Soil is a silent partner in humanity’s survival and progress, the very thread that stitches life together. It lays the foundation for human life, providing nutrients for plants to grow and generates food for the human population. The entire agricultural industry, and by extension all of humanity, owes much to the soil for generously allowing us to cultivate a wide variety of plants and crops. Soil’s contribution is not just limited to agriculture and sustaining human life; the soil itself is alive. Soil, like any other living being, is highly ordered. It grows, utilizes energy for its functioning, reproduces, and thus exhibits most of the characteristics necessary to be classified as a living thing. It is a reservoir of biodiversity, hosting billions of organisms, from microorganisms to larger invertebrates. In fact, there are more living things in the soil than on the earth. Through these lively things beneath, soil helps to sustain life on earth, particularly by regulating the carbon, nitrogen and water cycles, thereby maintaining ecosystem balance. The soil microbes (microorganisms) and bacteria play a key role in balancing these cycles. For instance, organic matters, such as plant and animal residues, are decomposed in the soil through microbial activity, releasing carbon dioxide (CO₂) back into the atmosphere or stabilizing it as soil organic carbon. Soil is also the biggest reservoir of carbon. The soil can store many times more carbon than trees can absorb. Latest research suggests that we should not randomly plant trees everywhere, like  grasslands, instead, let the soil store more carbon. Therefore, in every sense, healthy soil is the foundation for a healthy ecosystem. Without it, the intricate web of life would collapse, leaving humanity vulnerable to food shortages, climate change, and the loss of vital natural resources. That is why soil is rightly called the “soul of the earth”. 

An Icelandic landscape with soil formed from volcanic eruptions. These soils are mostly “Andosols” soils containing a lot of carbon and minerals and can hold a lot of water. The Icelandic soil is unique by the fact that they are very young, of Holocene age which began around 11, 700 years ago. I.e., after the last “ice age”. Photo taken during a field visit for the FutureArctic project.

Although soil forms the key to life on the earth, it is probably the least appreciated and often overlooked substance by us humans. Consequently, the soil has been often over-exploited and less cared for, leading to a substantial reduction in healthy soil.  According to the European Commission, more than 60% of the European soil has already become unhealthyl; so is the case all over the earth. The degradation of soil has major consequences, from climate changes to food and water shortages, severely impacting life on Earth.  What makes the degradation of soil more alarming is the fact that it is not easily replaceable or re-creatable. It can take thousands of years to form a centimetre of fertile soil, but we are losing it at a rate many times faster than that. 

A Belgian grassland. Belgium has a diverse soil structure with around 15 types of identified soil types, and   a colourful soil map 😉

One of the primary contributors to soil pollution is the unscientific use of synthetic fertilizers. There is no doubt that synthetic fertilizers greatly helped to sustain the population growth of the twentieth century and are an essential component of any modern farming practices. However, there is often a lack of knowledge on the right amount of fertilizers to apply and the right time for its application. Fertilizer requirements can greatly vary from crop to crop and field to field. For instance, tuber crops like potatoes normally require 80–150 kg N fertilizer per hectare. Whereas winter wheat typically requires 200–250 kg N/ha. However, these values are only a rule of thumb and are not quantified by considering other varying parameters. For example, if the potato is grown in a field where legumes were previously grown, then the N requirement can come down to 40–50 kg/ha. Thus, the quantity of fertilizer is affected by various parameters. Nonetheless, farmers are often advised to fertilize in excess to ensure the lack of nutrients. This has two important consequences; firstly, a major investment goes toward fertilizers. Although nitrogen fertilizers are subsidized in many countries, they still account for a significant portion of expenditure (Synthetic N is the most used fertilizer). Secondly, the plants absorb only the quantity of nutrients they require for their metabolic process. What happens to the remaining? It leaches to water bodies and sensitive environments! This exacerbates environmental damage, polluting both the soil and sensitive ecosystems. Excess nutrients, such as nitrate and phosphorus, leaching into aquatic systems pollute water bodies, reduce oxygen levels, and cause algal blooms, which harm biodiversity. In addition, excess usage of fertilizers often results in degradation of soil health, making many lands unsuitable for farming. When added in excess, fertilizer can increase soil PH and soil mineral concentration, which harms microbes.  Beyond all this, the carbon emission during the production of fertilizers poses another threat to the environment. Therefore, it is crucial to limit fertilizer use to the appropriate levels to maintain a healthy ecosystem.

The reddish laterite soil from the southern part of India. Laterite soils are not only suitable for agriculture but are used for construction by cutting out large bricks.  India has an even more diverse soil types and of course, a vibrant soil map!

What if the farmers know the exact amount of nutrients required for each crop and soil? Then, they can release the required quantity of fertilizers into the soil. This will have a significant positive impact on the overall process- optimum fertilizer usage, leading to reduced expenditure on fertilizers, improved soil health, reduced carbon emission, and no more leaching. However, to realize these outcomes, significant support from advanced technologies and innovations—often referred to as Precision Agriculture or Agriculture 4.0—is required. A key component of precision agriculture is the accurate estimation of nutrient levels in the soil, with high temporal and spatial resolution so that the farmers can be informed on when and where to apply fertilizer. This is, in fact, the backbone of precision agriculture. But surprisingly, the current standard methods available for sensing soil nutrients are highly inefficient and costly. Would you be surprised if I told you there are no cheap in situ measurement solutions so far available in the market for soil nutrients? Farmers all over the world rely on in-lab testing. That is, the soil sample is manually collected, prepared, and taken to the lab for testing. This may not be costly, but highly inefficient.  Of course, there are costly high-end portable tools like NIR spectrometers available.  But not everyone can afford it. Even if you can afford it, achieving high temporal and spatial resolution is difficult.   Well, then there are primitive methods relying on soil or leaf color. Again, they are neither accurate nor efficient.  Therefore, some alternate, low-cost, low-power sensing system is required. This is the problem we aim to address through our latest project, “SENSS: Sustainable and Energy Neutral Soil Sensing.” Through SENSS, we are working to develop low-cost, easily producible sensors that can be deployed in large numbers across agricultural lands, offering real-time data on various soil properties and conditions. We power these sensors with soil thermal energy, making them immune to dusty and untidy agriculture environments and boasting a real “deploy-and-forget” architecture. By combining state-of-the-art machine learning, both at the edge and in the cloud, real-time data from multiple tiny sensors, we aim to empower farmers with precise insights into their land’s fertilizer needs. 

For more updates on the developments, keep an eye on our project website!