4–6 times annually (4–6 annual harvests)

4–6 times annually represents the typical annual harvest frequency achievable with high-yield tropical perennial grasses cultivated as biogas feedstock, most notably Napier grass (Pennisetum purpureum) and its Bajra-Napier hybrids (BNH-10, NB-21, CO-3, CO-4). Under good agronomic management in Indian conditions — adequate irrigation, balanced NPK fertilisation, and rejuvenation pruning every 3–4 years — these grasses can be cut every 50–75 days during the productive growing season, yielding 4 to 6 harvests in a 12-month cycle.

The high harvest frequency results from three biological characteristics. First, rapid regrowth — Napier grass regrows from its stubble (basal stump) within 5–7 days of cutting, drawing on stored carbohydrates in the root system to push out new tillers. Second, continuous tillering — well-established stands produce 30–80 tillers per stool, with new tillers emerging year-round in suitable climates. Third, C4 photosynthesis — Napier uses the C4 carbon fixation pathway, which is 30–40% more efficient than C3 photosynthesis in hot, sunny conditions typical of peninsular and central India.

Each cut typically yields 10–15 tonnes per hectare of fresh biomass at 18–22% dry matter content. Over the year, this aggregates to 80–150 tonnes per hectare per year of fresh biomass or 15–30 t/ha/year of dry matter — among the highest land productivity of any cultivated crop. Indian operational practice in CBG-aligned plantations: first cut 75–90 days after planting, subsequent cuts every 50–60 days during March–November, with reduced winter productivity (one cut at most December–February in north India). Optimal harvest height is 5–10 cm above ground to preserve the stubble for regrowth. Mechanised harvesting using self-propelled forage harvesters costs Rs 800–1,500 per tonne, while manual cutting using sickles is Rs 1,200–2,000 per tonne in most Indian wage zones. The high cut frequency demands strict logistical coordination with the biogas plant to handle 20–30 tonnes of fresh material per cutting day from each 10-hectare block.