Intercropped Species Research Articles

An Appraisal of Farmers’ Termite Control Methods in Some Traditional Cropping Systems of West Africa

Between 1993 and 1997, farmers’ termite control methods were surveyed in maize and citrus-based systems in Nigeria, and in groundnut-based systems in five West African countries. Interviews and field observations showed that the same species of termites, Macrotermes attacked the main crops and some of the intercrop species. Nasutitermes spp. that attacked citrus were not associated with any of the companion crops in citrus intercrops. Farmers reported 5-100 % damage to maize, 0-20 % damage to cassava intercropped with maize, 0-40 % and 12-90 % damages to citrus and ground nut respectively. Although chemical and cultural control methods were applied by less than 35 % of the farmers in each of the three main crops, most of the pesticides used against termites were not ideal for meaningful termite control and may have contributed to the unsatisfactory control results. Only about 20 % of the farmers that controlled termites indicated satisfactory results. An appraisal of the cultural control practices of farmers involving the use of indigenous live plants or their extracts to repel termites in infested farms was made. Those that have been found to be effective and those that need further evaluation were highlighted. The consumption of termites as a means of termite population reduction was also discussed.

Pathogenicity and Vegetative Compatibility of Verticillium dahliae Kleb. Isolates from Olive in Morocco

AbstractThirty‐eight strains of Verticillium dahliae Kleb. from diseased olive stems originating from the most important regions of olive in Morocco, were tested by vegetative compatibility analysis to investigate their genetic diversity. Two media, water agar chlorate (WAC) and minimal medium chlorate (MMC) were used to induce the nit‐mutants. The WAC medium generated a higher frequency of nit‐mutants than MMC medium. Based on complementarity of nit‐mutants, 47% of isolates were assigned to VCG4B, 32% in VCG2 (A or B) and the 18% remaining isolates could not be grouped to any VCGs tested. These latter belonged to southern regions. Pathogenicity and aggressivity of twelve isolates from this population were assessed on four plant species which are frequently intercropped with olives. These were tomato, eggplant, cotton and pepper. All isolates were pathogenic and highly aggressive on cotton and eggplant. On cotton, the isolates from southern regions induced more severe symptoms than those from northern regions. Weak to moderate symptoms were induced by all isolates on tomato and they differed in aggressivity. No isolate was pathogenic on pepper, while four isolates from northern regions were recovered from basal stems of inoculated plants. The cor‐ relation between VCGs and pathogenicity on the intercropped species is discussed with regard to the regional distribution of V. dahliae population from olive.

Root distribution at various distances from clove trees growing in Indonesia

Efficient fertilizer application requires an understanding of the distribution of roots and soil nutrients in the soil profile. Cultural practices for clove trees in Indonesia has resulted in phosphorus (P) fertilizer being applied at the canopy edge; however, in these high P fixing soils efficient P fertilizer application should occur with the highest root densities. The objective of this study, therefore, was to determine the rooting distribution at various distances from the tree and soil depths for clove (Eugenia aromatica OK; variety Zanzibar) trees growing on an Andosol soil at Modoinding, Indonesia. Root distributions were determined to a 100-cm soil depth using soil cores at 0.5, 1.0 and 1.5 times the canopy radius for five 10-year-old clove trees grown on either level terrain or 23% slopes. Clove root length and weight densities decreased with soil depth and distance from the tree base. Fine clove roots (1 mm dia) comprised 72% of the total root length and was three to five times higher underneath the canopy than that outside the canopy. Roots were concentrated in the upper soil horizons; however, up to 36% of the total root length was found at a depth of 50–100 cm. Clove roots for trees growing at the level landscape position had the highest root length densities. Intercropped species root length densities were higher than clove root length densities at 1.5 times the canopy radius whereas intercropped root weight densities were higher than that for clove roots at both 1.5 and 1 times the canopy radius. Results suggest that fertilizer applications should be placed closer to the tree trunk rather than at the canopy edge to maximize P uptake by clove roots.

Comparative economic analysis of perennial, annual, and intercrops for biomass production

Herbaceous crops may be an important source of renewable energy. Production costs can be more competitive by increasing yields so that overhead costs are applied to more biomass. Most previous economic studies of energy crops have concentrated on the production of switchgrass ( Panicum virgatum L.). This study analyzes the biomass yield and economic potential of several high-yielding annual and perennial crops on prime and marginal, sloping land. Crops evaluated were reed canarygrass ( Phalaris arundinacea L.) harvested twice per year; switchgrass and big bluestem ( Andropogon gerardii Vitman var. gerardii); alfalfa ( Medicago sativa L.); and sweet sorghum, forage sorghum [both Sorghum bicolor (L.) Moench], and maize ( Zea mays L.). The intercropping of the two sorghum species into reed canarygrass and alfalfa was also analyzed. All crops but alfalfa were fertilized with 0, 70, 140, or 280 kg N ha −1 , with economic analysis performed assuming 140 kg N ha −1 . Sorghums were most productive, with more than 16 t of dry matter ha −1. Switchgrass was the highest-yielding perennial crop. Costs per ton of biomass produced were lowest for sorghum, somewhat higher for switchgrass, higher still for big bluestem, and highest for alfalfa and reed canarygrass. Yields per ton for intercropped species were higher than for perennial species but lower than for monocrop sorghum. Costs per ton for intercropped species were less than for either alfalfa or reed canarygrass, but were higher than costs per ton of monocrop sorghum. Although the sorghums had the highest yields, high potential for erosion on sloping soils may preclude their use on these soils.

Effect of Intercropping on Oviposition and Emigration Behavior of the Leek Moth (Lepidoptera: Acrolepiidae) and the Diamondback Moth (Lepidoptera: Plutellidae)

We compared the effect of intercropping on oviposition and emigration behavior of two related specialist moth species. The effect of height of the intercrop species (red clover) on oviposition was studied in field cages, using the leek moth, a specialist on Allium species, and the diamondback moth, a specialist on Brassica species. The moths were also evaluated in an open field experiment. Emigration of both moths was studied in the laboratory and in the field in cages with host plants, red clover (nonhost), host plant and red clover, and bare soil. The possible influence of noncontact stimuli was also studied in the laboratory. The leek moth laid the same amount of eggs in monoculture as in intercroppings with high and low clover. White cabbage intercropped with high clover received fewer eggs of the diamondback moth compared with a cabbage monoculture. Intercropping with low clover did not reduce the amount of eggs laid. Intercropping did not appear to affect the emigration of either the leek moth or the diamondback moth. Leek moths were less likely to emigrate than diamondback moths during the first 4 h of the study. We conclude that diamondback moth may be more likely to be controlled by intercropping than leek moths.

Intercropping corn with soybean, lupin and forages: yield component responses

Intercropping systems influence yield variables of the component crops, such as harvest index, hundred seed weight, number of reproductive organs and number of seeds, within each reproductive unit. Two experiments were carried out at each of two sites during 1993 and 1994. The first experiment investigated the effects of seeding soybean or lupin alone or in combination with one of three forages (annual ryegrass, Lolium multiflorum Lam.; perennial ryegrass, Lolium perenne L.; red clover, Trifolium pratense L.) with corn on the yield components of corn, soybean and lupin. The second experiment examined the effects of seeding date (simultaneous with corn or 3 weeks later) and number of rows of large seeded legumes (one or two) seeded between the corn rows. Corn grain yield was generally not affected by any intercrop treatment, although in 1993 some simultaneously seeded treatments resulted in decreased yields. Soybean grain yield was decreased by most treatments, although some simultaneous seedings produced yields similar to soybean monocrops. Lupin grew poorly as an intercrop component, producing little or no grain. Corn harvest index was not affected by any intercrop treatments. Seeding corn and large-seeded legumes simultaneously resulted in decreases in corn hundred seed weights by as much as 6.6 g compared with the monocropped corn. In 1993 (a year with normal precipitation levels), the hundred seed weight and number of seeds per soybean pod were decreased by intercropping, although the harvest index was not affected. In a high precipitation year (1994), the soybean harvest index was decreased by intercropping, but not the seed components. The underseeded forages, annual ryegrass, perennial ryegrass and red clover, had no effect on yields or yield components of the other intercropped species.

Intercropping and Pest Management: A Review of Major Concepts

Intercropping is the agronomic practice of growing two or more crops in the same field at the same time (Andrews and Kassam 1976). Crops may be planted without regard to rows (mixed intercropping), in alternating rows, or with different crops alternating within the same row. Relay intercropping refers to the planting of one intercrop species before another so that their life cycles partially overlap (Kass 1978). The broader term “polyculture” includes intercropping but also encompasses combining crops and weeds intentionally and combining crops with beneficial noncrop plants, such as cover crops or nursery crops (Andow 1991a). Perrin and Phillips (1978) included mixtures of crop cultivars in their definition of intercropping, because such combinations may possess some of the advantages associated with conventional intercropping.

Capacity for biocompatibility assessment in tissue culture and hydroponic systems

In vitro and hydroponic intercropping systems were compared to examine the biocompatibility responses between ‘Fiona F1’ tomato (Lycopersicon esculentum Mill.) and ‘Spunta’ potato (Solanum tuberosum). The biological response of monocultures (with four plantlets per vessel) of each species (including change in medium electrical conductivity (EC), osmotic potential (OS), and tissue mineral element content) were directly compared to intercropped cultures of the following tomato:potato; 1:1, 2:1, 3:1, 1:2, 1:3, and 2:2 plantlets per vessel. The in vitro intercropping systems were performed using a Murashige and Skoog (MS) shoot proliferation medium (5.0 μM BA and 0.5 μM IBA). The parallel hydroponic intercropping system was performed using a Hoagland's solution. Monoculture of both species grows better in both systems than intercropped species. In the intercropped vessels, tissue mineral content decreased, medium pH became more acidic, OS decreased and EC increased as compared to monocultures in parallel vessels. A lettuce seedling bioassay did not indicate evidence of allelopathic compound accumulation in either hydroponic or in vitro intercropped systems.

Aboveground and belowground competition between intercropped cabbage and young Eucalyptus torelliana

An expanding market for planted timber in the Philippines is providing a strong incentive for upland farmers to incorporate trees into their farming systems. Farmers often intercrop young timber species with well-fertilized annuals in expectation that inter- species competition for nutrients and light will be minimal while the trees are small, and that the trees will benefit from intensive nutrient and weed management of the intercrop. The relative level of aboveground and belowground competition in a vegetable/timber intercropping system was investigated in the uplands of Mindanao, the Philippines. Eight 5-m2 microplots were established containing one nine-month-old Eucalyptus torelliana and four rows of cabbage (two on each of the north and south sides of the tree, 0.5 and 1.0 m from the stem base). The tree canopy shaded north rows. Monocrop cabbage microplots (2 m2) were also installed. Four tree/cabbage microplots and all cabbage-only plots were fertilized with 15 5N-labeled ammonium sulfate (100 kg N ha−1); remaining microplots received unlabeled fertilizer. Cabbage yields were reduced by 16% in the north rows when compared to the south rows, and by 15% in rows closer to the tree when compared to rows further from the trees. Belowground competition in the first cabbage row, possibly for moisture, is supported by the high proportion of tree roots found in the top 30 cm of soil. Competition did not appear to be for N or other nutrients. Foliar analyses revealed no row differences in mineral concentrations in cabbage, uptake of applied N, or percent of N derived from fertilizer. The modest amount of 15N found in aboveground tree parts (4.5% of N applied to four cabbage rows) improved overall N-use efficiency in the intercropped plots. An improved understanding of the tradeoffs between improved nutrient efficiency and depressed intercrop growth, as well as management options to reduce competition, will help farmers design systems to improve efficiency without increasing competition.

Resource capture and utilization in intercropping; non-nitrogen nutrients

The capture and utilization of P and K, two non-mobile soil resources, were examined by decomposing crop production/unit area into uptake/unit area (capture) and production/unit uptake (utilization efficiency). Resource capture and utilization efficiencies by intercrops were compared to those of sole crops by contrasting intercrop means against the weighted means of sole crops. Weightings were based on the proportion of each species in the intercrop. On average, intercrops took up 43% more P (−4 to 83%) and 35% more K (− 10 to 87%) than the sole crops. Where nutrients were not limiting, P and K uptake increased as dry-matter yield increased, evidence that uptake was a function of crop growth rather than conversely. Even where soil P was deficient, uptake by a dominated crop was decided more by factors that determined the outcome of competition than by P availability. The combined root systems, likely to be larger and functional for a longer duration under intercrops than under either sole crop, were postulated to explain the greater capture of non-mobile nutrients like P and K. An enlarged root system provides an expanded root surface area to which non-mobile nutrients can diffuse. For mobile nutrients which move to root surfaces largely by mass flow, shading of the dominated canopy may explain the positive association observed between intecrop dry-matter accumulation and Ca capture. Shading reduces carbon assimilation and transpiration of the understory canopy and, therefore, would reduce mass flow of Ca as well. Competition for P and K by intercropped species, even when nutrient supplies were abundant, was affected by degree of growth concurrency, canopy domination and planting geometry. When a dominating species was harvested much earlier than the dominated species, the uptake rate of the longer-duration crop usually recovered from competition after the first crop was harvested. Exceptions occurred when development of the dominated crop was so badly impaired during concurrent growth that vegetative enlargement was inhibited after harvest of the early species. Uptake rates by pigeon pea and cassava, which are exceptionally long-maturing species that have relatively low daily P and K uptake requirements, appeared capable of fully recovering even on soils in which nutrient availabilities were marginal for other species.

Genotypic requirement for intercropping

An important aspect of an intercropping system is the extent of competition between the crops. Where this is large, there is likely to be a significant genotype × cropping systems interaction. Even when the correlation between sole-crop and intercrop yields is positive, there may be significant departures from the trend which can be exploited by plant breeding. The traits required for intercropping are those which enhance the complementary effect between species. The setting of objectives must take into account not only the influence of a particular trait on the target crop's yield, but its potential effect on another crop. A useful strategy for areas with unreliable rainfall distribution is to intercrop a relatively short-duration crop with a long-season indeterminate crop, for which the periods of maximum demand on water resources are different. Photo-sensitivity provides a mechanism for timing precisely the flowering of particular cultivars. The plant types of the intercropped species should be selected to complement each other. Cultivars of species which are compatible in this way can be planted at higher density, and this is a major factor contributing to the ability of intercrops to yield more than sole crops. Plant breeding is costly. An intercropping system targeted for breeding must clearly be of major significance, cover a large area and be sufficiently unique to justify a separate programme. A cereal/ legume intercrop in excess of 0.5 million hectares is estimated to be sufficiently large to justify a full-scale crossing and selection programme. For adaptive variety trials, bivariate analysis is the preferred approach, in order to remove background correlated effects between the two crop yields in an intercrop. An alternative is to select on the basis of income. Farmers, however, may use a wider range of criteria to select cultivars. The best way of accounting for these is to involve farmers in the selection process. Early generation selection in a breeding programme should first focus on the highly heritable traits identified as contributing to intercrop efficiency. Early generation yield evaluation of genotypes of beans intercropped with maize was found to be feasible and effective. Selection under farmers' own management should be introduced at as early a stage as possible, once a set of promising lines has been identified. Breeding for intercropping will be most effectively carried out in the context of regional collaboration or international programmes, focusing on improving and extending the use of cropping systems which are already widely practiced.

A comparison of the diversity of Jivaroan Gardens with that of the tropical forest

The proposition that tropical polycultural gardens simulate the structure and dynamics of the surrounding forest is examined in the light of research on Jivaroan manioc cultivation. Garden transects were used to measure the diversity of intercropped species and of locally recognized varieties of manioc. Huambisa and Aguaruna Jivaro gardens have much lower species diversities than the surrounding forest, even though crop compositions reflect the age, topography, and soil type of the swiddens. Furthermore, the number of manioc varieties is far greater than that of all other crop species combined. It is argued that a pure stand of Jivaroan manioc can itself be considered a polycrop of distinct cultivars with differing branching patterns, leaf shapes, and growth periods.

Lithium as a non-radioactive tracer for roots of intercropped species

A technique is described for investigating the rooting pattern of species when intercropped, using Lithium as a non-radioactive tracer. The technique was tested on pure stands and mixtures of barley (Hordeum sativum) and field beans (Vicia faba), with 10% LiCl solution placed at depths of 0, 10, 25 and 62 cm.