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 interactions involved would require the input from a multidisciplinary team of scientists. This review addresses the nutrient elements individually and we emphasise research directed towards the organ, whole-plant and field level. We have attempted to synthesise the literature and reconcile results from experiments conducted in a variety of conditions such as soil and solution cultures, those using mixed and single-salt (only NaCl) compositions, and those 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 nutrient availability, competitive uptake, transport or partitioning within the plant. For example, salinity reduces phosphate uptake and accumulation in crops grown in soils primarily by reducing phosphate availability but in solution cultures ion imbalances may primarily result from competitive interactions. Salinity dominated by Na+ salts not only reduces Ca2+ availability but reduces Ca2+ transport and mobility to growing regions of the plant, which affects the quality of both vegetative and reproductive organs. Salinity can directly affect nutrient uptake, such as Na+ reducing K+ uptake or by Cl- reducing NO3- uptake. Salinity can also cause a combination of complex interactions that affect plant metabolism, susceptibility to injury or internal nutrient requirement. Despite a large number of studies that demonstrate that salinity reduces nutrient uptake and accumulation or affects nutrient partitioning within the plant, little evidence exists that adding nutrients at levels above those considered 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 supplemental 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 occur 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.