Nitrogen Dynamics in Cropping Systems in Southern Malawi Containing Gliricidia sepium, Pigeonpea and Maize

This study tested the hypothesis that incorporation of green leaf manure (GLM) from leguminous trees into agroforestry systems may provide a substitute for inorganic N fertilisers to enhance crop growth and yield. Temporal and spatial changes in soil nitrogen availability and use were monitored for various cropping systems in southern Malawi. These included Gliricidia sepium (Jacq.) Walp. trees intercropped with maize (Zea mays L.), with and without pigeonpea (Cajanus cajan L.), sole maize, sole pigeonpea, sole gliricidia and a maize + pigeonpea intercrop. Soil mineral N was determined before and during the 1997/1998, 1998/1999 and 1999/2000 cropping seasons. Total soil mineral N content (NO₃⁻ + NH₄⁺) was greatest in the agroforestry systems (p<0.01). Pre-season soil mineral N content in the 0–20 cm horizon was greater in treatments containing trees (≤85 kg N ha⁻¹) than in those without (<60 kg ha⁻¹; p<0.01); however, soil mineral N content declined rapidly during the cropping season. Uptake of N was substantially greater in the agroforestry systems (200–270 kg N ha⁻¹) than in the maize + pigeonpea and sole maize treatments (40–95 kg N ha⁻¹; p<001). Accumulation of N by maize was greater in the agroforestry systems than in sole maize and maize + pigeonpea (p<0.01); grain accounted for 55% of N uptake by maize in the agroforestry systems, compared to 41–47% in sole maize and maize + pigeonpea. The agroforestry systems enhanced soil fertility because mineralisation of the applied GLM increased pre-season soil mineral N content. However, this could not be fully utilised as soil N declined rapidly at a time when maize was too small to act as a major sink for N. Methods for reducing losses of mineral N released from GLM are therefore required to enhance N availability during the later stages of the season when crop requirements are greatest. Soil mineral N levels and maize yields were similar in the gliricidia + maize and gliricidia + maize + pigeonpea treatments, implying that addition of pigeonpea to the tree-based system provided no additional improvement in soil fertility.     

Influence of Agroforestry and Traditional Management of Maize (Zea mays L.) on Soil Fertility

The aim of the work was to evaluate soil nutrient concentration at 0–5, 5–10, and 10–20 cm in maize (Zea mays L.) grown in sequence with black oats (Avena strigosa Schreb.) under Leucaena diversifolia alley cropping agroforestry system (AFS) and traditional management system/sole crop (without trees–TS), following a randomized block design. The experiment was carried out at the Brazilian Association of Biodynamic Agriculture, in Botucatu, São Paulo, Brazil. The treatments were: control (C), chemical fertilizer (F), biomass of L. diversifolia alley cropping (B), and biomass of L. diversifolia alley cropping + chemical fertilizer (B+F).

After 2 yr, it was observed that pH, organic matter, and nutrient content had a tendency to show higher values in the treatments biomass+fertilizer, biomass, and fertilizer application, in both systems. Higher values in pH, organic matter, phosphorus, potassium, calcium, magnesium, sum of bases, cation exchange capacity, percentage base saturation, boron, copper, and manganese tended to occur in the agroforestry system.     

Distribution of mycorrhizal fungal spores in soils under agroforestry and monocultural coffee systems in Brazil

Deep-rooting trees in agroforestry systems may promote distribution of spores of arbuscular mycorrhizal fungi (AMF) at deeper soil levels. We investigated the vertical distribution of AMF spores in Oxisols under agroforestry and monocultural (unshaded) coffee systems in on-farm experiments (Brazil). The number of AMF spores was considered as an indicator of mycorrhiza incidence in soil. Spores were extracted from 0–1, 2–3, 5–7.5, 10–15, 20–30, 40–60 cm soil-depths in agroforestry and monocultural coffee systems, of three different age groups (young, medium-aged and old), using centrifugation methods, and counted. Fine roots were collected and dry-weighed from 0–30 cm in young and old systems and from several depths in medium-aged systems. Soils were characterised with respect to texture, pH, organic matter, calcium, magnesium, phosphorus and potassium. Agroforestry had a higher percentage of spores (12–21% of the total number of spores) and roots (on average 1.5 g L^–1 soil) in deeper layers (20–60 cm), and a lower percentage (79–88%) closer to the surface (0–15 cm) than the monocultural fields (respectively 3–12%, 0.6 g L^–1 soil and 88–97%). Greater numbers of spores in the deeper soil layers may be explained by greater amounts of roots and may be an indicator of greater incidence of mycorrhiza in agroforestry than in monocultural coffee systems. Greater mycorrhizal incidence at deeper soil layers in the agroforestry system may change the dynamics of phosphorus cycling in soil, making this nutrient more available to plants.This revised version was published online in November 2005 with corrections to the Cover Date.     

Partitioning of applied <Superscript>15</Superscript>N fertilizer in a longleaf pine and native woody ornamental intercropping system

The cultivation of ornamentals to produce woody floral products—the fresh or dried stems that are used for decorative purposes—may be an attractive option for southeastern landowners looking to generate income from small landholdings. Since many shrubs native to the understory of the longleaf pine (Pinus palustris Mill.) ecosystem have market potential, one possibility is the intercropping of select species in the between-row spacing of young longleaf pine plantations. The objective of this study was to evaluate how interspecific competition affects the fate of ¹⁵N fertilizer when American beautyberry (Callicarpa americana L.), wax myrtle (Morella cerifera (L.) Small) and inkberry (Ilex glabra (L.) A.Gray) are intercropped with longleaf pine. Nitrogen derived from fertilizer (NDF), utilization of fertilizer N (UFN) and recovery of fertilizer N (RFN_soil) were compared between agroforestry and monoculture (treeless) treatments to assess the effects of competition. Results varied by species, with NDF being higher for C. americana foliage and lower for all M. cerifera tissues in the agroforestry treatment. No effect was observed for I. glabra. UFN was lower for all species in the agroforestry treatment. RFN_soil was higher in the agroforestry treatment for I. glabra, but no treatment effects were observed for C. americana or M. cerifera. Overall, while it is clear that interspecific competition was present in the agroforestry treatment, the inefficiency of fertilizer use suggests that nitrogen was not the most limiting resource. Management interventions, particularly those that address competition for water, will likely be critical to the success of this system.     

Arbuscular mycorrhizal symbioses in a cut-and-carry forage production system of legume tree Gliricidia sepium and fodder grass Dichanthium aristatum

Arbuscular mycorrhizal (AM) symbioses may alter the competitive abilities of plant species and facilitate positive interactions such as nutrient transfer between plants. They are therefore particularly interesting components in agroforestry systems. We studied spatial variation of AM colonisation on a cut-and-carry fodder production site (agroforestry plot) of the legume tree Gliricidia sepium and the fodder grass Dichanthium aristatum. Roots of the two plant species were sampled under the tree canopies and on the adjacent grass plot at 1 and 3.5 m from the first tree row where G. sepium roots also occur. Roots of D. aristatum were also sampled on a nearby grass monocrop. Colonisation of arbuscules, vesicles and hyphae in root samples was visually determined, and AM fungal species were identified by DNA sequencing. Colonisation and frequency of types of AM formations varied statistically significantly between the species and sampling points. Arbuscular colonisation in G. sepium roots was higher under the tree canopies than on the adjacent grass plot. Soil nutrient content, particularly P and N, and interspecies competition are the most probable explanations for the observed variation in AM colonisation. Both arbuscular colonisation and arbuscule:vesicle ratio in D. aristatum roots was lower on the D. aristatum monocrop than on the agroforestry plot under or near the tree canopies. Intercropping could stimulate AM symbiosis in D. aristatum. Both plant species formed symbiosis with Rhizophagus intraradices, indicating potential for interplant N transfer via common mycelial networks of AM-forming fungi.     

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 ha⁻¹ with corresponding water use efficiencies of 4.3, 8.8 and 1.7 kg mm⁻¹ ha⁻¹, 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. This revised version was published online in June 2006 with corrections to the Cover Date.     

Alley cropping of maize with nine leguminous trees

A maize-leguminous tree alley cropping system was studied on N-deficient soils in Hawaii to determine mulch effects on maize yields. Calliandra calothyrsus, Cajanus cajan, Cassia siamea, Gliciridia sepium, KX1 — Leucaena hybrid (L. pallida X L. diversifolia), L. leucocephala, L. pallida, L. salvadorensis, and Sesbania sesban were evaluated for green manure and yield of intercropped maize. S. sesban, G. sepium, L. pallida, and KX1 produced between 5 and 12 dry t/ha/yr green manure with nitrogen yields between 140 and 275 kg N/ha in 4 prunings. Maize yields responded linearly to nitrogen applied as green manure. Maize yield increased 12 kg for each kg of nitrogen applied. Additions of prunings from hedge rows were able to support maize grain yields at about 1800 kg/ha for two consecutive cropping seasons, while control plot yields averaged less than 600 kg/ha. Maize yields reflected the amount of nitrogen applied as green manure, regardless of tree species from which the nitrogen was derived. In March, maize yields decreased 34% in the row spaced 40 cm from the hedge, relative to the one spaced 110 cm away. In July, increasing the distance away from the hedge to 60 cm and coppicing the hedge earlier in maize growth, significantly improved grain yield. Grain yields decreased only 10% in the row closest to the trees.     

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 ha⁻¹ year⁻¹) 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 ha⁻¹ year⁻¹ respectively). Improvements in maize yield in the tree-based systems also became significant in the third year, when c. 3.0 Mg ha⁻¹ 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. This revised version was published online in June 2006 with corrections to the Cover Date.     

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 ha^–1, in factorial combination with inorganic N fertilizer at 0 or 48 kg N ha^–1 (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 (r ² = 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.This revised version was published online in November 2005 with corrections to the Cover Date.     

Comparative growth performance of some multipurpose trees and shrubs grown at Machakos,Kenya

Growth rates of 29 multipurpose trees grown in an agroforestry arboretum for six years at a sub-humid to semi-arid climatic zone are presented. Exotic species such as Grevillea robusta, Sesbania grandiflora, Leucaena leucocephala, Cassia siamea and Sesbania sesban, some of which were outside their traditional climatic zones, had higher diameters, heights and bole volumes/tree (upto 130% more in certain cases) than of the indigenous species. However, poor performance of several species (both exotic and indigenous) would limit their agroforestry potentials at the evaluation site or other similar areas.     

A seedling inoculation test for screening Sesbania sesban for resistance to the seedling defoliator, Mesoplatys ochroptera

The seedling beetle Mesoplatys chroptera is a serious pest of Sesbania sesban and other Sesbania spp. that are important agroforestry species. Sesbania sesban was compared to Sesbania micrantha, Sesbania goetzi and Sesbania cinerascens, in a seedling inoculation test for resistance to Mesoplatys ochroptera using copulating adult instars as inoculum. The uniform susceptibility of Sesbania sesban including accessions from western Kenya was confirmed. But S. cinerascenswas found to be resistant to the pest. This revised version was published online in June 2006 with corrections to the Cover Date.     

The root-knot nematode problem in sesbania fallows and scope for managing it in western Kenya

Sesbania (Sesbania sesban), which is promoted as a short-duration-fallow species in eastern and southern Africa, is an alternative host to root-knot nematode (Meloidogyne spp.). Therefore, it is important to know the extent of sesbania infection by the nematode on farms and its effects to crops grown in rotation with sesbania. A survey of 14 farms in western Kenya indicated that sesbania was infected by root-knot nematode in all the farms. The potential to build up the nematode population was much greater on farms where maize (Zea mays) was previously intercropped with a susceptible bean (Phaseolus vulgaris). Screening of 30 single plant accessions of four sesbania provenances (Kakamega, Siaya, Kisumu, and Kisii) from western Kenya in pots indicated limited scope for selecting material resistant to the nematode. All four provenances were infested by the nematode, and they increased its population in soil and root. A rangewide collection of sesbania germplasm needs to be screened to determine the scope of finding nematode-resistant material. Transplanted seedlings produced in heat-sterilized, nematode-free soil showed less nematode infection than direct-seeded plants. However, both direct seeding and transplanting seemed to increase nematode population similarly. A number of Crotalaria spp. that were found resistant to nematodes can be considered as alternatives to sesbania-planted fallows, but further field-scale testing is necessary to select appropriate species based on biomass production. Among other species suitable for short-duration fallows, only pigeonpea (Cajanus cajan) and senna (Senna siamea) showed promise. Species such as neem (Azadirachta indica), casuarina (Casuarina junghuhniana), and grevillea (Grevillea robusta) that are suitable for boundary plantings were free from the root-knot nematode.This revised version was published online in November 2005 with corrections to the Cover Date.     

Maize and sesbania production in relay cropping at three landscape positions in Malawi

The relay cropping of sesbania (Sesbania sesban) — a N₂-fixing legume — with maize (Zea mays) has been proposed as a strategy to increase soil fertility and food production in densely populated areas in southern Africa. We determined the production of relay-cropped maize and sesbania at three landscape positions under researcher-designed and farmer-managed conditions in southern Malawi. Three landscape positions (dambo valley or bottomland, dambo margin with < 12% slope, and steep slopes with > 12% slope) were examined in factorial combination with N sources for maize (no added N, relay-cropped sesbania, and calcium ammonium nitrate fertilizer). Relay cropping of sesbania with maize increased maize grain yield, as compared to unfertilized sole maize in two of three years. Split application of 96 kg N ha^–1 as N fertilizer, however, was more effective than sesbania in increasing maize yields. Survival of sesbania seedlings and biomass production of sesbania were greater in the dambo valley and dambo margin than on steep slopes. Maize yields tended to be lower on steep slopes than in the dambo valley and dambo margin areas. Biomass production of sesbania and hence the potential benefits of intercropping sesbania with maize appear greater in the dambo valleys and dambo margins than on steep slopes.This revised version was published online in November 2005 with corrections to the Cover Date.     

Land-use effects on phosphorus fractions in Indo-Gangetic alluvial soils

Phosphorus (P) in soil exists both in organic and inorganic forms and their relative abundance could determine P supplying capacity of soil. Differential input of exogenous and plant-mediated phosphorus and carbon in soil under different land-uses could influence P availability and fertilizer P management. While the effect of land-use on soil organic carbon (SOC) is fairly well-documented, its effect on soil P fractions is relatively less known. We investigated the effect of different land-uses including rice–wheat, maize–wheat, cotton–wheat cropping systems and poplar-based agroforestry systems on soil P fractions and organic carbon accrual in soils. Total P concentration was the highest under agroforestry (569 mg P kg^?1) and the lowest under maize–wheat (449 mg P kg^?1) cropping systems. On the contrary, soils under rice–wheat had significantly higher available P concentration than the agroforestry systems, probably because of higher fertilizer P application in rice–wheat and prevailing wetland conditions during rice growth. In soils under sole cropping systems viz. rice–wheat, maize–wheat and cotton–wheat, inorganic P was the dominant fraction and accounted for 92.2–94.6% of total P. However, the soils under agroforestry had smaller proportion (73%) of total P existing as inorganic P. Among soil P fractions, water soluble inorganic P (0.13–0.26%) represented the smallest proportion inorganic P in soils under different land-uses. Agroforestry showed significantly (p < 0.05) higher concentrations of SOC than the other land-uses. Soil organic C was significantly correlated with soil P fractions. It was concluded that poplar-based agroforestry systems besides leading to C accrual in soil result in build-up of organic P and the P supplying capacity of soil.     

Intercropping system of tropical leguminous species and Eucalyptuscamaldulensis, inoculated with rhizobia and/or mycorrhizal fungi in semiarid Brazil

For the purpose of reforestation and wood supply the leguminous tree Anadenanthera peregrina, a native species, was intercropped with Eucalyptus camaldulensis in a degraded semiarid area of Brazil. Single and mixed stands of these species were inoculated with Rhizobium and/or arbuscular mycorrhizal fungi (AMF). The growth of all species in mixed stands did not differ from those cultivated in monoculture and land equivalent ratio (LER) exceeded unity in intercropped plots. Inoculated plants showed greater height and diameter growth and dry matter and nutrient concentration in plants of A. peregrina was higher in inoculated single plots. The distribution, composition and density of AMF species was related to the rhizosphere effect of plant species. The intercropped model where all the plants were inoculated achieved soil AMF diversity patterns similar to those of the preserved area and showed also higher soil organic matter, nutrient content as well as a reduction in soil macroporosity. This model of intercropping may be considered as an efficient system for reforestation under semiarid conditions.     

Cropping System Intensification as a Management Method Against Vectors of Viruses Causing Maize Lethal Necrosis Disease in Kenya

Maize Lethal Necrosis Disease (MLND) has emerged as a great threat to maize production in East Africa. It is caused by a synergistic infection of maize by sugarcane mosaic virus (SCMV) and maize chlorotic mottle virus (MCMV). This study was carried out in Bomet County, Kenya, to determine the potential of various cropping systems to manage vectors of MLND–causing viruses. Plots measuring 7.5 m × 5.25 m were planted with maize (Zea mays L.) intercropped or bordered by elephant grass (Pennisetum purpureum Schumach.), coriander (Coriandrum sativum L.), pearl millet (Pennisetum glaucum (L.) R. Br.) and Gadam sorghum (Sorghum bicolour (L.) Moench). Maize monoculture was used as a control treatment; the nine treatments were arranged in a randomized complete block design and replicated four times for two seasons (December 2014 to April 2015 and April 2015 to September 2015). Data on corn thrips and corn leaf aphid infestation, MLND severity and incidence, MCMV and SCMV viral load, and yield were recorded. The sorghum border was the only companion crop that tested positive for MCMV and none tested positive for SCMV. Maize intercropped with elephant grass had significantly (P?<?0.01) the least incidence of disease. However, this treatment produced significantly lower yields (P?<?0.01). Coriander was the only companion plant most preferred by both corn thrips and corn leaf aphids (P?<?0.001). Maize from all cropping systems tested positive for MCMV (P?<?0.001) while maize grown with coriander tested negative for SCMV (P?<?0.001). Yields from plots surrounded by sorghum and coriander were significantly similar to those from maize monoculture plots. These findings suggest that maize should be intercropped with coriander due to its potential to trap corn leaf aphids and protect maize from SCMV. In addition maize should be grown surrounded by a sorghum border to maximize yield in areas where MLND is prevalent.     

Sesbania sesban improved fallows in eastern Zambia: Their inception, development and farmer enthusiasm

In eastern Zambia, nitrogen deficiency is a major limiting factor for increased food production. Soil fertility has been declining because of nearly continuous maize (Zea mays) cultivation with little or no nutrient inputs. The use of short-duration tree fallows was one of several agroforestry options hypothesized to restore soil fertility. Sesbania sesban, an indigenous N₂-fixing tree was the most promising among species tested in screening trials. Several studies since 1987 have demonstrated the dramatic potential of two- or three-year sesbania fallows in restoring soil fertility and increasing maize yields. Analyses showed that these improved fallow systems were feasible, profitable, and acceptable to farmers. Results suggest that high maize yields following fallows are primarily due to improved N input and availability by the fallows. The potential to increase maize production without applying mineral fertilizers has excited thousands of farmers who are enthusiastically participating in the evaluation of this technology. The number of farmers who are testing a range of improved fallow practices has increased from 200 in 1994 to over 3000 in 1997. Presently, a strong network of institutions comprising government, NGOs, development projects, and farmer organizations is facilitating the adaptive research and expansion of improved fallow technology in eastern Zambia. Key elements in the research process that contributed to the achievements are effective diagnosis of farmers' problems, building on farmers' indigenous knowledge, generating several different fallow options for farmers to test, ex-ante economic analysis, farmer participation in on-farm trials, and development of a network for adaptive research and dissemination.This revised version was published online in November 2005 with corrections to the Cover Date.     

Agroforestry and forestry on the Cape Verde Islands

The geography, socio-economy, climate and agriculture of the Cape Verde Islands are introduced. Forestry and agroforestry provenance trials are described for coastal and inland areas in the semi-arid climate of Cape Verde. Sesbania sesban var. nubica showed promise as a drought tolerant, fast growing agroforestry species and Acacia bivenosa is recommended for soil stabilisation of exposed coastal areas. At a saline coastal site Atriplex lentiformis and A.halimus were the fastest growing of seven Atriplex species.     

Alley cropping on an Ultisol in subhumid Benin. Part 1: Long-term effect on maize, cassava and tree productivity

In southern Benin, West Africa, two alley cropping systems were studied from 1986 to 1992. Yield development was followed in a maize and cassava crop rotation vs. intercropping system, with alleys of Leucaena leucocephala (Lam.) de Wit and Cajanus cajan (L.) Millsp. vs. a no-tree control, with and without NPK fertiliser. Without alleys, NPK fertilisation maintained high yield levels of 2–3 t maize dry grain plus 4–6 t ha^–1 cassava root DM in intercropping, 3–4 t ha^–1 maize and 6–10 t ha^–1 cassava in solercropping. Without NPK, final yields seemed to stabilise at about 1 t maize plus 2 t cassava in intercropping and twice as much in each solecrop. Alley cropping induced significant yield increases by about 50% with both tree species in unfertilised, intercropped maize, and with Cajanus in fertilised, solecropped cassava. In monetary terms, the NPK-fertiliser response of stabilised yields was significant for all treatments except the solecropped Leucaena alleys. It is concluded that on Ultisols with low nutrient status in the upper rooting zone, alley cropping with low-competitive tree species may improve food crop yields but the greatest monetary output is achieved by intercropping with mineral fertiliser independent of the presence or absence of an agroforestry component.     

Screenhouse performance of VAM-inoculated seedlings of Leucaena leucocephala (Lam.) De wit. in a phosphorus-deficient and aluminum sulfate-treated medium

The effect of 3 species of vesicular-arbuscular mycorrhizal (VAM) fungi on the growth of Leucaena leucocephala (Lam.) De Wit. in a phosphorus-deficient and aluminumsulfate (AIS)-treated medium was investigated in a screenhouse experiment. Plant height, root length, nodulation, phosphorus uptake and nitrogen fixation were used as indices of plant performance.While there were significant differences among mycorrhizal plants with respect to these indices, they outperformed their non-mycorrhizal counterparts in all respects except in nitrogen content. Of the 3 mycorrhizal species studied, Glomus etunicatum (Becker and Gerd) was the most efficient, followed by Glomus fasciculatum (Thaxter) Gerd and Trappe, and finally, Gigaspora margarita (Becker and Hall). Both aluminumsulfate and mycorrhizal treatments increased shoot dry weight.