Water relations and irrigation requirements of onion (Allium Cepa L.): a review of yield and quality impacts

The results of international research on the water relations and irrigation needs of onions have been synthesized in an attempt to link fundamental studies on crop physiology to irrigation practices, and consequent impacts on crop yield, quality and storage. Following a brief introduction on its origins and centres of production, a synthesis of research on crop development including plant water relations, crop water requirements, yield response to water, irrigation systems and scheduling are presented. Most of the evidence stems from research conducted in arid and semi-arid regions notably the USA, India, Spain and Turkey. The findings confirm that onion seasonal water requirements are highly variable depending on agroclimate, location and season, as are the crop coefficients (Kc) which range from 0.4 to 0.7 (initial stage), 0.85 to 1.05 (middle development) and 0.6 to 0.75 (final stage). Seasonal irrigation needs are reported to vary from 225 to 1040 mm to produce between 10 and 77 t ha-1. The most sensitive stages for water stress are at emergence, transplanting and bulb formation. Final crop quality can also be affected by water excess. Water stress at specific stages can negatively impact on quality leading to reduced size and multi-centred bulbs. In recent years, pressure on water resources, retailer demands for quality assurance and rising production costs have meant that onion irrigation has switched from traditional low efficiency (furrow) methods to more efficient advanced (sprinkler and drip) technologies. For scheduling, optimal soil water potential thresholds for triggering irrigation were found to be between -17 kPa and -27 kPa for drip and furrow irrigation. Research is underway to maximize water use efficiency in onions, but the deficit irrigation regimes being tested under experimental conditions have yet to be adopted commercially

Phase behavior of the systems n-decanephosphonic acid/water and n-dodecanephosphonic acid/water

The n-decanephosphonic acid/water and n-dodecanephosphonic acid/water systems were studied by differential scanning calorimetry, hot stage polarized light microscopy, and FT-IR spectropetry. There is a rich polymorphism: in both systems there are three liquid crystalline phases (lamellar L? and L? and an inverse cubic phase) plus the isotropic liquid and two solid phases. One of the solids is an ordinary cristalline phase and the other is a waxy crystal in which the polar headgroup network is rigid and ordered but in which the alkyl chains are partially fluid and disordered. The water in these systems exists in two distinct forms: water bound to the headgroups and water which is effectively free. The polymorphism of the heptyl and octyl analogues has been studied by Klose et al

Efecto del período de conservación sobre algunas propiedades nutracéuticas y organolépticas en los bulbos de cultivares nacionales de cebollas (allium cepa l.) en el valle inferior de rio negro

La cebolla posee atributos culinarios y nutracéticos que están fijados genéticamente, pero su expresión está fuertemente regulada por factores ambientales y de manejo. El objetivo de este trabajo fue caracterizar a un grupo de cultivares nacionales por algunos de los componentes internos de los bulbos, responsables de dichos atributos y evaluar el efecto que les produce un prolongado período de conservación. Los cultivares ensayados fueron Valcatorce INTA, Cobriza INTA, Navideña INTA, Valuno INTA y Antártica INTA. La conservación de los bulbos se realizó mediante la construcción de pilas en el campo y el período de conservación duró 90 días. Antes de ingresar a las pilas y al finalizar el experimento, se realizaron las siguientes determinaciones, en cada cultivar: pH, contenido de materia seca (MS), sólidos solubles (SS), azúcares totales (AT), pungencia y fenoles totales (FT). El pH fue similar en todos los cultivares y no varió durante la conservación. Antártica INTA fue superior en MS, SS, y AT; mientras el resto de los cultivares no difirieron entre sí. Al finalizar la etapa de poscosecha el único parámetro que se incrementó significativamente fue el contenido de AT, en todos los cultivares. Los resultados de Pungenica determinaron que todos los cultivares fueron inicialmente «moderadamente pungentes», y salvo Antártica INTA que logró mantenerse, los demás descendieron a «pobremente pungentes». Valcatorce INTA, Navideña INTA y Valuno INTA registraron valores similares de FT significativamente mayores que los de Cobriza INTA, y Antártica INTA fue inferior a todos. Se concluyó que Cobriza INTA, Valcatorce INTA, Navideña INTA y Valuno INTA resultaron semejantes en la mayoría de los parámetros evaluados y que el período de conservación bajo la modalidad de pilas, generó cambios significativos en el contenido de AT y en la pungencia. Por lo tanto, existe el riesgo de que los bulbos almacenados cambien su caracterización durante la conservació