Abstract
Understanding the composition and dynamics of ecological communities is challenging because of the large number of organisms present and their numerous interactions. Among agricultural ...systems, intercropping considerably increases the complexity of communities compared to monocultures and alternative host plants can influence insect pest damage. Using literature records, we construct and analyse connectance trophic webs of date palm (
Phoenix dactylifera
) agro-ecosystems, including and excluding intercrops. Estimates of connectance (community complexity) are relatively low and little affected by consideration of intercrops. Plant–herbivore overlap is relatively high, suggesting that herbivores are typically not specialists. Herbivore–natural enemy overlap is greater when intercrops are considered, suggesting that diffuse apparent competition regulates pest populations. We pay particular attention to how trophic web structure might affect
Batrachedra amydraula
(Lesser date moth), an important economic pest. Records indicate it having 15 species of natural enemies and sharing 9 of these with other herbivores; these may maintain populations of natural enemies when the moth is seasonally rare, contributing to pest suppression. The estimated potential for apparent competition between the lesser date moth and other herbivores is higher when intercrops are considered. The consequent expectation of less severe infestations in plantations that are intercropped compared to monocultures matches empirically derived reports. Further, comparing results obtained from the literature on one country (Oman) and from 15 Middle Eastern countries, we find that community metric estimates are relatively little affected by the geographical scale considered. Overall, our results suggest that literature-based trophic web construction can provide an efficient and robust alternative, or in addition, to direct empirical methodologies and that the presence of intercrops will contribute to major pest suppression via indirect apparent competition.
We conducted a survey of aflatoxin and fumonisin in maize in western Kenya. In a regional survey of aflatoxin conducted in 2009 across three agroecological zones within three administrative regions, ...milled maize samples were collected from 985 patrons of 26 hammer mills. Aflatoxin contamination was detected in 49% of samples and was above the regulatory (10 ppb) in 15% of the samples overall; 65% of samples from a drought-prone area were over the limit. In a detailed survey in Bungoma County, we investigated aflatoxin and fumonisin contamination in four popular maize varieties at harvest and after 2 and 4 months of storage. We collected whole-grain samples from farmers' storage sheds and milled samples from patrons of local mills. Mean aflatoxin contamination was identical for storage sheds and mills at 2.3 ppb. In all, 41% of the samples from mills had detectable aflatoxin, with 4% over the regulatory limit, whereas 87% had detectable fumonisin, with 50% over the regulatory limit (1 ppm). Mean contamination levels did not change during storage. Maize varieties differed in fumonisin contamination, with the most popular varieties vulnerable to both mycotoxins and weevils, which are potential factors in exacerbating mycotoxin contamination. Mycotoxin surveillance is important not just in areas known previously for aflatoxin contamination and acute poisoning but also is needed in all maize-producing regions.
Growing mixtures of annual arable crop species or genotypes is a promising way to improve crop production without increasing agricultural inputs. To design optimal crop mixtures, choices of species, ...genotypes, sowing proportion, plant arrangement, and sowing date need to be made but field experiments alone are not sufficient to explore such a large range of factors. Crop modeling allows to study, understand, and ultimately design cropping systems and is an established method for sole crops. Recently, modeling started to be applied to annual crop mixtures as well. Here, we review to what extent crop simulation models and individual-based models are suitable to capture and predict the specificities of annual crop mixtures. We argued that (1) the crop mixture spatio-temporal heterogeneity (influencing the occurrence of ecological processes) determines the choice of the modeling approach (plant or crop centered). (2) Only few crop models (adapted from sole crop models) and individual-based models currently exist to simulate annual crop mixtures. Crop models are mainly used to address issues related to both crop mixtures management and the integration of crop mixtures into larger scales such as the rotation. In contrast, individual-based models are mainly used to identify plant traits involved in crop mixture performance and to quantify the relative contribution of the different ecological processes (niche complementarity, facilitation, competition, plasticity) to crop mixture functioning. This review highlights that modeling of annual crop mixtures is in its infancy and gives to model users some important keys to choose the model based on the questions they want to answer, with awareness of the strengths and weaknesses of each of the modeling approaches.
Aims
In comparison to the accumulated knowledge related to the legume-cereal intercrops, very little is known on both basic and applied aspects of the legume-brassica intercrops. In fact, the ...potential of legume-brassica intercrops was enormous to improve crop yields, biomass, nitrogen uptake, the economic reliability via land equivalent ratio, and so on. Therefore, in the present study, the Chinese milk vetch (
Astragalus sinicus
L.)-rape (
Brassica napus
L.) intercropping system was investigated. The specific objective of this study was to investigate how Chinese milk vetch affects the soil microbial community in rhizosphere of rape.
Methods
A series of bucket experiments based on Chinese milk vetch-rape intercrops, included root separation and straw mulching, were employed to explore the soil properties and soil microbes in rhizosphere of rape.
Results
Intercropping substantially decreased the organic carbon content and the total nitrogen content and changed the C/N ratios. Intercropping also decreased the soil microbial biomass in rape rhizosphere (including the total PLFAs, bacteria, actinomycete, AM-fungi, and so on). In addition, intercropping and straw mulching also changed the structure of soil microbial community in rape rhizosphere, which was significantly correlated with 16:1w9c and 18:3w6c (6, 9, 12). At the same time, under the influence of intercropping Chinese milk vetch, soil microbial functional activity in rape rhizosphere was significantly reduced. Soil microbial community functional composition in rape rhizosphere was also changed greatly by intercropping, which was significantly correlated with
d
-glucosaminic acid and g-1-phosphate under no straw mulching, and glycogen,
d
-xylose and 2-hydroxy benzoic acid under straw mulching.
Conclusions
Intercropping Chinese milk vetch decreased soil microbial biomass and functional activity and changed greatly the soil microbial community structural and functional composition in rape rhizosphere. Our findings revealed that root interaction between Chinese milk vetch and rape was a crucial factor to manage the crop intercropping, which might, in turn, determine the soil microbe on rhizosphere.
Soil and nutrient losses due to soil erosion are pronounced in potato growing areas of East Africa due largely to the rugged topography and high soil disturbance associated with potato cultivation. ...This study intercropped potato (Solanum tuberosum L.) with three grain legumes: lablab bean (Lablab purperous L.), garden pea (Pisum sativa L.) and climber bean (Phaseolus vulgaris L.) in runoff plots and assessed their impact on soil and nutrient losses in central Kenya highlands. Bare plots and sole potato stands were included as controls. Vegetal cover was measured at different potato growth stages while runoff and soil loss were quantified at every runoff generating event and used for nutrient analyses. Yields were expressed as potato equivalents (PEY) at the end of each season. Mean cumulative sediment yield decreased from 169 t/ ha in sole potato plots to 50–83 t/ ha in potato-legume intercropping, representing a reduction of 51–70%. The eroded sediment exported in large quantity the SOC (16.6–39.5 kg C ha−1 yr−1), N (5.5–29.8 kg N ha−1 yr−1), P (3.9–16.4 kg P ha−1 yr−1) and K (5.2–14.6 kg K ha−1 yr−1) and were consistently higher in sole potato plots relative to potato-legume intercropping. These losses occurred mainly at potato emergence following fertilizer application. Stronger associations of sediment nutrient enrichments was found with the micro-aggregates (250–50 μm) than with the macro-aggregates (>250 μm) pointing to the different degree of nutrient mobilization and distribution in eroded sediment. The PEY were significantly greater in potato-lablab bean system than in sole potato, while intercropping with garden pea and climber bean showed similar PEY to that of sole potato, suggesting that potato-lablab system may be preferred by the smallholder farmers. These results justify the need to intercrop potato with indeterminate legume intercrops, a strategy that must be done in a way guaranteeing high yield stability to the smallholder farmers.
•Soil loss and runoff occurred mainly when groundcover was <40%.•Intercropping potato with lablab lowered cumulative soil loss by up to 87.2 t/ ha.•Nutrient loss was 23–34% less with intercropping than with sole potato.•Yields were significantly greater in potato-lablab system than in sole potato.
AIMS: To evaluate the productivity and N₂ fixation of a range of Mediterranean forage legume species as well as their ability to be grown in mixture with a forage grass, and to verify whether N ...transfer occurs from the legume to the non-legume component of the mixtures and, if so, to what extent this process is affected by legume species. METHODS: Seven legume species (Hedysarum coronarium L., Medicago scutellata L., Trifolium resupinatum L., Trifolium squarrosum L., Trigonella foenum-graecum L., Vicia sativa L., Vicia villosa Roth) were grown alone or in mixture with annual ryegrass (Lolium multiflorum L.). Biomass and N yields and biological N₂ fixation (¹⁵N dilution technique) were measured. N transfer from legume to the non-legume component was also assessed. The efficiency of the intercrops was evaluated using the land equivalent ratio (LER), aggressivity index, and competitive ratio. RESULTS: Differences were observed among the monocropped legumes for biomass yield, N₂ fixation, and ability to utilize inorganic soil N. Moreover, the proportion of legume species to the total biomass yield of the intercrop varied from 30 % (T. resupinatum) to 69 % (T. foenum-graecum). All intercrops showed an advantage over monocrops in terms of biomass and N yields (LER and NLER values always >1). No N transfer occurred from legume to ryegrass in any of the mixtures. CONCLUSIONS: The large differences observed among the studied legumes must be taken into account when trying to develop cropping systems with more efficient N use. Moreover, as all legume–ryegrass intercrops used natural resources more efficiently than pure crops, intercropping is a relevant cropping strategy for sustainable agricultural systems in Mediterranean environments.
Introduction
Intercropping has a potential to reduce the CO
2
emission from farmlands. Limited information is available on the underlying reasons.
Methods
This study investigated the effect of milk ...vetch (
Astragalus sinicus
L.) (MV), rapeseed (
Brassica napus
L.) monoculture (RS) and intercropping (Intercrop) on soil CO
2
emissions, moisture and temperature in a bucket experiment during 210 days from October 2015 to May 2016 on Chongqing, China.
Results
The results showed that soil CO
2
efflux of MV, RS and Intercrop was 1.44, 1.55 and 2.08 μmol·m
-2
·s
-1
during seedling and stem elongation stages and 3.08, 1.59 and 1.95 μmol·m
-2
·s
-1
during flowering and podding stages. At seeding and stem elongation stages Intercrop had 1.4 times higher soil CO
2
efflux than the mean of MV and RS. In contrast, MVhad 1.6 times higher soil CO
2
efflux than Intercrop thereafter, which shows it was inhibited if milk vetch presents as Intercrop only. Decreased sensitivity of soil respiration to temperature in 1.4 times and lower soil moisture by Intercrop were found compared to MV. Intercrop decreased soil moisture, especially at the seedling and stem elongation stages, compared to the monoculture. The fluctuation on soil respiration in RS and Intercrop was slight with changes in soil moisture.
Conclusion
Thus, milk vetch-rapeseed system has a potential to decrease CO
2
emission from farmland, however soil moisture should be regulated properly.
Residue burning to prepare soil for maize growing deprives the soil of both protective cover and organic matter, and it exacerbates environmental issues such as Southeast Asia's haze problem. This ...paper reports on a study that evaluated the effectiveness of maize/legume intercropping as an alternative to maize cultivation with residue burning. Cowpea (Vigna unguiculata), mung bean (V. radiata), rice bean (V. umbellata), and lablab (Lablab purpureus) were sown into a standing maize crop 30 days before harvest, and the results were compared with a maize crop grown using residue burning as the method for land preparation at Pang Da Agricultural Station in Chiang Mai, Thailand, in a replicated trial conducted over 3 growing seasons from 2012 to 2014. Intercropping increased maize grain yield by 31–53% and left 70–170% more residue containing 113–230% more nitrogen than the maize sown after residue burning, depending on the legume, and decreased weed dry weight by two-thirds after 2 seasons. Soil biodiversity was enriched by the intercrops, with a doubling in the spore density of arbuscular mycorrhizal fungi in the root-zone soil and increased abundance, diversity (Shannon index), and richness of the soil macrofauna. The abundance of soil animals increased with crop residue dry weight (r = 0.90, P < 0.05) and nitrogen content (r = 0.98, P < 0.01). The effect of intercropping on maize grain yield and accumulation of residue and nitrogen were then confirmed in a participatory experiment involving farmers in 2 highland villages in the Phrao and Chiang Dao districts of Chiang Mai Province with maize and rice bean in 2015. The effects of maize/legume intercropping—increased nitrogen accumulation and crop residue, enhanced soil biodiversity, suppression of weeds, and protection of the soil surface, which enabled the maize to be sown without land clearing with fire—should all contribute to sustainable highland maize production.
Aim This study assessed whether growing cowpea can increase phosphorus (P) availability in the rhizosphere and improve the yield of legume-cereal systems. In alkaline Mediterranean soils with P ...deficiency, it is assumed that legumes increase inorganic P availability. Methods A field experiment was conducted at the Staoueli experimental station, in Algiers province, Algeria, to compare the growth, grain yield, P availability, and P uptake by plants with sole-cropped cowpea (Vigna unguiculata L. cv. Moh Ouali) and maize (Zea mays L. cv. ILT), intercropped cowpea-maize, and fallow. Results P availability in the rhizosphere was increased in both sole cropping and intercropping systems compared with fallow. It was highest in intercropping. The increase in P availability was associated with (i) significant pH changes of the rhizosphere of cowpea in sole cropping and intercropping systems, with the rhizosphere acidification significantly higher in intercropping (−0.73 units) than in sole cropping (−0.42 units); (ii) significant increase in the rhizosphere pH of intercropped maize (+0.49 units) compared to fallow; (iii) increased soil respiration (C-CO2 from microbial and root activity) in intercropping compared with sole cropping and fallow; and (iv) higher efficiency in utilization of the rhizobial symbiosis in intercropping than in sole-cropped cowpea. Conclusion With cowpea-maize intercropping, cowpea increased the P uptake, by increasing the P availability by rhizosphere pH changes in an alkaline soil. Overall, this study showed that intercropping cowpea improved the plant biomass and grain yield of maize in this soil.
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