Nitrate in upper groundwater on farms under tillage as affected by fertilizer use, soil type and groundwater table

Abstract

Indicators are needed to check whether policies on protection of groundwater are effective and if regulations are complied with. We evaluated various indicators at different scales, both in space and in time, and at different degrees of complexity. Groundwater was sampled on 34 arable farms for 3 years. Nitrate concentration in upper groundwater was low on clay soil. On sandy soil, peat layers reduced the nitrate concentration with about 80 mg/l on average. Sandy soils with high groundwater tables had nitrate concentrations that were less than half of those at sandy soils with low groundwater tables. The relationship between different fertilization variables and nitrate in groundwater was investigated for sandy soils without peat layers. N surplus poorly correlated with nitrate concentrations in groundwater when individual sampling points were studied, but clearly increased when data were averaged at the farm level. Soil mineral nitrogen correlated best with nitrate concentrations in groundwater. The relationships show that especially on well drained soil drastic measures will be inevitable to reach good water quality.

Nitrate contamination of groundwater in an agroecosystem in Zhangye Oasis, Northwest China

“…A study indicated that low groundwater tables caused the contamination (Ruijter et al 2007). In this investigation, most of the groundwater samples in which the NO 3 --N concentration was greater than the allowed values set by the WHO were sampled from less than 20-m depth.…”

Assessment of the predictive quality of simple indicator approaches for nitrate leaching from agricultural fields

“…Delgado, 1998;Van Eerdt and Fong, 1998;Jansons et al, 2003;Sieling and Kage, 2006;Rankinen et al, 2007;Schröder and Neeteson, 2008). However, it has been reported that the N balance is often a poor predictor of N amounts lost actually to the environment and only weakly correlated with N losses actually measured, at least on the field scale and for singleyear data (Schröder et al, 2004;Sieling and Kage, 2006;De Ruijter et al, 2007;Rankinen et al, 2007). This is mainly because Nbal does not consider soil hydrology and water movement (Shaffer and Delgado, 2002), and dynamic changes in the N status of the soil (mineralization, immobilization) (Oenema et al, 2005).…”

“…(Meisinger and Delgado, 2002;Havlin, 2004). Utilization of experimental methods to determine N loading, such as analysis of leachate water obtained by suction cups (Sieling and Kage, 2006), monolithlysimeters (Bohne et al, 1997;Knappe et al, 2002), analysis of percolate from tile drains (Kladivko et al, 2004;Tiemeyer et al, 2008), N concentrations in groundwater (De Ruijter et al, 2007), and also measurements of mineral nitrate content in the soil profile (Wehrmann and Scharpf, 1979), is restricted in practice. The main reasons for this are that routine application of such labordemanding methods is mostly not viable, measurements can be made only afterwards, and the experimental data are often not suited for generalization (because of the effects of different years with varying weather patterns, different management practices, fertilizer application rates, etc.).…”

“…However, correlations of N balances with measured N losses often proved to be weak (e.g. Schröder et al, 2004;Sieling and Kage, 2006;De Ruijter et al, 2007;Rankinen et al, 2007).…”

“…Such studies are relatively scarce: for instance, in the Netherlands several source-based NLIs were tested and compared (Ten Berge, 2002;De Ruijter et al, 2007), in France, output validations of simple source-based NLIs using the "Receiver Operating Characteristic" methodology were conducted (Bockstaller et al, 2008;Makowski et al, 2009).…”