David Chikoye

Response of speargrass (Imperata cylindrica) to cover crops integrated with handweeding and chemical control in maize and cassava

Speargrass [Imperata cylindrica (L.) Raeuschel] is a noxious weed widespread in most tropical zones of the world. Studies were conducted in the savannah of West Africa from 1997 to 1999 to evaluate crop yield, speargrass control, and net benefit from the use of cover crops integrated with handweeding and chemical control in maize and cassava. Glyphosate and handweeding were main treatments. Subplot treatments were type of cover crop [velvetbean, Mucuna cochinchinensis (Lour.) A. Chev., kudzu, Pueraria phaseoloides (Roxb.) Benth, and velvetbean intercropped with kudzu] and plots without cover crops. Weeding five times or applying glyphosate was more effective than weeding twice in preventing crop yield losses and suppressing speargrass. Plots that received glyphosate or those weeded five times had 28–59% higher crop yields than plots weeded twice at all locations. In maize, subplots without cover crop had 30% more maize grain yield than plots with cover crops. In cassava, subplots without cover crops at Ezillo and plots where kudzu was intercropped with velvetbean at Ogoja had the lowest cassava tuber yields. Speargrass was more effectively suppressed in plots with cover crops than in plots without cover crops. Across all main treatments, velvetbean nearly eliminated rhizomes of speargrass within 2 years of treatment application at Avrankou. It was cheaper to use glyphosate than handweeding for speargrass control in both crops. Cover crops generally gave better economic benefit in cassava while in maize an opposite trend was observed. r 2002 Elsevier Science Ltd. All rights reserved.

Cogongrass suppression by intercropping cover crops in corn/cassava systems

Abstract Cogongrass is a difficult weed to control in small-scale farming systems and often causes significant crop yield reduction. Field experiments were conducted from 1996 to 1999 at three sites located in the forest/savanna transition zone of Nigeria to determine the influence of intercropping cover crops on cogongrass, corn, and cassava growth. Total cogongrass biomass (shoots and rhizomes) at the onset of the study was highest at Ijaiye (889 g m−2), followed by Umumba (445 g m−2), and least in Ezillo (138 g m−2). Velvetbean had the highest percent ground cover at Umumba and Ijaiye (67 to 89%) 10 wk after planting and shaded the ground longer at all locations. Twelve months after planting, plots with cover crops had 66, 71, and 52% lower cogongrass biomass than the weedy control without cover crops at Ijaiye, Umumba, and Ezillo, respectively. Velvetbean at all locations, L. purpureus at Ijaiye, and tropical kudzu at Umumba and Ezillo were the cover crops most effective in reducing rhizome biomass of cogongrass. Annual weeds dominated the plots sown to cover crops after 2 to 3 yr. At Ijaiye and Umumba, cogongrass competition affected the yield of cassava more than the yield of corn. At all locations, cover crops and weeded control treatments had 27 to 52% more corn grain yield than the weedy control. At Ijaiye, corn grain yields from velvetbean and L. purpureus plots were similar to that from the weeded control plot. At Umumba, all plots with cover crops had corn grain yields similar to that of the weeded control. At all locations, almost all cover crop treatments had cassava root yields higher than the weedy control. Except at Ijaiye, root yields from weeded control plots were 17 to 88% higher than in cover-cropped treatments, suggesting competition between cover crops and cassava. Nomenclature: Cassava, Manihot esculenta Crantz ‘TMS 30572’; cogongrass, Imperata cylindrica (L.) Beauv. IMPCY; corn, Zea mays L. ‘SUWAN 1 SR’; Lablab purpureus (L.); tropical kudzu, Pueraria phaseoloides (Roxb.) Benth.; velvetbean, Mucuna cochinchinensis (Lour.) A. Chev.

Seedling emergence model for tropic ageratum (Ageratum conyzoides)

Abstract The timing of weed seedling emergence relative to the crop is important in planning and optimizing the time of weed control, but very little work has been done to predict seedling emergence of tropical weed species, especially in low-input and small-scale farms. We developed a simple model based on hydrothermal time to predict seedling emergence of tropic ageratum. Hydrothermal time at 2-cm soil depth was calculated from soil moisture and soil temperature simulated from several micrometeorological and soil physical variables. The model was developed using 5 yr of field emergence data from a continuous corn–cassava production system in southwestern Nigeria. Percentage of cumulative seedling emergence from the 5-yr data set was fitted to cumulative soil hydrothermal time using a Weibull function. The predicted cumulative emergence curve significantly matched observed field emergence (r2 = 0.83). Model predictions were evaluated with root mean square error (RMSE) using four field emergence data sets from southeastern Nigeria (RMSE ≤ 10.1) and Los Banos, Philippines (RMSE = 8.9). RMSE values ≤ 10 indicated that predictions represented observations well. With such models, extension personnel working on tropical soils, especially in West Africa, may be able to provide additional advice to farmers on the appropriate time for the management of tropic ageratum. Nomenclature: Tropic ageratum, Ageratum conyzoides L. AGECO; cassava, Manihot esculenta Crantz; corn (maize), Zea mays L.

Influence of fallow type and land-use intensity on weed seed rain in a forest/savanna transition zone

Abstract Weed seed rain was monitored in field plots under three fallow types and four land-use intensities in Ibadan, Nigeria, in 1994 and 1995. The fallow types were natural bush, planted Leucaena leucocephala, and Pueraria phaseoloides. The land-use intensities consisted of continuous cropping, involving Zea mays/Manihot esculenta and fallowing for 1, 2, and 3 yr, with each fallow period followed by 1 yr of Z. mays/M. esculenta cultivation. In 1994, seed rain in plots cropped after P. phaseoloides fallow was significantly lower than in plots cropped after bush or L. leucocephala fallow. Pueraria phaseoloides plots had similar seed rain as bush fallow plots in 1995, and the seed rain in these plots was significantly lower than in L. leucocephala plots. Weed seed rain was significantly higher in continuously cultivated plots across all fallow types than in plots that were cultivated after one or more years of fallow. The lowest seed rain was in plots that were cropped once after a 3-yr fallow. The largest quantity of weed seed input in the plots occurred in either August or September, reflecting the life cycle of the annual weeds that dominated the vegetation. Individual species differed in pattern and duration of shedding seeds within the fallow systems and land-use intensities. Annual weeds dominated the seed rain in continuously cropped plots, and seeds of perennial weeds were dominant in plots fallowed for more than 1 yr before cultivation. Weeds flowered earlier in continuously cropped plots than in plots that were cropped after 2 or 3 yr of fallow. Increased land-use intensity caused an increase in seed rain and consequently increased the soil seed bank. Pueraria phaseoloides fallow was more effective in shading weeds and probably reducing the quantity of light reaching them than the natural bush and planted L. leucocephala fallow systems, and this may have been the basis of the significantly lower seed rain in P. phaseoloides plots. Nomenclature: Leucaena leucocephala (Lam.) de Wit LUAGL, leucaena; Manihot esculenta Crantz ‘TMS 30572’, cassava; Pueraria phaseoloides (Roxb.) Benth. PUEPH, tropical kudzu; Zea mays L. ‘TZSRW’, corn.

Field performance of improved cowpea varieties under conditions of natural infestation by the parasitic weed Striga gesnerioides

Cowpea is an important food crop in the dry savannas of West and Central Africa because of its high protein content. Yields are, however, considerably reduced by the parasitic angiosperm Striga gesnerioides. Field trials over 2 years in two localities in northeast Nigeria evaluated the performance of diverse cowpea varieties under conditions of natural infestation by Striga. Grain yield was higher in Tilla than in Damboa where the higher Striga infestation may be caused by the lower rainfall and the sandy nature of the soils. Two varieties (IT97K-499-35 and IT90K-82-2) were confirmed to be resistant to Striga. Yield gain from IT97K-499-35 over the local variety ranged from 30% in Tilla in the northern Guinea savanna to 126% in Damboa in the Sudan savanna. The local variety Borno Brown and two improved varieties were found to be as susceptible to Striga as the susceptible control, TVX-3236, and therefore may not be recommended for cultivation in areas where Striga infestation is a problem. One variety, reported previously to be resistant to one or two races of Striga supported moderate levels of emerged Striga, suggesting that it is not totally resistant to the Striga race in the two localities. However, it produced grain yields that were comparable to the resistant varieties in the locality that was most infested, suggesting that it is tolerant to Striga. There are concerns about the adoption potential of the Striga-resistant variety IT97K-499-35 because of its medium-sized white seeds. Farmers in this zone prefer large-seeded brown cowpea. We recommend that efforts be made to develop Striga-resistant varieties that satisfy end-user preferences.

Characterization of Legume Cover Crops for Weed Suppression in the Moist Savanna of Nigeria

Multilocational characterization of selected herbaceous and shrub legumes was carried out over a 3-yr period at lowland and midlatitude sites in the moist savanna agroecological zone in Nigeria where a south–north gradient exists for rainfall, length of growing season, and insolation. One study site each was located in coastal–derived savanna (DS), southern Guinea savanna (SGS), and northern Guinea savanna (NGS). A fourth site was located in the plateau of the NGS. Only one legume cover crop, lablab, produced adequate ground cover and good weed suppression in three locations irrespective of rainfall amount, duration, and distribution. Velvetbean was superior to other legume cover crops in the lowland savanna locations where rainfall exceeded 1,100 mm/yr but not in the plateau of the NGS where rainfall was less than 1,000 mm. Pigeonpea grew luxuriantly and produced canopy cover that effectively suppressed weeds in the DS where rainfall was high. Centurion grew well and suppressed weeds effectively only in the SGS site where rainfall of 1,120 mm was well distributed over a 5-mo period. Sunnhemp grew well and suppressed weeds only in the NGS study sites where rainfall duration was 4 mo and the length of the growing period was short. Weed density was negatively correlated (P < 0.05) with percentage ground cover of those legume cover crops that were effective in weed suppression in all locations. Redundancy analysis revealed significant associations between weed species and cover crops at each of the locations. Nomenclature: Centurion, Centrosema pascuorum Mart. Ex Benth. #3 CENPA; lablab, Lablab purpureus (L.) Sweet # LABPU; pigeonpea, Cajanus cajan (L.) Millsp. # CAJCA; sunnhemp, Crotalaria ochroleuca G. Don # CROOC; velvetbean, Mucuna pruriens (L.) DC. var. utilis (Wright) Burck # MUCPR. Additional index words: Legume ground cover, weed density, weed species composition. Abbreviation: WAP, weeks after planting; DS, coastal–derived savanna; SGS, southern Guinea savanna; NGS, northern Guinea savanna; RDA, redundancy analysis.

Cover crops for cogongrass (Imperata cylindrica) management and effects on subsequent corn yield

Abstract Cogongrass is widespread in the moist savanna and forest zones of West Africa, where recurrent fires, tillage, weeding, and other farm activities continuously disturb land. Field experiments were conducted in the forest–savanna transition zone of Nigeria from 1996 to 2000 to evaluate the potential of two cover crops (velvetbean and tropical kudzu) for reclaiming land that had been abandoned to cogongrass. Cover crops were grown on the same plots for 3 consecutive yr (1996 to 1998). The control was natural fallow dominated by cogongrass in 1996 to 1998. Corn was planted in all treatments in 1999 and 2000. Total dry matter of cogongrass before the treatments were imposed was 9,000 kg ha−1, and rhizomes contributed 49% of this. At all subsequent sampling dates, plots with cover crops had lower cogongrass shoot and rhizome dry matter than plots without cover crops. Shoot dry matter was reduced to zero 65 wk after planting in both cover crops; rhizome dry matter was reduced to zero after 97 wk in velvetbean plots and after 105 wk in tropical kudzu plots. Corn grain yield was 60% higher in plots with tropical kudzu and 102% higher in plots with velvetbean than in control plots without any previous cover crops. Further research is required to integrate use of cover crops with other control methods for improved cogongrass management. Nomenclature: Cogongrass, Imperata cylindrica (L.) Beauv. IMPCY; corn, Zea mays L. ‘Oba Super II’; velvetbean, Mucuna cochinchinensis (Lour.) A. Chev. MUCCO; tropical kudzu, Pueraria phaseoloides (Roxb.) Benth. PUEPH.

Farmers' Adoption of Soil Conservation Technologies: A Case Study from Osun State, Nigeria

Abstract The main objective of this study was to determine the attitude of farmers towards erosion and the adoption of appropriate soil conservation technologies (SCTs). For the survey, farmers were selected from the communities Esa Oke, Elwure and Owode-Ede and Akoda in Osun State in Nigeria. In the first three communities farmers did receive training on soil conservation, in the fourth not. About 60 farmers were interviewed to obtain information on personal and socio-economic characteristics, awareness of environmental problems, attitude towards erosion control and experiences with SCTs. Statistical data analyses (analyses of frequencies, correlation, t-test, χ2-test) were made to examine possible relationships among parameters and the influence of factors on adoption. Most respondents were advanced in years, responsible for large households and characterized by low levels of income and literacy. Soil erosion was seen as a problem confronting agricultural production only to a small extent. The adoption rate of SCTs was low, as only mulching, cover cropping, contour tillage and cut-off drainage were practised and often rejected. Low labour-demand, the availability of common equipment, low costs of application, ease of practice and compatibility with the existing farming system influenced adoption. The observed positive correlation between level of education, knowledge of appropriate technologies, farming experience and the number of SCTs adopted emphasizes the importance for farmers of education and training. Strengthening agricultural extension agencies for capacity building is an important tool for improving soil conservation in Nigeria. The paper clarifies with specific examples the causes of the low rates of adoption of available technologies, with a reduced impact of research and of efforts to achieve food security and sustainable production at village level.

Changes in size and composition of weed communities during planted and natural fallows

Abstract The use of trees and herbaceous cover crops for weed management in smallholder farms is a promising alternative to the unsustainable traditional shifting cultivation system. The reported experiment was conducted from 1993 to 1996 in fallow plots established in 1989 to rehabilitate a degraded Alfisol after 10 years of continuous cultivation of maize/cassava. Treatments consisted of four plots each of woody legume species ( Acacia auriculiformis, A. leptocarpa, Leucaena leucocephala , and Senna siamea ), and a herbaceous legume cover crop ( Pueraria phaseoloides ). Two controls (natural bush fallow and continuous maize/cassava) were included. Each treatment was cleared and cultivated in 1993 and 1995 (after 4 and 6 year fallow). Cultivation was repeated in 1994 for plots cleared in 1993 and in 1996 for subplots cleared in 1995. In all the years, weed density and dry weight was lower in planted fallows than in the controls. Per capita weed population growth rate decreased in all the fallow treatments most notably in A. auriculiformis and S. siamea fallow. All fallow species except A. auriculiformis would require more than 6 years of fallow to prevent growth of the weed population over the long term. The weed seed bank was 75% lower in A. auriculiformis and P. phaseoloides fallow than the control plots. Canonical correspondence and redundancy analysis indicated differences in species composition between treatments in the aboveground weed flora and in the weed seed bank. Cynodon dactylon and Digitaria horizontalis dominated continuously cultivated maize/cassava plots. Chromolaena odorata occurred more in natural bush fallow. In contrast, annual broadleaf weeds dominated the planted fallow treatments. Die Einsatz von stickstoffbindenden Baumen und Bodenbedeckungspflanzen zur Unkrautbekampfung in kleinbauerlichen Anbausystemen ist eine vielversprechende Alternative zum traditionellen Wanderfeldbau. Zwischen 1993 und 1996 wurde auf einem degradierten Alfisol ein Feldversuch durchgefuhrt, mit dem Ziel, den Einfluss von verschiedenen Brachesystemen auf den Unkrautbefall zu ermitteln. Die Versuchsflache hatte seit 1989 brachgelegen, zwischen 1979 und 1989 wurde die Flache alljahrlich zum Anbau von Mais und Maniok genutzt. Der Versuch beinhaltete funf Behandlungen mit verbesserter Brache: Acacia auriculiformis , A. leptocarpa , Leucaena leucocephala und Senna siamea als Baumleguminosen and Pueraria phaseoloides als stickstoffbinden Bodenbedecker. Als Kontrollbehandlungen dienten Naturbrache und jahrlicher Anbau von Mais/Maniok. Alle Parzellen wurden nach 4- und 6-jahriger Brache in 1993 and 1995 kultiviert, die Bodenbearbeitung auf diesen Parzellen wurde jeweils im folgenden Jahr wiederholt. In allen Jahren waren die Unkrautdichte und Unkrauttrockenmasseertrage in den Baum- und P. phaseoloides Parzellen geringer als in den Kontrollparzellen. Die Abnahme war deutlich niedriger in A. auriculiformis und in S. siamea . Mit Ausnahme von A. auriculiformis , wurden alle verbesserten Brachesysteme mehr als 6 Jahre benotigen, um die Wachstumrate der Unkrautpopulation zu hemmen. Die Unkrautsaatgutdichte im Boden war 75% niedriger in A. auriculiformis und in P. phaseoloides Parzellen als in der Kontrolle. Canonical Korrespondenz- und Redundanzanalysen zeigten, dass die Behandlungen die Zusammensetzung der Unkrautarten sowie die Unkrautsaatgutdichte beeinflussten. Cynodon dactylon und Digitaria horizontalis waren die dominanten Arten in den Parzellen, auf denen jahrlich Mais/Maniok angebaut wurde. Chromolaena odorata war die dominante Art in Parzellen mit Naturbrache wahrend einjahrige, zweikeimblattrige Unkrautarten in den verbesserten Bracheparzellen vorherrschend waren.

Cover crops reduce weed seedbanks in maize–cassava systems in southwestern Nigeria

Abstract Weeds are a major constraint to crop production in smallholder farms in tropical Africa. The weed seedbank and annual recruitment are the main sources of weed infestation in crops. This study was carried out in Ibadan, Nigeria, to evaluate the effect on the seedbank of two types of planted fallow (alley cropping with leucaena and live mulch with tropical kudzu) and a natural bush fallow under four land-use intensities. Type of fallow was the main plot. Land-use intensities, consisting of continuous cropping of maize intercropped with cassava, 1 cropping yr of maize–cassava followed by 1, 2, and 3 yr of fallow, were the subplots. Averaged over a 3-yr period, the seedbank was 55% lower in the tropical kudzu plots and 43% lower in the leucaena plots compared with natural bush. The difference in seedbanks between plots cultivated after leucaena and natural fallow was 23%. Seed density of annual broadleaf weeds was high and dominated the seedbank of both planted and natural fallow. Overall, seeds of grasses occurred at low densities in all plots cultivated after 2 to 3 yr of fallow, whereas seeds of sedges occurred more in continuously cultivated plots and plots cultivated after 1 yr of fallow in all the fallow types. Seed density of perennial broadleaf weeds increased as land-use intensity decreased. Live mulch with tropical kudzu, especially when combined with 2 to 3 yr of fallow, lowered the seedbank more than the leucaena and traditional bush fallow systems. Nomenclature: Leucaena, Leucaena leucocephala (Lam.) de Wit LUAGL; tropical kudzu, Pueraria phaseoloides (Roxb.) Benth. PUEPH; cassava, Manihot esculenta Crantz; maize = corn, Zea mays L.