Abstract
The application of synthetic nitrogen (N) fertilizers has boosted crop yields globally. However, it has also imposed on environmental pollution problems. An estimation of actual fertilizer N inputs at the crop field level is needed to establish effective N management plans to control groundwater NO3-N contamination. Here, a survey to collect the types of cultivated crop and fertilizer application rate was conducted during 2016–2018, covering 44,253 small crop fields (7730 ha) in the western part (Hanrim and Hankyung regions) of Jeju Island, South Korea. Foreign vegetables, citrus fruits, and bulb vegetables are the major crop types grown in the total cultivated areas of 2165.6 ha, 1718.7 ha, and 944.9 ha, respectively. For several crops (green garlic, potato, and chives), the over-use of N fertilizers is observed, the amount of which is 1.73–4.95 times greater than the standard fertilizer application rate. The highest level of fertilizer N input is observed for bulb vegetables in both the regions (Hanrim: 500.5 kg/ha, Hankyung: 487.1 kg/ha), with nearly 80% of the N fertilizer input turned into surplus N loading. A comparison between a spatial interpolation map of the fertilizer N input and that of the groundwater NO3-N concentration implies that the excessive use of synthetic fertilizer results in the degradation of groundwater quality by NO3-N. N management plans for the study area are suggested based on the N fertilizer input at the crop field level. This study highlights that sustainable N management plans should be arranged at the crop field level, considering the spatial heterogeneity of N fertilizer use.
Highlights
Nitrogen (N) is an essential nutrient for plant growth
As crops only use approximately half of the N fertilizer with a 0.45 global nitrogen use efficiency (NUE) [2], the remainder of the applied fertilizer remains in the soil and groundwater, causing adverse environmental problems such as eutrophication [3,4], greenhouse gas emissions [5,6], soil acidification [7], and NO3 -N pollution in surface water and groundwater [8,9,10]
The results showed that a total of 1314.9 t of surplus N for the six months would reach the groundwater table, with an average NO3 -N concentration of 33.5 mg/L, exceeding the MCL
Summary
The mass production of synthetic N fertilizers was initiated using the Haber-Bosch process in the early 1900s, which resulted in a significant increase in crop yield. The development of synthetic fertilizers has resulted in a tremendous increase in crop productivity, it has negatively influenced the ecosystems. As crops only use approximately half of the N fertilizer with a 0.45 global nitrogen use efficiency (NUE) [2], the remainder of the applied fertilizer remains in the soil and groundwater, causing adverse environmental problems such as eutrophication [3,4], greenhouse gas emissions [5,6], soil acidification [7], and NO3 -N pollution in surface water and groundwater [8,9,10].
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