Abstract
The agricultural sector faces looming challenges including dwindling fertiliser reserves, environmental impacts of conventional soil inputs, and increasingly difficult growing conditions wrought by climate change. Naturally-occurring rocks and minerals may help address these challenges. In this case, we explore opportunities through which the geosphere could support viable agricultural systems, primarily via a literature review supplemented by data analysis and preliminary-scale experimentation. Our objective is to focus on opportunities specifically relating to emerging agricultural challenges. Our findings reveal that a spectrum of common geological materials can assist across four key agricultural challenges: 1. Providing environmentally-sustainable fertiliser deposits especially for the two key elements in food production, nitrogen (via use of slow release N-rich clays), and phosphorus (via recovery of the biomineral struvite) as well as through development of formulations to tap into mineral nutrient reserves underlying croplands. 2. Reducing contamination from farms—using clays, zeolites, and hydroxides to intercept, and potentially recycle nutrients discharged from paddocks. 3. Embedding drought resilience into agricultural landscapes by increasing soil moisture retention (using high surface area minerals including zeolite and smectite), boosting plant availability of drought protective elements (using basalts, smectites, and zeolites), and decreasing soil surface temperature (using reflective smectites, zeolites, and pumices), and 4. mitigating emissions of all three major greenhouse gases—carbon dioxide (using fast-weathering basalts), methane (using iron oxides), and nitrous oxide (using nitrogen-sorbing clays). Drawbacks of increased geological inputs into agricultural systems include an increased mining footprint, potential increased loads of suspended sediments in high-rainfall catchments, changes to geo-ecological balances, and possible harmful health effects to practitioners extracting and land-applying the geological materials. Our review highlights potential for ‘geo-agriculture’ approaches to not only help meet several key emerging challenges that threaten sustainable food and fiber production, but also to contribute to achieving some of the United Nations Sustainable Development Goals—‘Zero Hunger,’ ‘Life on Land,’ and ‘Climate Action.’
Highlights
Inorganic rocks and minerals dominate the foundations of agricultural production
Inclusive of the topics discussed above, we identify four key areas where the geosphere could significantly rejuvenate agricultural production systems: (1) offering new sustainable fertiliser reserves of key nutrients, (2) mitigating nutrient contamination in farming catchments, (3) protecting agri-ecosystems during environmental stresses— drought, and 4) mitigating climate change impacts caused by agricultural activities
Geo-based technologies can contribute to several emerging challenges in the agricultural sector. These include offering new viable fertiliser sources, especially for N and P, preventing environmental contamination in the form of eutrophication, which is combined with the prospect of returning up to
Summary
Inorganic rocks and minerals dominate the foundations of agricultural production. They comprise, on average, >95% of the soil’s dry mass [1] and have been demonstrated to be critical to several key soil processes including water retention [2,3] and nutrient cycling [4,5,6,7,8,9].Several researchers have advocated ‘geo-agricultural’ approaches to help support cropping practices.In 2002, van Straaten published ‘Rocks for Crops: Agrominerals of Sub-Saharan Africa.’ The author detailed the chemical composition of the most commonly encountered bedrock types in 48 African countries with potential identified for using these sources for nutrient supplementation as well as moisture retention in agronomic enterprises in that region [10]. Following on from van Straaten’s (2002) foundational work, Edwards and Lim [11] reviewed the potential for land application of crushed volcanic rocks to mitigate against climate change. The weathering of these particular rock types results in the formation of stable mineral carbonate phases, effectively ‘mopping up’ CO2 from the atmosphere. They note that the delivery of macronutrients to plants is potentially associated with an agricultural benefit in these settings These authors recognised possible downsides for using crushed volcanic rocks in tropical agriculture, including the associated mining footprint and increased sedimentation in catchments during heavy rainfall
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