During a recent seminar at the Agricultural Research Centre (ARC) for Soil, Climate and Water in Pretoria, the harsh realities of climate change were put under the microscope by various experts in the agricultural and climatology sector.
The event was facilitated by Dr Mokhele Moeletsi, research team manager at the Agriculture Research Council and the speakers included Dr Francois Engelbrecht, professor of climatology and global change institute of the University of Witwatersrand, Dr Caroline Ajilogba, NRF post-doctoral fellow at the ARC, Dr Brian Mantlana, competence area manager at CSIR and Michael Kidson, chief research technician at the ARC.
The impact of conservation agriculture
Michael Kidson supports various research projects that centre around soil science and is currently enrolled in a PhD programme at Unisa. His PhD project studies the sequestration potential of conservation agriculture (CA) soils versus ploughed soils through examining the flow of carbon as it travels from plant to soil using a heavy carbon isotope (13C) and metagenomics.
The importance of Michael’s research was made evident when he explained the impact that conservation agriculture has on carbon, CO2 emissions and micro-organisms in the soil.
A study conducted in Central Park revealed more than 120,000 different microbial life-forms inhabiting the park’s soil, most of which not yet examined. However, this diversity in microbial activity is not exclusive to New York but found across various biomes around the globe.
According to Michael, conservation agriculture preserves microbial life in the soil thereby tapping into benefits like reduced water evaporation, lower soil temperatures, decreased run-off and improved infiltration. Ultimately, an abundance of microbial organisms help to keep the soil healthy and enables sequestration of carbon (removing CO2 from the atmosphere and storing it in the soil carbon pool), which enables all plant-life to flourish.
According to Michael, conservation agriculture gives us the means to support and sustain healthy soil by creating an ideal environment for soil microbes to thrive in. “Conservation agriculture refers to the planting of a crop with reduced tillage. It’s based on the three legs of conservation agriculture as defined by the FAO, which is reduced soil disturbance, keeping the soil covered with a dead or living mulch and crop rotation. Crop rotation is especially important for reducing pests and weeds in crop fields, whereas ploughing refers to the conventional method of crop reduction,” he added.
Mitigating climate change
With the world’s gaze fixed on fossil fuels as a means to reducing greenhouse gas emissions, Michael pointed out that the effects of natural CO2 soil flux cannot be overlooked.
During a ploughing trial at Roodeplaat, which Dr Hendrik Smit (a conservation agriculturalist at Grain SA) initiated, Michael performed CO2 flux measurements on both conservation agriculture and ploughed soil. The study was done in triplicate and was conducted over a span of five years.
Michael found that conservation agriculture soil gave off 27% less CO2 compared to ploughed soil, effectively contributing towards healthy soil structure and reducing greenhouse gas emissions. “It is estimated that carbon that’s released into the earth’s atmosphere takes about 100 years to be fully utilised by plants, so if we stop using fossil fuels immediately it’s going to take another 100 years for everything to stabilise,” he added.
With increased levels of CO2 in the atmosphere, global warming is giving rise to higher temperatures which significantly impact microbial life and biodiversity in our soils, added Michael. “Beneficial microbes can become dormant or even die when temperatures exceed 100°C, resulting in reduced microbial species composition. According to a study done by Wan et al 2016 which examined a denitrifying microbe at various carbon dioxide levels from 0 to 30 000 ppm CO2, other ramifications can include microbe cell wall damage, inhibited protein electron carriers, reduced decomposition rates and various chemical reactions in the soil which can include nitrification and denitrification.”
Studying microbial activity
By building a specialised instrument using a CR1000 data-logger, Michael will be able to automate CO2 measurements in different soil samples at different temperatures during pot trials. This will help him to test for microbial viability and function. “In my carbon study, I’ve been using carbon-13 which my plants incorporate into the carbohydrates they manufacture. I then measure the CO2 flux coming off the soil and the various plant exudates.
“As the microbes reproduce, they will incorporate the stable isotope into their DNA. We will then be able to separate the microbes with and without the stable isotope and then establish, through metagenomics, what microorganisms are present and their various roles. Furthermore, we will be looking at the carbohydrate chemical reactions taking place in the soil. This study is being performed at three temperatures in order to measure the effect of temperature on the carbon cycle, microbial activity and various reactions in the soil,” he concluded. – Claudi Nortje, Plaas Media