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Wairegi L.W.I.,Center for Agricultural Bioscience International | Van Asten P.J.A.,International Institute Of Tropical Agriculture
Experimental Agriculture | Year: 2012

Poor soil fertility is a constraint to coffee production. Targeting fertiliser recommendations to nutrient deficiencies can contribute to improved crop response to fertiliser. This study aimed to derive and compare the Compositional Nutrient Diagnosis (CND) and Diagnosis and Recommendation Integrated System (DRIS) norms for Arabica and Robusta, and to investigate nutrient interactions using data derived from 164 plots. The high-yield sub-populations of Arabica had significantly (p < 0.01) higher P (0.23 vs. 0.14) and K (2.87 vs. 2.04), and lower N (2.96 vs. 3.61), Ca (0.99 vs. 1.50) and Mg (0.40 vs. 0.23) than those of Robusta.With respect to the CND norms, Arabica had significantly (p < 0.001) higher P and K, and lower N, Ca and Mg means of row-centered log ratios than Robusta. The relationship between the CND and DRIS indices had coefficient of determination (R2) = 0.75-0.99 for both coffee types. The relationship between nutrient imbalance indices for CND and DRIS had R2 of 0.95 (Arabica) and 0.76 (Robusta). Both coffee types had negative N-Ca, P-Mg and K-Mg interactions. Arabica had positive N-Mg and K-Ca interactions and Robusta had positive N-K, P-K and Ca-Mg interactions and negative N-P, N-Mg, P-Ca and K-Ca interactions. The study concludes, there is a need for cultivar-specific norms, but such norms developed under one set of conditions may not be applicable under different conditions. The study also concludes that both CND and DRIS can be used to determine nutrient imbalances, and fertiliser requirements could be cultivar-specific. © Cambridge University Press 2012. Source


Wagacha J.M.,International Crops Research Institute for the Semi Arid Tropics ICRISAT | Wagacha J.M.,University of Nairobi | Mutegi C.,International Institute Of Tropical Agriculture | Karanja L.,Center for Agricultural Bioscience International | And 2 more authors.
Crop Protection | Year: 2013

A survey was conducted in Nairobi, Nyanza and Western provinces in Kenya between March and July 2009 with 1263 peanut products sampled out of which 705 samples underwent microbial analysis. The study aimed at determining the incidence of fungal species - emphasis on Aspergillus section Flavi - associated with peanut products. A 0.5kg representative sample was obtained from each surveyed vendor and the colony forming units (CFU) of fungal species determined. The samples were also analyzed for total aflatoxin level while isolates of Aspergillus flavus and Aspergillus parasiticus were screened for production of aflatoxin B1, B2, G1 and G2. Eight fungal species were detected in the samples and were in decreasing order of CFU/g of sample: A.flavus S-strain (467), A.flavus L-strain (341), Penicillium spp. (326), Aspergillus niger (156), Aspergillus tamari (27), Aspergillus alliaceus (21), A.parasiticus (10), and Aspergillus caelatus (5). The overall incidence of A.flavus S-strain in samples from Nairobi was 92 and 1425% higher than samples from Nyanza and Western regions, respectively. The combined incidence of A.flavus and A.parasiticus was varied significantly (. p≤0.05) with peanut product: peanut flour (69%), shelled raw peanuts (53%), spoilt peanuts (49%), boiled podded peanuts (45%), podded peanuts (39%), peanut butter (31%), fried peanuts (22%) and roasted peanuts (20%). Seventy three percent of A.flavus and A.parasiticus isolates produced at least one of the aflatoxin types, with 66% producing aflatoxin B1. The total aflatoxin level among peanut products ranged from 0 to 1629μg/g; and there was a positive correlation (. r=0.2711) between the incidence of A.flavus and A.parasiticus, and total aflatoxin level. The high incidence of aflatoxin producing fungi in peanuts traded in Kenyan markets implies a risk of aflatoxin contamination, highlighting the need for stakeholders to promote sound practices at all stages of the peanut value chain in order to minimize market access by non-complying products. © 2013 Elsevier Ltd. Source


Schmidt A.,Helmholtz Center for Environmental Research | Auge H.,Helmholtz Center for Environmental Research | Auge H.,German Center for Integrative Biodiversity Research | Brandl R.,University of Marburg | And 8 more authors.
Basic and Applied Ecology | Year: 2015

Sustainable management of agricultural systems includes promoting nutrient cycles, which can reduce the need for application of fertilizer. As rice is one of the most important food resources in the world, sustainable management of rice paddies is increasingly in demand. However, little is known about the influence of invertebrates on decomposition processes in these ecosystems. We hypothesized that invertebrates contribute significantly to the decomposition of rice straw in paddies and that their relative contribution is affected by the distance to other landscape structures within fields. We placed rice straw in litterbags of two different mesh sizes which prevent (20. μm. ×. 20. μm) or allow (5. mm. ×. 5. mm) access of invertebrates in six irrigated rice fields for 84 days. In each field, bags were set on three transects running from the bund to the center of the field. Invertebrates significantly increased total rice straw litter mass loss by up to 45% (total decomposition: fine-meshed bags 64%; coarse-meshed bags 83%). Litter mass loss in bags accessed by invertebrates decreased with increasing distance from the bund. Such a spatial trend in litter mass loss was not observed in bags accessed only by microbes. Our results indicated that invertebrates can contribute to soil fertility in irrigated rice fields by decomposing rice straw, and that the efficiency of decomposition may be promoted by landscape structures around rice fields. Nachhaltigkeit im bewässerten Tiefland-Reisanbau ist ein wesentlicher Bestandteil zur Sicherung der Nahrungsgrundversorgung eines großen Teils der Weltbevölkerung. Das Verständnis der komplexen Prozesse im Nährstoffkreislauf in Agrarökosystemen kann zu einer Erhöhung der Bodenfruchtbarkeit führen und den Bedarf an Düngemitteln drastisch reduzieren. Die Grundlage für eine natürliche Stickstoffzufuhr, zur Förderung des Pflanzenwachstums, ist die Zersetzung von totem organischem Material, was eine stabile Gemeinschaft von Bodenorganismen voraussetzt. Nichtsdestotrotz ist das Wissen über den Einfluss der Makrofauna auf Zersetzungsprozesse im Boden von Reisökosystemen rar.Ziel dieser Studie war es, den Einfluss von Invertebraten auf die Zersetzungsrate von Reisstroh zu untersuchen und deren Effektivität in Abhängigkeit landschaftlicher Strukturvielfalt in direkter räumlicher Nähe zu den Untersuchungsflächen einzuschätzen. Um zu differenzieren, wie stark der jeweilige Anteil von Invertebraten und Mikroorganismen am Streuabbau ist, wurden Streubeutel mit zwei verschiedenen Maschenweiten (20. μm und 5. mm) verwendet und für 84 Tage auf die Bodenoberfläche bewässerter Reisfelder gelegt. Der Einfluss der Entfernung vom Reisfeldufer auf die Zersetzungsrate sollte mit Hilfe von Transekten, die vom Rand bis zur Mitte von sechs Versuchsfeldern gezogen wurden, ermittelt werden.Invertebraten erhöhten nicht nur die Menge an insgesamt abgebautem Stroh bis zu 45%, verglichen mit der reinen mikrobiellen Zersetzung, ihr Einfluss nahm auch vom Rand zur Mitte des Feldes hin ab. Die Abbaurate der Mikroorganismen blieb innerhalb des Feldes dagegen relativ konstant.Unsere Ergebnisse zeigen deutlich, dass Invertebraten einen großen Einfluss auf die Zersetzung von Reisstroh haben und damit die Bodenfruchtbarkeit positiv beeinflussen können. Zusätzlich konnte eine positive Korrelation zwischen Ufernähe und Abbaugeschwindigkeit von Invertebraten in Reisfeldern nachgewiesen werden, was auf eine höhere Nährstofffreisetzung in den Randbereichen der Felder hindeutet. © 2015 Gesellschaft für Ökologie. Source

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