12 Research continued from page 11 is suggesting we’ve undervalued how much carbon is below ground in roots, root exudates and in the rhizosphere microbe community.” It is worth remembering that reduced tillage approaches protect the soil from erosion. By keeping soil in the field SOC and total N also remain in the field. This is one way to ‘build’ soil health in reduced tillage systems. 3) Potential of red clover to build SOC depends on amount of N applied. Hooker explains that the potential for underseeded red clover to build SOC depends on good red clover stands, but the results in this trial show red clover biomass depends highly on the amount of fertilizer N applied to the wheat. “This is a confounding effect,” he notes, “and further explorations are underway to tease apart this interaction.” GENERAL CROP PRACTICE GUIDANCE Crop rotation, tillage system, and nitrogen rates may have a greater influence on SOC and total N levels; however, detecting changes is challenging due to the inherent variability in soil sampling over time and spatially across different cropping systems. “This lack of effects could be due to many things, including a relatively short time, 13 years, of sampling to observe carbon stocks increase,” says Van Eerd. “It could also be due to a plateau in the rate of organic carbon accumulation or soil saturation (where no additional SOC storage would be expected) or a combination. Research is underway with Dr. Adam Gillespie to explore other possible reasons, such as partitioning of carbon in particulate organic matter and mineralassociated organic matter in surface soil.” Nevertheless, Van Eerd and her colleagues recommend that the research is consistent with the principles of Ontario’s ‘Soils For Life’ program — recognizing that each farm is different. These principles are to build SOC over time, keep the soil covered, minimize soil disturbance (no-till or strip-till when possible), diversify crop rotations (as well as animals), and keep living roots all year. FOR MORE Van Eerd worked with her ‘Soils at Guelph’ team to explain soil carbon, a task that is especially difficult in agricultural soils. Find out more at soilsatguelph.ca•
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