Monitoring SOC on commercial direct-seeded fields across Saskatchewan – Phase 4

Funding Partners: Saskatchewan Ministry of Agriculture – Agriculture Development Fund (ADF), Saskatchewan Canola Development Commission (SCDC), Saskatchewan Pulse Growers, Prairie Oat Growers Association (POGA), Saskatchewan Barley Development Commission (SaskBarley), Saskatchewan Flax Development Commission (SaskFlax)

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Project Description

This project’s aim is to measure and analyze the change in soil organic carbon (SOC) using the Prairie Soil Carbon Balance Project network (PSCB) site’s samples.

There is increasing scientific criticism that conservation agriculture with no-till is not providing important SOC increases. PSCB has a network of 136 benchmarks on commercial farm fields scattered across the agricultural portion of Saskatchewan. There is no prescribed management for these fields other than that they were converted to direct seeding and diverse rotations in 1997. Consequently, the network provides a unique and powerful means to investigate the SOC change on actual farm fields. The network has now reached year 20 since the management change and the duration has traditionally been assumed to be the end of C sequestration. Thus, this is the ideal point to add measures of soil organic carbon quality to improve our understanding of the stability and future sequestration potential capacity.

The project will compare the field-derived results with those on conventional small plot experiments and with modelled results using sophisticated models of carbon and nitrogen dynamics. Collectively, the results of the project will enable Saskatchewan producers to position themselves confidently and appropriately in the public policy debate over how crop production should be treated in carbon tax schemes and/or within trading schemes for greenhouse gas emission offsets produced through SOC sequestration. This project will also provide new knowledge of how carbon sequestration is occurring that is necessary to make more reliable estimates of future sequestration potential and the future stability of sequestered SOC.

Research Results

Soils are the largest terrestrial carbon sink on Earth and increasing soil organic carbon (SOC) content is a means of sequestering atmospheric CO2. Limited work has been done to examine the effect of long-term conservation agriculture management practices on the stability of SOC in prairie soils. The objective of this study was to assess the nature and permanence of sequestered SOC in contrasting Saskatchewan soils after 21 years of conservation management practices.

Ninety fields were sampled in 1996 and again at the same locations in 2018. The fields represent a diverse collection of soil types from within the five soil zones of the province. Comparisons were made between the 1996 and 2018 soils (0-10 cm) in SOC concentration, along with various labile and dynamic SOC fractions: water-extractable (WEOC), light fraction (LF-C), microbial biomass (MB-C), and respirable CO2-C during a six-week incubation. Spectroscopy (isotope mass and FTIR) was also used to determine the chemical nature of the SOC. Regardless of soil zone, soils with the smallest initial SOC content accumulated more SOC (ranging from 4.7-9.8 Mg C/ha or 220-454 kg C/ha/year). There was a minor increase in WEOC content (3%), no change in LF-C content, and a substantial increase in MB-C content (41%). Except for greater CO2-C emissions from the 2018 Black soils, there was no difference in CO2-C emissions or percentage of SOC respired between 2018 and 1996 soils, which suggests similar or greater permanence of the sequestered SOC.

Our results suggest that after 21 years of conservation management practices, more of the SOC is present in an active, dynamic fraction that contributes to soil health and nutrient cycling.