Mesoplatys ochroptera Stål (Coleoptera: Chrysomelidae) is a serious pest of the tropical legume sesbania (Sesbania sesban (L.) Merrill) widely used for soil fertility improvement in southern Africa. Surveys were conducted between October 1997 and June 1999 in order to identify the predators of M. ochroptera in sesbania fallows in eastern Zambia. The Heteroptera Afrius yolofa (Guérin-Méneville), Glypsus conspicuus (Westwood), Macrorhaphis acuta Dallas, Mecosoma mensor (Germar), Rhinocoris segmentarius (Germar), and Deraeocoris ostentans (Stål), the carabid beetle Cyaneodinodes fasciger (Chaudoir), the ants Tetramorium sericeiventre Emery and Pheidole sp., and the lacewing Mallada sp. were recorded as predators of M. ochroptera for the first time. The pentatomid bugs G. conspicuus, M. acuta and M. mensor were the most common predators in sesbania fallows. Adults and the different nymphal stages of the three species preyed on larvae, adults and occasionally on eggs of the beetle. In the insectary, the adults of G. conspicuus, M. acuta and M. mensor consumed a significantly higher number of larvae (p < 0.001) compared to adults of M. ochroptera under both free-choice and no-choice conditions. The voracity of the three species showed a positive response to prey density. The fifth instar nymphs showed variation in daily consumption of larvae, the highest number of prey being consumed two to three days after the fourth molt. These predators also attacked other pests associated with sesbania and crop plants. The potential role of the predators in the natural control of pests in agroforestry systems is discussed, with a review of their prey species.
Tag: fallow
Effect of rotational fallows on abundance of soil insects and weeds in maize crops in eastern Zambia
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.
Water balance and maize yield following improved sesbania fallow in eastern Zambia
Sesbania [Sesbania sesban (L.) Merr.] fallows are being promoted as a means for replenishing soil fertility in N-depleted soils of small-scale, resource-poor farmers in southern Africa. Knowledge of soil water distribution in the soil profile and water balance under proposed systems is important for knowing the long-term implications of the systems at plot, field and watershed levels. Soil water balance was quantified for maize (Zea mays L.) following 2-year sesbania fallow and in continuous maize with and without fertilizer during 1998–1999 and 1999–2000 at Chipata in eastern Zambia. Sesbania fallow increased grain yield and dry matter production of subsequent maize per unit amount of water used. Average maize grain yields following sesbania fallow, and in continuous maize with and without fertilizer were 3, 6 and 1 Mg ha1 with corresponding water use efficiencies of 4.3, 8.8 and 1.7 kg mm1 ha1, respectively. Sesbania fallow increased the soil-water storage in the soil profile and drainage below the maximum crop root zone compared with the conventionally tilled non-fertilized maize. However, sesbania fallow did not significantly affect the seasonal crop water use, mainly because rainfall during both the years of the study was above the normal seasonal water requirements of maize (400 to 600 mm). Besides improving grain yields of maize in rotation, sesbania fallows have the potential to recharge the subsoil water through increased subsurface drainage and increase nitrate leaching below the crop root zone in excess rainfall seasons.
Implications of local policies and institutions on the adoption of improved fallows in eastern Zambia
Planted-tree fallows (syn. improved fallows) have demonstrated great biophysical potential for improving soil fertility on smallholders’ farms but efforts to scale up their adoption to more farming households are constrained by lack of permanent ownership rights over land, incidence of bush fires and browsing of tree biomass by livestock. To resolve these institutional bottlenecks, some traditional authorities in Zambia enacted bylaws to prohibit these incursions. Using a combination of village workshops, expert opinion surveys and structured questionnaires, this study assessed the effectiveness of the bylaws across the major cultural communities in eastern Zambia, identified factors that influence the effectiveness of the bylaws and the lessons emanating from the bylaws in the scaling up of improved fallows. The results indicate that fire poses greater risks to the scaling up of agroforestry than does grazing in terms of the risk of occurrence and the extent of damage. Respondents identified mice hunters and `jealous’ neighbors as main causes of fire outbreaks. The effectiveness of the bylaws is influenced by many factors such as ambiguous interpretation of the bylaws, relying exclusively on moral persuasion to enforce the bylaws and lack of well defined responsibilities for enforcing the bylaws, conflict of economic interests among different stakeholders within the communities. Formal documentation of the bylaws will be helpful, but that would not be an exclusive panacea to solve all the constraints. The pattern of distribution of benefits (or costs) of an agricultural technology among various sectors of a community may be important factors that affect widespread adoption of a technology. Technological characteristics are important but not exclusive condition for sustained widespread adoption of soil fertility management options. Privatizing seasonal commons is an important issue in the development of institutional regulations within communities. Policy dialogue among community members, increased awareness and diversification of options appear to be the way forward to improve the effectiveness of the bylaws.
Tephrosia species and provenances for improved fallows in southern Africa
Seeking an alternative to Sesbania spp. tree fallows, a Tephrosia species and provenance trial was conducted at Msekera Research Station, Chipata (Zambia) to evaluate eleven Tephrosia vogelii and three Tephrosia candida provenances. They were tested for biomass production, quality of biomass, resistance to root-knot nematodes, nitrogen release, and for their effects on soil nitrogen dynamics. At the end of 1.5 years, the T. candida provenances 02970, 02971 and 02972 from Madagascar produced two times greater amount of aboveground biomass than the T. vogelii provenances. There was little variability among the T. vogelii provenances in terms of litter and biomass production. Weed growth was significantly greater under T. vogelii than T. candida provenances. While Tephrosia vogelii provenance 98/02 from Zambia and T. candida 02972 were highly tolerant to the Meloidogyne incognita nematodes, T. vogelii provenances 02977, 98/03, 02973 from Kenya, Zambia and Malawi, respectively, were highly susceptible to the nematodes. The Tephrosia species and provenances showed a wide variability in terms of N, lignin and polyphenol concentration in their foliage. Mineralization of N in the foliage of T. candida provenances 02970 and 02971 and T. vogelii provenances 98/04 and 02974 from Malawi occurred rapidly within 14 weeks of incubation. At the end of the 2-year growth period, there was significantly greater total inorganic N under T. candida provenance 02972 (12.5 mg kg1) than T. vogelii (5 mg kg1) provenance Mungwi 98/02. Maize (Zea mays L.) yields after T. candida provenances were greater than those after T. vogelii provenances. Further testing of the most promising provenances is needed for their effects on subsequent maize yields under a range of farm conditions.
Adoption of improved fallow technology for soil fertility management in Zambia: Empirical studies and emerging issues
In the subsistence-agricultural region of eastern Zambia, less than 10% of the households have adequate supply of maize (Zea mays L.), the staple food, throughout the year. A major constraint to increasing crop production in the region is poor fertility status of the soil. In order to address this problem, improved fallow has been introduced as a technology for improving soil fertility within a short span of two to three years. Farmers have been testing the technology and a number of empirical studies have been undertaken over the years to identify the factors influencing farmers’ decision to adopt the technology. This paper presents a synthesis of the results of adoption studies and highlights generic issues on the adoption of improved fallows in Zambia. The synthesis indicates that farmers’ decision on technology adoption does not have a simple directed relationship of some technological characteristics only, but constitutes a matrix of factors including household characteristics, community level factors, socioeconomic constraints and incentives that farmers face, access to information, local institutional arrangements and macro policies on agriculture. The adoption of improved fallows is not strictly speaking a binary choice problem but a continuous process in which farmers occupy a position along a continuum in the adoption path. Further, adoption of improved fallows may not take place in a policy vacuum but needs to be facilitated by appropriate and conducive policy and institutional incentives. Several questions and issues that require further study emerge from the synthesis. These include determination of the relative importance of the factors in the adoption matrix, identification of the conditions under which farmers use a combination of inputs and their profitability under changing price scenarios, exact definition to delineate between `non-adopters’, `testers’ and `adopters’ of agroforestry technologies, and understanding the impact of cash crop farming in farmers’ adoption decisions of improved fallows (where off farm opportunities exist). Further, there is a need to determine the inter-relationship between household poverty, labor availability and the adoption of improved fallows and, to evaluate a combination of policy interventions at both national and local level to promote the adoption of agroforestry-based soil fertility management.
Effect of field establishment methods on root-knot nematode (Meloidogyne spp) infection and growth of Sesbania sesban in western Kenya
Pot studies indicated that root-knot nematode (Meloidogyne javanica) infection reduces sesbania (Sesbania sesban) growth and planting methods modify the nematode damage, but their effects on sesbania biomass production at the field scale are not known. A field study was conducted in western Kenya for 2 yr, comparing direct seeding of sesbania with transplanting of bare-rooted seedlings in pure stands, with and without nematicide application in the field and in the nursery. In moist conditions, neither planting method nor nematicide had any influence on seedling survival and early growth. When early season rainfall was low and erratic, transplanted seedlings survived and grew better than seedlings from direct sowing, and nematicide application in the field and/or nursery improved seedling survival. Direct seeded sesbania had significantly less nematode galling and smaller nematode populations in the roots than transplanted sesbania. Both the establishment methods produced similar quantities of biomass, but direct seeded sesbania produced significantly greater biomass than the transplanted crop, if seedlings were already infected with nematodes in the nursery. Nematode infection on average reduced total sesbania biomass by 19%. Where sesbania cover crops have to be established by transplanting for socio-economic reasons, it is essential to use healthy seedlings free from nematodes for a good plant stand and early growth. Nematode-free seedlings can be produced on farms by at least one month of solarization of seedbeds. Neither field establishment method, nor nematicide application altered the soil nematode populations over a 12-month period. This means that the potential threat of increased Meloidogyne populations to nematode-susceptible crops following sesbania cover crops remains the same irrespective of how sesbania is established.
Adoption of improved fallows in the Nyando basin and lessons from eastern Kenya
Approaches to improved fallows and N-fixing herbaceous and fodder species in the Nyando Basin have been disappointing. Short-term fallows might therefore be inadequate to rehabilitate the severely degraded soils in Nyando. Indeed, there is no difference in maize yields from 4 years of sequential improved fallows and from a control maize crop, and projections show a declining trend, implying that coppicing fallows are a better option (Girma et al). But Gacheru and Noordin aver that maize inter-planted with mixed fallows performs better than maize alone. However, it is not easy to show the effect of improved fallows on yields because of other factors leading to controversies around improved fallows. Also, the effect of fallows on striga was difficult to capture because of poor establishment as a result erratic rainfall, browsing of the fallows by livestock, and pests and diseases. We therefore need a multidisciplinary approach to address issues such as how to assess impacts and yield, who does this assessment, identify the best way forward with improved fallows, and what baskets of options/technologies can be offered to farmers for different objectives. The analysis/synthesis should also include a candid and objective self-appraisal on the basis of scientific measures of the costs (labor included) and benefits of improved fallows. Agroforestry may not be or is not a panacea for all places and more knowledge is needed on different fanning systems. To help inform this debate more, work by Walsh, Hailu and Verchot on effects of tree legume fallows on maize yields in Eastern and Southern Africa should be appropriately documented. The ARIDSAK project success in Eastern Kenya is due to an integrated, collaborative, multi-disciplinary, participatory, and inclusive approach, and incorporation of training and field visits (farmer-to-fanner challenges). Drawbacks include wildlife and roaming livestock, unfavorable climate conditions, inadequate staff, resource poverty of farmers and socio-cultural factors. The field visit to Kibwezi was a revelation to ICRAF staff working in western Kenya, and it exposed them to different ways of doing things (presenting baskets of options/processes to farmers, flexible and adaptive implementation approaches and good researcher-farmer linkages. A key lesson was the breakthrough transformation of the formerly pastoral Maasai to adopt live fences, fodder trees, seeds, and vegetables production. This approach is useful and can be applied to lead Nyando farmers away from unprofitable maize to activities that are more productive. Participants found the meeting very constructive as a first forum for critical assessment of improved fallows, with open discussion of pertinent questions and issues, including negative aspects. We need an integrated approach because cunently we are only dealing with one aspect (improved fallows) YET farmers are multi-objective. As researchers, we can bonow a leaf from the farmers and think more broadly, work as a team, and investigate and remove the research -extension disconnects. This should lead to design and delivery of appropriate basket(s) of options to farmers, covering various aspects such as soil fertility, fodder, firewood and erosion control. Before the TransVic Project Second Phase, we need to discern /determine: 1) what works; 2) where it works; 3) what can or should be done; and 4) especially; do we need more research Transvic project could be more effective in Nyando if the project incorporates farmer perspectives and integrated production approaches, as is the case with ARIDSAK project.
Diversity of plant-parasitic nematodes and their relationships with some soil physico-chemical charateristics in improved fallows in western Kenya
A survey was conducted in the food crop production area of western Kenya to characterise the nematode communities in different cropping systems and to monitor the effect of improved fallows on the abundance, diversity and community structure of plant-parasitic nematode assemblages. Soil samples were taken from short-term natural fallows (20 years), maize/beans cultivated fields and improved fallows with Crotalaria grahamiana, Sesbania sesban and Tephrosia vogelii. The Shannon diversity index and evenness were used to assess nematode diversity in the different cropping systems. The relationships between plant-parasitic nematodes and the soil physico-chemical properties were investigated with principal component analysis and co-inertia analysis.Planting trees/shrubs as improved fallows in croplands dramatically increased the populations of nematodes in the soil. However, the diversity of plant-parasitic nematodes was reduced. The distribution of plant-parasitic nematodes was correlated with that of some soil physical and chemical properties. Scutellonema spp. were dominant in the improved fallows where the highest values of magnesium and potassium were recorded. The plant-parasitic Dorylaimida (Xiphinema spp. and Paratrichodorus minor) were more abundant in the maize/beans plots and this abundance seemed related to high soil bulk density. Meloidogyne spp. and Rotylenchulusborealis had a strong positive correlation with soil organic matter and clay, and were abundant in the long-term natural fallows.The correlations between soil physico-chemical properties and nematodes indicate that, apart from the direct influence of the host plant, the soil characteristics play an important role in the abundance, distribution and structure of nematode communities. This validates the potential of nematodes as bio-indicator organisms of soil status.
Dry-season sesbania fallows and their influence on nitrogen availability and maize yields in Malawi
Nitrogen deficiency is widespread in southern Africa, but inorganic fertilizers are often unaffordable for smallholder farmers. Short-duration leguminous fallows are one possible means of soil fertility restoration. We monitored preseason topsoil (0 to 20 cm) ammonium and nitrate, fallow biomass production and grain yields for three years in a relay cropping trial with sesbania [Sesbania sesban (L.) Merr.] and maize (Zea mays L.). Sesbania seedlings were interplanted with maize during maize sowing at 0, 7400 or 14,800 trees ha1, in factorial combination with inorganic N fertilizer at 0 or 48 kg N ha1 (half the recommended rate). After maize harvest, fallows were allowed to grow during the seven-month dry season, and were cleared before sowing the next maize crop. Both sesbania fallows and inorganic N fertilizer resulted in significantly greater (P < 0.01 to 0.05) preseason topsoil nitrate-N than following unfertilized sole maize. In plots receiving no fertilizer N, preseason topsoil inorganic N correlated with maize yield over all three seasons (r2 = 0.62, P < 0.001). Sesbania fallows gave significantly higher maize yields than unfertilized sole maize in two of three years (P < 0.01 to 0.05). Sesbania biomass yields were extremely variable, were not significantly related to sesbania planting density, and were inconsistently related to soil N fractions and maize yields. Short-duration fallows may offer modest yield increases under conditions where longer duration fallows are not possible. This gain must be considered against the loss of pigeonpea (Cajanus cajan L. Millsp) harvest in the similarly structured maize-pigeonpea intercrop common in the region.