The effects of plant density and weed competition on the growth, yield and yield. components of pigeon pea (cajanus cajan (l.) millsp.)
Oluoch, P O
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Two experiments were conducted at the National Horticultural Research Station, Thika, Kenya, at an altitude of 1550 m, latitude 1001'S and longitude 370 06'E. Tne experiments were .to determine the influence of spacing on weeds, and on growth and yield of pigeon~ea; and the critical'weed competition period and effect of the length of this period on the performance of this crop. Two introduced short maturing and open pollinated culti~ars of pigeonpea, NPP 203/3 and NPP 291 were used in this study. Eight weeding treatments were imposed on these cultivars in the first experiment. In the second experiment, however, only one cultivar, NPP 203/3, was used with four weeding and 13 spacing treatments. Results obtained in the first experiment showed that weeding treatments did not affect the stand count,plant heightJ date to 50 per cent flowering, ·number of seeds per pod and a hundred seed weight. However, it was observed that the longer the weeds were allowed to grow with the crop, grain yield, number of primary branches and number of pods per :plant decreased. It was also shown that the plots which were kept weed-free throughout the season, upto nine weeks and after.three weeks, did not differ significantly (P <0.05) ~~grain yield. These results suggest that the critical weed competition period in the two cultivars is between three and nine weeks. The twq cultivars differed significantly in days to 50 per cent flowering, plant height, number of primary branches, number of pods, and grain yield, but not in stand count, number of seeds per pod and a hundred seed weight. Soil moisture was also slightly higher in plots where weeds were not allowed to grow with the crop for a longer period and that those plots planted with cultivar N'PP 203/3 gave higher weed yields than those planted with cultivar NPP 291. In the second experiment, plant density did not affect a hundred seed weight, number of seeds per pod and plant height. Grain yield and shoot dry weight per hectare, however, increased with increasing plant density; whereas number of primary branches, number of pods, grain yield, per plant, shoot dry weight per plant and weight of dry,weeds per hectare decreased with increasing plant density. It was also observed that the longer the weeds were allowed to grow with the crop, the lower was the grain yield, shoot dry weight, number of primary branches, number of pods (xiii) per plant and soil moisture content. Plant height, number of seeds per pod and a hundred seed weight were not, however, affected by the various weeding treatments. An attempt has been made 'to discuss the results given above and some conclusions drawn.