Salinity mineral nutrient relations in horticultural crops

The relations between salinity and mineral nutrition of horticultural crops are extremely complex and a complete understanding of the intricate intera ctions involved would require the input from a multidisciplinary team of sc ientists. This review addresses the nutrient elements individually and we e mphasise research directed towards the organ, whole-plant and field level. We have attempted to synthesise the literature and reconcile results from e xperiments conducted in a variety of conditions such as soil and solution c ultures, those using mixed and single-salt (only NaCl) compositions, and th ose conducted over short (days) and long periods (months) of time. Crop performance may be adversely affected by salinity-induced nutritional disorders. These disorders may result from the effect of salinity on nutrie nt availability, competitive uptake, transport or partitioning within the p lant. For example, salinity reduces phosphate uptake and accumulation in cr ops grown in soils primarily by reducing phosphate availability but in solu tion cultures ion imbalances may primarily result from competitive interact ions. Salinity dominated by Na+ salts not only reduces Ca2+ availability bu t reduces Ca2+ transport and mobility to growing regions of the plant, whic h affects the quality of both vegetative and reproductive organs. Salinity can directly affect nutrient uptake, such as Na+ reducing K+ uptake or by C l- reducing NO3- uptake. Salinity can also cause a combination of complex i nteractions that affect plant metabolism, susceptibility to injury or inter nal nutrient requirement. Despite a large number of studies that demonstrate that salinity reduces nu trient uptake and accumulation or affects nutrient partitioning within the plant, little evidence exists that adding nutrients at levels above those c onsidered optimal in non-saline environments, improves crop yield. Nutrient additions, on the other hand, have been more successful in improving crop quality such as the correction of Na-induced Ca2+ deficiencies by supplemen tal calcium. Nutrient additions may also reduce the incidences of injury as has been observed in the reduction of Cl-toxicity symptoms in certain tree crops by nitrate applications. It is reasonable to believe that numerous salinity-nutrient interactions oc cur simultaneously but whether they ultimately affect crop yield or quality depends upon the salinity level and composition of salts, the crop species , the nutrient in question and a number of environmental factors. (C) 1999 Elsevier Science B.V. All rights reserved.