Spatial and temporal trends in soil properties and crop yield at a site under intensive up- and down-slope potato production in northwestern New Brunswick

Abstract

Few quantitative data are available to assess temporal changes in the soil quality of Canada’s agricultural lands. Site 20-NB was established in 1989 to monitor changes in an Orthic Humo-Ferric Podzol developed on coarse loamy till on a rolling landscape under intensive potato production in Atlantic Canada with soil compaction and water erosion the dominant forms of degradation. Sampling of soil and crop parameters was conducted on a 20 × 25 and 25 × 25 m grid basis with 66–90 sample locations. Baseline soil samples were collected in 1989 and the site was re-sampled in 1999. Samples were analysed for pH, available P, K, Ca and Mg, and total soil organic carbon (SOC). Field saturated hydraulic conductivity (Kfs) at 12–22, 27–37 and 50–60 cm, earthworm counts and crop yield measurements were conducted annually. 137Cs data were collected to estimate long-term soil erosion. Annual runoff (May 01 to Nov. 30) and soil loss were measured. Seasonal soil loss between 1989 and 1999 was only 6522 kg ha-1 yr-1 compared with 137Cs-estimated soil displacement of 53 000 kgha-1 yr-1, occurring over the 1960 to 1990 period. In the Ap horizon, soil pH and P increased by 8 and 5%, respectively, while SOC was reduced by 8%. Some changes were identified in the subsoil (50–65 cm) with a 7% increase in pH and a 27% reduction in P. There was little annual variation in the Kfs of the Ap, B and C horizons which ranged from 0.4 to 1.3, from 0.7 to 1.3 and from 0.8 to 2.0 cm h-1. Solum Kfs was significantly less than in an adjacent forested area by 52–80%. Earthworm numbers increased at a rate of 1.5 earthworms m-2 yr-1. Crop yield did not show any temporal trend over the 10-yr period other than that it appeared to be significantly influenced by crop rotation. Potato yield (CV = 12) tended to be less variable than barley (CV = 22) or clover (CV = 21). The benefits of site specific management were found to be questionable. 137Cs-estimated soil loss was most strongly related to SOC (r = −0.66) and average potato yield (r = −0.55). Key words: Soil quality, soil carbon, hydraulic conductivity, earthworms, water erosion