Coordinated nitrogen and sulfur management in S-deficient soils

Approximately, 60% of the current increase in atmospheric nitrous oxide (N₂O) emanates from agricultural soils. There is evidence that N₂O emissions increase in direct proportion to the sum of fertilizer and non-fertilizer nitrogen (N) inputs in agricultural and non-agricultural ecosystems, but other factors such as soil moisture and temperature, fertilizer N type/placement, accompanying phosphorus (P), potassium (K), and sulfur (S) fertilizer applications, crop type/rotation, inclusion of legumes, lime applications, microbial community diversity, and tillage all contribute to the variability of N₂O emissions. It has been shown that long-term N plus S fertilization increased soil organic matter content, compared to N fertilization without additional S fertilization in the S-deficient soils at the Breton Plots in west-central Alberta. There are few examples of long-term management effects or management legacy effect on current annual or growing season N₂O emissions.

A field study has been conducted over five growing seasons (2013 to 2017) in order to evaluate the effect of long-term fertilization history and crop rotation on cumulative growing season N₂O and carbon dioxide (CO₂) emissions (measured semi-weekly), wheat yield, wheat N uptake, soil properties, and N₂O emission intensity (kg N₂O/kg wheat N uptake or kg N₂O/kg wheat grain) in Gray Luvisolic soils at the Breton Classical Plots, Breton, Alberta, Canada. Fertility treatments included a check (no fertilizer) and manure amendments compared to inorganic fertilizer applications of NPKS, NPK, PKS in two contrasting crop rotations: 2-years of wheat-fallow (WF) and 5 years of wheat-oat-barley-alfalfa/brome hay (WOBHH). The greater long-term N inputs in the fertility treatments of the WOBHH rotation since the plots were established, was reflected in significantly greater total soil N in the top 15 cm compared to the WF rotation. Rotation was a significant factor affecting cumulative growing season N₂O emissions and, within each rotation, long-term additions of fertilizer or manure N increased N₂O emissions compared to the check treatment. When averaged across fertility treatments, cumulative growing season N₂O emissions from the 5-year rotation were 1.29 kg N₂O-N/ha, significantly higher than the 0.58 kg N₂O-N/ha in the WF rotation, but N₂O emission intensities were comparable between to the two rotations. Cumulative N₂O emissions were positively correlated to the total soil N (0 to 15 cm) and wheat N uptake, but N₂O emission intensities were negatively correlated to total soil N.

The results suggest that long-term crop rotation and balanced soil fertility treatments including N, P, K, and S increase yield and crop N uptake, and reduce the growing season N₂O emission intensity, or the volume of N₂O produced per unit of crop yield. The main conclusions are that long-term N balance drives productivity and N₂O emissions, with variability affected by different growing season weather conditions. Also, N balances are driven by rotation and fertilization, and all forms of soil N contribute to N₂O emissions.