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C L Coulson

Publications and source records attributed to C L Coulson.

6 recordsLinked to original sources
PubMed2001

Phenotypic nutrient up-take differences in an alley cropping system in semi-arid Machakos, Kenya.

Alley cropping of Cassia siamea and maize was studied in semi-arid Kenya for soil fertility improvement. Katumani composite maize was planted except in the short rains of 1988 (SR88) when a hybrid variety was sown. Therefore the grain yield per row increased differently in the alley cropped maize (CM). Sole maize (SM) and CM yields were higher in SR88 than in the long rains of 1988 (LR88) by 62% and 38%, while yields from the same treatments in LR89 were only 21% and 45% of those in SR88. These differences in relative maize yields are attributed to differences between the two maize varieties in competition under nutrient stress conditions.

Agriculture↗
PubMed2001

Understanding yields in alley cropping maize (Zea mays L.) and Cassia siamea Lam. under semi-arid conditions in Machakos, eastern Kenya.

Six seasons of experiments in Machakos, Kenya, revealed that above about 150 mm of rainfall, maize yields per row in alley cropped "replacement" agroforestry (AF) plots, of Cassia siamea Lam. and maize (Zea mays, cv. Katumani Composite B), may be expected to exceed those in the control (sole maize) plots. Such yields were insufficient to compensate for the area "lost" to the hedgerows. Below about 150 mm the control plots may be expected to perform better. This result was due to competition for water. Greater association of the fine roots of Cassia and maize was observed in the middle of the alleys than near the hedgerows. Photosynthetic consequences of shading were insignificant relative to other factors. In the alleys, reductions of soil temperature due to shade in the western and eastern maize rows were higher than in the middle row. Soil moisture extraction was higher in the AF than in the control plots. In the AF plots, moisture extraction was greater under the central maize rows than under those nearest the Cassia. Yield patterns followed such soil temperature and soil moisture patterns. Maize transpiration and photosynthetic rates were significantly higher in the control than in the AF plots during a below-average rainy season but not during above-average rainy seasons. It is concluded that alley cropping under semi-arid conditions should be approached differently from the system worked on. It must at least provide strong physical protection of crops and/or soils and have a strong economic incentive to be of interest to the farmers.

Agriculture↗
PubMed1972

Solution-flow in the Phloem: I. Theoretical considerations.

A mathematical model for the reversible exchange of THO between the sieve tube lumen and its surrounding phloem tissue is used to explain the difference between the apparent velocities of THO and (14)C-sucrose transport observed when both are supplied simultaneously. Theoretically predicted results show a close correlation with those obtained experimentally. This model may be used in evaluating previous work in which THO was used as a tracer. The calculations support the existence of a mass flow of sugars in aqueous solution along the path.

Journal Article↗
PubMed1972

Solution-Flow in the Phloem: II. Phloem Transport of THO in Beta vulgaris.

Translocation profiles along the path were studied using a modified flap-feeding technique for the simultaneous application of THO and (14)C-sucrose. A re-evaluation of a mathematical model for phloem transport with reversible lateral exchange of tracer along the path indicates that lower apparent velocities for THO as compared to labeled carbohydrate are primarily due to extensive lateral exchange of THO along the conduction path. Path-chilling experiments support the concept that THO and (14)C-sucrose exhibit different lateral exchange characteristics. The data presented are consistent with a solutionflow mechanism.

Journal Article↗
PubMed1972

Carbohydrate translocation in sugar beet petioles in relation to petiolar respiration and adenosine 5'-triphosphate.

Earlier studies have shown that the retarding effect of low petiolar temperatures on sucrose transport through sugar beet (Beta vulgaris L.) petioles is markedly time-dependent. Although the initial effect of chilling the petiole to near 0 C is severely inhibitory, translocation rates soon recover (usually within about 2 hours) to values at or near the control rate. In the present studies, selected metabolic parameters were measured simultaneously with translocation. No stoichiometric relationships among petiolar sucrose transport, petiolar respiration (CO(2) production), and calculated petiolar ATP turnover rates were evident. It appears that the major sources of energy input energizing carbohydrate transport in sieve tubes function mainly at either loading or unloading sites and not at the level of individual sieve-tube elements.

Journal Article↗