Lassaletta Et Al. Suppl. 1 (Long Term Changes in N Cycle in Spain) Regional Environmental

Lassaletta et al. Suppl. 1 (Long term changes in N cycle in Spain) Regional Environmental Change

Supplementary material 1

Methods (Detailed information)

We calculated an overall N budget for Spain for the 1961–2009 period, using the Net Anthropogenic N Input (NANI) concept (see Howarth et al. 1996; Howarth et al. 2012, and Swaney et al. 2012 for an overview of the NANI approach), adapted at the country level instead of the watershed level, the usual scale for this approach. To this purpose, we first estimated the total “new” anthropogenic N inputs entering the country, through synthetic fertilizers application, net atmospheric inputs, crop biological N fixation and net import of food and feed. These budgets were calculated for all Spain including the Balearic and Canary Islands.

Synthetic fertilizers and atmospheric inputs

Yearly data on synthetic N fertilizer application, under different N forms, for the entire period were obtained from the International Fertilizer Industry Association ( Discrepancies with the information provided by FAO are lower than 10% for the entire period.To estimate net atmospheric inputs we followed a slightly differentapproach from the procedure described by Howarth et al. (2006), where only deposition of oxidized N compounds is taken into consideration, while deposition of reduced N compounds is considered to be related to local redeposition of ammonia volatilization. In this case, we applied the procedure first used by Lassaletta et al. (2012), estimating a net balance of atmospheric deposition and emission: the deposition of both oxidized and reduced compounds is considered as N inputs, but emission of reduced N compounds is subtracted from this total, thus taking into account only the net deposition of reduced N forms. This procedure allows determining the balance between atmospheric inputs and export of reduced nitrogen forms across the country borders. We obtained national figures of emission and deposition of oxidized and reduced compounds from the Co-operative Programme for Monitoring and Evaluation of the Long-range Transmission of Air pollutants in Europe (EMEP; When available, we used the recalculated data for 2010. Information on the different emission sources was also gathered. The first available emission data are from 1980; we estimated the emissions for the 1961–1979 period assuming a similar evolution pattern of NOx emissions for Spain as for the OECD European countries estimated by the RETRO project (van het Bolscher et al. 2008). We estimated the deposition of reduced compounds before 1980 by means of a linear regression using total N in manure as the predictor (R2 = 0.74; p < 0.001). The relationship between emission and deposition is relatively constant in all the available series for reduced and oxidized compounds; we therefore applied this ratio to estimate the deposition in the years before 1980. Since there is no information available for the Canary Islands and they account for 1.4% of the total Spanish surface area, in a rough approach we added 1.4% to the emission and deposition results.

Biological nitrogen fixation

We estimated N fixation by the 24 Spanish N-fixing crops, including several legume species, and sugar cane. We applied the following relationship calculating N fixation as the difference between total N biomass produced (including underground and aerial non-harvested parts) minus N applied as fertilizer (Lassaletta et al. 2012):

N fix (kg N ha−1 yr−1) = α * Nyield – A

whereNyield is the harvested biomass expressed in N content (kg N ha−1 yr−1); α is the ratio of total biomass produced with respect to harvested biomass and A (kg N ha−1 yr−1) is the applied synthetic fertilizer. The values obtained were in the range of those reviewed by Herridge et al. (2008). In the case of rice, which is not an N fixing crop but is cultivated under conditions where N fixation by cyanobacteria occurs, a fixed rate of 33 kgN ha−1 yr−1 has been considered, following Herridge et al. (2008). We also estimated the N-fixation in pasture lands applying the proportion of N-fixation over total production proposed by the MMARM (2010) for Spanish grasslands.

International trade

To estimate the annual net import of agricultural products, we used the information provided by the Trade Module of the Faostat database ( We used the yearly information on import-export quantities for Spain (1961–2009) for 572 commodities. The N content of every product (394 vegetable products for food and feed, 100 animal products and 78 products used as materials) was gathered from different sources (McDougall et al. 1993; FAO, 2001; Asmala et al. 2011; USDA 2012; Lassaletta et al. 2012) and is provided in Suppl. 1. Knowing the total N traded every year embedded in agricultural commodities, we estimated the net N imported or exported. To compare the Spanish results with the neighboring countries, we did the same for 15 European countries for the years 1961 and 2007. Finally, using the data from the detailed trade data matrix from the Faostat database, we estimated and mapped the net N traded to Spain from every world country for the year 2007. We consider that any country has an anthropogenic N heterotrophic behavior when the primary production, including crops and pastures, is not enough to meet the demands of the livestock and people of this territory and the import of products is needed. On the contrary, those countries with a surplus of primary production that is available for export are considered autotrophic.

Crop, animal and manure production

We estimated the total yearly agricultural N production of the 117 vegetable products cultivated in Spain (1961–2009). To do so, the N content was assigned to each product and this was multiplied by their total production as given in the Production Module of the Faostat database. We added to this total value the estimation of N production in Spanish meadows and pastures. These ecosystems have different productivities according to their typology, and Spanish agricultural statistics provide the total surface of four different categories for the 1961–2009 period. We obtained an average productivity for each category in Spain (MMARM 2010) and we finally calculated the total agricultural production (cropland + pastureland). We estimated the proportion of every product used for food or feed by using the information provided in the Food Balance Sheets of the Faostat database. The amount of national or imported products used for bioethanol production (wheat, barley and maize) was obtained from CNE (2011). Production of animal products (ten types of meat, three types of milk and eggs) expressed as N was estimated by multiplying the total production provided by the Livestock Primary Production module of the Faostat database by its respective N content. Manure N production was also estimated by multiplying the N excretion factor by the number of heads of the different types of animals. We used the excretion factors provided by Bouraoui et al. (2011) for Spanish livestock. The contribution of the net balance of living animals for import/export was estimated for 2000 based on the information of the Spanish national statistics. Since its contribution to the total budget was negligible, we did not include these calculations in the general budget.

Human diet

Diet characteristics, namely N available per capita and year, and percentage of N of animal origin, were calculated for the 1961–2009 period from the Food Supply module of the Faostat database. We transformed the protein content to N multiplying the protein weight by 0.16. The values correspond to the N supply per capita before subtracting food waste. To compare the Spanish trend with trends in other countries, we also gathered this information for Western Europe, the USA, the Democratic Republic of the Congo, and China.

River nitrogen flows

The mean multi-annual N flow at the outlet of the main Spanish rivers was calculated using data on river flow and water quality for the 2000–2010 period obtained from several water authorities (ConfederacionesHidrográficas) in Spain. We selected those stations that were as close as possible to the river mouth and, for those rivers flowing into Portugal, those that were close to the Portuguese border. River discharge was in the form of daily flow and all data sets covered a minimum period of 10 years. Quality data were monthly values of several parameters, depending on the river and the monitoring network scheme. Few measurements of total nitrogen (TN) were available, so we used nitrate concentrations and applied the formula in Garnier et al. (2010) to estimate TN. Water quality data were given per month and in most cases without any specification of the precise sampling date. We therefore summed the daily flow values to obtain the monthly discharge and then multiplied this by the corresponding N concentration; monthly N export values were then summed to obtain the annual figures (Romero et al. 2013).

River flow was not available for the entire 2000–2010 period for the Guadalquivir River, where flow measurements stopped a few years before 2000. In this case, the available information was used to calculate an average year (i.e. a year in which each month corresponded to the average value of that month for the whole time series) of flow and N concentrations, and these were multiplied to obtain the average annual export. We used N concentrations and water discharges modelled by the Limnological research group of the Universidad de Cantabria for the 18 largest rivers of the ConfederaciónHidrográficadelCantábrico to estimate N exported by rivers to the Cantabric Sea (Project MARCE). In the end we obtained an estimation of N export corresponding to 84% of the Spanish territory. To obtain the total N export, we applied the N export rates estimated for temperate and Mediterranean areas to the 18,826 km2 and 45,939 km2 not evaluated in each Spanish region. We use the term “retention” to designate all the processes preventing nitrogen load from being transferred to the outlet of the drainage network, including definitive elimination as inert N2 through denitrification processes, emission as reactive N gases such as N2O, and storage in soil, perennial vegetation, groundwater, or sediments (Lassaletta et al. 2012).

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