Search

Management of grazing lands for the accumulation of soil carbon stocks ([C.sub.S]) has been proposed as an effective way to reduce net greenhouse gas emissions from agriculture. However, there are conflicting reports on the effects of grazing management on soil carbon. Most comparisons have involved some combination of no grazing, rotational grazing and set stocking. In the present study we compared two adjacent commercial grazing systems, distinguished on the basis of inputs and livestock productivity, located on New England basaltic landscapes experiencing a cool temperate climate. The high-intensity (H) system sustains an average stocking rate of 18 dry sheep equivalents (dse) [ha.sup.-1], with a turnoff rate of 9 dse [ha.sup.-1] [year.sup.-1], with high levels of investment in assets, management and fertiliser. The low-intensity (L) system, with less intensive management and half the fertiliser of the H system, sustains a stocking rate of 9 dse [ha.sup.-1], with a turnoff rate of 3 dse [ha.sup.-1] [year.sup.-1], which is slightly higher than the regional average. Pasture biomass production was inferred (back-calculated) from stocking rates and animal feed requirements using published data. From the H and L systems, seven paired landscapes from valley floor to upper hillslopes and plateaux were selected. The seventh included a forest reserve. One hundred and eighty-six undisturbed soil cores (0-0.5 m depth) were assessed for bulk density, total C and N, particulate C and a range of plant nutrients. There were few differences in [C.sub.S], soil pH and nutrient levels between H and L grazing systems. Average [C.sub.S] (0-0.3 m) in pasture soils was 103 Mg [ha.sup.-1], but was higher in the forest soil at 190 Mg [ha.sup.-1]. Regression of [C.sub.S] versus soil mass was a satisfactory method of dealing with the bias introduced by the higher soil bulk density in perennial pasture systems compared with the forest. The similarity of [C.sub.S] in H and L pasture soils was despite inferred net primary production being 1.9-3.6 Mg C [ha.sup.-1] [year.sup.-1] greater in H than L systems, implying higher rates of C turnover in the former. The global warming potential of the inferred annual emissions of C[H.sub.4] and [N.sub.2]O in the H and L systems was equivalent to approximately 19% and 13% of the cycling atmospheric-plant C[O.sub.2] carbon respectively. Additional keywords: grazing animal emissions, particulate soil carbon., Introduction Increasing soil carbon stocks ([C.sub.S]) via changes in management of agricultural land to both increase biomass production and introduce less exploitative practices is an attractive way to reduce net [...]

This study sought to quantify the influence of 'carbon fanning' practices on soil carbon stocks, in comparison with conventional grazing and cropping, in northern New South Wales. The study had two components: assessment of impacts of organic amendments on soil carbon and biological indicators in croplands on Vertosols of the Liverpool Plains; and assessment of the impact of grazing management on soil carbon in Chromosols of the Northern Tablelands. The organic amendment sites identified for the survey had been treated with manures, composts, or microbial treatments, while the conventional management sites had received only chemical fertilisers. The rotational grazing sites had been managed so that grazing was restricted to short periods of several days, followed by long rest periods (generally several months) governed by pasture growth. These were compared with sites that were grazed continuously. No differences in total soil carbon stock, or soil carbon fractions, were observed between sites treated with organic amendments and those treated with chemical fertiliser. There was some evidence of increased soil carbon stock under rotational compared with continuous grazing, but the difference was not statistically significant. Similarly, double-stranded DNA (dsDNA) stocks were not significantly different in either of the management contrasts, but tended to show higher values in organic treatments and rotational grazing. The enzymatic activities of β-glucosidase and leucine- aminopeptidase were significantly higher in rotational than continuous grazing but statistically similar for the cropping site treatments. Relative abundance and community structure, measured on a subset of the cropping sites, showed a higher bacteria : fungi ratio and provided evidence that microbial process rates were significantly higher in chemically fertilised sites than organic amendment sites, suggesting enhanced mineralisation of organic matter under conventional management. The higher enzyme activity and indication of greater efficiency of microbial populations on carbon farming sites suggests a greater potential to build soil carbon under these practices. Further research is required to investigate whether the indicative trends observed reflect real effects of management. Additional keywords: organic amendment, rotational grazing, soil carbon stock, soil microorganisms., Introduction Soil organic matter contains a large fraction of the global terrestrial carbon stocks (Batjes 1996). In recent years, the importance of soil organic matter as a significant carbon sink [...]

Biochar properties can be significantly influenced by feedstock source and pyrolysis conditions; this warrants detailed characterisation of biochars for their application to improve soil fertility and sequester carbon. We characterised 11 biochars, made from 5 feedstocks [Eucalyptus saligna wood (at 400°C and 550°C both with and without steam activation); E. saligna leaves (at 400°C and 550°C with activation); papermill sludge (at 550°C with activation); poultry litter and cow manure (each at 400°C without activation and at 550°C with activation)] using standard or modified soil chemical procedures. Biochar pH values varied from near neutral to highly alkaline. In general, wood biochars had higher total C, lower ash content, lower total N, P, K, S, Ca, Mg, Al, Na, and Cu contents, and lower potential cation exchange capacity (CEC) and exchangeable cations than the manure-based biochars, and the leaf biochars were generally in-between. Papermill sludge biochar had the highest total and exchangeable Ca, CaC[O.sub.3] equivalence, total Cu, and potential CEC, and the lowest total and exchangeable K. Water-soluble salts were higher in the manure-based biochars, followed by leaf, papermill sludge, and wood biochars. Total As, Cd, Pb, and polycyclic aromatic hydrocarbons in the biochars were either very low or below detection limits. In general, increase in pyrolysis temperature increased the ash content, pH, and surface basicity and decreased surface acidity. The activation treatment had a little effect on most of the biochar properties. X-ray diffraction analysis showed the presence of whewellite in E. saligna biochars produced at 400°C, and the whewellite was converted to calcite in biochars formed at 550°C. Papermill sludge biochar contained the largest amount of calcite. Watersoluble salts and calcite interfered with surface charge measurements and should be removed before the surface charge measurements of biochar. The biochars used in the study ranged from C-rich to nutrient-rich to lime-rich soil amendment, and these properties could be optimised through feedstock formulation and pyrolysis temperature for tailored soil application. Additional keywords: carbon sequestration, soil fertility, pyrolysis, Boehm titrations, heavy metals, surface acidity., Introduction Increasing atmospheric C[O.sub.2] is an important global issue of the 21st century, and long-term storage of carbon in soil is considered an important option to mitigate the increasing level [...]