Micronutrient (trace elements)

Micronutrients are essential plant nutrients required in very small quantities — typically 1–500 grams per hectare per crop cycle — that nonetheless serve as cofactors for enzymes critical to photosynthesis, nitrogen fixation, hormone biosynthesis, and cell wall formation. The standard list includes zinc (Zn), iron (Fe), manganese (Mn), copper (Cu), boron (B), molybdenum (Mo), and chlorine (Cl); some classifications also include nickel (Ni). Indian soils widely show micronutrient deficiencies — ICAR mapping indicates 49% of soils are zinc-deficient, 23% iron-deficient, 13% manganese-deficient, and 33% boron-deficient.

The economic consequences of micronutrient deficiency are out of proportion to the small quantities involved. Zinc deficiency in wheat and rice depresses yield by 20–40% and reduces grain protein and zinc content (a public health concern under the National Mission on Mineral Nutrition). Boron deficiency in mustard and groundnut causes flower abortion and yield losses of 15–30%. Iron chlorosis in citrus and pulses in calcareous soils (pH above 8) reduces fruit set and biomass by 25–50%. Each deficiency can be corrected at ₹500–2,000 per hectare with foliar sprays or soil application of micronutrient salts, making the return on diagnosis extremely high.

Biogas digestate sold as Fermented Organic Manure carries meaningful micronutrient content because feedstocks like cattle dung, press mud, and food waste concentrate trace elements through the plant-to-animal-to-waste pathway. Typical Indian CBG digestate carries 30–80 mg/kg Zn, 200–500 mg/kg Fe, 50–150 mg/kg Mn, and 10–30 mg/kg Cu on dry basis. At an application rate of 2 tonnes of FOM per hectare, this delivers roughly 100–200 g of Zn — close to a complete crop requirement. This is a significant selling point that progressive CBG plants now highlight on product labels alongside NPK, particularly in zinc-deficient regions of the Indo-Gangetic Plain.

• Essential plant nutrients required in small quantities: Zn, Fe, Mn, Cu, B, Mo, Cl.
• Indian soils widely deficient: 49% Zn, 33% B, 23% Fe, 13% Mn (ICAR data).
• Yield losses of 15–50% from individual deficiencies; correction cost is small.
• CBG digestate carries meaningful Zn, Fe, Mn, Cu content — a marketable advantage on FCO labels.