C.M. Grieve

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.

Tolerance of vegetable crops to salinity

Global constraints on fresh water supplies and the need to dispose of agricultural, municipal, and industrial waste waters have intensified interest in water reuse options. In many instances, the value of the water is decreased solely because of its higher salt concentration. Although quantitative information on crop salt tolerance exists for over 130 crop species, there are many vegetables which lack definitive data. Vegetable crops are defined as herbaceous species grown for human consumption in which the edible portions consist of leaves, roots, hypocotyls, stems, petioles, and flower buds. The salt tolerance of vegetable species is important because the cash value of vegetables is usually high compared to field crops. In this review some general information is presented on how salinity affects plant growth and development and how different measurements of salinity in solution cultures, sand cultures, and field studies can be reconciled to a common basis. The salt tolerance of vegetables has been condensed and reported in a uniform format based on the best available data. Discrepancies and inconsistencies exist in some of the information due to differences in cultivars, environments, and experimental conditions. For a great number of species little or no useful information exists and there is an obvious need for research.

Evaluation of salt tolerance in rice genotypes by multiple agronomic parameters

AbstractThe lack of an effective evaluation method for salt tolerance in the screening process is one of the reasons for limited success in conventional salt tolerance breeding. This study was designed to identify useful agronomic parameters for evaluation of salt tolerance and to evaluate genotypes by multiple agronomic parameters for salt tolerance at different growth stages. Twelve genotypes were grown in a greenhouse in sand and irrigated with nutrient solutions of control and treatments amended with NaCl and CaCl2 (5:1 molar concentration) at 4.4 and 8.2 dS m-1 electrical conductivity. Wide genotypic differences in relative salt tolerance based on seedling growth were identified. The duration of reproductive growth between panicle initiation and anthesis was either reduced or increased by salinity, but the response was not strictly correlated with relative salt tolerance in seed yield among genotypes. Wide genotypic differences in relative salt tolerance based on spikelet and tiller numbers were identified. Few genotypic differences were identified for fertility and kernel weight. Spikelet and tiller numbers contributed most of the variation to seed yield among parameters investigated. When genotypes were ranked for salt tolerance based on the means of multiple parameters, dramatic changes of salt tolerance at early and seed maturity stages were observed in two genotypes, GZ5291-7-1-2 and GZ178. IR63731-1-1-4-3-2 was identified with a favourable combination of salt tolerance at early seedling and seed maturity stages. Cluster group ranking of genotypes based on multiple agronomic characters can be applied in salt tolerance breeding to evaluate salt tolerance and may have great advantage over conventional methods.

Purslane (Portulaca oleracea L.): a halophytic crop for drainage water reuse systems.

Drainage water reuse systems have been proposed for the west side of the San Joaquin Valley of California in order to reduce the volumes of water requiring disposal. Implementation of this system requires development of a cropping system with successively higher salt tolerance. A major limitation is the need to identify alternate species that will be suitable as the final, most salt tolerant crop in the series. These crops must be productive when irrigated with waters that are typically high in sulfate salinity and may be contaminated with potentially toxic trace elements. This study was initiated to evaluate the interactive effects of sulfate salinity and selenium on biomass production and mineral content of purslane (Portulaca oleracea). Plants were grown in greenhouse sand cultures and irrigated four times daily. Treatments consisted of three salinity levels with electrical conductivities (ECi) of 2.1, 15.2, and 28.5 dS m−1, and two selenium levels, 0 and 2.3 mg L−1. In the initial harvests, shoot dry matter was reduced by 15 to 30% at 15.2 dS m−1 and by 80 to 90% at 28.5 dS m−1. Regrowth after clipping above the first node was vigorous and biomass from plants irrigated with 15.2 dS m−1 water was nearly double that from the 2 dS m−1 treatment. Purslane appears to be an excellent candidate for inclusion in saline drainage water reuse systems. It is (i) highly tolerant of both chloride- and sulfate-dominated salinities, (ii) a moderate selenium accumulator in the sulfate-system, and (iii) a valuable, nutritive vegetable crop for human consumption and for livestock forage.

Evaluation of salt tolerance in rice genotypes by physiological characters

AbstractThe use of physiological characters as selection criteria in salt tolerance breeding requires the identification of the contribution each individual character makes to salt tolerance. Rice genotypes were evaluated for salt tolerance in terms of grain yield and physiological characters. Plants of twelve genotypes were grown in sand tanks in a greenhouse and irrigated with Yoshida nutrient solution. Sodium chloride and calcium chloride (5:1 molar ratio) were added at two concentrations to give moderate (4.5 dS m-1) and high (8.3 dS m-1) salinity treatments. One set of plants was harvested at 635 °Cċd (accumulative thermal time) after planting to determine LAI and mineral ion concentrations. Another set of plants was allowed to grow to maturity. High genotypic diversity for LAI and shoot ion contents was observed. LAI contributed the most to the variation of the grain yield under salt stress. Significant correlations between LAI and yield components in both salt-tolerant and-sensitive genotypes further confirmed the significant contribution of LAI to grain yield. K-Na selectivity increased with increasing salinity. Conversely, Na-Ca selectivity decreased with increasing salinity. Significant correlations were identified between grain yield and both Na-Ca and K-Na selectivity. Highly significant (p<0.001) correlations were identified between Na-Ca selectivity and the rankings among genotypes for grain yield. Thus, Na-Ca selectivity could be one salt tolerance component and an useful selection criterion in screening for salt tolerance.

The importance of initial seed size in wheat plant response to salinity

Large initial seed size frequently confers distinct advantages on cereal crops in terms of seedling vigor, hardiness, improved stand establishment, and higher productivity. This study was conducted to determine if these advantages inherent in the plants grown from large seeds persist when the crop is subjected to salinity stress. Two hard red spring wheat cultivars, ‘Yecora Rojo’ and ‘Anza’ were grown in greenhouse sand cultures from seed of two size classes that differed in weight by a factor of 2. The cultures were irrigated four times daily with complete nutrient solutions to which NaCl and CaCl2 (2:1 molar ratio) were added to achieve osmotic potentials of −0.05. −0.55, and −0.70 MPa with electrical conductivities of 1.8, 12.8, and 15.8 dS m-1, respectively. In response to both salinity and small initial seed size, the following plant characteristics decreased: leaf appearance rate, blade area, tillers per plant, spikelets per spike and seeds per spike. Plants grown from large seeds out-yielded those from small seeds by 8, 37, and 27% for Yecora Rojo and by 15, 30, and 23% for Anza at osmotic potentials of −0.05, −0.55 and −0.70 MPa, respectively. Compared to the corresponding nonsaline controls, the yield of Yecora Rojo grown at −0.55 MPa was 51% for the plants from large seed and 35% from the small seeds. For Anza salinized at −0.55 MPa, these values were 49 and 40%, respectively. Exploitation of the benefits derived from large initial seed size may be a cost-effective management strategy for improving wheat productivity in salt-affected areas.

Biomass accumulation and potential nutritive value of some forages irrigated with saline-sodic drainage water

A controlled study using a sand-tank system was conducted to evaluate 10 forage species (bermudagrass, ‘Salado’ and ‘SW 9720’ alfalfa, ‘Duncan’ and ‘Polo’ Paspalum, ‘big’ and ‘narrow leaf’ trefoil, kikuyugrass, Jose tall wheatgrass, and alkali sacaton). Forages were irrigated with sodium-sulfate dominated synthetic drainage waters with an electrical conductivity of either 15 or 25 dS/m. Forage yield was significantly reduced by the higher (25 dS/m) salinity level of irrigation water compared to the lower (15 dS/m) level. There was wide variation in the sensitivity of forage species to levels of salinity in irrigation water as reflected by biomass accumulation. With the exception of bermudagrass, which increased accumulation at the higher level of salinity, and big trefoil, which failed to establish at the higher level of salinity, ranking of forages according to the percent reduction in biomass accumulation due to the higher level of salinity of irrigation water was: Salado alfalfa (54%) = SW 9720 alfalfa (52%) > Duncan Paspalum (41%) > narrow leaf trefoil (30%) > alkali sacaton (24%) > Polo Paspalum (16%) > Jose tall wheatgrass (11%) = kikuyugrass (11%). Bermudagrass and Duncan Paspalum were judged to be the best species in terms of forage yield and nutritive quality. Kikuyugrass, which had the third highest biomass accumulation, was judged to be unacceptable due to its poor nutritional quality. Although narrow leaf trefoil had a relatively high nutritional quality, its biomass accumulation potential was judged to be unacceptably low. Alfalfa cultivar’s biomass accumulations were the most sensitive to the higher level of salinity, among forages that survived at the higher salinity level, although actual accumulations at the higher salinity were high relative to other forages. Increased salinity influenced several forage quality parameters, including organic matter (OM), crude protein (CP), neutral detergent fibre (NDF), and in vitro gas production, generally leading to higher nutritional quality at the higher salinity level, although their significance varied amongst species and cuttings.

Effect of high boron application on boron content and growth of melons

Management options for reducing drainage water volumes on the west side of the San Joaquin Valley of California, such as reuse of saline drainage water and water table control, have the potential to adversely impact crop yields due to a build up in soil solution boron concentration. An earlier experiment had shown that extrapolation of B soil tests to field conditions provided poor predictability of B content of melons despite statistically significant relationships. Consequently, three tests for extractable soil B were evaluated for their ability to predict conditions of potential B toxicity in melons grown under controlled conditions. Melons were grown for 95 days in two consecutive years in containers of Lillis soil (very-fine, smectitic, thermic Halic Haploxerert) that had been pretreated with solutions containing B concentrations as great as 5.3 mmol L−1. Extractable soil B was determined using ammonium acetate, DTPA-sorbitol, and a 1:1 aqueous soil extract at the beginning and end of the experiment. The B treatments caused various deleterious effects on melon growth and development. Fresh and dry plant matter decreased significantly with increasing B concentrations, while B concentration of plant leaves, stems, and fruits increased significantly with increasing B. The number of days to first flowering was significantly delayed from 35 days at B treatments < 2 mmol L−1 to 51 days at B treatments > 3 mmol L−1. Fruit set was completely inhibited at the highest B treatment of 5.3 mmol L−1. Plant analysis revealed a highly significant relationship between soil extract B obtained with all three extractants and leaf, stem, and fruit B content. Correlation coefficients for plant stems and fruits were much higher than for plant leaves. Correlation coefficients for all soil tests were almost equivalent, although the highest values were obtained for the DTPA-sorbitol extract indicating the greatest predictive capability. The soil tests were well able to predict B damage to melons in a container experiment.

Plant growth and ion relations in lucerne (Medicago sativa L.) in response to the combined effects of NaCl and P

The combined effect of NaCl and P on the growth of lucerne was studied in two hydroponic greenhouse experiments. NaCl concentrations were identical in each experiment (0, 50 and 100 mM NaCl) while external P concentrations were low (viz. 0.002, 0.02 and 0.2 mM measured as 0.006, 0.026 and 0.2 mM, respectively) in one experiment and higher (0.5 and 5.0 mM) in the second. Plant biomass was reduced more by the low P levels than by high concentrations of NaCl. A significant NaCl*P effect was found where external P concentrations were low (0.006–0.2 mM) but there was no difference in plant production between the two P concentrations of 0.5 and 5.0 mM. Shoot and root concentrations of Na and Cl increased significantly with increasing NaCl concentration in both experiments and there were some differences in the concentrations of these ions at different external P levels. At low P, NaCl had no significant effect on shoot concentrations of P; however, root P concentrations tended to decrease with increasing NaCl level. Increasing external P from 0.006 to 0.2 mM led to significant increases in P concentrations in both roots and shoots. At higher P, concentrations of P in both the shoots and the roots did not differ with external NaCl or P conditions. Our results illustrate the complex relationship that exists between NaCl and P at low P levels. We conclude that high or non-limiting concentrations of P (0.2 – 5.0 mM) do not affect lucernes response to NaCl.

The response of lucerne (Medicago sativa L.) to sodium sulphate and chloride salinity

Sodium and sulphate-dominated salinity is a serious environmental problem occurring in soils and groundwater in many parts of the world. The effect of Na2SO4 and NaCl, at electrical conductivity levels ranging from 2 to 17 dS m-1, on the growth and tissue ion concentrations of 16 lines of lucerne (Medicago sativa L.) was examined in the greenhouse over a 2 month period. Averaged across all lines, plants grown at 17 dS m-1 produced 66% of the dry matter of plants grown at 2 dS m-1. However there were significant differences among lines in relative salt tolerance (as defined by the slope of the reduction in dry matter) versus electrical conductivity. Dry matter production was negatively correlated with shoot concentrations of Na+, Cl- and S2- and generally lines that were more tolerant to salinity had lower concentrations of those ions in the shoots. We conclude that lucerne is moderately tolerant to Na2SO4 -predominated salinity, and that the degree of intraspecific variation that exists within this species will allow more tolerant lines to be selected for establishment in conditions where sulphate salinity is a problem.