Intercropping in Ireland

By Dr Kamel Badr
Intercropping Scientist & Guest Writer

Showcasing GRI’s Intercropped Paludiculture Trials on HEATED

Scientists globally are intensifying efforts to address the adverse environmental impacts of agriculture. However, the real challenge lies in finding practical solutions for farmers to be able to facilitate these changes. Intercropping, an ancient farming practice of growing multiple crops simultaneously in the same space, has gained renewed attention as a powerful tool for enhancing agricultural sustainability. In this blog, we’ll explore the various aspects of intercropping, its environmental impact, and its application in wetland agriculture, also known as paludiculture. 

Intercropping Systems

Intercropping encompasses a broad variety of practices where the common denominator is that two or more crops are growing simultaneously in the same plot. The crops can be planted fully mixed or in alternating strips or rows, depending on the crops, the intended use and the farming system.

A variety of crops can be combined, sometimes with both crops intended for harvest, sometimes with one or more plants solely having a support function. The most subtle form of intercropping uses multiple cultivars of the same species to reduce the risk of crop diseases. More obvious systems use two or more different species, which are all harvested. In full-season intercropping systems, crops are planted and harvested together, which is an option if the harvest is baled together, e.g. for silage, or if the crops can be separated mechanically, later. Alternatively, in a practice called relay cropping, a second crop is planted after the establishment of the first crop, which allows harvesting of the first crop without damage to the second crop, which is still small.

In other intercropping systems, one of the intercropped species is not intended for harvest, but mainly serves to support the growth of a main crop. These nurse crops can help the main crop by fixing nitrogen or harvesting nutrients from deeper soil layers; providing structural support, shade or shelter from the wind; suppressing weeds and lowering the occurrence and severity of pests and diseases.

Intercropping is rich and varied and the above techniques can be (and are) combined in smart and innovative ways to suit specific conditions and objectives.

Strip Intercropping

Nutrition and Soil Health

Intercropping offers numerous advantages across nutrition, soil health, and environmental factors.  

Legumes are a very common component in intercropping, because of their nitrogen-fixing qualities. In some cases, the legume crop can completely fulfil the nitrogen requirement of the other crop(s), but even when additional N-fertilization is required, legumes present considerable environmental and financial savings. Additionally, a well-designed intercropping system uses crops with different root distributions (deep and superficial) to minimize competition between plants. This will improve nutrient use efficiency and minimize leaching, lowering both fertilizer requirements and environmental losses.  

A cover crop can minimize soil erosion by binding the soil with its roots and catching the rain on its leaves. The leaves and stems also provide a physical barrier, which slows run-off and increases soil water absorption. Moreover, cover crops may absorb excess nutrients while the main crop is establishing and release them after the cover crop dies, ideally when the main crop needs extra nutrients. 

Finally, because of the higher planting density, and better root distribution, there is a higher and more uniform input of fresh organic matter in the soil. This enhances carbon sequestration and improves biological soil health and physical soil structure, which are both vital for long-term productivity. 

Wheat multi cultivars with Clover mixed in.

Weed Control

Intercropping offers effective and cheap weed suppression by effective competition for resources and natural herbicide.

The higher density of plants in intercropping can reduce the amount of light reaching the soil surface, which reduces the growth of weeds. Intercropping with cover crops is especially effective in suppressing weeds by shading, and can continue to do so even after death if they form a dense mulch. However, some care is required to prevent the main crop from being outcompeted by an intercropped cover crop.

Due to the higher planting density and complementary root distributions, weeds may have a harder time competing for nutrients and water than in a monoculture. This effect further contributes to weed suppression and reducing weed biomass.

Finally, some intercropping components may exhibit an allelopathic effect on weeds, meaning that they release chemical components that are toxic to other plants or prevent seed germination.  

Disease & Pest Control

Increasing plant diversity in agricultural fields through intercropping can help reduce pest and disease damage, lowering reliance on pesticides and fungicides. Intercropping influences disease dynamics through various mechanisms like the dilution effect, physical barriers, and chemical effects. 

In intercropping, the distance between plants of the same species is larger than in a monoculture, which means diseases or pests must cover more ground to reach their next host. Moreover, the non-host species acts as a physical barrier, further delaying the spread of pests and diseases. These mechanisms are only effective, however, if a pest or disease is selective for one of the crops, so choosing the right intercropping components is essential for successful pest control.  

Intercropping can also change the spread of disease by altering the microclimate. A higher plant density reduces wind speeds in between crops, which decreases the spread of spores. Moreover, temperature and humidity tend to be more stable in between dense vegetation, which may reduce the sensitivity of plants to infection. However, the same factors can also be said to increase humidity and slow evaporation after rainfall, increasing the time leaves are wet and making a crop more susceptible to disease. Whether a dense canopy is desirable depends on climatic conditions. It is vital, therefore, to select intercropping components to achieve an appropriate canopy density for the conditions at a particular site.  

Certain plants emit volatiles that can repel pests, while others reduce pest occurrence by attracting predators. Moreover, the increased biodiversity in intercropping systems will provide a more balanced ecosystem, which tends to lower pest pressures. For greatest success, plants must be tailored to repel the most harmful pests for a crop, or attract the most effective predator for a certain pest. In many cases, yields are significantly increased without any additional pesticide or lower pesticide applications are needed, showing a clear benefit to farmer health and finances as well as the environment. 

An interesting form of active pest control in intercropping is trap cropping, which involves luring pests to a strip of attractive plants. For greater effectiveness, trap cropping can be combined with repellent crops in between the cash crop, a technique known as push-and-pull. The pest can be eliminated in the trap crop, before it can spread to the main cash crop. Even if done with pesticides this method is more economical and far less environmentally harmful than treating the whole field, which would require a much higher quantity of pesticide.  

Example of Cash Crops alongside Traps Crops

Economic and Social Factors

Intercropping presents significant economic and social benefits. With higher yields, typically averaging 20-30% more for cereal/legume intercrops, farmers can enjoy increased income and excellent stability in yields, reducing financial risks. Especially in low-input farming systems intercropping offers a way to increase yields and increase crop quality by e.g. boosting grain nitrogen and protein content in wheat by intercropping with legumes. 

However, the economic benefit of intercropping is highly context-dependent. Often, yield, relative to the monoculture of its components, is used as the sole metric. However, there are many more factors which determine the profitability of a farming system: prices of inputs and returns, labour, and risk management are all part of the equation that sees the farmer through to the next year, or not.

Nevertheless, it is hard to deny that intercropping is a promising prospect: higher yields and lower inputs, with lower environmental impact and a healthier more resilient soil to boot. Multispecies swards, also a form of intercropping, are already giving promising results for beef and dairy farmers in Ireland, in terms of yield, input requirements, climate resilience and greenhouse gas emissions. Moreover, arable silage mixtures are already commercially available to grow a high protein winter fodder during a ley, while actively enriching the field with nitrogen before reseeding with grass. In summary, while intercropping systems can be less straightforward to implement, the rewards and benefits are multiple, including increased resilience to the impacts of climate change. 

Intercropping in Paludiculture

Thanks to the Farm Carbon EIP, Green Restoration Ireland is actively using intercropping practices as part of its paludiculture trials. Paludiculture, a new form of agriculture that implements sustainable agricultural practices on restored wetland ecosystems, provides an ideal platform for testing the effectiveness of intercropping in enhancing agricultural productivity, soil health, biodiversity and avoiding carbon emissions. In its paludiculture trials, GRI is testing the potential benefits of intercropping. Among our trials are mixes of rhubarb and broccoli and chokeberry and mint, as illustrated in the photos below, as well as a variety of multispecies swards, tailored to deal with the specific challenges of moist peat grasslands. 

GRI’s Paludiculture Trials

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Peer Reviewed Final Copy by Dr Kamel Badr, Dr Doug McMillan & Dr Bastiaan Molleman

Copy Edit by Kaela Bernardino