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In this work, clover was shown to respond to infection with Rhizobium leguminosarum bv. trifolii by producing reactive oxygen species. Superoxide radical and hydrogen peroxide were detected in infection threads and nodule primordia. The role of reactive oxygen species in clover-Rhizobium leguminosarum bv. trifolii symbiosis is discussed
Forage legumes are used to enhance soil fertility of the agroecosystem. Understanding their effect on the agroecosystem during their growing period is essential. The objective of this field study was to evaluate annual clovers intercropping and earthworm activity on the growth of weeds. The field experiment was carried out during the 2006–2007 growing seasons at the research farm of the Seed and Plant Improvement Institute, Karaj (Iran) involving various mixed cropping ratios of berseem clover (Trifolium alexandrinum L., B) and Persian clover (Trifolium resupinatum L., P) (B : P = 1 : 0, 3 : 1, 1 : 1, 1 : 3) with and without earthworm Pheretima sp. inoculation. Nitrogen content of plants and weeds as well as biomass was measured. Forage yield was higher in 2006 than 2007 but had similar response to cropping systems and earthworm inoculation. Total forage yield was highest in mixed cropping system (MCS). While in the first cut, the berseem sole crop (SC) tended to greatly suppress the growth of weeds, in the second cut Persian clover sole crop further suppressed weeds. The greater total crop biomass had an even higher weed suppression. Earthworm activity did not affect cut 1 but increased forage and weed biomass yield in cut 2. However in cut 1, berseem tended to greatly suppress the growth of weeds, which may be explained by the greater nitrogen accumulation in monocultures and intercrops, Persian clover in cut 2 had greater suppression on weed biomass production. Nitrogen accumulation of crops and weed increased under earthworm activity in the second cut.
It was found that red clover utilizes from 1.1 to 1.4 kg of CO2 from the atmosphere to produce 1 kg of dry mattter. This means that 1400 to 1600m3 of atmospheric air become completely purified from carbon dioxide. Red clover plants usually lose 40.9% of their crop weight during the winter. This results from organic carbon loss equal (in CO2 units) to 41.8% for physiolopical processes. In the same period however, the ash fraction, larger grows as a simple consequence of actual carbon loss. It is reasonable to assume that the plants do intake mineral compounds from the deeper, not frozen horizons of the soil also during winter.
Rhizobium leguminosarum bv. trifolii (Rlt) establishes beneficial root nodule symbiosis with clover. Twenty Rlt strains differentially marked with antibiotic-resistance markers were investigated in terms of their competitiveness and plant growth promotion in mixed inoculation of clover in laboratory experiments. The results showed that the studied strains essentially differed in competition ability. These differences seem not to be dependent on bacterial multiplication in the vicinity of roots, but rather on complex physiological traits that affect competitiveness. The most remarkable result of this study is that almost half of the total number of the sampled nodules was colonized by more than one strain. The data suggest that multi-strain model of nodule colonization is common in Rhizobium-legume symbiosis and reflects the diversity of rhizobial population living in the rhizosphere.
In field and pot experiments the effect of selected pesticides on the atmospheric nitrogen fixation, number of microorganisms in soil and yield of red clover has been investigated. The results obtained indicate that crop protection preparations applied in the experiments (Funaben T seed dressing compound and Pivot 100 SL herbicide) resulted in reduction of nitrogenase activity on the active strain of Rhizobium leguminosarum bv. trifolii KGL both in pot and field experiment conditions. Moreover, the authors observed the toxic effect of the pesticides used on nodulation, root development and yield of clover. The herbicide and fungicide applied also inhibited the multiplication of the microorganisms in soil under red clover plantations in the first days upon application and, later on, stimulated their multiplication.
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