Abstract
Besides the importance of dissolved organic matter (DOM) in soil biogeochemical processes, there is still a debate on how agricultural intensification affects the leaching of terrestrial DOM into adjacent aquatic ecosystems. In order to close this linkage, we conducted a short-term (45 day) lysimeter experiment with silt loam and sandy loam undisturbed/intact soil cores. Mineral (calcium ammonium nitrate) or organic (pig slurry) fertilizer was applied on the soil surface with a concentration equivalent to 130 kg N ha−1. On average, amounts of leached DOC over 45 days ranged between 20.4 mg (silt loam, mineral fertilizer) and 34.4 mg (sandy loam, organic fertilizer). Both, mineral and organic fertilization of a silt loam reduced concentration of dissolved organic carbon (DOC) in the leachate and shifted its composition towards a microbial-like signature (BIX) with a higher aromaticity (Fi) and a lower molecular size (E2:E3). However, in sandy loam only mineral fertilization affected organic matter leaching. There, lowered DOC concentrations with a smaller molecular size (E2:E3) could be detected. The overall effect of fertilization on DOC leaching and DOM composition was interrelated with soil texture and limited to first 12 days. Our results highlight the need for management measures, which prevent or reduce fast flow paths leading soil water directly into aquatic systems, such as surface flow, fast subsurface flow, or drainage water.
Highlights
Soil stores twice as much carbon as the atmosphere [1], with an estimated soil organic carbon storage of 1462 to 1548 Pg in the first 100 cm of the soil profile [2]
Results of the PERMANOVA were visualized in principal response curves (PRC; vegan package) for each soil texture individually in order to illustrate the impact of fertilizer type and their interaction with time on the dissolved organic matter (DOM) composition
As suggested by [62], DOM indices with a species weight between −0.5 and +0.5 were not shown, because they were likely to show either a weak response or a response that is unrelated to fertilization and their interaction with time
Summary
Soil stores twice as much carbon as the atmosphere [1], with an estimated soil organic carbon storage of 1462 to 1548 Pg in the first 100 cm of the soil profile [2]. Soil carbon storage is increasingly threatened by the conversion of land into areas for intensive agricultural production. Water 2020, 12, 1617 of land to agricultural areas is expected to increase further, and the production per square meter is predicted to intensify [4]. The latter, intensive production, is often achieved through the application of nitrogen-based fertilizers, with a predicted annual application of 118 million tons of N globally by 2020 [5]. Decades of high fertilizer application rates have increased the overall nitrogen content in soils, fueling mineralization rates which, in turn, enhanced the depletion of naturally occurring soil organic carbon [6]
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