Nitrogen in temperate crop and pasture plants

Nitrogen concentrations were determined in the tops of 24 annual crop and pasture varieties grown together in ungrazed plots on a lateritic gravelly sand at Gidgegannup, W.A., and sampled at three stages during growth and at maturity. All legumes had higher nitrogen concentrations in the tops than all non-legumes, but considerable variation was evident within each group. Among pasture legumes, Ornithopus compressus and O. sativus had the highest concentrations, especially towards maturity, and Trifolium subterraneum cv. Yarloop and Clare the lowest. Nitrogen concentrations in all Lupinus spp. fell rapidly towards maturity, and they were unique in suffering substantial net nitrogen losses from the tops. The herb Erodium botrys grew better and took up more nitrogen under conditions of deficiency than did the grasses. Its nitrogen concentration was nevertheless very low. Among the grasses, Bromus rigidus consistently had the highest nitrogen concentration and Lolium rigidum the lowest. There was some evidence among non-legumes of a correlation between high nitrogen concentrations and/or total uptake and observed adaptation to sandy soils. The superior adaptation of legumes in the experimental environment was demonstrated. It is suggested that crop legumes could make a more important agronomic contribution than hitherto in this and similar environments

Field responses to cobalt and molybdenum by different legume species, with inferences on the role of cobalt in legume growth

Six legume species were sown over two seasons on a sandy lateritic soil of marginal cobalt and molybdenum status, with varying rates and combinations of applied cobalt and molybdenum. The seeds were from plants previously grown on the same soil without cobalt or molybdenum addition. Species differed in their responses. Lupinus angustifolius responded strongly to cobalt, which increased dry matter yield by nearly 50%, but at most only marginally to molybdenum. Lupinus cosentinii, Vicia atropurpurea and Trifolium subterraneum responded to molybdenum but not to cobalt. Lupinus luteus, and more doubtfully Trifolium hirtum, responded to neither element. Yield responses to molybdenum were always accompanied by increased nitrogen concentrations in the tops. Cobalt application resulted in either no change or a reduction ir, nitrogen concentration in the tops, even when yield was increased. No interaction was evident between the two elements. Neither element increased nodule numbers, which were ample in all treatments, but in L. angustfolius cobalt markedly increased both nodule size and to a lesser extent crown nodule incidence and slightly increased leg-haemoglobin concentration. Possible reasons are discussed for the unexpectedly unchanged or reduced nitrogen concentrations in the tops of L. angustifolius showing yield responses to cobalt. One suggestion is that enhanced rhizobium and nodule growth resulted in greater cytokinin production, with a greater effect on top growth under the conditions of the experiments than that stemming from increased nitrogen fixation

Mineral elements in temperate crop and pasture plants. 3. Copper

Concentrations and total amounts of copper in the tops were measured in 24 varieties of 21 annual crop and pasture species, grown in the field on a lateritic gravelly sand with three levels of copper application and sampled at three growth stages and maturity. Copper applications at the normal commercial rate in Western Australia and at three times this rate did not increase yield. Both rates increased copper concentrations slightly in young plants, but this effect had largely disappeared by flowering. Copper application did not change the relative order of species when ranked according to their copper concentrations. Copper concentrations in the tops declined with age in all species, but at differing rates. All species continued to accumulate copper up to harvest 3 (near maturity), with the exception of lupins which suffered net losses from the tops after flowering. Species varied greatly in their copper concentrations. In cereals and grasses, copper concentrations increased linearly with increasing nitrogen contents, with a tendency towards higher copper/nitrogen ratios as concentrations of both elements increased. Legumes had higher copper concentrations than grasses and cereals, especially late in the growing season, but lower and more variable copper/nitrogen ratios. Within taxonomic groups, species adapted to sandy and copper-deficient soils tended to have the highest copper concentrations and copper/nitrogen ratios, and to translocate most copper to the seeds