Effects of land use change and grazing on soil carbon dynamics in the semi arid Chaco, Argentina

In recent years deforestation of the Gran Chaco of Argentina has increased dramatically to make way for agricultural expansion.&#160; Extensive cattle ranching in particular is widespread across the country, and in the Chaco region of the north west much of the natural vegetation has been cleared for beef and crop production.&#160; The effects of forest clearance and grazing over time on soil carbon dynamics are unclear, with some evidence suggesting that soil carbon can to some extent recover under low intensity grazing practices, whilst others find that conversion to pasture followed by years of grazing consistently decreases soil carbon stocks.&#160; This study investigates the effects of land use change from forest to pasture over time on soil carbon stocks in the dry Chaco of north western Argentina, through the measurement of biological, physical and chemical variables within the soil.&#160; The hypothesis leading to this work is the key idea that livestock grazing can promote the accumulation of carbon in the soil over time through processes such as the stimulation of root growth of pasture grasses.&#160; In turn, increased carbon inputs can lead to net carbon sequestration, with great potential to mitigate the greenhouse gas emissions of the livestock sector.&#160; Using a chronosequence experimental design, destructive soil samples were taken from reference forest patches and pastures of 0-5, 10-15 and >20 years since deforestation and were tested for carbon, nitrogen, and phosphorus contents, root biomass, pH, electrical conductivity and texture. The research aims to investigate and explain the carbon dynamics of pastures in the years following deforestation, identify potential biotic and abiotic drivers of such dynamics, and predict potential future changes in soil carbon stocks.

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Agriculture in the Boreal Forest: Understanding the Impact of Land Use Change on Soil Carbon for Developing Sustainable Community Food Systems

10.5194/egusphere-egu21-6071 ◽

2021 ◽

Author(s):

David Bysouth ◽

Merritt Turetsky ◽

Andrew Spring

Keyword(s):

Climate Change ◽

Land Use ◽

Land Use Change ◽

Boreal Forest ◽

Soil Carbon ◽

Food Systems ◽

Agricultural Land ◽

Carbon Stocks ◽

Soil Carbon Stocks ◽

Carbon Losses

Climate change is causing rapid warming at northern high latitudes and disproportionately affecting ecosystem services that northern communities rely upon. In Canada&#8217;s Northwest Territories (NWT), climate change is impacting the access and availability of traditional foods that are critical for community health and well-being. With climate change potentially expanding the envelope of suitable agricultural land northward, many communities in the NWT are evaluating including agriculture in their food systems. However, the conversion of boreal forest to agriculture may degrade the carbon rich soils that characterize the region, resulting in large carbon losses to the atmosphere and the depletion of existing ecosystem services associated with the accumulation of soil organic matter. Here, we first summarize the results of 35 publications that address land use change from boreal forest to agriculture, with the goal of understanding the magnitude and drivers of carbon stock changes with time-since-land use change. Results from the literature synthesis show that conversion of boreal forest to agriculture can result in up to ~57% of existing soil carbon stocks being lost 30 years after land use change occurs. In addition, a three-way interaction with soil carbon, pH and time-since-land use change is observed where soils become more basic with increasing time-since-land use change, coinciding with declines in soil carbon stocks. This relationship is important when looking at the types of crops communities are interested in growing and the type of agriculture associated with cultivating these crops. Partnered communities have identified crops such as berry bushes, root vegetables, potatoes and corn as crops they are interested in growing. As berry bushes grow in acidic conditions and the other mentioned crops grow in more neutral conditions, site selection and management practices associated with growing these crops in appropriate pH environments will be important for managing soil carbon in new agricultural systems in the NWT. Secondly, we also present community scale soil data assessing variation in soil carbon stocks in relation to potential soil fertility metrics targeted to community identified crops of interest for two communities in the NWT.&#160; We collected 192 soil cores from two communities to determine carbon stocks along gradients of potential agriculture suitability. Our field soil carbon measurements in collaboration with the partnered NWT communities show that land use conversions associated with agricultural development could translate to carbon losses ranging from 2.7-11.4 kg C/m2 depending on the type of soil, agricultural suitability class, and type of land use change associated with cultivation. These results highlight the importance of managing soil carbon in northern agricultural systems and can be used to emphasize the need for new community scale data relating to agricultural land use change in boreal soils. Through the collection of this data, we hope to provide northern communities with a more robust, community scale product that will allow them to make informed land use decisions relating to the cultivation of crops and the minimization of soil carbon losses while maintaining the culturally important traditional food system.

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