RESUMO
Improving bulb yield and allicin content of garlic is important in meeting fresh and pharmaceutical market demands. Garlic plants have a high demand for sulfur (S) since allicin contains S atoms. Two experiments were conducted to identify the effect of S application rate on garlic yield and quality. In a field trial assessing six S application rates (0-150 kg S ha-1), cultivar 'Glenlarge' produced the greatest bulb weight (~90 g) and allicin content (521 mg bulb-1) with the application of 75 kg S ha-1. In contrast, cultivar 'Southern Glen' showed no response in bulb weight or allicin. This was likely due to high soil background S concentrations masking treatment effects. Subsequently, a solution culture experiment with cv. 'Glenlarge' evaluated six S application rates (188 to 1504 mg S plant-1, nominally equivalent to 25-200 kg S ha-1). In solution culture, bulb weight and allicin concentration increased with S rate. Highest bulb weight (~53 g bulb-1) and allicin concentration (~11 mg g-1 DW) were recorded at an S application of 1504 mg S plant-1. This is the first report to conclusively demonstrate the effect of S on yield and allicin in garlic grown in solution culture.
RESUMO
Tropical regions of the world experience high rates of land-use change and this has a major influence on terrestrial carbon (C) pools and the global C cycle. We assessed land-use change from agriculture to reforested plantings (with endemic species), up to 33â¯years of age, using 10 paired sites in the wet tropics, Australia. We determined the impacts on 0-50â¯cm below-ground C (soil organic C (SOC), charcoal C, humic organic C, particulate organic C, resistant organic C), C stored in roots (fine and coarse), C stored in living above-ground biomass and debris C pools. Reforested areas accumulated ecosystem C at a rate of 7.4â¯Mgâ¯ha-1â¯yr-1. Reforestation plantings contained, on average, 2.3 times more ecosystem C than agricultural areas (102â¯Mgâ¯ha-1 and 233â¯Mgâ¯ha-1, respectively). Most of the C accumulation was in living above-ground and below-ground biomass (60 and 30%, respectively) with a smaller amount in debris pools (16%). Apart from C in roots, soil C accumulation was not obvious across sites ranging from 8 to 33â¯years since reforestation, relative to the agricultural baseline. Differences in SOC (and associated SOC pools) to a depth of 50â¯cm, did exist between reforested areas and adjacent agriculture at some sites, however there was not a consistent trend in SOC associated with reforestation. Local site-based factors (e.g. soil texture and mineralogy, land-use history and microbial activity) appear to have a strong influence on the direction of the change in SOC. While reforestation in the tropics has great potential to accumulate C in biomass in living vegetation, and debris pools, it is likely to take approximately 50â¯years before C stocks of reforested areas resemble natural ecosystems. Accumulation of SOC through reforestation is difficult to achieve, highlighting the need to conserve carbon pools in remnant forests in the tropics.