Soil’s secret helpers: harnessing microbial power in agriculture 

And those concerns are valid. Studies show that just one gram of soil from the rhizosphere—the space around plant roots—can contain up to one billion bacteria. This region is bustling with countless other microbes too, including tiny worms called nematodes, fungi, algae, viruses, and parasites.

While we try to avoid these microbes, plants actually depend on them for their survival. In fact, without these microscopic helpers, plants as we know them wouldn’t even exist.

Scientists have been exploring the world of microbes for over four centuries, starting with Antonie van Leeuwenhoek in the late 17th century, who crafted microscopes to examine various materials, including soil. He discovered tiny living organisms and called them "animalcules" long before "microbe" was even in use.

This is where our journey begins—at the fascinating intersection of microbiology, soil science, plants, and agriculture. Let’s explore the vital roles that soil microbes play in the life of plants and how this knowledge has transformed agriculture.
 

Humans, agriculture, soil science, and microbes

Humans began cultivating plants about 23,000 years ago¹, and soil fertility was key to early agriculture. Civilizations like Mesopotamia managed soil fertility over 6,000 years ago², laying the foundation for soil science. In ancient Rome, Cato the Elder wrote about composting and using animal manure³. China’s oldest agricultural text, by Fan Shengzhi⁴, also emphasized enhancing soil fertility.

For centuries, soil was seen as a source of fertility, but it wasn’t until the late 19th century that scientists like Vasily Dokuchaev⁵ and Jean-Baptiste Boussingault⁶ recognized soil as a natural body worthy of study and identified nitrogen as essential for plant growth. Pioneering scientists like Martinus Beijerinck⁷ and Sergei Winogradsky⁸ later discovered bacteria that fix nitrogen, turning atmospheric nitrogen into a form plants can absorb. Beijerinck identified Rhizobium bacteria living on legume roots that form a mutually beneficial partnership with plants.

Winogradsky built on this, finding bacteria that convert ammonia into nitrates, forms of nitrogen plants can use. These discoveries paved the way for understanding how microbes like nitrogen-fixing bacteria and nitrifying bacteria support plant life.

But nitrogen-fixing is just one of the many critical roles that soil microbes play in supporting plant life. Since the 19th century, microbiologists have been delving into the fascinating world of soil microbes, uncovering numerous species that aid plants in various ways.
 

The relationship between soil microbes and plants

Soil is much more than just a base for plants to anchor their roots. Soil microbes play a crucial role in ensuring that plants grow strong and healthy. Let’s explore some of the key ways they help plants:

1. Providing nutrients: Soil microbes break down minerals and organic materials, turning them into forms plants can absorb. For example, Bacillus amyloliquefaciens helps plants absorb phosphorus, a key nutrient for growth and photosynthesis.

2. Boosting disease resistance: Some microbes act as natural defenders. Bacteria like Pseudomonas fluorescens protect plants from harmful fungi and bacteria while strengthening their immune systems. Similarly, bacteria like Streptomyces lydicus compete with harmful fungi, reducing the need for chemical pesticides.
    
3. Improving soil structure: Mycorrhizal fungi form partnerships with plant roots and create a mycelium (a root-like structure of fungi) network in the soil as well as produce exudates (secretions) that bind soil particles together. Both of these attributes improve crop access to nutrients and water.
    
4. Helping plants tolerate stress: Soil microbes help plants manage challenges like drought and toxins. Pseudomonas putida bacteria form a protective layer around roots, helping plants resist drought. Other microbes can detoxify heavy metals or help plants in salty soils.

We’ve just scratched the surface

Humans have only begun to understand soil microbes and the complex relationships they have with plants. The world of soil microbes is immense. A recent study estimated that about 59 percent of all life on Earth may live in the soil⁹, including over 50 percent of all bacteria and 90 percent of fungi. This suggests there could be more than three trillion types of bacteria and over five million types of fungi in the soil!

Unfortunately, we’ve only identified a tiny fraction of these soil microbes. Despite this limited understanding, the knowledge we do have about soil microbes has already led to significant advancements in agriculture. What are these exciting changes? Welcome to the world of Biosolutions for Agriculture, in short BioAg.

Despite limited understanding of the vast world of soil microbes, scientists have made significant advances in agriculture. One of the earliest successes was the development of Nitragin in 1896, a microbial inoculant designed to boost legume yields by ensuring plants get a nitrogen boost. Nitragin, still in use today, contains nitrogen-fixing bacteria that coat seeds and help plants absorb nitrogen from the soil.

Beyond Nitragin, scientists are developing more BioAg products using microbes to help plants absorb nutrients and fight off harmful microbes. As research on soil microbes advances, more bacteria and even fungi are being made available as biosolutions for farmers. These solutions do more than just supply nitrogen; they help plants absorb more phosphorus, potassium, and other essential nutrients from the soil. Additionally, some biosolutions use beneficial microbes to act as a protective shield, fighting off harmful microbes that can cause diseases and infections in plants.

This new era in agriculture harnesses the power of soil microbes to improve sustainability and crop productivity.
 

Dawn of a new era in agriculture

You will never look at the humble soil the same way again, will you? Humans have come a long way from seeing soil merely as a medium for growing plants. Now, we recognize soil as a vibrant community filled with diverse microbes that are essential for plant health. Thanks to incredible advances in biotechnology, we’re not just studying these tiny helpers; we’ve begun harnessing their power to transform agriculture in the 21st century. This marks a new era where soil microbes are the source of revolutionary innovations. So let’s celebrate the thriving world of microbes beneath us!