Improved fallows or the rotation of fast growing nitrogen-fixing legume species with cereals have been shown to accumulate nitrogen and organic matter, recycle nutrients in the soil and improve soil physical and chemical properties, and increase crop yield compared to traditional fallows. However, the effect of soil nutrients added by fallow species on the incidence of pests, weeds and pathogens in the subsequent crop has not been assessed in southern Africa. In this study, we assessed the relationships between nutrients in the soil after fallows of crotalaria (Crotalaria grahamiana), pigeon pea (Cajanus cajan), sesbania (Sesbania sesban), tephrosia (Tephrosia vogelii), and their mixtures, and the incidence of soil insects, namely, snout beetles (Diaecoderus sp.) and termites, and weeds in eastern Zambia. Rotational fallows of sesbania+crotalaria, sesbania+tephrosia, sesbania+pigeon pea and tephrosia+pigeon pea increased infestation of maize by snout beetles as compared to the natural fallow or unfertilised maize grown continuously in monoculture. The beetles showed aggregated spatial distribution, influenced mainly by the nitrate and total inorganic nitrogen content of the soil. Termite incidence was higher in maize after a natural fallow and pure crotalaria, which had 11 and 7 times as much damage as maize planted after pigeon pea+tephrosia mixture. Total weed biomass in maize grown after a natural fallow was six times higher than in maize planted after pure sesbania fallows. The weed biomass was correlated positively with the potassium content of the top 20 cm soil and negatively with plant litter on the soil surface. It is concluded that organic inputs from pure sesbania, sesbania+pigeon pea, sesbania+tephrosia and tephrosia+pigeon pea reduce infestation by termites and weeds, and give maize grain yield comparable with the recommended rates of inorganic fertilisers. However, these fallows have the potential to increase infestation by snout beetles. This is the first study on the snout beetle in Africa, and we recommend more systematic investigation on its ecology in agroforestry systems.
Tag: cajanus cajan
Tree and crop productivity in gliricidia/maize/pigeonpea cropping systems in southern Malawi
This study examined the hypothesis that incorporation of Gliricidia sepium (Jacq.) Walp.) (gliricidia), a fast-growing, nitrogen-fixing tree, into agroforestry systems in southern Malawi may be used to increase the input of organic fertilizer and reduce the need for expensive inorganic fertilizers. The productivity of maize (Zea mays L.), pigeonpea (Cajanus cajan L.) and gliricidia grown as sole stands or in mixed cropping systems was examined at Makoka Research Station (latitude 15° 30 S, longitude 35° 15 E) and a nearby farm site at Nazombe between 1996 and 2000. Treatments included gliricidia intercropped with maize, with or without pigeonpea, and sole stands of gliricidia, maize and pigeonpea. Trees in the agroforestry systems were pruned before and during the cropping season to provide green leaf manure. Maize yields and biomass production by each component were determined and fractional light interception was measured during the reproductive stage of maize. Substantial quantities of green leaf manure (2.4 to 9.0 Mg ha1 year1) were produced from the second or third year after tree establishment. Green leaf manure and fuelwood production were greatest when gliricidia was grown as unpruned sole woodlots (c. 8.0 and 22 Mg ha1 year1 respectively). Improvements in maize yield in the tree-based systems also became significant in the third year, when c. 3.0 Mg ha1 of grain was obtained. Tree-based cropping systems were most productive and exhibited greater fractional light interception (c. 0.6 to 0.7) than cropping systems without trees (0.1 to 0.4). No beneficial influence of pigeonpea on maize performance was apparent either in the presence or absence of gliricidia at either site in most seasons. However, as unpruned gliricidia provided the greatest interception of incident solar radiation (>0.9), coppicing may be required to reduce shading when gliricidia is grown together with maize. As pigeonpea production was unaffected by the presence of gliricidia, agroforestry systems containing gliricidia might be used to replace traditional maize + pigeonpea systems in southern Malawi.
Legumes for improving maize yields and income in semi-arid Kenya
An experiment was conducted at the research station of the International Centre for Research in Agroforestry (ICRAF) at Machakos, Kenya from November 1989 to February 1996 to evaluate the effect of annual and perennial legumes on soil fertility, cereal yields and economic returns. The study evaluated six cropping systems: (1) continuous sole maize, (2) maize rotated with short-duration legume, cowpea (Vigna unguiculata L. Walp.), (3) maize rotated with long-duration legume, pigeonpea (Cajanus cajan L. Millsp.), (4) maize intercropped with pigeonpea, (5) hedgerow intercropping of maize and a perennial legume, gliricidia (Gliricidia sepium), and (6) continuous sole maize, green-manured with gliricidia prunings produced from an equivalent area outside the cropped field (‘biomass transfer technology’). Maize–cowpea sequential and pigeonpea/maize intercropping systems produced, respectively, 17 and 24% higher maize yields than continuous sole maize, but maize–pigeonpea rotation yielded only marginally better. Hedgerow intercropping did not increase maize yields because increased yields during the few high rainfall seasons did not compensate the yield losses in other seasons due to the competition of hedgerows for water with crop. Green manuring with gliricidia prunings increased maize production by 27%, but this technology was not economical because of high labour costs for production and application of prunings to the crop. The annual grain legume-based cropping systems were 32–49% more profitable than continuous sole maize, making them attractive to small farmers in semi-arid tropics. Both cowpea and pigeonpea were affected by pests and diseases, which indicated the need for integrated pest management for realising the potential benefits of these legume-based systems.
Farmer assessment and economic evaluation of shrub fallows in the Humid Lowlands of Cameroon
Food crop production in highly populated areas around major cities of the humid lowlands of Cameroon is highly dependent on a fallow system (two–four years duration) mainly of Chromolaena odorata. Where such fallows have been in use for some time, problems of soil fertility with declining crop yields and higher incidence of weeds were reported. Although improved fallows have been widely adopted in sub-humid zones, there is no evidence of successful adoption of agroforestry-based technologies for soil fertility improvement in the humid forest areas. In response, ICRAF has developed a short fallow system with Cajanus cajan for soil fertility improvement in the humid lowlands of West Africa. Farmers’ response to these cajanus fallows is positive. Benefits reported are higher crop yields after cajanus fallows compared to natural fallows, clearing of cajanus is easier and the shrubs shade out the weeds. Women particularly appreciate the technology for its low labour demand and for the fact that these shrubs can be planted on land with less secure tenure. Economic analysis of cajanus fallows compared to natural fallow over six years shows that cajanus fallows are profitable under most tested scenarios, both in terms of returns to land and to labour. It seems that improved fallows with Cajanus cajan are a good response to shortening natural fallows for households in the humid lowlands of Cameroon with land constraints. However, wider dissemination of the technology requires a targeted extension approach and adequate seed supply strategies, which should be based on joint efforts between farmers, extension services and research.
Multipurpose tree prunings as a source of nitrogen to maize under semiarid conditions in Zimbabwe. 1. Nitrogen-recovery rates in relation to pruning quality and method of application
Decomposition- and N-mineralization rates of multipurpose tree prunings applied as a source of N to annual crops in agroforestry systems are affected by the chemical composition and method and time of application of the prunings and the soil type. In a greenhouse study undertaken on two contrasting Zimbabwean soils, there was a significant interaction of pruning quality with time and method of pruning application on nitrogen recovery by maize and residual effects on a subsequent maize crop on both soil types. Incorporating prunings in the soil at planting gave higher nitrogen recovery compared to surface application at two or four weeks after planting for all three MPT species used.Flemingia macrophylla showed prolonged N immobilization on an Alfisol (sandy clay loam) but not on the Psamment (sandy soil). Nitrogen recovery by the second maize crop (residual effect) was influenced by pruning quality, time of application, and soil type. Low-quality prunings such asFlemingia macrophylla andAcacia angustissima applied four weeks after planting gave higher residual effect on N recovery on the Alfisol than on the Psamment (3% vs. 6%).