Subtropical Legumes Research Articles

Seed pelleting to improve nodulation of tropical and subtropical legumes. 6. The effects of dilute sticker and of bauxite pelleting on nodulation of six legumes

In a field experiment at Beerwah, Queensland, bauxite pellet applied with 4 per cent methyl cellulose sticker and 1 per cent methyl cellulose as a simple sticker for the inoculant were compared with the standard treatments used successfully in a previous series of experiments. These were peat applied with 4 per cent methyl cellulose, and Florida rock phosphate pellet with 4 per cent methyl cellulose sticker. Legumes and Rhizobium strains tested were Desmodium uncinatum and D. intortum, inoculated with Rhizobium CB627, Lablab purpureus (formerly Dolichos lablab), Glycine wightii (three cvs. Clarence, Cooper and Tinaroo), and Macroptilium atropurpureum (formerly Phaseolus atropurpureus), all inoculated with Rhizobium CB756, and Lotononis bainesii inoculated with Rhizobium CB376. All were planted after 2-day and 28-day storage of inoculated seed. The effectiveness of the treatments was checked by nodule counting and by serologically identifying the strains in a random sample of nodules from each treatment. The majority of nodules formed came from the applied inoculants, but there were no differences between the inoculation treatments in nodulation criteria or effect on yield. The experiment confirmed that bauxite is a satisfactory pelleting material for tropical legumes, but the application of the inoculant peat with 1 per cent methyl cellulose leads to equally good nodulation.

Seed pelleting to improve nodulation of tropical and subtropical legumes. 5. The contrasting response to lime pelleting of two Rhizobium strains on Leucaena leucocephala

In a field experiment at Samford, Queensland, on a loam of pH 5.0 (water), nodulation of Leucaena leucocephala was compared after inoculation with two contrasting types of Rhizobium. Peat culture of each was applied to the seed in three ways: using 2 per cent and 4 per cent methyl cellulose (m.c.) sticker and 4 per cent m.c, with a lime coating. Inoculated seed was sown after storage for one and 28 days. After one day storage the acid-producing strain NGR8 formed nodules only when the seed was pelleted with lime, but the alkali-producing strain CB81 nodulated equally well by all three inoculation procedures. After 28 day storage strain CB81 did not survive on the seed when applied simply with sticker, but survived as well as strain NGR8 when lime-pelleted. It is suggested that where leucaena is to be established on acid soils, CB81 or a rhizobial strain of similar type be used and that the seed be always lime-pelleted.

Seed pelleting to improve nodulation of tropical and subtropical legumes. 4. The effects of various mineral dusts on nodulation of Desmodium uncinatum

In field experiments at Beerwah, Queensland, in two successive seasons lime and Florida rock phosphate were compared as seed pelleting materials with 18 other mineral dusts. Desmodium uncinatum was used as the test legume, strains CB627 and CB1517 as the test inoculant strains, and methyl cellulose (4 per cent) and gum arabic (40 per cent) as the stickers. Seed was planted after storage for two days and again after 28 days to separate immediate effects of materials on nodulation from effects of storage on survival of bacteria on the seed. The nodulation resulting from the various pellets was assessed by comparison with inoculation done with the sticker alone. Lime pelleting in both seasons gave a stimulation of nodulation at the first planting followed by a severe decline, both absolute and relative to sticker alone, after storage for 28 days, which was attributed to a faster death rate of the inoculant bacteria. Rock phosphate on average gave the best nodulation and the bacteria apparently survived well also under a bauxite pellet. On the basis of nodulation performance combined with ready availability and ease of grinding, the two most promising materials for further test were indicated to be Christmas Island 'c' grade calcined rock phosphate and bauxite. Rhizobium CB627 was a superior inoculant to CB1517, and there was no important difference between the performance of the two stickers Methofas and gum arabic.

Factors in the physical and biological environment affecting nodulation and nitrogen fixation by legumes

The effects of root temperature on the four main stages of nodule formation and function are reviewed. Compared with results obtained under optimal conditions, lower root temperatures retard root hair infection more than they affect nodule initiation, nodule development (including bacteroid tissue development and degeneration), or nitrogen assimilation. Higher root temperatures upset the formation of bacteroid tissue and hasten its degeneration. Tropical and subtropical legumes have higher minimum temperatures for nodule formation than temperate species. Low and high shoot temperatures affect nodulation and nitrogen fixation, but the effect is less severe than that of similar root temperatures. Various approaches to minimise adverse environmental effects are considered. These include the selection of appropriate biological material (both host plants and bacterial strains) for the prevailing conditions, and the adoption of management practices designed to utilise the environment or to minimise its adverse effects. The importance of increase in bacteroid volume in relation to increase in rate of nitrogen fixation is considered, and the concept of compensation in nodule production and activity is examined. The limited information on defoliation effects on the nodulation of both temperate and tropical legumes is reviewed and aspects requiring examination are discussed.

Effects and interaction of lucerne and subtropical legumes in a Sorghum almum pasture

An experiment was carried out at Lawes in south-east Queensland to examine the behaviour of subtropical legumes (mixture of Glycine wightii and Phaseolus atropurpureus), of lucerne, and of all three legumes together in a Sorghum almum pasture. Two grazing regimes were imposed, both averaging almost one beast an acre a year, but one involving longer breaks between grazings. A final year of common grazing was used to obtain a better assessment of treatment effects. There was no evidence of any difference in persistence between the Nunbank and Crooble cultivars of S. almum. Initial growth of legumes was poor due to strong competition from S. almum, but in the second year they made a substantial contribution to total yield of dry matter and nitrogen, and in the following two years they also increased significantly the yield of S. almum. In general the sub-tropical legumes yielded more than lucerne, and were also more effective in increasing S. almum yields. There were only minor effects on the nitrogen content of S. almum. Lucerne and subtropical legumes were strongly competitive when sown together, in that each yielded less and had a smaller effect on S. almum than in separate mixtures with the grass ; the effects of lucerne were particularly marked. These competitive effects were less pronounced with less frequent grazing. Soil nitrogen in the 0-12 inch soil layer declined during the first two years of the pasture but increased during the following two, the accumulation occurring mainly in the surface 3 inches of plots containing legumes. Over the total pasture phase (four years), there was a small nett loss of nitrogen from the 0-12 inch layer. Volunteer species associated with a follow-up crop of Sorghum vulgare showed positive responses to residual nitrogen from lucerne but no response to subtropical legumes. It is suggested that this was associated with a slower turnover of nitrogen from lucerne root systems. There was no response in the crop itself.

Seed pelleting to improve nodulation of tropical and subtropical legumes. 3. A field evaluation of inoculant survival under lime and rock phosphate pellet on Dolichos lablab

Use was made of a soil, in which the indigenous rhizobia are incapable of nodulating Dolichos lablab, to study nodulation of this species resulting from lime pelleted and rock phosphate pelleted seed after storage for one day and one, two, four, six, and eight weeks at 27�C. Cellofas A was used as sticker and two strains of Rhizobium were compared. From each sowing plants were dug at eight weeks of age, and the treatments compared using the criteria : number of plants in row, per cent plants nodulated, number of nodules per plant, per cent of nodules on the crown and yield of dry matter per row. Rock phosphate pelleting was superior to lime pelleting in survival of inoculant on the seed, survival of plants in the row, and promotion of nodulation. Lime pelleting depressed yield at eight weeks of age but not at four months. Both strains of inoculant survived one month's storage satisfactorily when simply applied with sticker. Total nodule number fluctuated greatly with time of planting, and was inversely related to per cent crown nodulation, suggesting chat soil moisture at planting may have had a significant effect on nodulation. Strong interactions of inoculant strain with pelleting treatment and time of planting stressed the difficulty of interpreting nodulation effects resulting from pel!etinp treatments. Rhizobium strain CB756 was greatly superior to CB159 in survival on stored seed, nodulation criteria, onset of N fixation and yield.

Seed pelleting to improve nodulation of tropical and sub-tropical legumes. 2. The variable response to lime and rock phosphate pelleting of eight legumes in the field

To determine whether a lime oy rock phosphate pellet has any beneficial effect on nodulation of tropical legumes two field experiments were done using Centrosema pubescens, Dolichos lab lab, Desmodium intortum, D. uncinatm, Lotononis angolensis, and Glycine wightii cvs. Cooper, Clarence and Tinaroo. At one site the experiment was sod-seeded into a Paspalum-Axonopus sward, at the other it was sown into cultivated soil. The second site was acid and calcium-deficient and lime was deliberately withheld to introduce bias towards a lime pellet response. At both sites each legume was tried separately with two effective Rhizobium strains and the effect of lime or phosphate pelleting was assessed by comparison with inoculation done with Cellofas sticker without pellet. Nodulation was assessed on 100 plants of each species at ages from seven to twelve weeks. At the sod-seeding site Lotononis and D. intortum did not establish, but the remaining twelve legume-Rhizobium combinations showed no benefit in nodulation from lime pelleting. At the calcium-deficient site lime pelleting in comparison with Cellofas inoculation improved nodulation with eight legume-Rhizobium combinations, had no effect with six combinations, and depressed nodulation with two combinations. Rock phosphate pelleting showed no benefit in nodulation in twelve combinations under sod-seeding. At the calcium-deficient site four combinations showed improved nodulation and 12 combinations no effect, but there were no negative effects. Good nodulation resulted from simple Cellofas inoculation at both sites, with the exception of D. uncinatum at Beerwah. Pelleting treatments gave no yield increases with the exception of D. uncinatum at Beerwah where yield was significantly increased by lime pelleting. No evidence in favour of routine pelleting with either lime or phosphate was provided bv these experiments. The superiority of certain rhizobial strains as field inoculants was demonstrated.

Correction - Seed pelleting to improve nodulation of tropical and subtropical legumes. 3. A field evaluation of inoculant survival under lime and rock phosphate pellet on Dolichos lablab

Use was made of a soil, in which the indigenous rhizobia are incapable of nodulating Dolichos lablab, to study nodulation of this species resulting from lime pelleted and rock phosphate pelleted seed after storage for one day and one, two, four, six, and eight weeks at 27�C. Cellofas A was used as sticker and two strains of Rhizobium were compared. From each sowing plants were dug at eight weeks of age, and the treatments compared using the criteria : number of plants in row, per cent plants nodulated, number of nodules per plant, per cent of nodules on the crown and yield of dry matter per row. Rock phosphate pelleting was superior to lime pelleting in survival of inoculant on the seed, survival of plants in the row, and promotion of nodulation. Lime pelleting depressed yield at eight weeks of age but not at four months. Both strains of inoculant survived one month's storage satisfactorily when simply applied with sticker. Total nodule number fluctuated greatly with time of planting, and was inversely related to per cent crown nodulation, suggesting chat soil moisture at planting may have had a significant effect on nodulation. Strong interactions of inoculant strain with pelleting treatment and time of planting stressed the difficulty of interpreting nodulation effects resulting from pel!etinp treatments. Rhizobium strain CB756 was greatly superior to CB159 in survival on stored seed, nodulation criteria, onset of N fixation and yield.

Seed pelleting to improve nodulation of tropical and sub-tropical legumes. 1. An examination of the validity of 'grow-out' nodulation tests in tubes

Nodulation resulting from various seed pelleting treatments of Lotus pedunculatus, Desmodium intortum, and D. uncinatum was investigated by the 'grow-out technique', in which single treated seeds are dropped into seedling nutrient agar tubes which are assessed for presence or absence of nodules after a standard time. Two cellulosic stickers, Cellofas A and Methofas were used, and pelleting materials included lime, gypsum, kaolin, calcium silicate, and four rock phosphates. Calcium silicate was quickly lethal to rhizobia. Malt extract was included in the sticker in several experiments and had a protective action on rhizobia. Significant effects of pellet treatment were observed on both seed germination and amount of nodulation. Results indicate that the relative performance of different pelleting treatments can be influenced both by ambient environmental factors and by the type of mineral nutrient agar chosen for the performance of the test. It is suggested that such tests may be quite misleading, and that they provide no real guide to what may occur in the field.

The nutritive value of protein in subtropical pasture species grown in south-eastern Queensland

Examination of the data from 138 indoor pen-feeding trials with sheep showed that, for 22 grasses and 6 legumes grown in south-east Queensland, crude protein digestibility was related to percentage crude protein content (R = 0.885 ; P<0.001) and to the nitrogen balance of the sheep (R = 0.776 ; P<0.001). The equations derived from these relations can be used to estimate the nutritive value of protein from the crude protein content. Under ad lib. feeding; zero nitrogen balance was estimated to occur at a crude digestibility of 49 per cent (95 per cent fiducial limits = 47, 52) and this digestibility was attained at a crude protein content of 8 per cent (95 per cent limits = 7.0, 9.0). The implications of these estimates are illustrated with the aid of some data on changes with age in the crude protein content of sub-tropical grasses and legumes.