Use of long-term monitoring data to derive a relationship between nitrogen surplus and nitrate leaching for grassland and arable land on well-drained sandy soils in the Netherlands

Abstract

The decrease in nitrogen (N) use in agriculture led to improvement of upper groundwater quality in the Sand region of the Netherlands in the 1991-2009 period. However, still half of the farms exceeded the European nitrate standard for groundwater of 50 mg/l in the 2008-2011 period. To assure that farms will comply with the quality standard, an empirical model is used to derive environmentally sound N use standards for sandy soils for different crops and soil drainage conditions. Key parameters in this model are the nitrate-N leaching fractions (NLFs) for arable land and grassland on deep, well-drained sandy soils. NLFs quantify the fraction of the N surplus on the soil balance that leaches from the root zone to groundwater and this fraction represents N available for leaching and denitrification. The aim of this study was to develop a method for calculating these NLFs by using data from a random sample of commercial arable farms and dairy farms that were monitored in the 1991-2009 period. Only mean data per farm were available, which blocked a direct derivation of NLFs for unique combinations of crop type, soil type and natural soil drainage conditions. Results showed that N surplus leached almost completely from the root zone of arable land on the most vulnerable soils, that is, deep, welldrained sandy soils (95% confidence interval of NLF 0.80-0.99), while for grassland only half of the N surplus leached from the root zone of grassland (0.39-0.49). The NLF for grassland decreased with 0.015 units/year, which is postulated to be due to a decreased grazing and increased year-round housing of dairy cows. NLFs are positively correlated with precipitation surplus (0.05 units/100 mm for dairy farms and 0.10 units/100 mm for arable farms). Therefore, an increase in precipitation due to climate change may lead to an increase in leaching of nitrate.

Model-Based Analysis of Nitrate Concentration in the Leachate—The North Rhine-Westfalia Case Study, Germany

“…In order to ensure that the nitrate concentrations in oxidized aquifers will not exceed 50 mg/L and to conserve the natural denitrification capacity of reduced aquifers, the German Working Group on water issues of the Federal States and the Federal Government (LAWA) requires that the nitrate concentration in the leachate should not exceed 50 mg NO 3 /L [28]. Similar considerations are reflected in the groundwater strategies of other countries [29,30]. Against this background, the nitrate concentration in the leachate can be considered as the decisive starting-point to determine the N reduction required [31].…”

Agriculture and stream water quality – future challenges for monitoring

“…Importantly, ADF empowers farmers to proactively address environmental issues and the paper discusses the development, guidance, principals and goals of ADF and contrasts this with other farm monitoring projects, where the sources of nutrient impairment are the subject of ongoing mitigation. Fraters et al (2015) address how to use long-term monitoring data to develop a method for calculating the nitrate nitrogen leaching fractions (NLFs) by using data from a random sample of commercial arable farms and dairy farms that were monitored during the period 1991-2009. The results showed that N surplus leached almost completely from the root zone of arable land on the most vulnerable soils, i.e., deep, well-drained sandy soils (95%) confidence interval of NLF (0.80-0.99), while for grassland only half of the N surplus leached from the root zone of grassland (0.39-0.49).…”

Peer Review #1 of "Estimation of nitrogen leaching load from agricultural fields in the Puck Commune with an interactive calculator (v0.1)"

“…According to Kupiec (2015), reference levels of N-surplus defining the risk of water hazards are quoted in various sources. Research results indicate that N-surplus can be a good predictor of groundwater nitrate pollution (Wick et al, 2012;Fraters et al, 2015;Huang et al, 2017).…”