Browsing by Author "Perez Ortola, Marta"
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Item Open Access Modelling the impacts of in-field soil and irrigation variability on onion yield(Cranfield University, 2013-11) Perez Ortola, Marta; Knox, Jerry W.; Hess, Tim M.Globally, onion (Allium cepa L.) represents an extremely important crop in terms of production, value and consumption. Similarly, in the UK onion production is considered to be one of the most important high-value field vegetables, with ca. 300,900 tonnes being produced from 8,448 ha (DEFRA 2010). However, a great variability in onion productivity (yield) has been identified due to a combination of environmental, genotypic, management and agronomic factors. The increasing demand for high quality vegetables and their supply year round is adding significant pressure on farming enterprises, which add to the challenges UK onion producers already face (e.g. crop management, irrigation and pest control decision-making). The aim of this research was to assess the impacts of in-field soil and irrigation variability on onion yield and quality. Therefore, the scientific evidence on the relationships between onion yield, crop water use, irrigation and crop quality were initially reviewed and the evidence corroborated with data from an industry survey. In order to evaluate the effects of soils and irrigation variability on yield, under different agroclimatic conditions, a crop growth model (AquaCrop) was calibrated and then validated using experimental field data. The scientific evidence in the literature and results from the industry survey were used to validate and calibrate the AquaCrop model for brown onion (cv Arthur). Statistical analyses were used to assess crop model goodness of fit. A series of scenario were then defined and the AquaCrop model used to assess the impacts of different onion cropping practices, production areas and typical and extreme climatic conditions on crop yield. The effects of irrigation non-uniformity (typical of a boom and linear move irrigation application system) on production were assessed under a series of agroclimatic conditions (five different years) and two contrasting soil types (sandy and sandy loam). The simulations showed that the lowest yield (8.6 t DM/ha) and greatest variability (standard deviation: 0.23 t DM/ha) occurred under the driest agroclimatic conditions. Production on sandy soils resulted in higher yield (in average 0.24t DM/ha) than on a sandy loam soil. The yield under hosereels fitted with booms were statistically significant (Kruskal-Wallis analysis) lower than for the linear move, although the difference was very small (average of 9.52 t DM/ha vs. 9.56 t DM/ha). Under ‘average dry’ conditions, the highest yield was produced on sandy soils (8.78 t DM/ha), contrary to ‘average’ agroclimatic conditions, where the highest yield was produced on sandy loam soils (9.55 t DM/ha). For the driest season, the effects of irrigation variability were only significant on sandy soils (8.80 t DM/ha and 8.73 t DM/ha for hosereel fitted with linear move and boom, respectively). The study of uniform versus non-uniform irrigation applications showed that onion yield was higher under uniform irrigation. The differences between yields produced under uniform and non-uniform irrigation increased with increasing climatic aridity (0.01-0.18 t DM/ha compared to average values). Differences were greater in cases of boom application systems. Onion yield generated by simulations of uniform conditions fell within the range found in the literature. The variability observed under non-uniform irrigation was the same (up to 30-40%) as the overall variation reported by growers.Item Open Access Water relations and irrigation requirements of onion (Allium Cepa L.): a review of yield and quality impacts(Cambridge University Press, 2014-11-05) Perez Ortola, Marta; Knox, Jerry W.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.