The tolerances of a range of tropical grain legumes to salinity were compared during early vegetative growth of plants grown in pots with NaCl added to a sandy loam soil to achieve electrical conductivities (sat. extract, ECe) over the range, 1.3-13.8 dS m-1. Tolerance, based on the ECe at 50% of maximum growth (in parenthesis) was of the order: Sesbania cannabina (13.2 dS m-1) > guar cv. CP 177 (10.1 dS m-1) > guar cv. Brooks (9.8 dS m-1) > cowpea cv. Caloona (9.0 dS m-1) > soybean CPI 26671 (6.7 dS m-1) > pigeon pea cv. Hunt (5.4 dS m-1) > black gram cv. Regur (5.0 dS m-1) > pigeon pea cv. Royes (4.9 dS m-1) > green gram cv. Celera (3.5 dS m-1). Genotypes exhibited differences in Na+ accumulation, with black gram, green gram and pigeon pea accumulating large quantities in shoot tissues, compared with effective exclusion of Na+ by Sesbania, guar and soybean. Smaller relative differences existed between species in terms of Cl- uptake, and the relative yield reduction was closely related to the amount of cl- in shoots. These results are discussed in terms of current understanding of the nature of salt tolerance in nonhalophytes.

At Katherine, N.T., swards of Townsville lucerne (Stylosanthes humilis H.B.K.) were sown in late November and late December, 1964, and sampled every two weeks during the growing season. At each harvest the dry matter, nitrogen, and phosphorus yields of stem, leaf and petiole, inflorescence, unshed pods, shed leaf, and shed pods were determined. Crop growth rates and net assimilation rates (leaf weight basis, ELW), were derived for both plantings and compared with calculated soil water storage. Drought in January and February restricted growth during the vegetative phase, but rapid growth resumed when water stress was relieved by rain in March. Maximum dry matter yield (5400 lb an acre) and mean crop growth rate (42.3 lb an acre a day) for the November sowing were similar to those measured for Townsville lucerne at Katherine and elsewhere. Maximum crop growth rates (250 and 110 lb an acre a day for the November and December sowings respectively) appear to be about the same as those recorded in the field for subterranean clover. The strong influence of water stress on growth was emphasized by the close relationship demonstrated between ELW and calculated soil water storage. Uptake of nitrogen and phosphorus was restricted during water stress and both were redistributed to reproductive parts of the plant during flowering and seeding, nitrogen more readily than phosphorus. Nitrogen and phosphorus contents (1.9-2.0 per cent N and 0.70-0.75 per cent P) were lower than those recorded for other tropical and temperate pasture legumes. The implications of the low phosphorus contents of Townsville lucerne as cattle feed are discussed.

Following burning (day 0) of a water-stressed sward of green panic and siratro, measurements were made both on unburned plants and on regrowth of burned plants of leaf water potential (�s) and stomatal conductance (gs) at 1.00 p.m. and of leaf extension. In the unburned plants �s, remained low (-23 to -45 bar for green panic, and -14 to -18 bar for siratro), the stomata were closed and no growth occurred. In the burned plants of both species, however, �s on day 12 was -9 to -11 bars, the stomata were open and growth occurred, presumably because the complete defoliation allowed the plants to make use of a limited store of soil water at higher water potential. In green panic �s fell rapidly, and growth stopped after day 19, but �s and g, in siratro were still high on day 28. Burning of droughted native pastures is a common management practice in the semi-arid tropics of Australia. The data may explain how the pastures are able to make the new growth that frequently occurs.

Cracking clay soils or vertisols occur in large areas of the subhumid regions of north-eastern Australia and frequently contain appreciable levels of salt in their subsoils. The comparative salt tolerance of some tropical pasture legumes was studied in pots with NaCl added to a clay soil to achieve electrical conductivities (saturated extract, ECe) over the range 2.0- 20.0 dS m-1. Tolerance, based on EC, at 50% of maximum growth (in parentheses) was in the order: Macroptilium atropurpureum cv. Siratro (10.6)> Macroptilium lathyroides cv. Murray (9.9) > Vigna trilobata (9.7) > Indigofera spicata (9.5) > Desmanthus subulatus (9.3) > Arachis pintoi (7.9) > Clitoria ternatea (6.4) > Stylosanthes scabra (5.6) > Indigofera schimperi (5.4) > Psoralea tenax (5.3) > Rhynchosia minima (5.1). The grass Panicum coloratum cv. Bambatsi was markedly more tolerant than any of the legumes studied, with 50% yield at an EC, of 16.4 dS m-1. Patterns of Na+ and Cl- uptake with increasing level of salt differed between species, but were not related to the degree oftolerance observed. The results are discussed in terms of the reported salinity tolerance of legumes generally and their implications to the search for persistent legumes for clay soils.

Three experiments were carried out to obtain data on the suitability for forage of ten oat (Avena sativa) cultivars; on optimum water and nitrogen regimes for growing oats for forage; and on the liveweight gains of cattle grazing forage oats. The early-flowering cultivars, Swan, Bentland and Benton, grew faster than the late-flowering cultivars, Trispernia and Algerian, but did not tolerate defoliation so well. The most practical treatment for growing oats for forage was watering each two weeks and applying 90 kg ha-1N at planting and another 90 kg ha-1N eight weeks later. Swan oats, Algerian oats and a Swan oats/vetch (Vicia atropurpurea) mixture, all sown in May, gave liveweight gains 373,300 and 370 kg ha-1 when grazed at 4.3 head ha-1, and 477,423 and 329 kg ha-1 at 5.7 head ha-'. Only Swan at both 5.7 and 4.3 head ha-1 and Algerian at 4.3 head ha-1 sustained liveweight gains for the whole 19-week grazing period. The prospects for profitable use of oats as feed for cattle in the Ord River Valley appear to be poor.