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ISHS Acta Horticulturae 1146: III International Symposium on Organic Matter Management and Compost Use in Horticulture

The phosphate/nitrate ratio of seepage waters as an indicator of macropore contributions to leaching in different agricultural land use

Authors:   D.-H. Yoon, K.W. Nam, M. Kuecke, J.-M. Greef
Keywords:   seepage water, macropore, phosphate/nitrate ratio, PCAPS
DOI:   10.17660/ActaHortic.2016.1146.30
The leaching of mineral and organic nitrogen and phosphorus was studied in relation to land use (grassland and arable land) and fertilisation (exclusive organic and mineral fertilisation). Passive capillary samplers (PCAPS, fibreglass wick sampler) were chosen to collect seepage water. PCAPS were installed below the undisturbed soil profile to collect matrix flux as well as macropore flux. Seepage waters were collected weekly, and nitrate, ammonium, total N, phosphate and total P concentrations were measured in the samples; organic N and P were calculated from the difference in total N (or P) and mineral N (or P). The highest concentrations of mineral-N (nitrate, ammonium) were detected in the late winter, and mineral P concentrations were highest in late summer. The average proportion of ammonium N out of the total N was 15% higher in seepage waters from arable land compared with grassland after long-term organic fertilisation, and was 6% higher from the arable land after long-term mineral fertilisation. The organic N concentrations in seepage waters from the experimental sites decreased noticeably in most cases when the organic P concentrations increased, and vice versa. From this observation, it was concluded that organic N compounds are leached separately from organic P compounds. In most cases, decreases in the drainage nitrate concentration occurred in parallel with increases in the phosphate concentration. In these situations, a higher contribution of macropore flow to leaching is assumed. From these results, it was concluded that the phosphate/nitrate ratio can be used to indicate macropore flow.

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