|Main authors:||Mart Ros, Gerard Velthof, Oene Oenema, Meindert Commelin, Susanne Klages, Linda Tendler, Jenny Rowbottom, Isobel Wright, Donnacha Doody, Luke Farrow, Birgitte Hansen, Morten Graversgaard, Irene Asta, Andrej Jamsek, Katarina Kresnik, Matjaz Glavan, Jean-François Vernoux, Nicolas Surdyk, Christophoros Christophoridis, Kate Smith, Irina Calciu, Sonja Schimmelpfennig, Hyojin Kim, Piet Groenendijk.|
|FAIRWAYiS Editor:||Jane Brandt|
|Source document:||»Ros, M. et al. 2020. Identification of most promising measures and practices: 2. Reduction nitrate transport from agricultural land to groundwater and surface waters by management practices. FAIRWAY Project Deliverable 4.3, 72 pp
|1. Literature review|
|3. Case studies|
A systematic search was performed through online databases, and a local/expert based search was done throughout Europe. The aim of the local search was to find high quality studies which are not easily accessible through online databases, but which contain valuable data. The criteria used for this search were:
- well documented (peer reviewed or reports),
- the article/report should provide the results of one or more experiments to decrease NO3 leaching to groundwater/surface waters,
- the article/report should present quantitative data of results and statistics to enable a meta-analysis. For the online systematic search online databases were used; CAB-Abstract/Ovid and Web of Science.
Query criteria used:
- (nitrate and (leaching or drain* or "surface water" or groundwater or "ground water" or runof*) and (mitigat* or measure) and (effect* or reduct* or decreas*) and(treatment or "field trial" or experiment))
Other options involved excluding of the key “model*” and including the key word “agricult*”. The final search yielded 496 results
- (nitrate and (leaching or drain* or "surface water" or groundwater or "ground water" or runof*) and (mitigat* or measure) and (agricult* or farm* or crop* or field*) and (effect* or reduct* or decreas*) and (treatment or "field trial" or experiment) not (model*))
In addition, university and institute libraries were examined in Member States of the European Union, because a significant fraction of the research on measures to reduce NO3 leaching and surface runoff has been conducted before the 1990s and 2000s when it was still common to publish the results in reports and documents. These reports and documents quite often have not been digitalized and made available to the international scientific audience and as such are not traced by the search machines of Google Scholar and Scopus.
To extend the literature study, we searched Google Scholar for additional review papers and meta-analyses, using the search query:
- (“Nitrate” OR “Nitrogen”) AND (“Mitigation” OR “Measure”) AND (“Meta-analysis” OR “Review”) AND “Agriculture”.
Data and results of reviewed reports and articles were categorized according to Table 2.1 and collected in Excel spreadsheets in a uniform manner. The Excel spreadsheets were subsequently transferred to a database for meta-analysis.
Table 2.1: Categories of measures to reduce nitrate losses.
|Nr||Name of the measure||Characterization of the measures|
|1||Nitrogen fertilization; balanced nitrogen fertilization (dose of application)||Matching nitrogen input to the average nitrogen demand of the crop is termed balanced nitrogen fertilization. This measure includes terms like “reduction in fertilization”, nutrient management planning, and more drastic measures such as withholding nitrogen fertilizer inputs. Typically, this measure has been studied in nitrogen fertilizer trials. This measure includes also the combined use of synthetic fertilizers, animal manures, organic fertilizers, bio-based fertilizers, composts, etc.|
|2||Precision nitrogen fertilization (optimization in space and time)||Precision nitrogen fertilization builds on balanced fertilization, and includes “variable rate fertilization” and “split applications”. This includes measures like a ban on fertilization in winter, on sloping land, on frozen land, etc.|
|3||Enhanced efficiency nitrogen fertilizers||Enhanced efficiency fertilizers include various types of nitrogen fertilizers, with or without nitrification inhibitors, urease inhibitors, special coatings (slow-release fertilizers).|
|4||Changes in crop types and/or crop rotations||Changes in crop types and rotation (without much change in nitrogen fertilization input) may change the nitrogen output with harvested crop and thereby nitrogen leaching. This measure includes a change to high-yielding crop varieties, and energy crops.|
|5||Cover crops||Cover crops or catch crops or green manures are grown after the harvest of the main crops, and serve to mop up residual mineral nitrogen from the soil and/or to improve soil quality. These crops may be sown in between the main crops (relay cropping) or after the harvest the main crop.|
|6||Mulching||Mulching refers to the covering of the soil with crop mulch or with plastic mulch, mainly to reduce evaporation, modify soil surface temperature, and suppress weed growth. Due to changes in crop yield and soil water flow and utilization, leaching may be suppressed.|
|7||Restricted grazing||Restricted grazing includes zero grazing, spring-season grazing only, and siesta-grazing. This measure refers to a decrease in the animal-grazing hours per year relative to year-round grazing or day-and-night grazing during the growing season.|
|8||Buffer strips||Buffer strips refer to the strips of land along water courses. These strips have adjusted management (fertilization, crops, tillage) and thereby minimize the leaching and overland flow to surface waters. The width and management of the strip are critical|
|9||Riparian zone||Riparian zones refer to wetland areas along water courses which intercept and scavenge nutrients from leaching and overland flow pathways before entering the water courses. It includes constructed wetlands. Special vegetation and management may increase the scavenging of nutrients and thereby the pollution of the surface waters|
|10||Irrigation||This measure includes sprinkler irrigation, drip irrigation, furrow irrigation, flood irrigation, and fertigation. Irrigation may both increase or decrease leaching, depending on irrigation practice, crop type, soil type and weather conditions.|
We used the R-package ‘metafor’ to conduct the meta-analysis (Viechtbauer, 2010). The goal of a meta-analysis is to combine all quantitative data from the collected studies and draw an overall conclusion on the effectiveness of a specific measure. In the reviewed studies the effect of a treatment was shown with different values and units. For a meta-analysis these different designs, units and approaches have to be normalized so they can be compared. To be able to compare effect sizes between studies all data was recalculated to the response ratio (R):
Where (XT ) ̅ represents the means of the treatment group and (XC ) ̅ the means of the control (Borenstein et al., 2009). For each study the mean, standard deviation and sample size was recorded. The distribution of R cannot be assumed to be normal, so the values for R were log-transformed before statistical analyses using the natural logarithm (Borenstein et al., 2009; Hedges et al., 1999). Commonly, the variance of each pairwise observation is calculated to weigh the individual observations. Records with a smaller error margin are then assigned a heavier weight when the average and confidence intervals are calculated However, as a large part of the observations in our database were missing a measure of variance, we performed an unweighted analysis of the data.
A random effects model was used to assess the effect of the different measures on combined observations of NO3 fluxes to drainage or surface water and NO3 concentrations in soil and water. Study was included in the model as a random factor, to account for different studies contributing a different amount of data points to the database. The resulting means per measure were presented. A 95% confidence interval (CI) was calculated, and the effectiveness of a measure is considered significant when there is no overlap with a response effect of 0%, indicating ‘no effect’.
Expert knowledge from nine FAIRWAY case studies (Figure 2.1) located across Europe was used to assess the effectivity, cost-effectiveness of measures, as well as the willingness to adopt them. These case studies are investigating measures to minimize pollution of ground- and surface drinking water resources by nitrates.
Questionnaires were sent out and experts were asked
- which measures were applicable in the region of their case study, and
- to evaluate the measures in terms of effectiveness, cost, and applicability (»Annex 2).
Table 2.2 gives a summary of the questions asked and the information that was provided. All experts are in close contact with land managers who apply the measures.
Table 2.2: Format for the description of measures used in the case study areas.
|Name of the measure||Explain the measure in one sentence|
|Description||Brief characterization of the measure in maximal three sentences; what is (are) the action(s) of the land manager/farmer/citizen|
|Mode of action||
Brief description of the mechanism(s) of the measure in maximal three sentences, addressing the following possible mechanisms:
Decrease of pollution (concentration or load); select one answer out of five options:
|Expected implementation cost||
Economic cost, in euro per ha of utilized agricultural land; select one answer out of five options:
|Underpinning of the measure||
Is the measure well examined, as shown by various reports; select one answer out of four options:
|Applicability of the measure||
Is the measure widely applicable; select one answer out of four options:
|Adoptability of the measure||
Do the land managers/farmers/citizen adopt the measure easily; select one answer out of four options:
Does the measure contribute to beneficial side-effects; select one or more answers out of four options:
|Disadvantages (other than implementation costs and labour)||
Does the measure contribute to negative side-effects: select one or more answers out of four options:
|References||Provide up to three key literature references|
For full references to papers quoted in this article see »References