Purple clover

Abstract: The current dissatisfaction with low productivity of annual medic (Medicago spp.) pastures has highlighted the need to seek alternative legumes to provide efficient N2 fixation in low rainfall, alkaline soil environments of southern Australia. Clover species adapted to these environments will have limited N2 fixation if effective rhizobia are not present in sufficient quantities. A survey of 61 sites was conducted across South Australia to determine the size, distribution and effectiveness of Rhizobium leguminosarum bv. trifolii (clover rhizobia) populations resident in these low rainfall, alkaline soil environments. Clover rhizobia were detected at 56 of the sites, with a median density of 230–920 rhizobia/g soil. Most rhizobial populations were poor in their capacity to fix nitrogen. Rhizobial populations from fields provided 11–89% and 10–85% of the shoot biomass of commercial reference strains when inoculated onto host legumes T. purpureum (purple clover) and T. resupinatum (persian clover), respectively. Rhizobial population size was correlated negatively to pH and the percentage of CaCO3 in the soil, and was significantly increased in the rhizospheres of naturalised clover, found at 17 sites. Management options for rhizobial populations to improve legume diversity and productivity are discussed in terms of rhizobial population dynamics and likely soil constraints to successful rhizobial colonisation.

Abstract: We used a series of fenced exclosures to examine whether herbivory by mammals affected the structure and dynamics of an old-field plant community in Virginia. Early in the 3rd yr of the study purple clover, Trifolium pratense, a dominant member of the plant community, occurred at higher densities where herbivores were excluded relative to control plots. Following a 1-mo time lag, Trifolium became infected by the rust-forming fungal pathogen Uromyces trifolii; the incidence of infection was higher in exclosures relative to control plots where herbivores were present. Early-to-late season changes in the abun- dance of Trifolium were related to the degree of fungal infection and not herbivore presence/ absence. Data from the following year (when the fungus and Trifolium were rare) showed clover abundance to be higher in control plots than in enclosures. These results suggest that the negative influence of the fungus not only persisted through time, but more strongly affected host plant abundance in a 2-mo period than did herbivory that occurred in both years. While the direct effect of herbivory on food plants is negative, by keeping plant abundance below that at which fungal infections become epidemic, the net effect of her- bivores on some forage plants may be positive. The existence of strong indirect interactions is further evidence that the emphasis in community ecology (and in plant succession) should be on interactive networks rather than on species pairs.

Abstract: Twelve cultivars and 10 F6-derived breeding lines of subterranean clover (Trifolium subterraneum) and two cultivars of purple clover (T. purpureum) were screened in the field for their response to clover scorch disease caused by race 2 of Kabatiella caulivora that is restricted in distribution in Western Australia but is generally more virulent than race 1. Two of the cultivars (viz. Coolamon subterranean clover and Electra purple clover), and the breeding line SL031 showed outstanding resistance, with disease scores significantly lower than the resistant cultivar Denmark that had a disease score of 3.3 (0–10 scale with 0 = no disease and 10 = death of all plants). A further two cultivars (viz. Goulburn, and Karridale) and four of the breeding lines (viz. SL019, SL027, SL029 and SM033) had similar levels of resistance to Denmark. Host responses to race 2 were compared with those against race 1 of K. caulivora. Genotypes, such as SL029 and SL031, with combined resistances to both races of K. caulivora were identified, and their potential for effective management of K. caulivora, in areas where both races occur, highlighted.

Abstract: The mainstream pasture legume species such as Trifolium subterraneum, T. repens and annual Medicago spp. used in the temperate pasture systems of southern Australia have high critical external requirements for phosphorus (P) (i.e. P required to achieve 90% of maximum yield). This work aimed to identify alternative pasture legume species that could be used in systems with lower P input. Shoot and root biomass of 12 species of pasture legume was measured in response to seven rates of P applied to the top 48 mm of soil in a pot experiment. Most species had maximum yields similar to T. subterraneum, but some required only one-third of the applied P to achieve this. The critical external P requirement of the species, ranked from lowest to highest, was as follows: Ornithopus compressus = O. sativus < Biserrula pelecinus < T. michelianum = T. vesiculosum = T. glanduliferum < T. hirtum = Medicago truncatula = T. purpureum = T. incarnatum < T. spumosum = T. subterraneum. An ability to maximise soil exploration through a combination of high root-length density, high specific root length and long root hairs (i.e. a large specific root-hair-cylinder volume) was associated with a low critical external P requirement. The results indicate that Ornithopus spp. could be used to achieve productive, low P-input pasture systems.

Abstract: Introduction During green manure application the relatively fast growing and huge yielding biomass providing plants are produced so as to get the green parts applied back into the soil by rotation (plowing) or by shallow mixing (e.g. by disc harrow or cultivator). Westsik (1965) studied green manure application of different pulses. Nevertheless there are numerous other plants involved in production for the above purpose, for example mustard, oil radish, phacelia, buckwheat, purple clover, forage radish, sweet clover, and different ration of mixture of the above plants. Production of these plants can be as a mainor as a secondary crop. The main seeding is not widely applied either in Hungary or abroad (Kahnt 1986), in Hungary there are backgrounds existing for the production of the second seeded green manure plants (Gyarfas, 1953). The green parts applied into the soil improve the physical and biological conditions and the nutrient state of the soil, contribute to increase of organic matter, protect the surface from windand water erosion. Due to the intense root development they also have a biological loosening effect in the soil decreasing this way the chance for formation of a compacted layer. Being produced the above plants as a secondary crop they reduce leaching of nutrients, mainly in very wet years. Primarily they take up nitrogen in huge amount, this way it can be utilized by the following plant directly (Birkas et al. 2002; Hansen and Djurhuus, 1997; Jamriska 2002; Sainju and Singh 1997). Some green manure plants can also be utilized to create a more diverse animal feeding. In this case specific parts of the green manure plants are chopped and fed by animals in fresh condition or as silage.