Low Soil Salinity Research Articles

Phosphate‐Fertilizer‐Induced Salt Toxicity of Newly Planted Apple Trees

AbstractMonoammonium phosphate (MAP) or triple superphosphate (TSP) added to planting holes often stimulates early growth of apple trees (Malus domestica Borkh.); however, high rates may stunt or kill trees. A greenhouse study was conducted on a Quincy sand (a mixed, mesic Xeric Torripsamment) and a Cowiche silt loam (a fine‐loamy, mixed, mesic Aridic Argixeroll) to examine effects of soil type, P source (MAP or TSP), and P rate (0–2.75 kg P/m3) on soil salinity, soil acidity, and apple tree growth in nonleaching soil systems during a 56‐d period after planting. Rootstock and old scion masses were not affected by soil type or P treatments. In the Quincy sand, new scion mass and root mass were inversely related to P rate in both MAP‐ and TSP‐amended soil; tree death occurred at P rates above 1.65 kg/m3. In the Cowiche soil, root mass was independent of and new scion mass was inversely related to P rate. At equivalent P rates, TSP produced lower soil salinity and greater soil acidity than MAP. For a given P source, soil salinity and acidity were positively related to P rate. Soil salinity decreased and soil pH increased over time. Relative new scion mass was inversely related to time‐integrated soil salinity; however, the relationships were soil‐specific. Total exchangeable soil acidity was positively related to P rate and was soil‐dependent. Exchangeable soil Al was detected only at the two highest TSP rates in the Quincy soil. Indirect evidence suggested that Mn, NH3, and NO2 phytotoxicities and any nutrient deficiencies were absent. The results suggest that transient soil salinization is the primary mechanism for MAP‐ and TSP‐induced apple tree phytotoxicity.

Effect of salt tolerancy levels on farming of date palm varieties: A case study

Abstract Soil and water investigations in Al‐Hassa oasis of Saudi Arabia indicated that before the introduction of the irrigation and drainage project to the oasis in 1972, the Akhlas date palm variety was grown only in farms with deep low saline soils, while the Ruzaiz date palm variety was grown in farms with moderate and highly saline soils. After the introduction of the project, the soil salinity and drainage conditions were improved and Akhlas variety showed successful growth in remote farms. It seems likely that the two local date palm varieties have different tolerance levels for soil salinity. Akhlas variety has a low tolerance level while Ruzaiz variety has a high tolerance level for soil salinity. This finding is expected to help in understanding and improving date palm farming.

Soil Salinity, Sun Exposure, and Growth of Acrostichum aureum, the Mangrove Fern

Populations of Acrostichum aureum growing under contrasting conditions of soil salinity and sunlight exposure were studied in two sites in the north coast of Puerto Rico. Plant size and density of clumps under full sun exposure are larger in sites with lower soil salinity. In shady habitats with relatively high soil salinity (understory of Laguncularia forests), plants grow larger but occur at lower densities as compared with nonshaded sites. Apparently salt stress in shady habitats is reduced due to lower evaporative demands. Osmotic concentration of leaf cell sap increases markedly with soil salinity (except in shade plants), a process accompanied by corresponding increases in leaf water content per unit leaf area, and reductions in leaflet size and specific leaf area. The major solutes responsible for increases in cell sap osmotic pressure are Na+, Mg2+, and sucrose. However, the largest relative response to salinity is shown by the cyclitol D-1-0-methyl-muco-inositol, a cytoplasmic compatible solute. Thus, this cyclitol can be considered as an accurate indicator of salt stress in A. aureum. The Cl-/Na+ molar ratios in the cell sap are consistently higher in A. aureum compared to L. racemosa and R. mangle (2.5 against 1.2 and 1.5, respectively). The K/Na molar ratio based on total content per unit tissue dry weight is also higher in the fern (2.6) compared to typical mangroves (less than 0.5). These results indicate a difference in ion selectivity at the root level.

Water requirement, yield and fruit quality of grapefruit irrigated with high-sulphate water

SummaryThe effect of irrigation with different amounts of high-sulphate water on the growth and yield of grapefruit trees was studied during a six-year period. Irrigation with 600–700 mm of water over the irrigation season, corresponding to 50–60% of pan evaporation, proved sufficient for high yield. Under-irrigation increased soil salinity associated with the highly soluble salts, and reduced tree growth (girth increase and seasonal vegetative growth). Although the fruit growth of the stressed grapefruit trees was delayed and yield was reduced, total soluble solids and acid percentage of the juice were increased significantly. Irrigation with the higher amounts of high-sulphate water resulted in gypsum precipitation/dissolution and a low persistent soil salinity which could not be leached.

Cattail Invasion and Persistence in a Coastal Salt Marsh: The Role of Salinity Reduction

The hypothesis thatTypha domingensis (cattail) can invade tidal marshes only after soil salinities are substantially reduced was tested experimentally by comparing the salt tolerance of seeds, seedlings, and plants reared from rhizomes. Germination rates for four southern California populations reached 100% in fresh water, decreasing to 2% at 20‰. The salt tolerance of seeds from three coastal populations was lower than that of the Salton Sea population. Salt tolerance of plants grown in the lab did not increase with age for seedlings up to 8 weeks old. Rhizome-bearing plants had greatly decreased growth at 10‰ and no growth at 25‰ However, rhizomes of about 5% of the plants survived 9 months at 45‰. The seeds and seedlings are salt sensitive, which explains why invasion into tidal marshes is restricted to prolonged periods of low soil salinity. The older, rhizome-bearing plants are salt tolerant, which explains how invading plants persist persist under hypersaline conditions.

Mangrove understory: an expensive luxury?

Recently, Janzen (1985) observed that mangrove forests lack a plant understory and proposed three hypotheses to explain the absence of reproducing unders ory herbs, vines (lianas), and shrubs in mangroves. Although the general observation of an absence of these plants in mangrove understory is true and had already been made by Chapman (1975, p. 13), there are, nevertheless, examples of plant understory in mangroves (e.g. Corlett 1986). Chapman lists well over a dozen vine, herb, fern, and palm species that grow in mangrove understory in Bangladesh (Sunderbans), Borneo, Malaysia, Martinique, India (Bombay), and the Philippines. All these examples are from high rainfall locations, the landward portion of mangroves, and/or ecotones characterized by low salinity soils (Chapman 1975). These examples suggest that hypotheses are needed to explain the general absence of plant understory in mangroves and why understory occurs when soil salinity decreases. I agree with Janzen's dismissal of his hypotheses 2 and 3 (however, for different reasons) but believe that his hypothesis 1 has merit. This hypothesis states that 'plants with low light resources cannot accumulate enough [sic] fast enough to meet the metabolic demands of the drain of the machinery and morphology of salt tolerance.' This formulation recognizes the need to balance the physiological and morphological cost of overcoming salinity stress with the light energy available to plants. However, there are other natural stressors and other energy sources that must be included in any evaluation of the plants growing on mangrove sites. Stressors include soils with high concentrations of hydrogen sulphide and low oxygen and loss of nutrients due to frequent tidal flushing or poor substrate conditions (Lugo 1978, Lugo et al. 1981). Oxygen to sustain root metabolism, freshwater to mitigate high salinity, and nutrients for biomass synthesis are vital energy subsidies to plants growing in mangroves, and they are all obtained, at least partially, from the substrate. Therefore, favourable conditions for root growth may be as important to plant survival on mangrove sites as light availability.

The Distribution and Growth of Salicornia Europaea on an Inland Salt Pan

The nature of the distribution of plant species along a soil salinity gradient at Rittman, Ohio, indicates that there is a definite relationship between soil salinity concentrations and the position of plant species along this environmental gradient. Only a single species of flowering plant, Salicornia europaea, was found growing at the most extreme portion of the salinity gradient. Soil samples collected from sites dominated by S. europaea had salinity levels which yielded in situ electrical conductivities ranging from 18.9 to 142.8 mmhos/cm, Atriplex triangularis grew at sites with intermediate levels of soil salinity, 3.9 to 40.0 mmhos/cm, and Hordeum jubatum dominated the least saline sites, 1.1 to 14.0 mmhos/cm, which were directly adjacent to a nonsaline meadow. Salicornia europaea had high levels of mortality during the spring and early summer months of the growing season, with the mean number of seedlings ranging from 58 plants per 100—cm2 quadrat in May to a mean value of 18 mature plants per quadrat at the end of the growing season in October. At the most highly saline sites containing S. europaea, seedling numbers ranged from a mean of 5 plants per 100—cm2 quadrat in May to 1 mature individual per quadrat by October. Transplants of S. europaea had the highest standing crop biomass levels in the Atriplex and Hordeum zones, with dry weight production decreasing in zones of both higher and lower soil salinity. Laboratory investigations indicated that S.europaea reached its optimal growth in nutrient solution treatments containing 170 meq/1 and 340 meq/1 NaC1. Germination of seeds of S. europaea under field conditions occurred over an extended period of time, from February through June, when soil salinity levels were lowest. Seed germination was not stimulated by treatments with salt and maximum germination percentages occurred in distilled water controls.

Phenology, Distribution and Survival of Atriplex triangularis Willd. in an Ohio Salt Pan

In an Athens Co., Ohio, salt pan, there were four vegetation zones: the Meadow, H or deum, Atriplex and Pan zones. These constituted a salinity gradient from the nonsaline Meadow to the highly saline Pan. The phenology, survival and distribution of the halophyte, Atriplex triangularis Willd., within this salt pan were investigated. The life cycle of A. triangularis spanned 9 months from February to October. The germination period extended from February to May. Flowers appeared in mid-July; seed development began in September. Senescence and death followed in late October. The population dynamics of A. triangularis were related to three main factors: soil temperature, soil moisture and soil salinity. Soil temperatures of 15 C appeared to trigger germination. High soil moisture values with consequent low soil salinity were prevalent during the winter-early spring germination period. Seedling establishment was particularly sensitive to salinity with severe mortality occurring in late spring and early summer when soil moisture values started to decline and salinity began to climb. The highest concentration of soil salts coincided with the flowering stage in July and August when soil moisture values dropped severely due to low rainfall and high evaporation. By the seed development and maturation stage in September, soil moisture levels had begun to rise due to heavy autumn rains and decreased evaporation which led to a decrease in total soil salts. The germination and survival of Atriplex triangularis were restricted in the main to the Atriplex zone. The relative absence of A. triangularis in the Meadow zone stemmed from the interference from the existing meadow vegetation. The rapid growth of Hordeum jubatum hindered the establishment of A. triangularis in the H or deum zone. High soil salinity within the Pan zone prevented the germination of A. triangularis.

GROWTH OF HORDEUM JUBATUM UNDER VARIOUS SOIL CONDITIONS AND DEGREES OF PLANT COMPETITION

Hordeum jubatum L. was grown in the greenhouse under various levels of soil moisture, soil salinity, soil fertility, and soil temperature, both alone and in association with other grasses. When grown alone it developed best under high soil moisture and high soil fertility, and low soil salinity. On wet, non-saline soils its growth was restricted by competition from Dactylis glomerata L. On wet, saline soils, where D. glomerata offered little competition, it developed freely. It developed only sparsely on dry or infertile soils. Agropyron elongatum (Host.) P. B. prevented development of H. jubatum on wet, saline soils, and Festuca arundinacea Schreb. and Phalaris arundinacea L. restricted its development to a high degree. H. jubatum growth was enhanced as soil temperatures were raised from 7 °C through 12° and 20°, to 27°.

Plant Community Composition and Net Primary Production within a Native Eastern North Dakota Prairie

The community composition and net primary production were studied for six community types within a native tallgrass prairie in eastern North Dakota. Estimates of green herbage production and litter weight were made using the harvest method. Six community types were examined: 1) Poa-Andropogon-Stipa on upland ridges with very low soil salinity and good internal drainage, 2) Bromus-Poa communities on small mounds having low soil salinity and good internal drainage, 3) Poa-Melilotus communities on a previously plowed low ridge, with somewhat saline soil with good internal drainage, 4) Distichlis-Hordeum-Poa on lowland sites with moderate soil salinity and poor drainage, 5) Distichlis-Hordeum communities on lowland soils with still higher soil salinity and poorer drainage, and 6) Salicornia-Suaeda communities on lowland sites with poorest drainage, highest soil salinity, and highest soil moisture. Floristically, the first type was the richest (46 species) and the last the poorest (only 4 species). Maximum observed green herbage weight within the six community types ranged from 109 to 353 grams/square meter; the first, second, and fourth community types being significantly higher than the others. Lowest green -herbage weight was recorded in the Salicornia-Suaeda communities. Litter weight within the unburned communities was highly uniform and ranged from 368 to 473 grams.

HIGH COUNTRY GRAZING IN THE WESTERN UNITED STATES

Between the deserts and the forests are vast expanses of basins, plateaux, and grasslands with a plant cover of grasses, broadleaved herbs, shrubs, and open, arid woodlands. The semi-arid grassland, the open woods, and the desert shrubland constitute the domain of the huge western livestock industry in the 17 states lying roughly west of the 100th meridian. These are known as the range states and they are likely to remain predominantly range states because of the low precipitation, rough topography, and shallow, rocky and saline soils.