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Advisor(s)
Abstract(s)
The present study describes a methodology to quantify the gross soil nitrogen balance (SNB) for agricultural land
use in the Tagus Nitrate Vulnerable Zone (TVZ) between 1989 and 2016, including effects of implementation of
the EC Nitrates Directive (ND, 91/676/EEC) since 2004. The study uses decadal information from National
Agricultural Census at parish level and is supported by a Geographical Information System (GIS). The average
SNB of the TVZ decreased significantly (p < 0.001) from 125 kg ha−1 in 1989 to 63 kg ha−1 in 2016 (on
average 1.8 kg ha−1 yr−1). The N input via irrigation water was particularly high in seven municipalities where
it represents up to 35% of the total inputs. Using a Monte Carlo approach, the average uncertainty of the SNB
was calculated at 12%. The most important sources of uncertainty were mineral fertilization, nitrate concentration
in groundwater used for irrigation and the percentage of farmers complying with ND measures. GIS
analysis shows that, at the scale of municipalities, the SNB has decreased since the ND implementation in regions
dominated by irrigated intensive crop production, while the SNB has stabilized in municipalities in the south of
TVZ with intensive livestock production (75% of area). We conclude that the implementation of ND and national
measures to reduce the SNB was not equally effective across the TVZ. Our results indicate that the most effective
measures to reduce the SNB in the future are increasing compliance of farmers with the ND related measures and
measures increasing the nitrogen use efficiency of livestock manures
Description
Keywords
Nitrates directive vulnerable zones to nitrates N surplus spatialization trend analysis Monte Carlo
Pedagogical Context
Citation
Land Use Policy 84 (2019) 278-293
Publisher
Elsevier