A study was made of the influence of sulphur on the nitrogen metabolismof subterranean clover (Trifolium subterraneum L.) and the non-legUmes oats(Avena sativa L.), Hax and linseed (Linum usitatissimum L.), andPaspalumdilatatum Poir. All these species responded to fertilizers containing sulphur onthe three soils used. Sulphates of aJl1lIlonium, potassium, sodium, and manganesewere all effective.

A study was made of toxicity in a field crop of oats on a soil developed in an area where ultrabasic rocks occur. An area selected for sampling showed a range of toxicity from the border where plants were normal to the centre where plants were most affected. The total nickel, cobalt, and chromium contents of the soil increased to high levels at the centre of the area. The concentration of the elements in soil solutions extracted with a centrfuge from soils at field capacity were in the order nickel > cobalt > chromium, the order in which they are found in natural waters. In the soil solutions nickel ranged from 0.13 to 3.25 p.p.m., cobalt from 0.03 to 0.14p.p.m., and chromium from 0.01 to 0.02p.p.m. The concentrations found in the soil solutions were compared with concentrations known to induce toxicities in oats grown in frequently renewed solution cultures. These comparisons indicated that the nickel ranged up to levels which were definitely toxic. At its highest level cobalt was present at less than one-tenth of the level needed to induce toxicity, while chromium was present at only one-hundredth of the minimum level for toxicity. Analyses of the toys of plants from the centre of the area indicated values of chromium which would be considered toxic, but because of the very low concentrations of chromium in the soil solutions it was considered more likely that the chromium detected was in soil material which the acid detergent washing procedure failed to remove. Evidence presented indicates the particular importance of contamination in the case of chromium. Nickel was present in much higher quantities at toxic levels. Cobalt was below toxic levels. The symptoms observed in the field and symptoms induced by the application of nickel to oats in pot cultures are described. A feature of these symptoms was a regular succession of chlorotic bands. The evidence suggested that the banding pattern, which is best developed in clear weather, relates to the changing conditions which influence the actively growing tissue as the leaf is emerging. The symptom provided us with a means of identifying nickel toxicity in the field. Degrees of toxicity were related to levels of elements in soil extracts and in the plants.

SummaryA study was made of the growth and nitrogen metabolism of plants in relation to molybdenum supply. Four soils low in available molybdenum were used in pot cultures for this work.Subterranean· clover (Trifolium subterraneum L.) responded to molybdenum on each of the soils. Flax (Unum usitatis8imum L.) responded to molybdenum on only one of the soils in the presence of a heavy dressing of manganese sulphate, which reduced the uptake of molybdenum and induced molybdenum deficiency. Oats (Avena sativa L.) did not respond to molybdenum on any of the soils, even where manganese sulphate was added.Deficiency of molybdenum decreased the percentage protein nitrogen in the flax and in the clover, but in different ways. Molybdenum increased the yield of flax only where combined nitrogen, either as nitric acid or ammonium sulphate, was provided. High nitrate accumulation occurred in the flax provided with nitric acid but without molybdenum. The percentage total nitrogen in flax was unaffected by molybdenum, but deficiency of molybdenum decreased the percentage protein nitrogen and increased the percentage non-protein nitrogen. Thus molybdenum was needed by the non-legume for the utilization of absorbed nitrate nitrogen.Molybdenum markedly increased both the yield and percentage nitrogen of clover where no combined nitrogen was provided, but had little or no effect where nitrogen was supplied as nitric acid or ammonium sulphate. This was despite the fact that each of these nitrogen compounds decreased the uptake of molybdenum by the clover. Deficiency of molybdenum decreased both the percentage protein nitrogen and the percentage non-protein nitrogen in the clover. The evidence with clover shows that molybdenum is directly concerned in symbiotic nitrogen fixation, and that the molybdenum requirement for optimum symbiotic nitrogen fixation is appreciably greater than the requirement for optimum utilization of nitrate nitrogen.

Preliminary pot culture experiments indicated that the yield of phalaris relative to that of perennial ryegrass was poor on the less productive soils, particularly on some of the soils of pH <5.0 as measured in 115 soil/water suspensions. On an infertile acid soil with a high content of exchangeable aluminium, lucerne and phalaris plants responded to lime in pot experiments while subterranean clover, white clover, and perennial ryegrass were depressed by liming. The evidence, including that based on chemical analyses of extracted soil solutions and of lucerne plants, indicates that where adequate nitrogen had been applied, aluminium toxicity depressed the growth of lucerne and phalaris on this acid soil. The plant roots did not show the stunting which is obvious in cases of more severe aluminium toxicity. Subterranean clover, white clover, and perennial ryegrass resisted the toxicity. There was little evidence of a negative interaction between lime and phosphate on yields through their effects on aluminium toxicity. In general, responses to phosphate increased as the level of lime increased. Where suboptimal levels of nitrogen were applied there were responses to lime which were not clearly attributable to the alleviation of aluminium toxicity. Where nitrogen was adequate and there was no effect of lime in counteracting aluminium toxicity, in most cases lime caused a decrease in the concentration of phosphorus in the plants as well as a decrease in the yield. Lime also caused a decrease in the phosphorus level in the extracted soil solutions. However, in some cases where lime counteracted aluminium toxicity it increased the concentration of phosphorus in the tops of the plants. The significance of the results in relation to the problem of the diagnosis of aluminium toxicity is discussed.

The literature offers conflicting information on the phytotoxicity of uranium (