Water quality and soil management for sustainable farming systems in South-Central Coastal Vietnam

Truc Do

The high permeability of the sands, the shallow groundwater, the intense wet season rainfall, high rates of soluble fertilizer applied to vegetable crops and the dependence on flood irrigation to grow crops on the sands of South - Central Coastal Vietnam suggest that this area would have a high risk of groundwater contamination. In the thesis, studies of groundwater quality and soil amendments and irrigation management strategies are indicated to alleviate the losses of nitrate and phosphate under irrigated vegetable crop production on deep sands. The researches were set up in Phu Yen and Ninh Thuan provinces which located in SCC Vietnam, from 2013 to 2015. N and P were considered in all the assessments for agriculture - dependent water quality and sand - amended effects. Groundwater quality in Phu Yen was affected by the contamination of phosphate and nitrate in wells used by households, with particularly up to 80 mg NO 3 - - N/L and the quality changed due to the weather with the lower concentrations during and immediately following the rainy season. While in Ninh Thuan province in which water is a limited resource in the long dry season, and exacerbated by high evaporation, high concentration of salt and nitrate in open wells in the dry season were found in more than 80% of the observed wells and the levels were up to 10 dS/m and 198 mg N - NO 3 - /L. The most likely source of nitrate contamination of the groundwater was fertilizer application to vegetable production lands. With the aim of increasing clay up to 5% in sandy soil, clay amendments such as zeolite, bentonite and clay - rich soil were added to sands. Yield responses were equivalent to 57 to 167 % increase for amendments of 100 t bentonite, 150 t zeolite and 300 t clay soil /ha. The threefold increase of CEC by up to 3 cmol c /kg had positive effects on soil water storage and exchangeable cations. An alternative local material, sugarcane residue, was also found to be an effective amendment of sands at 30 t/ha produced si milar benefits on sands as clay amendments regarding water and nutrient retention and crop yield increase. Moreover, the water use efficiency gains and water saving equivalent to 21 to 72% can be achieved depending on types of amendment and rates. Hence, i rrigation can be decreased depending on types of amendment and rates applied amendments. These amendments also increased in the percentage of crop/fertilizer N use efficiencies and N recovery but not to large extent. Despite the apparent increase in N use efficiency with clay amendments, only 3.8 to 19% of fertilizer N applied or 47.5 to 50.5% the green onion N demand were taken from fertilizer. Among the amendments, sugarcane residue was the most effective amendment due to achieving benefits equivalent to clay and bentonite additions despite the much lower level of application. Despite the increases in N use efficiency with sugarcane residue, clay - rich soil or bentonite, 63 to 73% of fertili s er N was not accounted for in the nutrient budget of the soil - plant system. The soil N was mainly retained in the 0 - 20 cm depth, and only trace amounts recovered at 20 - 40 cm depth. The clay amendments helped increase plant N accumulation and fertilizer N use efficiency, but sugarcane residue was a superior amendment to b entonite and clay soil. There is no apparent N leaching in the sandy soil regardless of amendments or irrigation type. Irrigation method applied to onion was an important factor since sprinklers improved fertilizer use efficiency.

Water quality and soil management for sustainable farming systems in South-Central Coastal Vietnam

Files and links (1)

Abstract

Details

Metrics