Monitoring Soil Quality Data with Remote Sensing

Soil is an essential and often neglected element of our environmental system. It contributes to basic human needs by supporting food provision and water purification, among other things. However, with the onset of intense climate change and detrimental anthropogenic activities, soil globally is under threat. Accordingly, constant monitoring of soil quality has become more important than ever. Monitoring soil and relevant soil quality indicators is also crucial as good soil quality is integral for meeting UN’s Sustainable Development Goal (SDG) targets 2 and 15, which call for sustainable agriculture and the protection and restoration of lands.

With about 30% of Earth’s surface comprising land, soil serves a dual purpose:

• It acts as a source of food by facilitating vegetation growth. In fact, agricultural land, which accounts for only 11% of Earth's total land surface, feeds almost 7.9 billion people.

• It is also one of the largest carbon sinks, second only to the ocean. According to a 2019 map released by The Food and Agriculture Organization of the United Nations (FAO), the top 30cms of the world’s soil contains about twice as much carbon as the entire atmosphere.

Relationship between Soil and Climate Change

Soil health and climate change are deeply interlinked with each other. While accelerated climate change can adversely affect the health and quality of soil, changes in land use and soil can either accelerate or slow down climate change.

Impact of climate change on soil

Extensive research has been carried out on the impact of climate change on soil health and quality. Evidence of climatic changes affecting soil quality and health can be witnessed in the case of extreme rainfall. Intense precipitation, both in terms of intensity and quantity, can adversely impact soil health by leading to runoff and erosion. This strips the soil of key nutrients needed to sustain agriculture. Conversely, reduced precipitation coupled with increasing heat will cause desertification and the loss of farm production in some areas. Frequent droughts and enhanced evaporation kill off the vital living soil ecosystems necessary to grow healthy crops whilst leaving less water to dilute pollutants.

Mounting scientific evidence indicates that soil health will be adversely affected by climate change and will lead to:

• Reduced soil organic matter content

• Decreased soil moisture content

• Deteriorated soil structure

• Increased vulnerability to erosion and other degradation processes

In addition to climate change, these mechanisms are also exacerbated by other anthropogenic impacts, including changes in land use, pollution, widespread habitat degradation, and the introduction of invasive species. This reduces the capacity of soil to maintain sustainable crop production as well as limits the exploitation of new crop systems, ultimately affecting food security. It is predicted that land degradation over the next 25 years could potentially reduce global food productivity by 12%, increasing food prices by as much as 30%.

In fact, it is estimated that, overall, 33% of soil is presently moderately to highly degraded due to erosion, salinization, acidification, contamination, or compaction. Additionally, 52% of agricultural land is already moderately or severely affected by soil degradation. Putting these statistics in monetary terms, the loss of soil due to degradation is estimated to cost the world US$400 billion per year.

Soil can fuel or mitigate climate change

The world is currently in the midst of a climatic crisis with consistently rising temperatures and atmospheric carbon concentration levels. Global temperatures until 2021 have already risen by about 1.1°C compared to the pre-industrial period, making it “almost inevitable” for humanity to at least briefly surpass the critical temperature threshold of 1.5 degrees highlighted in the 2015 Paris agreement. Hence, limiting the rise in global mean temperature levels would be pivotal in reducing the risks and impacts of climate change.

Soil can impact climate change and, in turn, climate change mitigation in two broad ways:

• By emitting greenhouse gases (GHGs)

Soil is made in part of broken-down plant matter. Accordingly, it contains the carbon that plants absorb from the atmosphere as part of the process of photosynthesis. This is commonly referred to as soil organic carbon (SOC). The first meters of soil contains between 1,500 and 2,400 Gt OC, i.e. three to four times the amount of carbon present in the vegetation (450–650 Gt C) and two to three times the amount of carbon in the atmosphere (~829 Gt C).

However, soil degradation due to climate change, unsustainable agriculture practices and other developments like deforestation, etc., results in the release of OC back into the atmosphere. In fact, the world’s cultivated soils have lost between 50 and 70 per cent of their original carbon stock, much of which has oxidized upon exposure to air to become CO2.

Extreme climatic events like wildfires also contribute to the increased GHG emissions. For instance, about half of the European carbon stock is stored in forest soil. When forests are burned, the heat of the fire alters the physical properties of the soil, and their stored carbon is released back into the atmosphere. In this case, forests may become net contributors of carbon to the atmosphere instead of carbon sinks.

• By sequestering organic carbon (OC)

On the flip side, SOC storage represents about 25% of the potential of natural climate solutions to offset global anthropogenic GHG emissions. Increasing SOC is also expected to provide other indirect benefits such as an improved capacity of soils to contribute to agricultural adaptation to climate change and to enhanced food security. In colder climates specifically, where decomposition is slow, soils can store—or “sequester”—this carbon for a very long time. Restoring soils of degraded and desertified ecosystems has the potential to store in world soils an additional 1 billion to 3 billion tons of carbon annually, equivalent to roughly 3.5 billion to 11 billion tons of CO2 emissions. (Annual CO2 emissions from fossil fuel burning are roughly 32 billion tons.)

The cyclical effect

Climate change and soil hence, exhibit a cyclical relationship as intensifying climate change is a major contributor to the deteriorating soil health, which in turn is adversely affecting global climate change and mitigation efforts.

Need for Monitoring

The interplay between climate change and soil makes monitoring of soil health critical for managing food security as well as achieving reduced carbon emissions.

Monitoring allows the tracking of changes in the features and characteristics of soil at specific time intervals under the influence of agricultural and non-agricultural human activity. It further helps determine the status of soil functions and environmental risks associated with production practices. However, soil quality assessment using IoT monitors has a number of shortcomings:

• It focuses mainly on the ability of the soil to provide plant nutrients; it doesn’t serve the purpose of measuring overall soil quality.

• It is laborious, expensive and doesn’t allow for continuous monitoring.

Geospatial data can address these shortcomings. As a result of technological advancements, combined with a significant number of satellite launches, it is now possible to monitor extensive areas in near real-time and gather insights like never before. Thus, it is a perfect tool for developing a standard soil quality monitoring infrastructure that can equip organisations in various sectors with decision-useful data.

While geospatial data is a great solution, obtaining valuable insights in its raw form is tedious, expensive, and time-consuming. An effective soil quality monitoring infrastructure would need to process and analyse vast volumes of earth observation satellite data. This points towards the need for organisations with analytical skills and computational capacity to integrate data from various sources, like satellites, and ground measurement monitors, to clean, optimise, and normalise the data, and then build multiple types and levels of analytical models. Further, disseminating this data both via easily integrable APIs for more extensive usage and adoption and via a simpler visualisation platform for any layperson is critical.

Standard Soil Quality Monitoring Infrastructure

An effective soil quality monitoring infrastructure developed using satellite data and AI can deliver the following key parameters:

• Soil Texture - Soil texture determines the soil health/ quality in the long term. It defines the porosity and hence the soil water holding capacity, gaseous diffusion and water movement.

• Soil Moisture - Soil moisture is the water content of the soil. Soil moisture levels affect air content, salinity, and the presence of toxic substances. Soil moisture regulates soil structure, ductility, and density and also influences soil temperature and heat capacity simultaneously preventing soil from weathering.

• Soil pH - Soil pH is an excellent indicator of the suitability of soil for plant growth. For most crops, pH of 6 to 7.5 is optimal. Extreme soil pH leads to a deficiency of many nutrients, decline in microbial activity, decrease in crop yields, and deterioration of soil health.

• Soil Organic Carbon and Organic Carbon Stock - Soil carbon is recognized as the largest store of terrestrial carbon. Globally, its storage capacity is much larger compared with the pools of carbon in the atmosphere and vegetation.

• Soil Temperature - Soil temperature is the factor that drives the germination of seeds and hence affects plant growth. Most soil organisms function best at an optimum soil temperature.

• Total Nitrogen - Soil nitrogen is really important for plant growth (structure), plant food processing (metabolism), and the creation of chlorophyll.

Stay tuned to find out more about each of these parameters.