manure treatments, liming had no effects on marketable yields, N, or cation uptake in all crops, or grain protein and N surplus in cereals. Soil acidification rates were greater in NPKS and PKS than in Manure and the Check treatments, regardless of liming. Cation exports in alfalfa-brome exceeded those in cereal crops and are associated with increased H+ release by alfalfa roots, and reduced soil base saturation capacity, especially in the NPKS and PKS treatments. Current findings suggest that soil acidification rates have likely increased with diversified crop rotations and fertilizer use, coinciding with conservation tillage.