The mean number of branches of KAT 60/8 were significantly (P<0.05) influenced by intercropping and varied from 2.2 to 5.9 (Table 5) and from 3.9 to 5.2 (Table 6). The number of branches of ICPL 87091 were significantly (P<0.05) influenced by intercropping with finger millet (Table 5). Similar results were observed during1998 (Table 6). The results indicated that intercropping had more influence on the number of branches of pigeonpea than locations and seasons. Treatments KAT 60/8 + Pese 1 and ICPL 87091 + Pese 1 with recommended sole-finger millet population of 33.3 plants m^-2 in both seasons produced the lowest number of branches, indicating a high influence of cereal competition to the branching capacity of pigeonpea. This influence was translated into reduced number of pods per plant and finally yield per unit area.

The mean number of pods of KAT 60/8 was significantly (P<0.05) influenced by intercropping and ranged from 10.3 to 30.2 in 1997 (Table 5) and from 35.9 to 55.3 in 1998 (Table 6). Similar influence was observed for ICPL 87091 intercrop where pod numbers varied from 9.5 to 29.4 (Table 5) and from 23.8 to 33.5 (Table 6). The number of pods of KAT 60/8 was influenced by intra-row spacing during 1997 and 1998 but ICPL 87091 was only affected in 1997 (Table 5). The high number of pods for KAT 60/8 intercrop at a plant density of 5.6 plants m^-2 was due to more branches formed, while for ICPL 87091 intercrop it was at a plant density of 11.1 plants m^-2 (Table 5) and 16.7 plants m^-2 (Table 6) thus the taller plants possibly gave the cultivar a better position for light interception and increased stimulation for pod formation leading to better yield. Obuo et al. (1996) reported that KAT 60/8 required 5.6 plants m^-2 for maximum grain yield.

The mean number of seeds of both cultivars in the two seasons and locations was not significantly influenced by intercropping, indicating the stability of this character. However, the estimated yield per hectare of both cultivars showed significant (P<0.05) influence, of intercropping with finger millet between seasons and locations. Estimated higher yields per hectare were observed at the highest plant density of 8.3 plants m^-2 for KAT 60/8 and at 16.7 plants m^-2 for ICPL 87091 intercropped with finger millet at the lowest plant density of 8.3 plants m^-2 . The lower yields were obtained at lowest plant density of 4.2 plants m^-2 for KAT 60/8 and at 5.6 plants m^-2 for ICPL 87091 intercropped with finger millet at the highest plant density of 33.3 plants m^-2 due to increased competition from finger millet.

The estimated yield per hectare of finger millet was influenced by intercropping with both cultivars, seasons and locations (Tables 5 and 6). Higher yields per hectare of intercropped finger millet were obtained in treatments where KAT 60/8 or ICPL 87091 intercrops provided less competition due to lower plant populations per unit area. This is probably the reason why the farmers treat the pigeonpeas in the intercropping systems as a minor component crop.

The total land equivalent ratio (LER) values of finger millet intercropped with KAT 60/8 varied from 1.12 to 1.18 (Table 5) and from 0.99 to 1.40 (Table 6) while ICPL 87091 intercrop gave total LER values which varied from 1.05 to 1.35 (Table 5) and from 0.93 to 1.19 (Table 6). The second season of 1997 (Table 5), produced total LER values greater than 1 while total LER values of less than 1 were recorded in some intercrops in 1998, indicating no land-use yield advantage of intercropping in these combinations (Willey, 1979; Mead and Willey, 1980). In the 1997 season, the highest yield advantage (LER=1.35) was recorded where ICPL 87091 was planted at the closer intra-row spacing of 10 cm (16.7 plants m^-2 ) with Pese 1 at the wider intra-row spacing of 20 cm (8.3 plants m^-2 ). In the same season, KAT 60/8 /Pese1 intercrop planted at the same intra-row spacing of 20 cm gave the highest LER value of 1.18 in treatments involving KAT 60/8. Planting finger millet at plant density of 33.3 plants m^-2 together with KAT 60/8 at 4.2 plants m^-2 and ICPL 87091 at 5.6 plants m^-2 gave significantly (P<0.05) higher estimated yield than from sole pigeonpea and/or sole finger millet (Table 5).

In the 1998 season, the highest yield advantage (LER=1.40) was from KAT 60/8 planted at the wider intra-row spacing of 40 cm (4.2 plants m^-2 ) with Pese 1 at the closer intra-row spacing of 5 cm (33.3 plants m^-2 ). Within the same season ICPL 87091 intercrop planted at the closer intra-row spacing of 10 cm (16.7 plants m^-2 ) with finger millet at the wider intra-row spacing of 20 cm (8.3 plants m^-2 ) gave the highest LER value of 1.19 in treatments involving KAT 60/8. For treatments involving ICPL 87091, the highest LER value of 1.17 was obtained when this cultivar was planted at the wider intra-row spacing of 30 cm (5.6 plants m^-2 ) with finger millet at the closer intra-row spacing of 5 cm (33.3 plants m^-2 ). This treatment also gave significantly (P<0.05) higher estimated total yield than that from the pure stand of finger millet indicating that the highest yield advantage from a pigeonpea/finger millet intercrop was influenced by the pigeonpea cultivar.

Yields from first season 1998 were significantly better than from the second season of 1997 indicating the influence of the amount of rainfall in the seasonal effect on the productivity of the pigeonpea/finger millet intercrop. The second season of 1997 had a mean monthly rainfall of 220.4 mm with a daily mean rainfall ranging from 1.96 to 10.98 mm while the second season of 1998 had 111.74 mm with a daily variation from 1.44 to 5.9 mm. The results of estimated total yields per hectare suggested that the pigeonpea/millet intercrop require low pigeonpea and high millet stand for better productivity per unit area. This explains productivity trends in the adopted traditional farming system where farmers regard finger millet as the main crop and the pigeonpea component as a minor crop (Ali, 1990).

The influence of the effect of plant row arrangement on the performance of pigeonpea and its sorghum intercrop are shown in Table 7. The plant row arrangement significantly (P<0.05) influenced all the yield and yield component characters within the pigeonpea cultivars KAT 60/8, ICPL 87091 and ICP 6927 used in the intercrops. The highest number of branches for KAT 60/8 and ICPL 87091 were obtained in a 2:2 row arrangement and the least branching in a 1:1 row arrangement. The high number of branches in a 2:2 arrangement could be attributed to a wider space which minimised competition from the sorghum for moisture, nutrients and light (Ali, 1990).

Number of pods per plant was significantly (P<0.05) influenced by plant row arrangement. Highest number of pods for each pigeonpea cultivar was obtained in the 2:2 row arrangement, and the lowest was in the 1:1 row arrangement. Highest number of pods obtained in the 2:2 row arrangement was due to less shading effect from the pigeonpea itself and the component crops thus allowing increased pod bearing on lower branches as light could reach the lower parts of the pigeonpea canopy (Ali, 1990).

Estimated grain yield of the pigeonpea cultivars KAT 60/8, ICPL 87091 and ICP 6927 were significantly (P<0.05) reduced due to inter-cropping, and plant row arrangement had a significant (P<0.05) effect on yield. The 2:2 row arrangement of pigeonpea and sorghum gave higher estimated yields of all the pigeonpea cultivars than in 1:1 and 1:2 row arrangements. Similarly, the 2:2 row arrangement gave better estimated sorghum yields without reducing the pigeonpea yield as much as was observed in the 1:1 and 1:2 row patterns.

The land equivalent ratio (LER) values suggested that the yield advantage of intercropping pigeonpea and sorghum was mainly from 1:2 and 2:2 row arrangements. The yield advantage was 19-57% in intercropping of KAT 60/8, 47-63% in intercropping of ICPL 87091, and 15-45% in intercropping of ICP 6927, with sorghum. Maximum yield (4075 kg ha^-1) and yield advantage (63%) was obtained by growing ICPL 87091 and Seredo together in a 2:2 row arrangement. Higher yield advantages (45%) for ICP 6927 and (57%) for KAT 60/8 were also obtained from a 2:2 row pattern. Higher yield advantages obtained from the double rows of pigeonpea grown between double rows of sorghum was due to efficiency in use of resources such as light, water, and soil nutrients between the crops in association (Willey et al., 1981). Rao and Willey (1983) and Ali (1990) reported that crops grown in paired rows yield more than those grown in uniformly spaced rows because 2:2 row arrangement of crops allows more radiation to reach the lower part of the canopy and minimises competition. In the second season 1997, the LERs of intercropping systems under 1:1 were close to 1.0, indicating no land-use advantage of intercropping pigeonpea and sorghum during this season (Willey, 1979). Natarajan and Willey (1985) reported similar results from intercropping of pigeonpea with sorghum in that arrangement.

Table 8 shows the effect of plant row arrangement on the performance of pigeonpea and its sorghum and finger millet intercrops during the first season of 1998. As was the case in 1997, number of branches for KAT 60/8 and ICPL 87091 intercrops were significantly (P<0.05) affected by the plant row arrangement. The highest number of branches for KAT 60/8 and ICPL 87091 were again obtained in a 2:2 row arrangement and the least branching was in a 1:1 row arrangement.

The number of pods also were significantly (P<0.05) influenced by plant row arrangement with higher pod numbers for all the pigeonpea cultivars being observed in the 2:2 row arrangement. Unlike in 1997, the 100-seed weights of pigeonpea were significantly (P<0.05) affected by different intercrops and plant row arrangement in 1998 (Table 8). The mean seed weights of the pigeonpea cultivars intercropped with sorghum were higher in 1997 than in 1998, suggesting that pigeonpea cultivars were less subjected to competition from the cereal component crop during 1997 than in 1998.

Intercropping and plant row arrangement effects were significant (P<0.05) on estimated grain yield of pigeonpea, finger millet and sorghum (Table 8). In this season also a 2:2 row planting of pigeonpea gave higher estimated yields of finger millet and sorghum than 1:1 and 1:2. Grain yield of both the pigeonpea cultivars KAT 60/8 and ICPL 87091 were also significantly (P<0.05) reduced by intercropping.

The land equivalent ratio (LER) values suggested the existence of yield advantage of intercropping pigeonpea and finger millet or sorghum except in the case of pigeonpea planted with sorghum in a 1:1 row arrangement. The yield advantage was 15-31% in intercropping of KAT 60/8, and 37-79% in intercropping of ICPL 87091 with finger millet and 21-35% in intercropping of KAT 60/8, and 0-45% in intercropping of ICPL 87091 with sorghum (Table 8). The maximum yield advantage (79%) was obtained by growing pigeonpea cultivar ICPL 87091 and finger millet in a 2:2 row arrangement.

Insect damage and chemical spray studies indicated that both cultivars ICPL 87091 and KAT 60/8 suffered significantly (P<0.05) more seed damage from spraying in the vegetative stage only or no spray at all (Table 9). Continuous spray from vegetative stage to pod formation did not control pod sucking bugs in ICPL 87091 better than the control, while spraying at vegetative stage alone or at flower stage to pod maturity in KAT 60/8 did not control the pod sucking bugs better than no spraying. Spraying at only vegetative stage in ICPL 87091 did not reduce seed damage by both pod borers and podfly compared to the controls. At all spraying regimes, pigeonpea gave higher grain yields than unsprayed (control), but yields obtained by spraying at only vegetative stage were not significantly different from the controls. The highest yield in ICPL 87091 and KAT 60/8 were obtained when spraying was done at flower bud initiation to pod formation and at pod formation to pod maturity, respectively. Cultivar ICPL 87091 is determinate and therefore highly vulnerable to flower destroying insects while KAT 60/8 is indeterminate and can compensate for flowers destroyed.

The results of cost-benefit ratios for spraying pigeonpea at various stages of growth are presented in Table 10. Spraying ICPL 87091 twice at flower bud initiation to pod formation (iii) and KAT 60/8 at pod formation to pod maturity (iv) with Nurelle-D was the most effective and economical with high cost-benefit ratios of 2.43 and 2.60, respectively. Minja (1996) reported little or no pesticide use to control insect pests in pigeonpea in Uganda because it was considered expensive. These results suggest that a judicious application of insecticides at the different critical stages of different cultivars is cost-effective.

CONCLUSIONS

Changing intra-row spacing significantly affected yield advantage of pigeon/cereal intercropping systems depending on the maturity group of the pigeonpea cultivars. Closer spacing for short duration and wider spacing for medium duration pigeonpeas cultivars had better land use for intercrops. Where moisture was not a constraint the inter-row spacing of 5 cm for finger millet and 15 cm for sorghum and wider inter row of 15-30 cm for pigeonpea was most advantageous. Yield advantage was also achieved when double rows of pigeonpea were planted in between paired rows of cereals. The study showed that spraying Nurelle-D twice at flower bud initiation to pod formation for short duration and pod formation to maturity for medium duration pigeonpea cultivars gave the most effective crop protection and best cost-benefit.

AKNOWLEDGEMENT

The research work reported in this paper was funded by European Union Contract No. ERBIC18CT960130.

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