Utilising basic soil data for the sustainable management of upland soils in Vietnam and Australia

• Institute of Agricultural Sciences of South Vietnam, Vietnam
• National Institute for Soils and Fertilisers, Vietnam
• World Vision of Vietnam, Vietnam

Traditional subsistence agricultural systems based on slash-and-burn practices have degraded soils in upland areas of Vietnam's central highlands. Extensive deforestation and land clearing have resulted, leading to erosion and soil fertility declines. Ethnic minorities who have practised this style of agriculture have high levels of poverty, and little knowledge of other agricultural practices. The Vietnamese Government has encouraged these minorities to settle in villages and undertake permanent agricultural production in surrounding areas. Soil productivity in these areas remains low, with knowledge of practices to ensure long-term sustainability negligible. Constraints to productivity are numerous and include nutrient deficiencies and toxicities in soils, and soil compaction.

A variety of soil information has been collected, mainly for soil classification purposes. Despite this information being available little has been made of the data in terms of assessing soil productivity constraints. Scientists have developed a simple Soil Constraints and Management Package ('SCAMP') that uses measures and properties (texture, colour, etc) of collected soil, or soil examined in the field, to identify constraints and indicates appropriate management strategies. Scaling this up for interpretation of soil constraints and strategies to ameliorate or manage these at the village level is needed to help develop improved practices.

The project sought to provide a decision support framework that allowed basic soil information to be interpreted in terms of soil constraints to productivity and to be synthesised into management strategies appropriate for maintaining the long-term productivity of upland soils. This would enable results obtained in a site-specific context to be applied at the provincial/catchment scale, through the use of existing geo-coded soil survey data and SCAMP.

The researchers interpreted basic soils information in terms of constraints to productivity and develop management practices at village level for sustaining the long term productivity of Vietnam's upland soils. They collated existing soils information and collected and analysed representative soil types. They also identified soil constraints for local crops at selected sites, using soil data along with assessment of local farmer practices. They also prepared a Land Evaluation and Use Report and determined appropriate management strategies to help carry out replicated field experiments.

Using locally available plant materials and animal manures, In both Vietnam and Australia they assessed the potential of innovative residue management to improve soil productivity. They determined the effects of selected plant residues on key soil properties and characterised plant residues, prior to correlating residue composition with effects on key soil properties. They also trained IAS staff in plant residue analysis.

They facilitated the application of SCAMP at village, provincial and national level by training extension personnel in its use (Vietnam) and by communicating results to catchment management organisations and the community in the Herbert River catchment (Australia). They trained project collaborators in the use and interpretation of SCAMP and held regular farmer/extension field days. Pamphlets were prepared on sustainable management practices for upland soils, and a SCAMP package was developed to train extension personnel in its use.

They used geo-coded soil data and SCAMP to produce soil degradation hazard, risk assessment and risk management maps for both Vietnam and Australia. They were able to determine soil constraints to productivity and, using SCAMP and PERFECT models, document the temporal relationship and reversibility of various management practices on the constraints to sugarcane production in the Herbert River catchment.

Although a soils map at 1:100,000 scale was available for Gia Lai Province, Vietnam, little use had been made of this information either to assess soil constraints to productivity at regional scale or to extrapolate findings from site-specific field experiments to other areas. SCAMP was introduced to facilitate the use of existing soils information for making informed decisions about sustainable soil management. Simple soil measurements and properties (e.g. texture, colour, drainage rating and soil pH) were entered into the SCAMP Access database and specific criteria in look-up tables were used to identify intrinsic soil constraints to long-term productivity.

Depending on the constraints identified for a soil, a report is derived from the SCAMP database indicating appropriate strategies for managing the constraints. Where geo-referenced soil survey data are available, the SCAMP Access database has been used to assign specific attributes to individual soil types, and because the database interfaces with Geographic Information Systems (GIS) such as MapInfo and ARCGIS, maps of constraints or specific soil attributes can be produced.

To demonstrate the ability of SCAMP to identify soil constraints at plot scale, the package was applied to soil data sets from the two major soil types (Ferralsols and Acrisols) of Gia Lai Province. Phosphorus (P) fixation, aluminium toxicity and low cation exchange capacity (CEC) were identified as common constraints to productivity on Ferralsols, and low plant available water capacity, compaction and low potassium (K) status as common constraints to productivity on Acrisols. Field experiments were undertaken on a Ferralsol site (two cropping seasons: 2005 and 2006) and two Acrisols (single sites in 2005 and 2006) to assess management strategies for minimising these constraints in the presence of adequate N, P, and K fertiliser.

In both years, maize (Zea mays) yields from the Ferralsol were increased by applying a plant amendment (Tithonia diversifolia) (selected to increase soil pH and decrease P fixation) and high activity clay (selected to increase CEC). Water-soluble P fertiliser recovery was increased in this high P-fixing soil by placing the fertiliser in a sub-surface band. In economic terms, the Tithonia treatments consistently produced the highest benefit/cost ratios (1.3 in 2005; 3.2 in 2006). For the Acrisol in 2006, maize was grown in mounded rows (to improve drainage) and yields were maximised by applying a super-absorbent material (selected to increase soil water holding capacity), high activity clay (selected to increase the low CEC of this soil) or incorporating green manure residues into the crop mound. The benefit/cost ratios obtained for these treatments were 4.1, 2.9 and 5.2 respectively.

To demonstrate the usefulness of SCAMP on a catchment/regional scale, maps identifying areas of low pH, high acidification hazard and low CEC were produced for the Herbert River catchment, Queensland. Maps were also produced for the Wet Tropics of north Queensland identifying the predominant pathway of off-site nutrient movement. The catchment management agency used this information to identify high-risk areas where awareness programs could help landholders to improve fertiliser management practices.

The SCAMP manual and supporting resource materials were translated into Vietnamese. Subsequently several SCAMP training courses were held for provincial and district extensionists and for project staff and leaders of World Vision agricultural development projects.