Earthworms, Nematodes and Fungi: The Soil Life Feeding Every Indian Farm

The top 30 centimetres of a healthy Indian agricultural field contains more living organisms per square metre than the entire human population of the country. Most of them have no common name, no visible body, and no advocate. They are also the reason food exists at all.

An earthworm does not simply loosen earth. It eats it. A single earthworm passes its own body weight in soil through its gut every day, and what comes out the other end is chemically transformed. The castings it leaves behind are richer in available nitrogen, phosphorus and potassium than the surrounding soil, sometimes by a factor of five to eleven, according to measurements taken in Indian Vertisols and alluvial soils by researchers at the Indian Council of Agricultural Research. The tunnels the worm bores as it moves are not random. They create a network of macropores that let rainwater sink rather than run off, and let oxygen reach the root zone. In a compacted field with few earthworms, a heavy monsoon shower sits on the surface. In a field with a healthy population, the same rain disappears into the ground within minutes. The species doing most of this work in Indian fields is Lumbricus terrestris in temperate zones and Metaphire posthuma across the Indo-Gangetic plain, a native species that has been here longer than agriculture. Intensive tillage and synthetic pesticide use have cut earthworm populations in many Indian fields by more than 60 percent over the past four decades. The soil looks the same from above. The structure is gone.

Nematodes are roundworms, mostly under a millimetre long, and they are the most numerically abundant animals on earth. A handful of healthy Indian farm soil contains several million of them. The word carries a bad reputation because a small fraction of nematode species are plant parasites, root-knot nematodes cause significant crop losses in tomato, brinjal and okra across India. But the majority of nematode species in agricultural soil are doing something else entirely. Bacterial-feeding nematodes graze on soil bacteria, releasing nitrogen locked inside bacterial cells back into forms that plant roots can absorb. Fungal-feeding nematodes do the same with fungal biomass. Predatory nematodes eat other nematodes, keeping the population structure from collapsing into monoculture. This grazing pressure is what keeps nutrient cycling moving. Without nematodes consuming bacteria, bacterial populations would spike, lock up available nitrogen in their own biomass, and starve the plant. The nematode is the release valve. Broad-spectrum soil fumigants used to control the parasitic minority kill the entire community, including the species doing the cycling. Fields treated this way often show a short-term yield boost followed by a long plateau, because the nutrient cycling machinery has been cleared.

Roughly 80 percent of terrestrial plant species form a partnership with mycorrhizal fungi, and most Indian crop plants, wheat, chickpea, sorghum, maize, are among them. The fungus colonises the root and extends outward through the soil in threads called hyphae, which are far finer than any root hair the plant can grow. A single mycorrhizal network in one square metre of soil can contain up to 200 metres of hyphae. The network reaches phosphorus deposits the root itself cannot access, and delivers them to the plant. In exchange, the plant sends between 10 and 20 percent of the sugars it produces through photosynthesis down to the fungus. This is not parasitism. It is a trade that has been running for approximately 450 million years, long before flowering plants existed. In phosphorus-poor soils, which describes much of the Deccan Plateau and large parts of Rajasthan, mycorrhizal colonisation can increase a crop's phosphorus uptake by 40 to 80 percent without any synthetic input. High applications of phosphate fertiliser suppress mycorrhizal colonisation, because the fungus becomes redundant when phosphorus is already abundant. The plant stops feeding it. The network collapses. When fertiliser prices rise or supply is disrupted, the plant is left without the partner it traded away.

Earthworms, nematodes and mycorrhizal fungi do not operate in separate lanes. Earthworm castings create microhabitats where bacterial and fungal populations concentrate, which in turn supports the nematodes that graze them. Earthworm tunnels give mycorrhizal hyphae pathways through otherwise compacted soil. Nematode grazing releases the phosphorus that mycorrhizal networks then carry to roots. The system is circular, and its output is soil fertility that requires no invoice. What takes decades to build can be disrupted in a single season of heavy tillage, fumigation, or waterlogging. Regenerative agriculture practices gaining ground in parts of Karnataka, Andhra Pradesh and Maharashtra, reduced tillage, cover cropping, compost over synthetic fertiliser, are not sentimental. They are attempts to keep this machinery running. The organisms doing the work are not charismatic. They have no face, no call, no migration pattern worth filming. They are also, in the most direct biological sense, the foundation of every meal.