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African Crop Science Journal, Vol. 9. No. 3, pp. 507-516

WEED PROFILES AND MANAGEMENT ASSESSMENT FOR INCREASED FINGER MILLET PRODUCTION IN UGANDA

P. NYENDE, J.S. TENYWA, J. ORYOKOT¹and M. KIDOIDO²

Department of Soil science, Makerere University, P. O .Box 7062, Kampala, Uganda
¹Serere Agricultural and Animal Production Research Institute, P. O. Box Soroti, Uganda
²Department of Agricultural Economics, Makerere University, P. O. Box 7062, Kampala, Uganda

Received 10 August, 2000
Accepted 2 January, 2001

Code Number: cs01070

ABSTRACT

Finger millet (Eleusine coracana L. Gaertn.), a staple and food security crop in Uganda, is appreciated for its nutritional value, tolerance to water deficits, and good storage qualities; however, production requires a lot of labour, particularly for weed control. Thus, there is need to develop weed management strategies that are profitable. Research was conducted on-farm in three districts of eastern Uganda, to evaluate the agronomic and economic efficiency of one or two weedings, with row seeding as compared to broadcast sowing. Weedings were at two or four weeks after sowing. The four treatments were in a randomised complete block design arranged in split-plots with sowing patterns in main plots and weeding frequencies in the sub-plots. Digitaria scalarum was difficult to control and was judged to be the most serious weed. Finger millet yield was least under broadcast sowing with one weeding, but was increased by 44.7% with a second weeding at four weeks after sowing. Higher grain yields were obtained with row spacing plus one weeding than with broadcast sowing and two weeding treatments. Yield was not significantly increased by a second weeding under row seeding. Weed population density for row seeding was 50% of that for broadcast sowing. Row seeding was four times more costly than broadcast sowing due to extra labour requirement, but weeding costs were less and returns were greater. The second weeding increased the variable costs of production with broadcast seeding by 55%, but the profit margin increased by 88% and the returns were greater. Second weeding with direct seeding increased variable production costs by 65% but the returns for the second weeding were 289%. Weeding twice is especially profitable with broadcast sowing, but also with row seeding.

Key Words: Digitaria scalarum, economics, Eleusine coracana, row sowing, Striga

Résumé

L'eulesine (Eleusine coracana L. Gaetn.), est une denrée de sécurité alimentaire en Uganda, qui est appréciée pour ses valeurs nutritives, sa tolérance au déficit hydrique, ses bonnes qualités de stockage, mais sa production exige beacoup de travaux, en particulier le contrôle des mauvaises herbes. Une recherche a été conduite en milieu réel dans trois districts de l'Uganda pour évaluer l'efficacité agronomique et économique d' un ou deux sarclage (s) avec une plantation en lignes comparée à la plantation en vrac. Le sarclage était fait à deux ou à quatre semaines après la plantation. Les quatre traitements étaient dans un dispositif des blocs complètement randomisés arrangés en split-splot dont la parcelle principale était constituée par les modes de sarclage. Digitaria scalarum était difficle à controler et a été considéré comme la plus dangereuse mauvaise herbe. Le rendement de l'eulesine était pauvre pour la plantation en vrac avec un seul sarclage mais a été augmenté de 44 % avec un deuxième sarclage à quatre semaines après plantation. Les rendements grains était élevé avec un espacement des lignes avec un seul sarclage plus qu' avec la plantation en vrac et deux sarclages. Le rendement n'était pas significativement amélioré par le deuxième sarclage dans les conditions de lignes des semences. La densité de population des mauvaises herbes était 50% pour la plantation en vrac. La plantation en lignes était quatre fois plus chère que la plantation en vrac suite aux travaux exigés , mais les coûts de sarclage étaient faibles et les revenus étaient élevés. Le deuxième sarclage a augementé de 55% les coûts variables de production pour la plantation en vrac, mais le marge bénéficiaire a augmenté de 88% et les revenus étaient plus grands. Le deuxième sarclage avec une plantation directe a augmenté les coûts des variables de production de 65%, cependant les revenus pour le deuxième sarclage a été de 289%. Sarcler deux fois est particulièrement profitable pour la plantation en vrac mais avec une plantation en lignes.

Mots Clés: Digitaria scalarum, économiques, Eleusine coracana, plantation en lignes, Striga

INTRODUCTION

Production of finger millet (Eleusine coracana L. Gaertn) and other staple crops needs to be increased to meet the demands of the growing human populations in Uganda and neighbouring countries, but productivity is often constrained by the competitive effects of weeds. Weed management for finger millet production requires plenty of labour from resource poor farmers (Tenywa et al., 1999) who lack knowledge and financial capability to use herbicides or mechanised weeding (Gowda et al., 1998). Labour is costly during periods of peak demand, such as at weeding. Moreover, the severity of weeds appears to be increasing and farmers are weeding more frequently (Nyende, 2000), but the economic feasibility of this increased weeding has not been assessed. The scenario has been further worsened by the dependence on family labour, which is already strained by the rising number of children going to school through the recently instituted Universal Primary Education programme, which offers free education to four children per family and thus reducing the labour force.

To some extent, the growing weed aggressiveness is linked to soil fertility decline in Uganda (Nyende, 2000) and elsewhere in the World (King et al., 1986; Santhy and Channal, 1997). This linkage, though widely reported, remains to be positively and quantitatively established, particularly in areas prone to drought and its diminishing effects on plant available soil moisture such as in eastern Uganda. Exploration of labour-saving weeding practices is imperative if the dream to bridge the gap between the current on-farm yield (400 kg ha^-1) and on-station production (2,500 kg ha^-1) is ever to be realised.

As a crop husbandry practice, broadcast sowing of finger millet is likely to be a barrier to swift and effective weeding. This is particularly so in eastern Uganda, where wild finger millet relatives (e.g. Eleusine indica) co-exist with the crop (Nyende, 2000). A shift from broadcasting to row seeding could greatly impact the weeding process by opening up opportunities for faster field operations including mechanised weeding.

Weed flora competition has shifted with time, as cropping systems have become more intensive with less fallow time. Efficient weed management for finger millet production requires good characterisation of the weed flora composition and abundance patterns (Afors, 1994). The choice of a weed management strategy for finger millet production will depend on its profitability to farmers. The practicability of this and other considerations raised above requires coherent investigations with deliberate involvement of the concerned farmers. The objective of this study was to characterise weed profiles and explore management options for agronomic and economic benefits for finger millet production in eastern Uganda.

MATERIALS AND METHODS

On-farm studies were conducted during the long rains of 1999 and 2000, in three districts (Kumi, Atutur sub-county: Pallisa, Putiput sub-county; and Kamuli, Namwiwa sub-county) in eastern Uganda. Mean annual rainfall of the region, though bimodal, is less than 1000 mm and minimum and maximum temperatures vary little throughout the year from the means of 15 and 36⁰ C, respectively (Harrop, 1967). The soils are classified as Ferralsols (FAO-UNESCO, 1971) and are generally low in N and available P, but relatively adequate in Ca, Mg, K and Na (exchangeable bases) (Tenywa et al., 1999). The cotton-finger millet farming system is common (Yost and Eswaran, 1990; MNR, 1994), and cowpeas (Vigna unguiculata L. Walp.), maize (Zea mays L.), cassava (Manihot esculanta Crantz), beans (Phaseolus vulgaris L.), sorghum (Sorghum bicolor (L) Moench) and sweetpotato (Ipomoea batatas) are grown in rotation or as intercrops.

Three farmers were selected randomly in each district with the help of agricultural extension staff and local authorities. Field sites were previously under continuous cultivation for more than ten years without deliberate fertilisation. Land earmarked by farmers for finger millet production was ox-ploughed to a depth of about 20 cm, according to farmers own practice, twice before the onset of rains. Early season grasses and forbs were buried into the soil to allow for decomposition before planting. The trials were located within the broader farmers' finger millet fields so that their (farmers') crop acted as a guard crop.
Broadcast sowing, where by finger millet was sown according to the farmers' own practice, was compared with row seeding at the recommended spacing of 6 cm and 30 cm (NARO/SAARI, 1991). An improved finger millet variety, PESE I, was row-planted in stick-drilled furrows, using a tin with a hole perforated at the base. Two weeding regimes were assigned to each of the planting patterns. The regimes included (i) weeding once at 2 weeks after crop emergence (WAE) and (ii) weeding twice at 2 and 4 WAE. The experiment was laid out in a randomised complete block design in a split-plot arrangement, with sowing method as the main-plot and weeding frequencies as sub-plot factors. Main-plot size was 12 m x 26 m and sub-plots were 12 m x 5 m. Weeding was done by hand using small hand-hoes commonly used by farmers. Pests and diseases were controlled across the treatments using appropriate methods. The study was researcher-designed but farmer-researcher-managed.

Parameters measured included (i) time required for weeding, (ii) prevalent weed species, (iii) number of individual weed species within 1 m² quadrant (weed density). Time taken to weed each plot of 12 m x 26 m was assessed using a stop-clock and the total number of hours required for a hectare computed. Three adult persons were used to weed the plots on each study farm. Only effective weeding time, i.e., excluding resting time, was considered in computing labour in person-days. One person-day was estimated to be equivalent to four hours. This assessment was done at two sampling times, namely, (i) at first weeding (2 WAE) and (ii) at second weeding (4 WAE). The common weed species in the plots were identified during weeding and the major weeds ranked by the farmers according to importance. Farmer rankings were performed on a district level and eventually extended to regional basis. Data were also collected on finger millet yield components, namely, straw and grain yields. Market prices for finger millet as well as for inputs, including labour, were collected. A simple cost-benefit analysis of the two planting methods and weeding schedules was computed following procedures discussed by Emery et al. (1997) as:

Profit = TR - TVC ............... [Equation 1]

Where: TR = Total revenue derived as quantity produced multiplied by market price per unit for the production period;

TVC = Total variable costs.

The biophysical data were analysed using the Genstat statistical computer package and the significant means separated using Fisher's Least Significant Difference (LSD) test at 5% probability level.

RESULTS

Major finger millet weed profiles in eastern Uganda. The farmer ranking of relative importance of weed species was similar in both seasons (Table 1). Digitaria scalarum was ranked the most abundant in all districts (Table 2). Six of the 14 major weed species were ranked as the most (43%) and six others as the least abundant (43%) in all the districts. Grass species were rated as more abundant than broadleaf species (Tables 1 and 2). Striga hermonthica and S.asiatica, occurred in the trial plots and in surrounding finger millet fields, and had a high ranking with regard to relative importance of the observed weed species. Most Striga plants emerged after the first weeding. The second weeding (4 WAE) was ineffective in its control.
Generally, row planting reduced weed intensity by nearly 50% over broadcasting for all weed species (Table 3). Digitaria scalarum was the most abundant weed, while Oxalis latifolia was the least of the 14 abundant species recorded. Though Striga was ranked as one of the most important weeds (third) by the farmers, the actual field counts were relatively low.

Finger millet growth and grain. Sowing method did not significantly influence plant height until 50% flowering (Table 4). Beyond flowering, row planting phenomenally boosted plant height over broadcasting (P=0.004). By physiological maturity, row planting had increased plant height tenfold over broadcasting.

Weeding frequency did not affect plant height until after 4 WAE, when two weedings resulted in increased plant height (Table 5). On the other hand, grain and straw yields were least with broadcast sowing and one weeding (Table 6), and were increased by 80 and 120%, respectively by weeding twice. Grain and straw yields were not significantly affected by weeding frequency for row sowing. These results show strong (P=0.009) interaction effects between planting method and weeding schedules in broadcast, but not with the row planting pattern.

Labour requirements and economic returns. Row seeding significantly reduced labour requirement for each weeding (P=0.001) (Table 7). The total person-power requirement for weeding twice was 22% more with broadcast sowing than with row seeding. The second weeding required less labour than the first for both planting methods (26.2 and 21.2 person-days ha^-1, respectively). Row sowing costed four times as much as broadcast sowing, but resulted in reduced weeding and harvesting expenses, and greater production (Table 8). The second weeding of the broadcast sown crop increased variable costs by 65% and the profit margin by only 8%, but the benefit to variable cost ratio was still 2.89. The profit margins for sowing compared to broadcast sowing, were approxi-mately three and two times as much for one and two weedings, respectively.

DISCUSSION

Major finger millet weed profiles in eastern Uganda. The major weed flora consisted mainly of Graminea family and a few broad-leaved ones. The existence of more grass species, which morphologically and physiolo-gically resemble finger millet, presents a difficult scenario in weed control. For instance, Digitaria scalarum, the most abundant species in the region, is regarded as the most troublesome of all East African weeds (Ivens, 1989). As with rhizomatous grasses, Digitaria scalarum is difficult to eliminate as the rhizomes penetrate and intertwine with the roots of the crop. Considerable damage can be inflicted by attempting to dig out the weed. Ivens (1989) asserts that rhizomatous weeds are practically impossible to eliminate from a crop after crop establishment. Because most grasses root in the same domain as finger millet, this implies occurrence of stiff competition for soil moisture, nutrients and other environmental resources, with finger millet. This is an unfortunate situation, especially in eastern Uganda, a region increasingly affected by lengthy droughts as well as nutrient depletion (Yost and Eswaran, 1990). The morphological similarity of some weeds with finger millet, such as Eleusine spp., is a major hindrance to efficient weeding; it is difficult to distinguish the crop from the weed. On a positive note, the similarity in weed species abundance in the region implies that a weed management strategy developed for one site could be directly applied to a wider recommendation domain with minimum adjustments at farm level based on the management capacity of the households.

The fairly high ranking position of Striga in finger millet fields, perhaps the most devastating weed in cereal crops in Africa (Oryokot, 1994), raises a fundamental question of the future productivity of this crop in eastern Uganda. Hardly any research work has been done on strategies to effectively mitigate the prolific spread of this weed in the country; neither has its current impact on crop productivity been quantified. Research elsewhere has shown that S. hermonthica maintains high levels of infestation as the fallow period becomes shorter and shorter, probably because this cropping trend causes an increase in Striga seed viability in the soil (Parker, 1991). In this study, most Striga plants emerged after weeding; and therefore, escaped the weeding process. Striga is known to attack and damage the crop even before it (Striga) emerges from the ground (Parker, 1991; Oryokot, 1994), hence, damage is inflicted on the crop before the weed is physically visible. There is need for an extra weed control strategy to mitigate Striga plants that emerge later in the season, to prevent it from setting seed. Such strategies could be of integrated nature such as use of trap crops and/or soil fertility improvement, which have shown potential success elsewhere (Ramachndra et al., 1991).

Effect of method of planting finger millet on weed abundance. The effective reduction in weed density of row planting over broadcasting for all weed species could be due to the former providing a more conducive environment for effective weeding than its broadcast counterpart. Weeds were better exposed and more easily accessed under row planting than under broadcast. Besides, small hand-hoes were more convenient for uprooting weeds under row planting, compared to the predominant hand-weeding under broadcast planting. Predominance of hand-weeding under the latter system inevitably resulted in incomplete weed removal. Hence, the remaining plant parts probably retained capacity to re-sprout into new plants earlier after weeding. The more efficient weed control under row planting could have also resulted into more vigorous finger millet growth, hence, causing shading of inter-row spaces, which in turn discouraged weed proliferation. It can, therefore, be concluded that weeding a row planted finger millet crop is more efficient and effective than weeding a traditionally broadcast crop. Hence, planting methods indirectly influence weed species population density through their impact on effective weed control. This fully conforms to the original premise for row planting of crops, which was intended to ease on field operations in crop management (Akobundu, 1986).

Row planting gave rise to more vigorous crop growth and taller plants than broadcast planting. This could have led to shading and, therefore, weed suppression through denial of solar radiation, and competitiveness in use of other resources such as water and nutrients. Afors (1994) reported plant canopy and, particularly, plant height to be positively correlated with weed suppression. According to Regnier and Janke (1990) finger millet is competitive enough to suppress weeds. Therefore, the greater plant height under row planting probably increased the crop's ability to smoother weeds. The row-planted crop was sown at the recommended spacing of 6 cm x 30 cm for eastern and northern Uganda (NARO/SAARI, 1991). This spacing was narrow enough to build up a more closed canopy than in the broadcast crop. Several reports indicate that crops planted in narrow spacings suppress weed growth more than when planted in wide spacings (Felton, 1976; Teasdale and Frank, 1983; Bendixen, 1988).

Effect of planting method and weeding frequency on finger millet growth parameters and yield components. The greater positive effect of row planting on plant height than the broadcast case demonstrates the superiority of this planting method to the latter. This observation has great implications, especially in the study soils where the need for considerable amounts of organic matter is critical. Increased biomass yield could be recycled to build up organic matter in the soil. Plant height is also important in cases where it is directly or indirectly related to grain yield, as was the situation in this study. The superior performance of the row planted crop could be due to the nearly optimal utilisation of resources by the latter than the former since row planting was done following judicious research recomme-ndations for finger millet in this region. In contrast, broadcasting was done following the traditional farmers' practice. It was clear in the field that the row-planted crop was nearly uniformly distributed in the field. On the contrary, the broadcast crop was characterised by over-crowding in some parts and sparseness in others. This plant distribution pattern could have adversely affected resource utilisation by plants. Overcrowding could have caused undue competition for resources (nutrients, water, light, etc.), while sparseness could have led to inept resource use. It should, however, be noted that plant population density was not within the scope of this study.

The superiority of yields under double weeding over single weeding is a reflection of the seriousness of the weed problem in the study region. Weeding twice requires extra labour yet weeding once implies reduced yields. There is need for an economic evaluation of the opportunity cost of second weeding under both broadcast and row planting regimes. Yield response to the second weeding under row planting was barely 24% that of broadcasting with the same weeding frequency. This observation again implies that row planted finger millet requires less weeding compared to its broadcast counterpart. It also implies that there is more efficient and effective weed control with single weeding under row planting than under broadcasting. Again, this justifies an economic assessment of weeding under both planting regimes, particularly against the extra labour needed for planting in rows versus broadcasting.

Finger millet labour requirements and economic returns under different weeding frequencies and planting patterns. The total person-power requirement for weeding twice the broadcast crop was 22% more than that for the row one. In general, however, second weeding required less labour than the first one. The reasons for the ease of weeding in the row planted versus the broadcast crop, lie in the original premise that row planting at the recommended agronomic spacing eases field operations including weeding (NARO/SAARI, 1991). This phenomenon is true at all levels of mechanisation including traditional hand-hoeing. Access to the weeds is greatly increased in the row-planted crop compared to the haphazard broadcast crop. These results are, to a large extent in agreement with the work of Shakya et al. (1991), who reported a significant weeding labour reduction accruing from row planting. This labour relief is important since weeding and harvesting of finger millet are the most labour consuming operations, accounting for about 25 and 14% of the overall production labour requirement, respectively (Nyende, 2000). In Uganda, however, the dilemma lies in the greater amount of labour needed to hand-sow in rows in the absence of simpler mechanised alternatives. Which of the two planting practices is economically viable requires an elaborate economic analysis comparing the cost of planting in rows versus the extra weeding requirement in broadcasts. Furthermore, the choice of whether to weed once or twice, should consider the ecological history of weeds in the area. This is due to the fact that some soil sites have a richer seed bank than others (Parker, 1991). This weed seed bank issue remains to be investigated in Uganda. The labour requirement values obtained in this study are fairly lower compared to 90 man days ha^-1 reported in a Serere on-station study (Anon., 1995) probably because the parameter for measuring labour is highly subject to the judgement of the researcher, and also, the people he/she is working with.

It is clear from this study that, in order to realise better economic returns to finger millet production, the method of planting and the frequency of weeding are critical. The cost-benefit analysis of weeding labour requirements in finger millet production, under broadcast or row planting and two weeding regimes, has shown a clear yield and economic advantage of row planting combined with weeding twice over broadcasting and weeding once. Although the cost of row planting was 4 times greater than that required in broadcast sowing, this extra cost was later offset by higher yields and greater estimated profit margins. The economic return from weeding once under row planting was 180% of that under broadcast, which required two weedings. In terms of labour requirements, the row planted crop needed barely 46% of the labour force required under broadcasting, for the corresponding weeding frequencies. Correspondingly, the yield ratio using similar comparisons was above 163%. These figures clearly indicate that row planting is a vital practice, and has great potential for shifting household level finger millet yields and economic returns to achieve food security and alleviate poverty.

CONCLUSIONS

Grassy weed species predominate in finger millet fields in eastern Uganda of which Digitaria scalarum, Cyperus rotundus and Eleusine indica appeared most important. Row planting reduces weed density by about 50% with increased finger millet straw and grain yields. Broadcasting requires more labour, but yield gains are less than those obtained under row planting. Weeding once at 2 WAE is economically adequate for a row-planted crop. Weeding twice is essential for profitability with broadcast sowing.

ACKNOWLEDGEMENTS

The assistance and co-operation of the district agricultural staff and local administration authorities of Kumi, Pallisa and Kamuli districts are gratefully acknowledged. Dr. M. Nabasirye of the Department of Crop Science, Makerere University is thanked for statistical advice. This research was financed through a grant from The Rockefeller Foundation's Forum on Agricultural Resource Husbandry, Grant number RF 98008 # 117.

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