Cover Photo by zahra kian on Unsplash

By Jorge Ferreira.

THE USAGE OF COVER CROPS IN ORGANIC FARMING, ESPECIALLY IN ORCHARDS, VINEYARDS AND OLIVE GROVES

Introduction:

Cover crops are cultures that farmers grow mainly to protect and improve the soil, rather than to harvest for food or sale. These cultures are usually planted between main crops (like corn, wheat or soybeans) or during the off-season, when fields would otherwise be bare.

In permanent crops as orchards, vineyards and olive groves, cover crops are made on the inter-row at autumn and winter season.

Their main functions are the following:

• Prevent soil erosion: The roots of the cover crops hold the soil together and reduce the loss of fertile topsoil due to erosion by wind and rain.

• Improve soil fertility: Some, like legumes (e.g., clover, vetch, faba beans, lupinus), can capture nitrogen from the air and add it to the soil naturally.

• Build soil health: Cover crops increase organic matter, improve soil structure and boost microbial activity.

• Suppress weeds: They shade the soil and compete with weeds, reducing the need for herbicides.

• Pest and disease management: Certain cover crops disrupt pest lifecycles or attract beneficial insects and can be used to increase biodiversity in the farm.

• Improve water management: They increase water infiltration, reduce runoff and help the soil retain moisture.

In short: cover crops are like a “living blanket” for the soil, keeping it protected and productive between main crops.

The following article focuses on the usage of cover crops in organic farming, especially its usage in orchards, vineyards and olive groves. It was written for Save Soil by Jorge Ferreira, an agricultural engineer and farming consultant from Portugal, with more than thirty years of experience as a consultant in organic farming. He is also the author of several books about this topic and could be reached at his company Agro-sanus (www.agrosanus.pt ).

DISCLAIMER: The opinions expressed in the following article are the opinions of its author and might not, in some instances, be in accordance with the opinions and postures of the Save Soil Movement. Therefore, this Movement shall not be liable for any of them.

ORCHARDS, VINEYARDS AND OLIVE GROVES IN ORGANIC FARMING

Best practices for regenerated and productive soil

1. Framework within the Common Agricultural Policy (CAP)

The European Commission (EC) strategy From Farm to Fork – “Our food, our health, our planet, our future” for agriculture in the European Union (EU), despite strong opposition from the largest conventional agriculture organisations and the fertiliser and pesticide industry, is an important document for ensuring that agriculture is increasingly part of the solution (environmental, climate, economic, social, health) and not part of the problem.  In addition to the five specific objectives identified therein, the following quantified targets to be achieved by 2030 are also set: 

a)    Reduce the use and risk of synthetic chemical pesticides by 50%; 

b)    Reduce the use of the most toxic pesticides by 50%; 

c)  Reduce fertiliser leaching by at least 50%, ensuring that soil fertility is maintained; 

d)    Reduce the use of chemical fertilisers by at least 20%; 

e)    Reduce sales of antibiotics for animal and agricultural production; 

f)    Increase the area of organic farming (OF) to 25% of the EU's agricultural area. 

These targets are the result of an assessment of the current situation of European agriculture and its environmental impact. In terms of climate change, European agriculture currently has a negative balance between greenhouse gas (GHG) emissions and the sequestration of carbon removed from the atmosphere (CO2) and stored in plants and soil. The EC's goal is to achieve carbon neutrality (net zero emissions) by 2050 (Lorant A. & Allen B., 2019). 

In the agricultural sector, this balance should be positive, as agriculture has the means to fix CO2 from the atmosphere and convert it into organic carbon. The means is the plant and the mechanism is photosynthesis. Much of this carbon should be converted into humus and sequestered into the soil, with climatic and agronomic advantages.  

A 1% increase in organic matter in the soil, in a 50 cm layer, corresponds to just over 30 tonnes of organic carbon per hectare, which for the Portuguese national UAA (Utilisable Agricultural Area) already exceeding 3,700,000 hectares, corresponds to more than 100 million tonnes of carbon removed from the atmosphere (CO2) and placed in the soil by agriculture. However, if instead of increasing the organic matter in the soil we reduce it, then instead of sequestration we have mineralisation of the soil's organic carbon and polluting CO2 emissions into the atmosphere. 

In most of Portugal's inland regions and in practically the entire agricultural area of the Alentejo and Algarve, most soils have organic matter content levels close to 1% or even less, which is the result of poor agricultural practices (replacement of manure or other organic fertilisers with chemical fertilisers, burning and slash-and-burn practices, excessive tillage and the use of herbicides). With these levels, we have no climate solution and no soil for sustainable agriculture that can feed new generations.

Calculation of soil organic carbon (C) per hectare, in the layer from 0 (zero) to 50 cm, for each 1% of humified organic matter (OM)  

1)    C content in humified organic matter or humus = 58% 

2)    Soil volume = 10,000 m² x 0.50 m = 5,000 m³ 

3)    Soil mass (depending on the bulk density, which varies with texture, from 1.2 in clay soil to 1.5 in sandy soil), in clay texture = 5,000 m³ x 1.2 t/m³ = 6,000 t/ha 

4)   Organic Matter (OM) on 1% of soil = 6,000 x 0.01 = 60 t/ha

5)   C (58% of OM) = 60 t x 0.58 = 34.8 t/ha (for a soil layer with 50 cm of depth)

Another problem, largely resulting from the misuse of nitrogen fertilisers used in conventional agriculture, is the pollution of groundwater with nitrates. We should remember that these are the most stable water reserves and our last resort, and that for more than twenty years Portugal has had nine nitrate-vulnerable zones. 

As for pesticides, they continue to be overused in many crops, partly because the principles and practices of integrated protection enshrined in Portuguese Law No. 26/2013, which is in force and applicable to all national agriculture, are often ignored.  

To make matters worse, following protests by some European (COPA-COGECA) and Portuguese (CAP, CONFAGRI) agricultural confederations, the European Commission gave in and dropped its targets for a 50% reduction in chemical pesticides. 

But if organic farming can achieve good yields without synthetic chemical pesticides, why is a 50% reduction not possible in conventional farming, including in integrated production?

2.    The strategy and practice of organic farming in orchards, vineyards and olive groves

In organic farming, there are basic or priority fertilisation practices and complementary practices. There are only three priority practices (and not all of them are applicable to orchards, vineyards and olive groves): 

a)    Crop rotation; 

b)   Manure from organically raised animals and/or agricultural residues, also from this mode of production; 

c)    Short-cycle cover crops, to be used as green manure. 

This is part of the principle and strategy that, in organic farming, we do not fertilise the plant directly but rather feed and improve the soil so that it can feed the crop. And with a trend towards gradual improvement and reduced dependence of agriculture on the fertiliser and pesticide manufacturing industry. 

And so that there are no doubts about the rules of production, Regulation (EU) 2018/848 of the European Parliament and of the Council sets them out in Annex II (Detailed production rules referred to in Chapter III), Part I (Rules applicable to plant production), point 1.9 (Soil management and fertilisation).

Soil management and fertilisation in organic farming - Annex II to Regulation (EU) 2018/848: 

1.9.1. In organic plant production, tillage and cultivation practices shall be used that maintain or increase soil organic matter, enhance soil stability and biodiversity and prevent soil compaction and erosion. 

1.9.2. Soil fertility and biological activity shall be maintained and increased:

a)    Except in the case of grassland and perennial forage crops, by multi-annual crop rotation, which shall include leguminous crops as a main or cover crop in the rotation and other crops for green manure;

b)   In the case of greenhouses and perennial crops other than fodder crops, by the use of green manure crops and short-cycle leguminous crops, as well as the use of plant diversity; 

c)    In all cases, by the application of animal manure or organic matter, preferably both transformed by composting, from organic farming. 

1.9.3. Where it is not possible to meet the nutritional needs of plants through the measures provided for in points 1.9.1 and 1.9.2, only fertilisers and soil improvers authorised under Article 24 for use in organic production may be used, and only to the extent necessary. Operators shall keep records of the use of such products.

In the case of permanent woody crops (orchards, vineyards, olive groves), where crop rotation is not possible and organic livestock manure is generally not available on the farm or on the market, organic farmers are left with green manure as their primary fertilisation practice.  

This means that commercial fertilisers, even if authorised for this type of production, cannot be applied without first (or simultaneously) planting cover crops as green manure. 

This has not always been the case in practice, but if we want to work rigorously and seriously, this is how it should be. Permanent crops (with the exception of pastures) without cover crops as green manure are not truly organic farming.

2.1. Cover crops as green manure – carbon and nitrogen produced in the field rather than in the factory 

Figure 1 – Inter-row cover crops as green manure in vineyards and orchards to produce organic carbon (through photosynthesis) and nitrogen (through biological and symbiotic fixation) – 1a-faba bell bean (Vicia faba ssp. minor) with bacterial nodules, from the soil and not inoculated, rhizobium (Rhizobium leguminosarum bv. Viceae) (Beja, Portugal, 2020); 1b – mixture of faba bell bean and triticale (Triticum x secale) in a table grape vineyard (Ferreira do Alentejo, Portugal, 2022); 1c – mixture of faba bell bean and oat (Avena sativa) in an apple orchard and its bedding with farm tools invented on the farm (Alandroal, Portugal, 2024)

Green manure is therefore essential in organic farming. We could even say that it is a mandatory agricultural practice in permanent non-forage crops, since the application of authorised commercial fertilisers is only permitted as a supplement to basic practices. 

For green manure to work, it must include a legume that is well adapted to the soil and climate, such as faba bell beans (Fig. 1a), which grow well in Mediterranean climates and in almost all types of soil, except for the most acidic and sandy ones. For soils with high acidity (pH < 5) and sandy texture, we have lupin (Fig. 2) or hairy vetch (= sand vetch) (Fig. 3).  

Adding a cereal to the legume is good practice for improving soil structure and drainage. In legumes, it is advisable to check for the presence of rhizobium bacteria nodules on the root (Figs. 1 and 2) and the good condition of these nodules by the reddish colouring they should have inside, which results from a substance produced by the bacteria, similar to haemoglobin in human blood (Fig. 2).

Figure 2 – Rhizobium nodule (Bradyrhizobium spp.) in cross-section, on the main root of the yellow lupin (Lupinus luteus), with a reddish colour indicating full activity in biological nitrogen fixation and natural ammonium synthesis (Palmela, Portugal, 2019) 

By using cover crops as green manure, we can replace most commercial nitrogen fertiliser, or even all of it in soils with higher fertility and medium to high organic matter content (Fig. 4). 

However, in most soils in Portugal, with organic matter content close to 1% (sometimes even lower), and unable to rely on soil nitrogen (which is found in organic matter, which is the majority), green manure is even more important, but not sufficient as a source of nitrogen. 

This practice, together with the shredding of pruned branches within the orchard, with no or minimal mobilisation and without herbicide, has increased the organic matter in the soil by 1% (one percentage point) in 10 years (in the first 10 years). In Agro-sanus' (the company of the author) oldest orchard, planted in 1999, the initial content was 1.5% and now, 25 years later, it is 3.5% in clay-limestone soil. In the orchard planted in 2015, in clayey schist soil, the increase has been faster, with a 1% increase in the last 4 years (from 3% to 4%). In this orchard, it is no longer necessary to apply organic fertiliser as a source of nitrogen, to achieve a yield of 20 kg/tree or 20 t/ha for the best varieties. The two sources of nitrogen are the soil itself and cover crops as green manure (Fig. 4).  

Figure 3 – Inter-row cover crops, sown and managed for green manure and, at the same time, to increase auxiliary fauna in the control of aphids and mites in apple and peach trees – 3a and 3b – hairy vetch (Vicia villosa) with green lacewing (Chrysoperla carnea), a polyphagous lacewing predator of various insect and mite pests in peach orchards; 3c – faba bell beans (Vicia faba ssp. minor) with seven-spotted ladybird (Coccinella septempunctata), a selective coccinellid predator of only aphids, but of several species, including those of broad beans and fruit trees, in apple orchards (Alandroal, Portugal, 2024)

Figure 4 – Organic apple orchard with varieties resistant to apple scab (Venturia inaequalis), planted in 2015 in clayey schist soil in northern Ribatejo (Portugal), with organic fertiliser applied only at planting, with root inoculation also at planting (mycorrhizal fungi, Trichoderma spp. fungi antagonists of pathogenic fungi, phosphorus-solubilising rhizosphere bacteria), with cover crop throughout the field (row and inter-row), shredding of pruned branches in the orchard together with the cover crop at the end of April, no tillage since the year of planting, with irrigation but without fertigation,  with 4% organic matter in 2024,  without the application of manure or other organic amendments, without fungicide treatment or even copper or sulphur, with biological treatment against the codling moth (Cydia pomonella), with mass trapping of the Mediterranean fruit fly (Ceratitis capitata) (Ferreira do Zêzere, Portugal, 2022)

2.2. Cover crops as ecological infrastructure in biological crop protection against pests 

Inter-row cover crops are grown not only to regenerate the soil and fix nitrogen, but also to increase the population of insects and mites that prey on and parasitise crop pests (Fig. 3).  

These organic farming practices in fresh fruit orchards, as well as in vineyards and olive groves, reduce the incidence of pests to such an extent that in most cases the application of pesticides is no longer necessary, or the number of phytosanitary treatments required is substantially reduced. 

This, which for many farmers and agricultural technicians may seem like mere theory, has been proven in practice in small and large cultivation areas and in different regions of Portugal, most often in organic farming and sometimes also in integrated production, when cover crops are grown between rows for this purpose and/or ecological infrastructure such as mixed hedgerows are installed. 

 2.3. Mixed hedges as ecological infrastructure for biological crop protection against pests 

Other important ecological infrastructures in orchards, vineyards and olive groves are mixed hedges of trees and shrubs that are favourable to predatory insects and parasitoids, as well as pollinators (Fig. 5). 

Figure 5 - Mixed hedges of trees and shrubs favourable to predatory insects and parasitoids, bordering conventional and organic apple orchards (Alandroal, Portugal, 2024) 

2.4. Varieties and rootstocks best suited to organic farming           

The three main criteria for farmers when choosing varieties and rootstocks for permanent tree crops to be planted should be as follows: 

a)    Commercial suitability with the best quality suited to consumer requirements; 

b)    Suitability to the soil conditions of the farm and the climate of the region (soil and climate conditions); 

c)    Resistance to diseases, especially those caused by fungi and bacteria that are most common and most difficult to combat, and resistance to pests that are also difficult to phytosanitarily protection. 

In apple trees, for scab (Venturia inaequalis), which is the main disease, resistant varieties with good characteristics are already available, such as the Italian varieties of the “Sweet resistants” group - Fujion, Gaia (Fig. 4), Gemini, Rene, Smeralda - the German Pinova and its mutation Evelina, or the French Inored Story. 

In our organic orchard planted in 1999, the Bravo regional apple tree (from Esmolfe village, Viseu city), although not considered resistant to scab, rarely shows symptoms of the disease even without any treatment. This can be explained by the fact that, without excess nitrogen and with sufficient mineral nutrients (P, K, Ca, Mg, B, Cu, Fe, Mn, Mo, Zn), resistance to the disease increases.

Final notes 

Good agricultural practices followed in organic farming, with special attention to cover crops to be used as green manure and ecological infrastructures, the usage of organic livestock manure and the rotation of annual crops, allow agriculture to be part of the environmental and climate solution, in particular with carbon sequestration in the soil, nitrogen production in the field and improved soil fertility and soil life. 

It is viable from a technical and economic point of view, and yields tend to be similar to those of conventional farming, when good agricultural practices are applied (Ponisio LC et al, 2015) providing, in the medium to long term, reduction of costs and quality food at more affordable prices.

Bibliographical references 

Ferreira J. et al (coord.) 2020. Good Agricultural Practices for Soil and Climate. Organic Farming Collection No. 1, Ed. Agrobook, Porto, 214 pp. 

Ferreira J. et al (coord.) 2025. Manual of Plant Protection in Organic Farming. Organic Farming Collection No. 2, Ed. Agrobook, Porto, 217 pp.

Ferreira J. & Marques, C. 2025. Guide to Production Inputs for Organic Farming, Ed. Agrosanus, Lisbon, 100 pp. 

Lorant A. & Allen B., 2019. Net-zero Agriculture in 2050: How to get there. Report by the Institute for European Environmental Policy. Brussels, 23 pp. 

Ponisio LC, M’Gonigle LK, Mace KC, Palomino J, de Valpine, P, Kremen C. 2015. Diversification practices reduce organic to conventional yield gap. Proc. R. Soc. B 282: 20141396 (http://dx.doi.org/10.1098/rspb.2014.1396)