Australia State of the Environment Report 2001 (Theme Report)
Prepared by: Ann Hamblin, Bureau of Rural Sciences, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06748 5
Nutrient and carbon cycling (continued)
Carbon stores in soil, litter, standing trees and fallen dead timber are crucial in providing habitats, as well as nutrients, for the majority of land biota, that is, the invertebrates, as well as to the better known but less abundant vascular plants and vertebrates. As described in earlier sections, the loss of surface soil, litter and associated woody materials has been very significant historically. In the past two to three decades, improvements have been made in a number of pastoral, agricultural and forestry practices that eventually restore the depleted A (organic rich) horizons found in many agricultural and pastoral soils.
Practices that are most important for this process are maintaining vegetation cover on pastures; stubble retention and conservation tillage (minimum or zero tillage); green cane harvesting of sugarcane; laying brushwood in the rangelands in patch mosaics; and retaining all non-harvestable timber as surface cover in forestry coups. These practices have been discussed in the section Accelerated erosion and loss of surface soil in relation to controlling erosion. This is why control of accelerated erosion is so vital as the starting point in the control of ecosystem function. It is instructive to consider one agricultural industry as an example of how environmentally sound practice may be adopted, and the limitations to universal adoption (see Green harvesting of sugarcane).
In response to the Kyoto Protocol, the Greenhouse Gas Abatement Program of the Australian Government offers investment incentives for projects that deliver cost effective, additional abatement by reducing fossil fuel consumption or through direct carbon sequestration. Carbon sequestration projects may include action to increase perennial vegetation, to control secondary salinity, or to control accelerated erosion.
Bush for Greenhouse, launched in 2000, aims to increase Australia's greenhouse gas sink capacity by increasing corporate investment in native vegetation. Revegetation removes carbon dioxide from the atmosphere.
The program builds on programs such as Bushcare and Greenhouse Challenge. Bush for Greenhouse seeks to build new partnerships between industry and landholders to achieve greenhouse and other environmental outcomes including prevention of land degradation.
The Australian Greenhouse Office has appointed a carbon broker to secure corporate investment and manage a pool of revegetation projects.
The National Carbon Accounting System (NCAS), established in the Australian Greenhouse Office, is gathering estimates of carbon stores in the environment as a part of Australia's responsibilities under the Kyoto Protocol on greenhouse gas emissions. Much of NCAS's work is currently in progress, with data relating to the situation in 2000 not yet available. Details of the approach, and progress to date can be viewed on the AGO's website (http://www.greenhouse.gov.au/ncas.html ). The program is carried out in four components: wood change, vegetation cover, soil change and tree change. Investment in farm forestry and commercial plantations has risen in recent years, stimulated in part by the potential of carbon credits from the increased sink that fast-growing tree crops represent. Without such information, it will be difficult to substantiate the extent to which different anthropogenic activities are contributing measurably to carbon sinks.
Sugarcane is grown in wet tropical regions. In Australia most cane is grown in Queensland, but extends south into northern NSW within 50 km of the coast, from latitude 17 harvested in the first year after planting. Traditionally cane was burnt before harvesting to allow access for cutters, but in the late 1970s mechanisation rapidly developed in Australia to offset rising labour costs. This provided the technical opportunity to the development of green cane harvesting, which was advocated as a way of overcoming the high erosion hazard that occurs in this region of intense rainfall. Green cane harvesting was rapidly adopted in the 1980s.
Green harvesting of sugarcane.
Source: AFFA (2003c)
In hot wet climates mulches (from the trash left after green harvesting) have an added advantage in keeping the soil surface cool and moist, stimulating rapid growth. This in turn has a yield advantage. However, further south, the mulches serve to slow the warming up of the cold wet soil in spring. This slows the rate of growth even more than would otherwise occur. Thus, despite the clear advantage of green cane harvesting for erosion control and soil organic matter retention, farmers in the southern regions have struggled to develop a system that does not retard growth and yield. Some varietal improvement in early maturation has been achieved, but in 1995 when the industry undertook an environmental audit of its practices, less than 50% of farmers in the southern and central cane-growing regions had adopted this practice. The percentage of farmers surveyed who had adopted green cane harvesting in 1995 were:
Far North 82 (90)
Northern 90 (45)
Central 37 (45)
Southern 35 (40)
(Figures in parentheses are industry estimates for the same year.)
Ironically it is in the southern and central regions where community pressure is greatest on growers, because urban encroachment onto farming land has resulted in protests at smoke pollution. Twenty-five percent of farmers surveyed said they had adopted green cane harvesting because of community pressure. Overall nearly 50% of farmers also left trash on the ground at harvest (whatever method of harvesting used), and only 23% burnt trash, while 32% incorporated the trash. Incorporation is often resorted to where pests such as slugs and snails build up. (Gutteridge, Haskins and Davey 1996).
Thus it can be seen that while most farmers recognise the need to cut cane green and retain trash, they must juggle the environmental benefits with the need to get a fast-growing, healthy and pest-free crop if they are to have profitable yields.