Improving the utilisation of water and soil resources for tree crop production in coastal areas of Vietnam and New South Wales

Central coastal Vietnam is the driest part of the country with most of the rain falling in only 3-4 months of the year. Rainfall in the wet season can be very intense causing flooding and erosion. It also has extensive areas of sandy soils which have low nutrient content and organic matter. In the long dry season agriculture in the region is highly dependent on irrigation water which is often in short supply. This project will develop, evaluate and extend practices which aim to increase the efficiency of use of scarce irrigation water and improve soil management in horticultural tree crops in central coastal; Vietnam and subtropical NSW. The projects activities in Vietnam are focussed in the provinces Ninh Thuan and Binh Binh.

The project aims to
Assess the potential sources, availability and costs of irrigation water in landscape units long central coastal Vietnam;
Identify current farmer practices and perceptions in relation to irrigation water and nutrient management.
Increase the technical capacity of the Agricultural Sciences Institute for Southern Coastal Central Vietnam
Evaluate water and nutrient management strategies to improve productivity and profitability of tree crops and resource use efficiency.

The water resource assessment indicates that irrigation from shallow groundwater is the dominant water source for farms in Binh Dinh. The sandy soils here occur across a flat to undulating riverine landscape extending 30 km from the coast. The watertable fluctuates from 4-6m between the wet and dry season. Wells are common and are used for both irrigation and domestic supplies. There are some farm dams and these fill from both groundwater and surface runoff.
There are three types of water resources for irrigation in the sandy soil area of Ninh Thuan. First, the coastal wind blown sands dune systems act as recharge areas for fringing wetlands and groundwater fed streams. Second, surface storage in small dams of runoff water and spring fed dams are found in the mid and upper sub-catchment valley floors and mountain toe slopes containing weathered granite colluvium. Third, groundwater and diverted river water are used in the alluvial levee soils on the floodplain near the river which is mainly sandy loams. Irrigation wells within a few kilometres of the coast have become saline due to seas water intrusion. Government reservoirs have been constructed in the higher parts of the catchment in Binh Dinh and Ninh Thuan to supply water for irrigation and hydroelectricity and more are planned.
A survey of farmer practices was conducted in Ninh Thuan and Binh Dinh. The survey questioned 150 farmers in each province about their farming system, water use and fertilizer use. Ninety five percent of farmers surveyed use wells for household water and irrigation. Irrigation water in Ninh Thuan is usually available for 3-6 months of the 9 month dry season. Most farmers use both animal manure and urea with most fertiliser being applied to high value crops such as vegetable, grapes, and apple. Nearly all farmers heavily cultivate the soil to construct furrows for water distribution.
As part of the capacity building objective, an irrigation course developed by NSW DPI was adapted to suit Vietnamese needs, translated and presented to a group of 30 Vietnamese researchers, extension officers and some NGO staff. The course ran over 3 days and covered soil and soil water characteristics, plant water requirements and scheduling, and assessing and managing locally appropriate irrigation systems to meet crop needs efficiently. The Vietnamese partners intend to use this course as part of a process for increasing farmer irrigation skills and productivity.
A nutrient management experiment and an irrigation experiment have been established on red ferrasol soils on the Alstonville Plateau, NSW. The nutrient management experiment is evaluating the effects on incorporation of biochar (10 t/ha, green waste and cattle feetlot waste biochars) on forage production (pinto peanut and annual ryegrass). Initial results indicate that dairy waste char enhanced growth of rye grass in the presence of N fertiliser and increased available nutrients. This was not the case with green waste char.
A simple daily crop-soil water balance model has been partially constructed to assess the average irrigation requirement of a closed canopy crop for each month of the year. The model also calculates the probability that soil moisture will exceed a given amount during each month of the year. The model uses long term climatic data (rainfall and potential evapotranspiration), crop factors, irrigation amount and rootzone soil water capacity as inputs. Following further testing and refinement, the model has application for assessing irrigation management strategies in both NSW and Vietnam. An irrigation experiment is being established on a blue berry orchard to evaluate partial irrigation strategies. These experiments will be used for training activities with visiting Vietnamese scientists.