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The effects of plant population density, defoliation and removal of pods and apical buds on dry matter, nodulation and nitrogen accumulation in field bean {Viciafaba L.) were investigated in the field in 1973 and 1974.In 1973 seed yield, dry matter and nitrogen accumulation were similar at 50 and 150 plants/m 2 while in 1974 40 plants/m 2 was significantly different from 80, 120 and 160 plants/m 2 which were similar in these attributes. At similar densities, these crops generally had similar leaf areas and nodule weights/m 2 during the early podfilling period while at earlier growth stages leaf area and nodule development were greater at the higher plant population densities. Leaf area and nodule weight per plant were positively correlated as were absolute growth rate per plant and nitrogen assimilation rate per unit weight of nodule. Substantial leaf removal reduced weight but not the nitrogen assimilation rate of nodules determined from plant nitrogen content. Leaf removal did not significantly reduce dry matter but reduced nitrogen yield by reducing seed yield provided that the removed leaves were accounted for.Pod removal reduced dry-matter and nitrogen yield as well as nitrogen assimilation rate of nodules. Pod removal, however, substantially increased number and weight of nodules. Most of these late-formed nodules were located on the older parts of the lateral roots. Removal of the shoot apex had minor effects on nitrogen yield but reduced nodulation towards the completion of pod-filling. nitrogen by the roots, but application of heavy doses of fertilizer nitrogen (125-375 kg N/ha) at Hodgson & Blackman (1956) observed that there planting time did not significantly increase the was a logarithmic reduction in the number of seed yield of field beans (McEwen, 1970a, b). mature pods per plant over a range of 10-67 plants/In field experiments carried out between 1973 m 2 of spring beans. They explained the plastic and 1974 nodulation and nodule nitrogen-fixing response of this yield component with increase in activity of field beans {Vicia faba L.) were studied plant density as partly due to a limited amount with a view to determining whether they were of available nitrogen to the plants (no measure-adequate to meet the demands of high yields, ments given) and to increasing internal competition especially during the reproductive phase of growth for available nitrogen between vegetative and and particularly at high densities, reproductive parts.

The effect of waterlogging the vines of two yam varieties for 24,48 and 72 hours at two stages of growth, with or without fertiliser application, was studied in the field.Waterlogging caused a progressive degeneration of the leaf starting with the development of fresh lesions on the lower leaf surface, through necrotic spots or portions, to complete leaf necrosis. The degree of leaf damage was greater with Um 680 (Dioscorea d a t a ) than with Obiaoturugo (D. rotundata). Waterlogging also caused the breakdown of the apical buds of the vines. The degree of damage increased with the duration of waterlogging. Younger plants suffered more damage than older plants, and plants treated with fertiliser suffered more than plants without fertiliser. Waterlogging ultimately hastened the final senescence of the yam vine.Waterlogging vines for 24 h had no effect on tuber yield, while waterlogging for 48 and 72 h reduced tuber yield by 32.4% and 43.2% respectively (P< 0.01).Waterlogging vines at the early growth stage produced 47.6% (P< 0.01) less yield than waterlogging at a later stage.It is suggested that short-term or long-term waterlogging of the yam vine, or parts thereof, is the main cause of reduced leaf area and low yield in unstaked compared with staked yam crops. Waterlogging may also be a predisposing factor to disease infection of yam vines by soil-borne micro-organisms.

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