Nine tropical and one temperate pasture legume species were grown in pots of soil with varying additions of phosphate. Growth responses and chemical conlposition of the plant tops were recorded, and from the latter, critical percentages of phosphorus were established. These were verified by using data from two soils in the pot culture investigation and a total of six field sites.Glycine javanica and Desmodium intortum were the most responsive species in pots, and Stylosanthes humilis and Lotononis bainesii were the least responsive species. The quantity of phosphorus per pot accumulated in the tops of the plants was greatest for Stylosanthes humilis and Lotononis bainesii at all treatment levels. Critical percentages of phosphorus in the tops of Phaseolus Iathyroides, Phaseolus atvopuvpureus, Stylosanthes humilis, Centrosema pubescens, Glycine javanica, Lotononis bainesii, Medicago sativa, Desmodium uncinatum, DesmorEium intortum, and Vigiza luteola sampled at the immediate pre-flowering stage of growth were 0.20, 0.24,O. 17,O. 16, 0.23,O. 17, 0.24, 0.23, 0.22, and 0.25 % phosphorus respectively.

This paper describes the effect of phosphorus on nitrogen concentration and on the total and individual concentrations of the cations calcium, magnesium, potassium, and sodium in the plant tops of 10 tropical legumes and one temperate legume when grown on two soils of different type, a light-textured solodic soil and a gley soil. Species used were Phaseolus lathyroides, P. atropurpureus, Stylosanthes humilis, Centrosema pubescens, Glycine javanica, Lotononis bainesii, Medicago sativa, Desmodium uncinatum, D. intortum, Vigna luteola, and Leucaena leucocephala. The nitrogen concentrations in the plant tops were increased by phosphorus supply, and good correlations were established between the nitrogen and phosphorus concentrations in the plant tops. When sodium dihydrogen phosphate was used as the source of phosphate, the sodium concentration in V. luteola, M. sativa, and L. bainesii was increased. Other species were not affected. Increasing phosphate supply as monocalcium phosphate had little effect on plant calcium concentration, but brought about an increase of magnesium in P. lathyroides and P. atropurpureus. In the solodic soil particularly, increases in phosphate supply in most species caused reductions in the potassium concentration, partly compensated by increases in the magnesium and calcium concentrations. Concentrations of the cations in the plants reflected the soil exchangeable cation composition. Plant species differed in their cation status. P. atropurpureus and P. lathyroides were relatively high in magnesium, L. bainesii and D. intortum in potassium, V. luteola, L. bainesii, M. sativa, and P. lathyroides in sodium, and C. pubescens and S. humilis in calcium.

Nine tropical pasture grasses were grown in pots of a phosphate-deficient solodic soil with varying additions of phosphate. Growth responses and chemical composition of the plant tops were recorded, and from these, critical percentages of phosphorus were established. All species responded to phosphate addition. Under the conditions of this experiment Melinus minutiflora was the most responsive species and Pennisetum clandestinum the least responsive. Critical percentages of phosphorus in the tops of Melinus minutiflora, Cenchrus ciliaris, Paspalum dilatatum, Panicum maximum, Chloris gayana, Sorghum almum, Setaria anceps, Digitaria decumbens and Pennisetum clandestinum sampled at the immediate pre-flowering stage of growth were 0.18, 0.25, 0.25, 0.20, 0.22, 0.20, 0.21, 0.16, and 0.22% respectively of the dry matter. Phosphate applications decreased the concentration of plant potassium, had no significant effect on calcium, increased magnesium in most species, and in four species increased sodium. The increases in magnesium and sodium are considered to result in part from reduced potassium uptake and the plant's ability to preserve cation balance. Three species, C. gayana, P. maximum and D. decumbens, had relatively high concentrations of sodium (58, 46, and 46% of total cations respectively). In contrast S. anceps had a relatively high concentration of potassium (56 % of total cations) and low sodium (7%). Phosphate applications decreased the concentration of nitrogen, and had little effect on chloride.

SummaryFor two Glycine species (wightiit and tomentella) varying in sensitivity to salt the development of stress over a range of salinities was traced through changes in growth, water content, and chemical composition of tissues of different type and age.The general picture of salt stress appears to be one of immediate growth reduction through an initial water stress approximately proportional to the concentration of salt applied. At 40 m-equiv/l of sodium chloride osmotic adjustment apparently occurs, control growth rate is regained, and, the data suggest, is likely to be maintained without significant tissue injury developing. At 80 m-equiv/l of sodium chloride, the trends in tissue water content indicate that some osmotic adjustment may occur, particularly in the older leaves, but at this level of salinity and especially at 160 m-equiv/l of sodium chloride the rapid and excessive chloride accumulation injures the leaves and growth rate falls progressively in relation to that of the control. The detrimental effects of salt on nutrient and water content are more pronounced in the young leaf tissue developing during salt treatment than for the older leaves.Species difference in sensitivity appears associated with the leaf injury phase of salt stress. It is thought that leaf injury is greater in tomentella than wightii because of the faster initial increase in chloride concentration in tomentella, particularly in the younger leaf tissue, and also that a reduced potential for protein synthesis in these leaves in tomentella may have aggravated the situation.Analysis of time trends in growth rate and other plant attributes, a technique largely ignored in salt resistance studies, helps to distinguish between the osmotic and toxic effects of ions.

Adaptability to salinity stress was related to the productivity of Glycine wightii (G. javanica) cultivars by the technique of comparing the multivariate characteristics of response for 22 accessions that are representative of the world centres of origin. Roots and tops responses were compared to clarify the metabolic relations between glycines, as salinity was increased from that required for normal growth and metabolism to levels almost causing death due to excess sodium chloride in the substrate. There was a range and pattern of response that suggested grouping among the glycines. One group in particular was more resistant to salinity stress than others. These glycines exemplified to a greater degree than others the tendency of all to exclude sodium and to a lesser extent chloride from the plant tops. These were also the more vigorously growing glycines with a higher potassium, phosphorus, and nitrogen content in both control and saline treatments. In them, vigour of growth and control of ion content were associated, and both these factors were important determinants of tolerance to salinity stress. Sodium appeared to be more toxic than chloride to plant growth. These aspects of growth and metabolism are discussed in relation to differences in ploidy between the groups of glycines. The technique used shed further light on the important agricultural problem of combining adaptability and high productivity.