Extensive nutrient loss is one of the most challenging issues faced by agricultural production regions worldwide. However, diffuse pollution in the subtropical mountainous watersheds is rarely simulated. A watershed model with regional parameter values is essential for watershed management. In this study, SWAT, one of the most popular models was applied to simulate daily discharge (years of 2008-2014), NO3-N flux (2012-2014), and tea yield (2012-2014) in the Ping-Lin watershed (PLW) of Taiwan, as well as to test the effectiveness of a modified fertilization strategy. The results demonstrated that SWAT was capable of simulating daily discharge variation, daily riverine NO3-N flux, and tea yield in the PLW. NO3-N yield of the tea farm (47 kg/ha/yr) was 9 times higher than that of the forest (5.1 kg/ha/yr). A significant proportion (~ 50%) of the input nitrogen (including dry/wet deposition and fertilizer) infiltrated into the soil, resulting in a poor fertilizer uptake efficiency of the tea tree. It was demonstrated that the modified fertilization strategy (apply fertilizer in small rainfall event, i.e., daily rainfall < 20 mm/day, and not in a single day) could increase the nitrogen uptake and harvest yield of the tea tree by 14% and 4%, respectively, with a 10% reduction in nitrogen input. Furthermore, this strategy significantly reduced the nitrogen yields from surface flow (75%), lateral flow (36%), percolation (50%), and groundwater (48%). A popular model with verified parameter values could help in developing a win-win strategy for both farmers and regulators, thus realizing the goals of sustainable agricultural practices.
Keywords: Diffuse pollution; Fertilization strategy; Nitrate flux; Sustainable agricultural practices; Taiwan.
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