Biological, ecological and agronomic significance of plant phenolic compounds in rhizosphere of the symbiotic legumes

Phenolics are low molecular compounds ubiquitous in all tissues of higher plants with great significance in plant development. Our understanding of some phenolic compounds in the last few decades has greatly improved. However, their biological, ecological and agronomical significance in therhizosphere of most symbiotic legumes is much less clear. Further understanding of these biomolecules will increase our knowledge of their contribution in soil and water conservation, weed management,mineral element nutrition, their impact as signal molecule in certain symbiotic relationships, and their role as defence molecules against soil pests and pathogens. This article reviews the bioecological and agronomical significance of phenolic compounds in the rhizosphere of a few studied symbiotic legumes and other plants

Reclamation of sodic soils in northern Tanzania, using locally available organic and inorganic resources

Sodic soils could produce useful maize (Zea mays L.) crop yields if reclaimed by appropriate techniques. A field experiment was conducted on the selected lowlands of northern Tanzania using a randomised complete block design to study the effectiveness of supplying gypsum (CaSO4.2H2O) or farmyard manure (FMY) alone or both mixtures on the reclamation of a sodic soil. Sodic soil and FYM were characterised to establish their quality status before any intervention was introduced. The treatment used included: control, FYM alone (25 t ha-1), FYM (25 t ha-1) combined with gypsum (12.5 t ha-1) and gypsum alone (12.5 t ha-1). The treatments were replicated four times. Selected numbers of soil physical and chemical properties were then investigated. Results from our study revealed that regardless of the amendments used, maize yield and all soil physical and chemical properties tested were improved in Year 2 (Y2) relative to Year 1 (Y1). Our results also showed that combining FYM with gypsum significantly (p0.05) improved pH, electrical conductivity of the saturated paste (ECe), exchangeable sodium percentage (ESP), infiltration rate (IR), osmotic potential (OP) and available water capacity (AWC) of sodic soils. The FYM was the second-best treatment in the improvement of pH, ESP and EC whereas gypsum was second in the improvement of ESP, IR and maize yield

Selected soil enzymes: Examples of their potential roles in the ecosystem

Soil enzymes regulate ecosystem functioning and in particular play a key role in nutrient cycling. In this review we briefly summarise potential roles of selected enzymes such as amylase, arylsulphatases, -glucosidase, cellulose, chitinase, dehydrogenase, phosphatase, protease andurease in the ecosystem. We also highlight areas where further research is needed to increase our understanding of other possible role(s) of enzymes and factors that may affect their activities in the ecosystem

Effect of legume plant density and mixed culture on symbiotic N2 fixation in five cowpea (Vigna unguiculata L. Walp.) genotypes in South Africa

Abstract A field experiment involving two plant densities (83,333 and 166,666 plants per hectare), two cropping systems (monoculture and mixed culture) and five cowpea (Vigna unguiculata L. Walp.) genotypes (3 farmer-selected varieties: Bensogla, Sanzie and Omondaw, and 2 breeder-improved cultivars: ITH98-46 and TVuI509) was conducted for two years in 2005 and 2006 at Nietvoorbij (33°54S, 18°14E), Stellenbosch, South Africa, to evaluate the effect of these treatments on the growth and symbiotic performance of cowpea. The results showed that, of the five cowpea genotypes, plant growth and N2 fixation were significantly greater in the three farmer-selected varieties (Sanzie, Bensogla and Omondaw) relative to the two improved cultivars (ITH98-46 and TVuI509). Furthermore, plant growth and symbiotic performance (measured as tissue N concentration, plant N content, 15N natural abundance and N-fixed) were significantly (P:50.05) decreased by both high plant density and mixed culture (intercropping). However, the %Ndfa values were significantly (P:S0.05) increased by both high plant density and mixed culture compared to low plant density or monoculture (or monocropping). Whether under low or high plant density, the cv. Sanzie was found to accumulate significantly greater total N per plant in both 2005 and 2006, followed by the other two farmer varieties relative to the improved cultivars. Similarly, the actual amount ofN-fixed was much greater in cv. Sanzie, followed by the other farmer varieties, under both low and high plant density. The data also showed better growth and greater symbiotic N yield in cowpea plants cultivated in monoculture (or low plant density) relative to those in mixed culture (or high plant density). Our data suggest that optimising legume density in cropping systems could potentially increase N2 fixation in cowpea, and significantly contribute to the N economy of agricultural soils in Africa