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Carbon dynamics, nutrient cycling and the sustainability of cropping and pasture systems
Project ID
LWR2/1994/048
Commissioned Organisation
University of New England, Department of Agronomy and Soil Science, Australia
Project Leader
Dr Graeme Blair
gblair@metz.une.edu.au
Phone:
02 6773 2440
Fax:
02 6773 3465
Project Budget
$924,419.00
Start Date
01/01/1996
Finish Date
31/12/1998
Extension Start Date
01/01/1999
Extension Finish Date
30/06/1999
ACIAR Research Program Manager
Dr Kep Coughlan
Overview Objectives
ACIAR projects have developed three useful tools for managing organic matter - firstly, a formula for calculating a Carbon Management Index (CMI), secondly, an in vitro perfusion technique, and thirdly, a balance sheet for nutrient concentrations, particularly of carbon, sulfur and phosphorus. This project applied these tools to experiments in Australia, Thailand, the Philippines, Laos, Bangladesh, Tonga and Samoa. Experiments examined pastures, wheat, sorghum, cotton, sugarcane, rice, maize and root crops in combination with lucerne, chickpea, cowpea, oats, pigeon pea, horticultural crops, Sesbania, Gliricidia and Calliandra.
Project Background and Objectives
When land is first cleared of its native vegetation the soil is usually fertile, chiefly because it contains organic matter. However, in time the soil organic matter is depleted. The soil's structural properties become less favourable, the infiltration rate falls, and run-off and erosion increase. Intense farming systems aggravate losses. Adding organic manures and plant material helps restore soil fertility and sustainability. Fresh, soft crop residues and green manures break down relatively rapidly offering short-term benefits. Coarse, poor quality stubbles break down slowly, and adsorb soil nutrients. Inorganic fertilisers can speed up the decomposition, but may overstimulate the soil biota. Both coarse and soft organic inputs appear to be needed to rebuild soil fertility and structure for the long-term. Organic matter build-up affects the concentrations of soil carbon in its various 'pools', and modifies soil chemistry and crop yields, apart from changing the aggregation and porosity of the soil matrix.
Project Outcomes
Major achievements were:
evaluation and effective transfer to Thailand, the Philippines, and Tonga of the perfusion technique for assessing litter decomposition
further testing of labile carbon and the Carbon Management Index, in Australia in particular, as indicators of organic matter changes in response to management
results for the effectiveness of small (1.5 tonnes per hectare) applications of tree leaf litters in Thailand
useful nutrient balance studies, as influenced by organic material inputs, in Thailand and the Philippines
results for the effect of mulching on crop yield in Tonga
The field experimental program produced useful results but it is unclear whether some of these will have any substantial impact. The further evaluation and application of methods for assessing the ease of decomposition of plant litters and the forms of soil carbon (labile C and the Carbon Management Index) was successful.
Collaborative relationships were fostered between the five countries. An impressive program included training of PhD students and the transfer of some laboratory methodologies from University of New England. However, the provision of in-country training fell short of requirements in some cases.
An extension of six months was agreed on to allow completion of the soil and plant analyses required to conduct a carbon and nutrient audit for the field experiments, a task central to the project objectives, and to enable experimental data for Lao PDR and Thailand to be collated, synthesised, and interpreted.
The project was deemed successful in the area of post-graduate training, and in the significant number of scientific publications produced. It was also found to have an impact in Australia, where interest in using the soil carbon measurement to assess sustainability of cropping practices is high. There was no initial uptake of mulching technologies and green manuring, probably because experiments were carried out on research stations with little active farmer involvement.
Reviewers recommended that any future ACIAR project in the area of integrated nutrient management should involve on-farm research, and have a significant socio-economic component.
Location
There are no project locations defined for this project.
