Decomposition of roots and shoots of perennial grasses and annual barley-separately or in two residue mixes

Little is known about the decomposition rates of shoot and root residues of perennial grasses. This knowledge is important to estimate the carbon sequestration potential of the grasses. An incubation experiment was carried out in a sandy clay loam with shoot and root residues of three native perennial grasses (Wallaby grass, Stipa sp. and Kangaroo grass) and the annual grass barley either separately or in mixtures of two residues. Respiration rate was measured over 18 days, and microbial C and available N were measured on days 0 and 18. Decomposition was lower for roots than for shoots and lower for residues of perennial grasses than for barley. Cumulative respiration was positively correlated with water-soluble C in the residues but not with residue C/N. In the mixtures, the measured cumulative respiration was higher than the expected value in five of the nine mixes usually where the differences in cumulative respiration between the individual residues were relatively small. Lower than expected cumulative respiration were found in two of the mixtures in which barley shoots (high cumulative respiration) were mixed with residues with low cumulative respiration. There was a negative correlation between the change in microbial biomass C concentration from day 0 to day 18 and cumulative respiration on day 18. In the amended soils, the available N concentration decreased from day 0 to day 18. It is concluded that the low decomposition rate of perennial grasses residues should favour C sequestration, but that mixing residues of similar decomposition rate may accelerate their decomposition.Andong Shi, Chris Penfold, Petra Marschne

Bayesian adaptive design: improving the effectiveness of monitoring of the Great Barrier Reef

Ann McNeil

Challenges of formulation and quality of biofertilizers for successful inoculation

The interest in biofertilizers is increasing and so is the potential for their use in sustainable agriculture. However, many of the products that are currently available worldwide are often of very poor quality, resulting in the loss of confidence from farmers. The formulation of an inoculant is a crucial multistep process that should result in one or several strains of microorganisms included in a suitable carrier, providing a safe environment to protect them from the often harsh conditions during storage and ensuring survival and establishment after introduction into soils. One of the key issues in formulation development and production is the quality control of the products, at each stage of the process. This review presents the different components and the major steps involved in the formulation of good quality biofertilizers, including the techniques used to assess the quality of the products following production. The quality of currently available inoculants is also reviewed, emphasizing the need for better quality control systems worldwide. (Résumé d'auteur