| Main authors: | Berit Hasler, Ingrid Nesheim, Morten Graversgaard, Susanne Klages, Doan Nainggolan, Claudia Heidecke, Luke Farrow, Isobel Wright, Gerard Velthof, Sandra Boekhold |
| Editor: | Jane Brandt |
| Source document: | »Hasler, B. et al. (2021) Identification of cost-effective and coherent management models for drinking water protection in agriculture. FAIRWAY Project Deliverable 6.4R 55 pp |
The purpose of this detailed analysis of catch crops is to provide information on potentials and barriers for catch crops as a water protection measure and how positive incentives can be better incorporated into European water policies, using experiences from the literature and experiences from the six European countries.
1. Introduction
Catch crops are particularly relevant to illustrate potential coherence or conflicts between policies that affect water quality, e.g. nutrient and pesticide policies. This is because catch crops can increase nitrogen utilization and reduce losses, but also increase pesticide application.
In »Overview and assessment of measures and instruments we assess best management practices for all 13 FAIRWAY case studies. The in depth analysis of catch crops applies a comparative analysis between six of these cases, representing six European countries where the level of implementation of catch crops differs. The chosen country cases include Denmark (DK), England (UK-EN), Germany (DE) (Lower Saxony chosen), Netherlands (NL), Northern Ireland (UK-NI) and Norway (NO) (specifically the south eastern part of Norway where agricultural production is intensive). These countries are all Northern or central European countries, yet climate conditions, biogeography, crops, and policies differ, and there are significant differences in the use of catch crops as a measure. The choice of countries and regions for the detailed comparative analysis is therefore suitable for identification of potentials and barriers to increase the implementation rate and the success of implementing this measure.
The policy instruments used to implement catch crops include both mandatory and voluntary, economic policy instruments. In order to manage water pollution at large, the European Union has developed an extensive set of policies during the last few decades, e.g. the EU Drinking Water Directive (DWD), the Water Framework Directive (WFD), the Groundwater Directive (GWD), the Nitrates Directive (ND) and the Directive on the Sustainable Use of Pesticides (PD). Countries in the EU and in the European Free Trade Association (EFTA), such as Norway have a legal obligation to implement these environmental directives.
There are examples of mandatory and voluntary implementation of catch crops and other types of soil cover as parts of the ND, e.g. in the Nitrate Vulnerable Zones (NVZ) where catch crops are part of the code of good Agricultural Practice on a voluntary basis, and maintenance of vegetation cover during autumn and winter is mandatory in some countries.
The directives and related policies interact with the conditions for farmers in the EU given by the EU Common Agricultural policy (CAP). The CAP has up to now included both direct payments and greening requirements as part of CAP Pillar I, as well as environmental schemes, part of Pillar II, namely the Agricultural Environmental Schemes (AES) that are part of the Rural Development Programs in the European Member states, funded by the European Agricultural Fund for Rural Development (EAFDR).
In addition to these EU regulations and subsidy schemes, the national EU and EFTA member states implement national and regional specific regulations (e.g. in federal states), and catch crops are part of these regulations in most countries.
2. Method for the comparative analysis
The approach used is a comparative analysis between European countries where the level of implementation of catch crops differs. Six different countries/regions are chosen to identify and illustrate differences in regulation and governance of catch crops in Europe. The chosen country cases are all part of the EU project FAIRWAY, and include Denmark (DK), England (EN), Germany (DE) (Lower Saxony chosen), Netherlands (NL), Northern Ireland (NI) and Norway (NO) (specifically the south eastern part of Norway where agricultural production is intensive). These countries are all Northern or central European countries, yet climate conditions, biogeography, crops, and policies differ, and there are significant differences in the use of catch crops as measure. The choice of countries and regions for the comparative analysis is therefore suitable for identification of potentials and barriers to increase the implementation rate and the success of implementing catch crops.
Here we assess which policy instruments and incentives to implement catch crops have proven to be effective and cost-efficient, what factors affect uptake of catch crops as a nitrogen abatement measure in farming systems in NO, EN, NI, NL, DE (Lower Saxony) and DK, and how do farmers preferences, attitudes and risk considerations explain the uptake of the measure.
We focus on analyzing policy documents, lessons learnt in the literature and data from existing surveys including stakeholder and expert surveys and opinions, and consultation as part of the case studies in FAIRWAY. The analysis explains differences in catch crop cultivation between European regions and policy regimes, presents barriers to implementation, and discusses potentials to increase catch crop cover and the environmental effects.
3. Definitions of catch crops as an abatement measure
Catch crops and cover crops are frequently used as synonyms in the literature (Agostini et al., 2010, Aronsson et al. 2016; Shackelford et al., 2019; Tonnito et al, 2006), as both of these crop types are used as measures to reduce leaching, loss of nutrients and erosion. They both also seem to have beneficial effects for soil structure (Aronsson et al. 2016, Meyer et al., 2018). However, the intention of using catch crops and cover crops can also differ, and management practices and costs for the farmer differs for catch crops and cover crops.
Catch crops are mainly grown to prevent nutrient losses to surface water and ground water sources and cover crops are mainly grown to prevent erosion. Eurostat (here from Smit2019) defines the three types of soil cover as cover crops intended to reduce soil erosion, green manure crops (which are crops cultivated to maintain soil organic matter and fertility, and catch crops grown to prevent leaching. Catch crops can be sown together with the main crop, or under sown just before harvest of the preceding main crop.
This means that catch crops are grown with the purpose to prevent nitrogen leaching, and to reduce the risk of surface runoff of nutrients to surface water, compared to bare soil (Valkama et al., 2015, Shackelford et al., 2019, Thorup-Kristensen et al., 2003). Excess nitrogen may derive from preceding crop or it may be mineralized after harvest (from soil organic matter), and catch crops reduce leaching and run off by incorporating the soil mineral nitrogen into its plant biomass, but they also counteract leaching due to a reduction of drainage water (Meyer et al., 2019).
In several catch crops schemes it is a requirement that catch crops are not fertilized, and some schemes also prohibit legume crops as catch crops because the fixation of nitrogen by legumes which will increase the nitrogen content in the soil. Another difference between catch- and cover crops, which affects the costs, is that catch crops can be sown together with the main crop or under sown in the main crops (relay cropping), while cover crops are more often sown after the main crop. But the main difference between catch and cover crops is that cover crops grown after the harvest of the main crop in the autumn reduce erosion, because the land would otherwise be uncovered and susceptible to losses to water and to wind (Storr et al. 2019,). Cover crops might therefore require more seedbed preparation, and additional seeding compared to catch crops, especially in the circumstances where catch crops are sown together with the main crop (which is only practiced in a few countries).
Green manure crops is another type of under sown crop. The purpose of such crops is to supply the soil with nutrients or make nutrients available for crops, and thus the purpose and the impact on soil nutrients differ. Green manure is traditionally used in organic farming where nitrogen-fixing legumes provide new nutrients to the soil.
Cover crops and catch crops comply with EU requirements for “green direct payment” (“greening”) referring to farmers in member states who adopt or maintain farming practices that help meet environmental and climate goals. In this paper we focus on catch crops, but where relevant we use experiences and literature on assessment of the implementation of cover crops, where the aim of that cover crop includes reduction in nitrate leaching.
Effectiveness
The effects are defined as the nitrogen leaching from the root zone. There can be other measures of effectiveness, such as the nitrogen uptake or the reduced nitrogen loads /transport to water bodies. The effects on other nutrients (e.g. phosphorus) are also relevant, and so are the effects on carbon storage, which is relevant for climate change mitigation, or pesticides application and biodiversity. In this paper we only address the effects on nitrogen leaching, because of the relevance for water quality protection.
Barriers and potentials
An aim of this study is to analyze potentials and barriers for effective and cost-effective management and implementation. UN’s climate panel defines barriers as “"any obstacle to reaching a potential that can be overcome by a policy, program, or measure".
Our definition of barriers and potentials include factors that hinder or support effective and cost-effective implementation at policy, program and farm level. Factors that hinder, or support, effective and cost-effective implementation involve climatic and production factors, soil and hydrology conditions, other agronomic factors, policy requirements as well as farmers preferences and decisions. Farmers’ decision-making is of course related to the natural and agronomic conditions, but can also be explained by individual preferences and attitudinal factors such as environmental, agricultural and political positions, cultural norms and tradition. The policy requirements include direct constraints and regulations related to the cultivation of catch crops, but also requirements posed by other policies and regulations that can hinder or support the implementation of catch crops.
The barriers and potentials can be summarized following Bøe et al. (2020) according to these factors: Economic conditions, markets; knowledge, behavior, agronomy, climate; part-time/fulltime and ownerships.
4. Effectiveness of catch crops as a nitrogen abatement measure in European water policies
Extensive research and field trials have been undertaken to identity and select effective catch crops species. Effective species take up nutrients, and are efficient in reducing leaching and run off in the autumn by incorporating soil mineral nitrogen into its plant biomass, without competing with the main crop (where under sown, or sown together). Identified species to serve as catch crops include grasses and crucifers; which are the allowed species varies between regulations and schemes. Several studies indicate that catch crops with legumes do not reduce the risk of nitrogen leaching or reduce this risk only to a minor extent (Valkama et al., 2015; Shackelford et al., 2019; Salmeron et al., 2015, Thapa et al. 2018). Yet, studies show that the effectiveness also by non-legume catch crops species, differs among catch crop species types, among species of the main crop, and according to climate conditions and soil types (Bøe et al. 2019; Aronsson et al. 2016).
Typically, effective reduction of nitrogen leaching is characterized by non-legume catch crops, early sowing dates, prompt germination and fast growth rate at both above and below-ground levels, and a deep root apparatus (Thorup-Kristensen 2001; Kristensen and Thorup-Kristensen 2004, Agostini et al, 2010). Catch crop species that do not compete with the main crop are characterized by fast growth rate primarily after harvest of the main crop (Bøe et al. 2020).
Catch crop main effects differ between regions. In central Europe Tonnito et al. (2005), concluded that that nitrogen leaching was reduced by 70 %, and that on average yields in the main crop under non-legume catch crops were not significantly different from crops grown without catch crops. Thala et al. (2018) conclude, that non-legume catch crops reduce nitrate leaching by 56 % in comparison to bare soil based on meta- analysis of 238 observations from 28 studies. In the Netherlands Schröder et al. (1996; 2013) showed that catch crops strongly reduced nitrate concentrations in upper groundwater of sandy soils cropped with silage.
In the Nordic region the period between harvest of the main crop and the frost is relatively short, and the risk of leaching in autumn high if crop residues are incorporated into the soil. The preferred system includes a frost-tolerant catch crops under sown in the main crop, with rapid growth after harvest and no soil tillage during early autumn (Thorup-Kristensen and Pedersen 2006; Aronsson et al 2016; Hansen and Djurhuus (1996). Valkama et al. (2015) conclude that non-legume catch crops represent an effective method for the reduction of nitrogen leaching in the Nordic countries when implemented in spring cereal production.
Ideally, the catch crops retain and then release the nutrients to be available for the next crop. It is most important that the nitrogen available for the following crop should be included in the fertilizer planning the subsequent year if the catch crop is to be effective (e.g. Eriksen et al 2020).
Catch crops can reduce the risk for nitrous oxide emissions in winter (Li et al. 2015).
Studies indicate that catch crops are rarely harvested or used for grazing. In Germany, Klages et al. (2020) state that catch crops may be used in dry years when a lack of forage occurs. In the Netherlands, grass catch crops after silage maize are often used for grazing (sheep) or mowing in the spring the following year.
The biomass of catch crops has to be incorporated into the soil before the next main crop can be established. Typically, farmers use herbicides (e.g. Glyphosate) to destroy plant biomass before establishing the seed bed for the following crop (; CTIC-SARE, 2016). Storr et al. (2018) highlight one management issue of cover crops that can have a negative impact on water quality—the potential increased use of slug pellets to control slug populations as a result of using cover crops. Metaldehyde present in some slug pellets is often detected in surface water above the EU statutory drinking limit (Castle et al., 2017). However, it should be noted that 53% of respondents in the Storr et al survey report no change in their use of slug pellets whilst using cover crops. Lescot et al. (2013) compared agri-environmental measures for pesticide loss reductions and found that the effectiveness of catch crops was very low compared to other types of measures such as buffer strips, when pesticide loss reduction was the aim. So even though catch crops were found to be relatively inexpensive, the very low effect made this measure irrelevant for pesticide pollution control. This means that catch crops can have negligible or even negative effects on pesticide contamination of water sources, and this may affect the coherence of pesticide and nutrient policies – they can be conflicting. This is important, but pesticides are beyond the scope of this paper.
Constantin et al (2012) studied long term effects of catch crops using models, and the results suggest that long-term use (60 yrs) of catch crops each year, along with reduced use of N fertilisers leads to reduced N leaching (in the study they indicate a range between 33 – 55%), whilst yield remains stable. N sequestration rates also increase to a maximum of 430 – 750 kg N ha-1 after 23 – 45 yrs (in comparison to bare soils). Mineralisation rates will reach 38 – 65kg N ha-1 yr-1. Mineral N usage rates need to be tailed off in response to N mineralisation rate in the soil for optimal crop yield management.
Hansen et al. (2015) have also studied the effects of catch crops for fodder, and conclude that growing the right fodder crop for the environmental conditions can reduce leaching. They point to these three barriers for effective implementation: ifcurrent farming practice involves removal of straw (e.g. for bioenergy), the capacity of the soil to immobilise N may be reduced, even when catch crops are included: evidence is mixed for this conclusion, however. Performance of the catch crop is influenced by when it is planted. It may be necessary to adjust the catch crop planted in response to weather and cash crop demands and this will impact reduction in leaching achieved.
Table 3.1: Review summary effects of catch crops
| References | Effect studied | Positive effect | Agronomic barriers | Country | Method |
| Thorup-Kristensen, K., 1994 | N leaching/soil nitrogen reduction | Reduction of soil nitrogen | DK | Field experiment | |
| Thorup-Kristensen, K., 1994 | N leaching/soil nitrogen reduction + preservation | Winter hardy catch crops preserve soil N in biomass | DK | Field experiment | |
| Thorup-Kristensen, K., 1994 | N leaching/soil nitrogen reduction | non winter hardy catch crops show less soil nitrogen reduction | DK | Field experiment | |
| Thorup-Kristensen, K., 1994 | N leaching/soil nitrogen reduction + preservation | non frost persistant catch crops may lose 50-80% of nitrogen | DK | Field experiment | |
| Valkama et al., 2015 | N leaching | Average N leaching loss reduced by 50% | Nordic countries (DK, SW, NO FI) | Meta analysis, non legume undersown catch crops | |
| Valkama et al., 2015 | Nmin in autumn | Average Nmin reduction in autumn by 35% | Nordic countries (DK, SW, NO FI) | meta analysis, non legume undersown catch crops | |
| Valkama et al., 2015 | grain yield | Grain yield reduced by 3% | Nordic countries (DK, SW, NO FI) | meta analysis, non legume undersown catch crops | |
| Valkama et al., 2015 | N content in grain | no effect | no effect | Nordic countries (DK, SW, NO FI) | meta analysis, non legume undersown catch crops |
| Valkama et al., 2015 | N leaching | no reduction of risk of leaching | Nordic countries (DK, SW, NO FI) | meta analysis, legumous undersown catch crops | |
| Valkama et al., 2015 | grain yield | increase of grain yield by 6% | Nordic countries (DK, SW, NO FI) | meta analysis, legumous undersown catch crops | |
| Valkama et al., 2015 | N content in grain | increase of N-content by 6% | Nordic countries (DK, SW, NO FI) | meta analysis, legumous undersown catch crops | |
| Shackelford et al., 2019 | N leaching | reduction of N leaching (sigificant) | Mediterranean climate | meta analysis, non legume catch- and cover crops | |
| Shackelford et al., 2019 | soil nitrogen reduction | reduction of soil nitrogen (sigificant) | Mediterranean climate | meta analysis, non legume catch- and cover crops | |
| Shackelford et al., 2019 | cash crop yield | reduce cash crop yield by 7% | Mediterranean climate | meta analysis, non legume catch- and cover crops | |
| Shackelford et al., 2019 | N leaching | no reduction of N leaching (sigificant) | Mediterranean climate | meta analysis, legumous catch- and cover crops | |
| Shackelford et al., 2019 | soil nitrogen reduction | no reduction of soil nitrogen (sigificant) | Mediterranean climate | meta analysis, legumous catch- and cover crops | |
| Shackelford et al., 2019 | cash crop yield | increase in cash crop yield by 16 % | Mediterranean climate | meta analysis, legumous catch- and cover crops | |
| Salmeron et al, 2011 | N leaching | reduction of N leaching (sigificant) | Mediterranean climate (Spain) | field trials, non legume catch crops, irrigated | |
| Salmeron et al, 2011 | soil nitrogen reduction | reduction of soil nitrogen (sigificant) | Mediterranean climate (Spain) | field trials, non legume catch crops, irrigated | |
| Salmeron et al, 2011 | cash crop yield | reduction of maize yield by up to 4 mg/ha | Mediterranean climate (Spain) | field trials, non legume catch crops, irrigated | |
| Salmeron et al, 2011 | N leaching | no reduction of N leaching (sigificant) | Mediterranean climate (Spain) | field trials, legumous catch crops, irrigated | |
| Salmeron et al, 2011 | soil nitrogen reduction | no reduction of soil nitrogen (sigificant) | Mediterranean climate (Spain) | field trials, legumous catch crops, irrigated | |
| Salmeron et al, 2011 | cash crop yield | no reduction of maize yield | Mediterranean climate (Spain) | field trials, legumous catch crops, irrigated | |
| Li et al. 2015 | Y? cash crop yield | Increased yields | Reduced yields | DK | Field trials, legumes Catch crops increased yields, of succeeding unfertilised spring barley, Autumn harvest of catch crops, especially legume based catch crops, tended to reduce crop yield. |
| Li et al. 2015 | climate gas emissions | Reduced N2O emissions | increased N2O emissions | DK | Field trials |
| Molteberg et al. 2005 | cash crop yield | Reduced yields 0-12% | NO | Field trials, reduced yields depending on catch crops species, cash crop species, growing conditions. | |
| Bøe et al. 2020 | cash crop yield | Reduced yields 1-3 % | NO | Review: Field trials show that reduced leaching vary with Catch crops species, Catch crops cover, Catch crops sowing data and weather conditions. | |
| Aronsson et al. 2016 | N leaching | reduced N leaching 0,7-3,8kg N/daa | DK, NO, SW, FI | ||
| Molteberg & Tangsveen 2004 | N leaching | reduced N 2,5- 3,5 kg N /daa | NO | Field trial | |
| Bøe et al. 2019 | Soil nitrogen | reduced soil nitrogen autumn | NO | Review: Field trials show italian rye grass reduces mineral nitrogen in soil (60%), westerwold rye grass reduces by 25%, legumes can increase mineral nitrogen. | |
| Bøe et al. 2019 | Soil structure | Soil structure improvements | Quantitative estimates difficult | NO | Review |
As can be seen from Table 3.1, which is a review and summary of studies related to the effects of catch crops on nitrogen leaching, most studies find positive effects on nitrogen leaching from cultivation of catch crops, but no-effect and negative effects are found, although infrequently. There are more examples on both negative and positive effects on subsequent cash crop yields. As can be seen from »Overview and assessment of measures and instruments a study by JRC (Smit et al, 2019) of farmers in four European countries (Spain, Netherlands, France and Romania) found that farmers also perceived both negative and positive effects on yields. These effects on yields are important barriers for the implementation.
5. Costs and cost-effectiveness of catch crop implementation
The cost-effectiveness of catch crops refers to the costs of the catch crop measure relative to the effects achieved on reduced nitrogen loss and leaching from implementing the measure. This could be described as cost-efficiency. Both direct production costs as well as the transaction costs are important cost categories for evaluating cost-effectiveness for farmers and for society as a whole. The direct production costs are attributed to farmers, while the transaction costs are attributed to both farmers and administration. All the above costs are important for society as a whole.
In the following we compare the average reduction costs for catch crops on nitrogen leaching, measured as euro per kg N reduced and only with inclusion of the direct production costs. The comparison between the countries included in our analysis is based on national assessment, and the references are mentioned at the bottom of Table 2. The numbers and ratios mentioned are in some countries the official average effects and reduction costs used for ex-ante policy evaluation (e.g. in Denmark); in other countries this is the best available information. Information from Northern Ireland was not available for this comparison.
The comparisons in Table 3.2 reveal that there are large variations in both costs and effects, between countries but also large spans in both costs and effects within each country. The resulting estimates of Euro per kg N are calculated diferently as some of them are weighted by the sources used for the table comparison (mentioned in the row references). The averages presented also represent a large variation between soil types, farmers, catch crop types and cultivation etc.
The costs and effects for England are not directly comparable to the other countries, as cover crops are most often used as measure in England and there are less published data on catch crops because they are less frequently used in arable rotations. In the English assessment yield effects are not mentioned, but from Bhogal et al.(2020), the cumulative (2 year) margins for the key cover crop species and mixes can be summarised. Across seven experimental sites, there were twenty comparisons of cumulative (2 year) margins ± cover crop. Most (95%) showed a reduction in margin compared to no cover crops, with margins ranging from + £64/ha following oil radish on a clay loam, to - £476/ha following a two species mix on a clay soil (average: - £150/ha). (1£ is 1,1 EUR). The reductions in cumulative margin were due to lower cash crop yields following cover crops or the absence of a sufficient yield benefit to compensate for the additional seed and establishment costs.
Table 3.2. Effects and reduction costs of catch crops in 5 of the countries
| Countries: (Northern Ireland not included because of low implementation of catch crops) | NL | DE | EN (data for cover crops, very few catch crops grown) | DK | NO |
| Costs, EUR/ha | |||||
| Seedbed preparation (Harrow or rotary harrow) | 50 | 21-56 |
16.5 -33 (Broadcasting/direct drill system) 44 – 55 (Combination cultivation type drilling). |
na | |
| Seeding | 40 | 23-39 | 17-54 | ||
| Seed | 30 - 100 | 49-70 | 25-33 (often more if bought mixes) | 27-54 | 26-35 |
| Destruction catch crop (Incorporation of crop residue in soil) | 70 | 21-56 | 11-22 (Destruction only, but some will simply die off) | na | 11 |
| Soil tillage | 50 | 21-56 | na | na | |
| Costs of required crop change, EUR/ha | na | 183-331 | |||
| Reduced yields | na | 1-3 % | |||
| Total, EUR/ha | 100 - 250 | 135-277 | 53-110 | 44-108 | 97-154 |
| Total EUR/ha, with change in crop rotation | 227-439 | ||||
| Effect on N leaching | |||||
| kg N /ha | 30 | 0-40 | Average 38 | 12-45 | 5-55 |
| Cost-effectiveness/reduction costs | |||||
| EUR/kg N reduced | 12 | 4-7 | 1.4 - 3 | 0-35 | 3-22 |
| Countrywise explanations | Without rotation requirements (change from winter to spring crops): 0.4-7.5; with rotational requirements: 6.0-35 | The variation in EUR/kg N is due to both variation in N uptake, and costs, e.g. by undersowing, delayed sowing, reduced yields | |||
| References | de Haan 2015 | KTBL, 2019; Osterburg and Runge 2007 | Storr et al 2019, Agro Business Consultants 2017, NIAB TAG 2015, Bhogal et al 2020 | Eriksen et al 2020 | Øygarden et al 2018; Bøe et al 2019 |
6. Specific experiences in catch crop implementation from reviewed literature
In Germany it is reported that when farmers grow frost tolerant catch crops, they need special equipment to prepare a good seed bed, particularly grass sods like disk harrows, or strip-till as combined cultivation and seeding technique (Lütke Entrup et al. 2018). The costs of this special equipment are not included here, but might be important in areas with frost during winter, as species which are not frost tolerant will lead to degradation of plant biomass for mineralization during the main cropping period (Lütke Entrup et al., 2018).
In Norway it is reported that investment costs are somewhat higher for under sown catch crops because a seed aggregate needs to be purchased for this practice. With delayed sowing (before threshing of main crop), centrifugal spreader or seed drill can be used, equipment which the farmer often own, or which is more easily available by rental (Bøe et al. 2020).
From Table 3.2 it can be seen that changes in crop choice can be required, e.g. from winter crops to spring grown crops, and this can be costly. Effects on soil tillage and destruction of the catch crops are included as a cost in some countries and not in all – when considered these costs make up a significant share. Reduced yields in the subsequent main crop do not seem to be affecting the costs in most countries, with the exception of Norway and England. As can be seen from Table3. 2., these yield effects can be seen from many field experiments.
Seeds and seeding makes up a large part of the production costs, which is also confirmed in a study by JRC documented in Smit et al (2019). Smit et al conducted a farm survey among farmers in Spain, France, Netherlands and Romania in order to analyze factors affecting uptake of cover crops and catch crops, and while 46, 42 and 32% of the Spanish, Dutch and Romanian farmers respectively experienced an estimated benefit of growing catch crops or cover crops, only 15% of the French farmers did. 31, 16 and 46 % of the Spanish, Dutch and Romanian farmers respectively experienced a monetary loss, while 47% of the French farmers did. The French farmers also experienced a higher risk of reduced yields in the main crop.
The benefits represented saved nitrogen in the following crop, higher productivity in the following crop, higher organic matter, healthier soil, subsidy or avoiding penalty, fodder provision, soil coverage, crop diversification. The losses represented no harvest, costs of seeds, tillage, sowing and spraying costs higher than yield increase and saved nitrogen costs, dry sowing seasons, time restrictions in the right period, no subsidies. Furthermore swine fever from wild swine foraging (in the catch crop) was also mentioned.
In Table 3.3 the JRC estimates of the monetary benefits, losses and weighted averages from Smit et al (2019) are presented.
Table 3.3: Estimated monetary benefits and losses from catch crop cultivation in 4 EU countries (Smit et al 2019, page 35).
| Spain | Netherlands | Romania | France | Average | |
| Monetary benefit EUR/ha | 234 | 269 | 40 | 101 | 154 |
| Monetary loss EUR/ha | 133 | 185 | 356 | 91 | 194 |
| Weighted total average EUR/ha | 67 | 82 | -152 | -26 | -16 |
Adopted after Smit et al 2019
Additional farmer opinion/experience of economic and other factors for cover crops was published by Storr et al. (2018) for England. Note the focus was on cover not catch crops. On farm, cover crops need to be practical to implement—but less is known about the management considerations of using cover crops given the farmer perceived lack of relevant research literature for applications in an English context. The survey included 117 farmers representing 0.19% of the 63,000 agricultural holdings in the United Kingdom that would fulfil the arable criteria. 77 used cover crops and 39 did not.
Respondents observed benefits to soil structure, soil erosion control and water infiltration in addition to reductions in the use of chemical fertilizers, herbicide and fuel use, although increase of herbicide use was also identified. The survey was entitled “Sustainable Soil Management” to avoid biasing results in favor of only cover crop users. Of those that did use cover crops, time and labour requirement for the cultivation of cover crops were reported as a challenge with 17 and 40% of respondents reporting that it was “always” or “sometimes” an issue, respectively. However, 37% of respondents reported that the time and labor requirements associated with cover crops had never been an issue. In addition, 55% of cover crop users reported that cover crop establishment was “sometimes” an issue and 10% of respondents indicated that it was always an issue. Cover crop establishment had “never” been an issue for 19% of respondents and 13% reported that cover crop establishment was “no longer” an issue.
Disease concerns following a cover crop had never been a problem for 70% of the respondents using a cover crop.
The 39 respondents not using cover crops (following harvest 2016) cited the following top three reasons for lack of adoption; they do not fit the current rotation, expense and hard to measure their benefit, but most (92%) would consider their use in the future. The following top three reasons would influence their decision to consider using cover crops in the future: more detailed information on the economics of cover crops, more detailed information on the effect of cover crops and how to measure this on the farm and access to funds/grants to help with seed purchase and establishment costs.
The respondents indicated from barriers due to EFA rules. Of the respondents who used cover crops, 71% indicated that the EFA guidelines for cover (and catch) crops were not suitable. 37 gave recommendations for the improvement of EFA guidelines and a selection of the comments are reported below:
- “A greater diversity of crops to be included on the list of crops”. “I have cover crops that are too diverse to qualify as EFA”
- “To include other mixes that are more pertinent to our cropping regime, soils and area”
- “More species. Being allowed to graze them”
- “They are too prescriptive, there is no room for any experiments”
- “Include single species cover crops”
The report suggested that a change in the EFA guidelines for cover crop species would influence 20% of the respondents currently not using cover crops to do so in the future.
In terms of benefits, over 70% of respondents who used a cover crop reported a benefit from cover crops to soil structure, earthworm numbers and soil erosion control although soil type was found to be an influencing factor in the latter, with more positive responses on soil erosion from farmers with light soils compared to heavy soils. Over 50% of respondents observed positive benefits to organic matter and drainage/infiltration. The survey which included a high number of “don't know” responses concerning N-immobilization by cover crops, which the authors highlighted as an area that required further research in the UK to better inform farmers.
The analysis of Storr et al. (2018) shows that some farmers have not applied cover crops of reasons like crop rotation pattern, expenses and uncertainty of benefits. Farmers who have adopted cover crops in the analysis are in contrast more likely to observe a benefit to soil structure earthworm numbers and soil erosion control in the long run.
The NIAB TAG (2015) guide on cover crops cultivation for farmers, provides information based on current understanding on how to select, deploy and make the most of specific cover crops against identified end uses. Guidance was generated from a range of sources including research, grower feedback and other expert opinion. It focuses, as England generally does, on cover crops put in prior to a spring crop for multiple benefits, and can be seen as an example of effective advice for farmers. The guide indicates that benefits from cover crops accrue through improvements in nutrient cycling, water retention, soil structure, soil biology and other parameters and that these positive changes in these areas are a useful indication of a direction of travel and is often detectable before positive yield responses are seen. However, yield is the best absolute measure and is often seen in crops following cover crops, but sometimes cannot be detected until later in the rotation (or responses may require repeated cycles of cover crop use to become fully apparent). Over two long term (four years and longer) trials they found a potential cumulative grain return of c. 0.5 t/ha over cereal crops following the use of a cover crop at standard N applications.
In addition to the direct financial benefits, the guide indicates that cover crops can also provide wider value on farm (e.g. reduced soil erosion risk and improved surface drainage) and potentially contribute to longer term ‘climate smart’ improvements to soil (e.g. improved workability, moisture retention and soil organic matter) and the overall farm system (e.g. greater resilience).
Research carried out on OriginsTM sites (NIAB TAG 2015) suggested N leaching reductions of 25-54% (mean c. 40% or c. 38 kg/ha N); this N will therefore be retained to benefit crops and the wider soil system. The amount of N released by a cover crop depends on a range of factors, but is influenced by cover crop type, growth, the environment as well as C:N ratio (the carbon to nitrogen ratio in the material) and other biological compounds. Broadly, the guide indicates that if the C:N ratio is less than c.13, net mineralization is observed and N can become available to plants, but as it increases this availability reduces; as the ratio extends past 26 a net immobilization can occur (for example N is retained elsewhere in the systems by microorganisms). The extent to which N contributes to crop yield depends on time of the release as well as amount; this can be too early (may contribute to growth but not yield) or too late (could increase grain protein or still give a yield response in later crops in the rotation).
Roesch-McNally et al. (2018) studied barriers and motivations for cover crop implementation among American farmers, and based on qualitative farm interviews they classified the answers in field-level agronomic barriers and broader structural barriers. They found that difficulty in timing of management in catch crops is decisive, but in contrast benefits like erosion prevention, soil health and yield increase are also mentioned. The background for their study is that cover crops are known to promote many aspects of soil and water quality, but the coverage is low - in 2012 only 2.3% of the total agricultural area in the Midwestern USA . The survey method was focus groups, and the aim was to identify barriers as well as motivational factors among farmers. The findings indicate that farmers need to understand why catch and cover crops are important, as the authors conclude that farmers believe that there is a need to alter the whole approach to farming – livestock and cropping – to make it more sustainable, and that management of the whole environment s necessary to optimise the farm. The barriers identified are more concrete: Farmers were worried about the timing of management activities, particularly establishing crops in the autumn and terminating in the spring. They also noted that there was a lack of equipment to plant, manage and remove the crop, as well as lack of markets for crops that could be grown in place of current cash crops. Therefore catch crops will be low and slow to develop. Farmers also commented that cash crop production is expensive (e.g. purchase of seed, fertiliser and chemicals, rent), so adding the extra costs associated with catch crops may not be a viable option for some businesses. In addition, farmers that rent and improve the land might have adverse incentives as the value of the land may increase and it costs more to rent the land next time.
Bergtold et al. (2017) conducted a thorough review of direct production costs, indirect and opportunity costs, direct benefits, indirect benefits, risk and crop insurance, policy incentives and economic examination of cover-crop adoption and usage, especially regarding four different species of cover crops. In summary the costs vary between the species from 42 US$/ha to 120US$/ha. Depending on the grain crops, the adopters experienced increases of yield by more than 100 percent.
7. Summary of the cost assessment
The review presented here is not a full review of studies that measure the costs and cost-effectiveness of catch crops, but provides an overview and indication of the factors affecting the cost-effectiveness. Yield effects are essential and so is the cost of seeds, further operational costs for cultivation of catch crops varies between the countries studied here.
One lesson learnt from this scrutiny is that is seems that advice for farmers to reduce the yield effects (by timing, species, management) is important, which is also highlighted in the JRC study from 2019 (Smit et al 2019). Furthermore, the costs of seeds are pointed at as important, and covering these costs by subsidies might be an important incentive.
In »Policy instruments used for implementation of catch crops in Europe we review the literature to analyze whether the seed costs or other factors are found to be barriers for the implementation of catch crops.
Notes:
For full references to papers quoted in this article see