Maize was grown in the upland areas surrounding an inland valley in central Nigeria in a randomized block experiment using six cultivation techniques (manual cultivation with a hand hoe (MC); ploughing in both directions to throw up a ridge (DPL); single ploughing with the seed placed on the ridge (SPL); ridging with a wooden, single tine, locally made ‘bush’ plough (BPL); single ploughing with the seed placed in the furrow (FPL) and ridging with a conventional ridger (RID) with or without pre-emergence herbicide (PEH) with two replicates. Initial cultivation times ranged from 29 to 70 h/ha (BPL<RID<SPL<FPL<DPL<MC). Total weeding time ranged from 220 to 512 h/ha (MC<DPL<RID<FPL<BPL<SPL) with PEH and from 431 to 763 h/ha (MC<SPL<DPL<RID<FPL<BPL) without PEH. Ox cultivation techniques were associated with higher weeding times and larger weed burdens. Total times for all field operations were 568–758 h/ha (MC<FPL<DPL<BPL<SPL<RID) with PEH and 791–870 h/ha (BPL<MC<SPL<DPL<RID<FPL) without PEH. Thus, although ox cultivation saved time at the most critical time of year (cultivation and planting), it did not save time overall.

Amongst the ox cultivation techniques, work inputs were 6·3–34·1 MJ/ha (BPL<FPL<SPL<RID<DPL) and draught forces 387–1377N (BPL<DPL<FPL<SPL<RID).

Yields of maize cobs were 2·55–4·0 t/ha (SPL<FPL<MC<RID<DPL<BPL) with PEH and 1·65–3·55 (RID<BPL<FPL<DPL<MC<SPL) without PEH. Except for SPL, PEH was associated with increased yield especially when used with ox cultivation.

As regards crop yield, time inputs and work input, there was no advantage to be gained from using a separate (and expensive) ridger for maize compared with a locally made plough or the plough also used for the main cash crop (rice).

At 1992 prices, the cost of PEH was about the same per ha as the price of labour saved on weeding, but additional benefits associated with PEH use were the avoidance of mid-season labour bottlenecks and an overall increase in crop yield.