Thursday, November 8, 2007 - 9:45 AM
345-6
Green Manuring as a Source of Soil Organic Matter Build up in Dry Areas.
Mohammad Hamza and Wal Anderson. AUSTRALIA, Dept.of Agriculture, Department of Agriculture and Food, 444 Albany Highway, Albany, WA 6330, AUSTRALIA
Abstract
These experiments were intended to study the potential accumulation of soil organic matter (SOM) in two contrasting soils, sandy clay loam and loamy sand, using green manure crops under the severe conditions of high temperature and low rainfall that exist in the eastern wheat belt of Western Australia.
Cereals and legume crops were incorporated into the soils as green manure for four consecutive years. Two plant species were used to provide green manure, oat (Avena sativa ) as a cereal with high C:N ratio and either faba bean (Vicia faba), field peas (Pisum sativum) or lupin (Lupinus angustifolius) as legumes with low C:N ratios. These crops were arranged in three treatments for each soil type consisting of different crop sequences.
Between 14 and 20 t/ha of green material were incorporated into the top soil over four years. All treatments increased soil organic matter significantly compared to the initial soil values but no significant increases between treatments (crop sequences) were observed. Water stable aggregates and soil bulk density were significantly improved by all treatments but no significant differences were observed between treatments. The SOM increased from around 1.28 to 1.96%, or about 50%, but well below the critical value suggested in the literature for more humid areas to sustain healthy soil nor as high as expected from the high quantity of green material returned to the soil. The rate of accumulation of SOM was also well below that obtained from well-watered regions. These results point to the dominant role of soil and weather conditions in the low rainfall cropping zone of Western Australia in limiting the build-up of soil organic matter content, regardless of amount or species of green manuring.
These experiments were intended to study the potential accumulation of soil organic matter (SOM) in two contrasting soils, sandy clay loam and loamy sand, using green manure crops under the severe conditions of high temperature and low rainfall that exist in the eastern wheat belt of Western Australia.
Cereals and legume crops were incorporated into the soils as green manure for four consecutive years. Two plant species were used to provide green manure, oat (Avena sativa ) as a cereal with high C:N ratio and either faba bean (Vicia faba), field peas (Pisum sativum) or lupin (Lupinus angustifolius) as legumes with low C:N ratios. These crops were arranged in three treatments for each soil type consisting of different crop sequences.
Between 14 and 20 t/ha of green material were incorporated into the top soil over four years. All treatments increased soil organic matter significantly compared to the initial soil values but no significant increases between treatments (crop sequences) were observed. Water stable aggregates and soil bulk density were significantly improved by all treatments but no significant differences were observed between treatments. The SOM increased from around 1.28 to 1.96%, or about 50%, but well below the critical value suggested in the literature for more humid areas to sustain healthy soil nor as high as expected from the high quantity of green material returned to the soil. The rate of accumulation of SOM was also well below that obtained from well-watered regions. These results point to the dominant role of soil and weather conditions in the low rainfall cropping zone of Western Australia in limiting the build-up of soil organic matter content, regardless of amount or species of green manuring.