Increasing plant P supply has been shown to either increase or decrease the salt tolerance of many plants. Tomato plants (Lycopersicon esculentum Mill.) were grown in a greenhouse in a continuously flowing solution culture system to investigate whether P fertilization modified the detrimental effects of NaCl at low constant P concentrations similar to those in soil solutions. Increasing P fertilization enhanced the tolerance of tomato plants to NaCl. At 0.1, 1.0, and 10 mM P, the NaCl concentrations that reduced yields of fruit by 50% were 58,72, and 130 mM, respectively. Salinity reduced foliar P concentrations. This may have been mediated partly through ionic strength effects, which decreased the activity of H2PO4−1 by about 40%. Plants grown under saline conditions had higher internal P requirements. When the NaCl concentration was increased from 10 to 50 and 100 mM, the corresponding concentrations of P in the youngest mature leaf required to obtain 50% yield were increased from 1.8 to 2.4 and 3.0 g kg−1. The change in internal P requirement was also evident by the relative severity of foliar symptoms of P deficiency in plants growing in the saline treatments at any given foliar P concentration. Adequate P nutrition was essential for effective ionic compartmentation. Under saline conditions, increasing the solution P concentration from 1.0 to 10 μM decreased Na and increased K concentrations in immature leaves but increased Na and decreased K in the mature leaves. Accumulation of ions for osmotic adjustment and restriction of Na and Cl accumulation in immature leaves appear to be involved in P enhancement of salt tolerance of tomato plants.

Adverse effects resulting from fertilization with high rates of ammonium sulphate were determined on a kikuyu grass (Pennisetum clandestinum) pasture grown on a krasnozem in a sub-tropical environment. Corrective fertilizer practices using lime and phosphorus were evaluated.Ammonium sulphate application (336 kg N/ha/annum for 4 years followed by 672 kg N/ha/annum for 2 years) decreased soil pH from 5.0 to 4.0. Under these conditions, soluble A1 in the soil increased, while exchangeable Ca, Mg, and K decreased. Concentrations of Ca, Mo, and P in the kikuyu tops were lowered, while concentrations of Mn were raised. Liming to pH 5.5 promoted growth more at 672 kg N/ha/annum than at 134 kg N/ha/annum, while generally little further yield response occurred as soil pH was raised to about 6.0. Liming increased the concentrations of P, Ca, N, and Mo but decreased Mn in kikuyu tops.Phosphorus application decreased soluble aluminium in the soil in all nitrogen treatments, but only increased kikuyu yield where 672 kg N/ha/annum was applied. It did not alter plant chemical composition, except for an increase in P concentration.Yield increases to liming and P were attributed to the alleviation of A1 toxicity in the high N treatments. Lime responses in low N treatments were due to improved N nutrition resulting from mineralization of organic N.Lime application reduced the amount of N fertilizer required for maximum growth of kikuyu from 672 kg N/ha/annum on the unlimed soil to 134 kg N/ha/annum, while maintaining an adequate level of nutrients in the herbage and avoiding the problems of excess soil acidity.

Using NaCl or polyethylene glycol (PEG) solutions to progressively decrease the external osmotic potential of the peat casing of the growing medium used to culture the mushroom Agaricus bisporus resulted in proportionately decreased yields of sporophores. Over the range of -0.07 to -0.37 MPa, the extent of decrease in yield was similar with both types of osmoticum. However, with further decrease in external osmotic potential (from -0.37 to -0.62 MPa) there was a further proportional decrease in sporophore yield with PEG but a complete suppression of sporophore production with NaCl. Treatments with both NaCl and PEG decreased the concentrations of P, Mg, K, Fe and Mn, but not N and Cu, in sporophore dry matter. Treatment with NaCl solutions increased the concentrations of Na and CI ions in sporophore dry matter and decreased the concentration of Ca; PEG solutions had no effect. Ion toxicity associated with excessive accumulation of Na and C1 ions, or ionic imbalance associated with the concomittant decrease in Ca ions appear to be additional factors to osmotic stress in decreasing yield of sporophores when the growing medium becomes highly saline. The critical concentration of NaCl which caused 10% reduction in sporophore yield was 28 mM; A . bisporus is, therefore, moderately salt-sensitive.

was sampled at two week intervals over a period of one year. The concentrations of calcium throughout the year (0.15-0.28%) and phosphorus from late winter to early summer (0.20-0.28%) were well below the values normally considered to be required by milking cows and some classes of beef cattle. The nitrogen concentrations reached minimal values of 1.8-2.2% in winter, which appear to be adequate for milk production. From summer through to the end of winter, the ratio of K/(Ca + Mg) was much higher, and the Ca/P ratio was much lower, than those values reported to be associated with the occurrence of grass tetany in grazing cattle. Very high nitrogen concentratians in early summer (up to 5.2% N where 672 kg N ha-1 year-1 was applied) were in the range that has been associated with grass tetany in cattle. Lime application increased the nitrogen, phosphorus and calcium concentrations in the herbage throughout the year. The effect of lime in increasing nitrogen concentration in the herbage was maximal in late autumn and winter, at which time fertilizer nitrogen had little or no effect. The increased nitrogen concentration in the herbage through application of lime was associated with the development of a naturalized white clover component in the sward. Lime also increased the phosphorus concentration in the herbage, particularly from mid-winter to early summer, over which period phosphorus application per se had minimal effect. The application of lime allied with 134 kg N ha-1 year-1 maintained a high level of dry matter production as well as a more adequate and better balanced nutrient content in the kikuyu pasture throughout the year, and particularly in winter, when cattle grazing kikuyu pastures suffer a serious feed gap.