Divisi
A cover crop is a crop you grow to feed and shield your soil, not to sell — and in the gap between seasons it can hand your next maize up to 1.9 tonnes more grain per hectare (about 38 bags of 50 kg), for little more than the price of seed (field trials, East Uganda). Cut it and leave it, or dig it in, and it becomes green manure: fertiliser you grew yourself.
Here is the engine. A legume (a bean-family plant) teams up with soil bacteria to fix nitrogen — it takes nitrogen from the air and stores it in its leaves and roots, the same nitrogen you normally buy in a bag. A strong stand of mucuna or sunn hemp builds 7–8 tonnes of leaf and stem per hectare and can hold 190–320 kg of nitrogen per hectare (Infonet-Biovision; FAO) — then passes much of it to the next crop.
In an El Niño season this pays twice. Heavy rain strips bare topsoil; a thick living cover breaks the drops and sharply cuts soil loss (Infonet-Biovision). When the rain switches off, the same cover and its residue shade the ground and save moisture for planting.
Which cover crop should I plant — mucuna, lablab or cowpea?
Match the legume to your agro-ecological zone (your rainfall-and-soil belt):
Photo: HONG SON / Pexels
| Your zone | Best cover crops | Why |
|---|---|---|
| Semi-arid / Sahel (short, uncertain rains) | Lablab, cowpea, pigeonpea | Lablab keeps growing in drought (FAO); cowpea and pigeonpea also feed you |
| Sub-humid / humid (long wet season) | Mucuna (velvet bean), jack bean, sunn hemp | Fast, heavy cover; strongest weed and Striga control |
Note: mucuna and jack bean smother weeds hardest, but their raw seed is not food — it needs long boiling and soaking. Cowpea, lablab and pigeonpea give you a soil crop and a pot of beans.
How much seed, and how do I fit it around my maize?
Buy cover-crop seed by the kilogram. Sow at these rates, per hectare, with or relayed into maize (FAO):
Photo: Gilmer Diaz Estela / Pexels
| Cover crop | Seed rate (kg/ha) |
|---|---|
| Mucuna (velvet bean) | 100–120 |
| Lablab | 40–50 |
| Jack bean (Canavalia) | 70–80 |
| Sunn hemp (Crotalaria) | 40 |
| Pigeonpea | 25–35 |
Rates are per hectare (1 ha = 2.5 acres) — for a 0.4 ha (1 acre) plot, use just under half.
Three ways to fit it in:
- Relay — sow the cover crop between your maize rows 6–8 weeks after planting, when the maize is knee-high. It spreads after the maize matures and holds the ground through the dry gap. This is how Ugandan farmers lifted maize by 1.7–1.9 t/ha (Springer).
- Intercrop — plant it with maize from day one at a wider spacing. In Ghana, mucuna and jack bean intercrops still smothered 74–90% of weeds (Journal of Agronomy).
- Short fallow — rest one plot under a pure cover crop for a season, then plant maize into it next season.
When do I cut it — and can I eat any of it?
Slash the crop as it starts to flower — that is when the leaves carry the most nitrogen, and before it drops seed you did not plan for. No tool needed: first flowers = time to cut.
Then choose:
- Green manure (dig in): chop it and turn it into the topsoil about 2 weeks before you plant maize (FAO). Nitrogen releases quickly for that crop.
- Mulch (leave on top): lay the cut material down as a blanket. It rots slower but shields the soil, holds water and keeps smothering weeds — the conservation agriculture way.
Keep a handful of pods from your best plants for seed, so you buy only once.
Will it really give me more maize, or waste my land?
Across sub-Saharan Africa, maize after a herbaceous legume green manure yields on average 0.8 t/ha more — about 16 bags of 50 kg per hectare — than unfertilised maize (Sileshi et al. meta-analysis), and a well-run mucuna relay reached 1.7–1.9 t/ha (Springer). Mucuna and lablab also fight the parasitic weed Striga (Striga hermonthica) and choke back cogon/couch grass (Imperata cylindrica) (Infonet-Biovision).
Count the cost honestly:
- Land and time: a pure short fallow earns no cash that season — a relay or intercrop avoids that.
- Seed and labour: you buy seed and slash by hand.
- Not all edible: mucuna and jack bean are soil crops, not supper.
The trade usually wins, because you replace nitrogen you would have bought. Pair a cover crop with a little microdosed fertiliser and you spend less on both. Want a legume that also sells? Soybean does double duty.
Your next step this week
Choose one plot and one legume for your zone — lablab if you are dry, mucuna if you are wet — and buy the seed now while it is in the shops. Mark the date to relay it into your maize at knee-height (6–8 weeks after planting), and line up compost and cover for the same plot using build soil that holds water.
