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The Dirt on Intercropping (PCN Spring 2017) MAR 28 2017 | Consumers and Producers | Pulse Crop News

This article appeared in the Spring 2017 issue of Pulse Crop News.

A perfectly standing pea crop on the day of harvest remains the Holy Grail for most producers. Solving this challenge has been the quest of plant breeders, agronomists and pathologists since the time the very first combine hit the field.

The shift to semi-leafless pea varieties, finding the perfect plant density, and learning the ins and outs of managing Ascochyta blight along with proper fungicide timing have resulted in giant leaps forward to ensuring a crop that stands beautifully right through until the last hopper goes into storage. However, for the majority of the province, we aren’t there yet. Many producers get creative in their approaches and look outside the box of traditional ways of doing things.

Intercropping is not a new concept. Key to the discussion, however, is to clearly understand what exactly we mean when talking about intercropping. There are many variations on the same theme. At its most basic, intercropping is the purposed growing of more than one species of plant in the same space.

For example, a hay field of alfalfa and timothy is in fact an intercrop. Another familiar place where intercropping is common is in silage mixtures either to maximize quality or yield or both. In very dry locations, two crops (often a legume and a cereal) are planted simultaneously to provide weed control as well as potential for additional nutrient and moisture conservation benefits to the higher value crop. This is often done with clovers or peas/lentils and maize where only the corn grain is harvested. In other countries, two crops are planted together to maximize land use since each crop can be harvested at their own individual maturities because the harvests are done by hand.

From an ecological standpoint, planting two or more crops with different root sizes, shapes and depths, leaf structures, angles and heights, as well as different nutrient and water needs is a very effective way of maximizing resource use per unit land, managing water use and light use efficiently and may even provide risk mitigation against diseases, drought, flooding, etc. After all, there is no such thing as a monoculture found in nature. Production agriculture could perhaps be enhanced mimicking natural environments.

Plants are much more aware of their surrounding environment than one would think. Researchers have shown that plants can create natural insecticides and fungicides, complex molecules, and exude chemical messengers that trigger a response throughout the plant to begin producing natural pesticides. Researchers have also shown that the type of natural insecticides produced are not only determined by insect mouthparts, but that plants can change the type of response based on mouthparts of different insects.

This research has focused mostly on tobacco, and other species of plants most commonly used in laboratory studies. The question remains whether or not plants can communicate across species, if these plants are aiding and abetting their neighbours, or whether neighbouring species of plants are simply eavesdropping, picking up chemical messaging signals around them and responding to that environmental stimuli.

Mycorrhizae fungi, a complex hyphae of mycelial webbing in the rhizosphere, are nutrient, mineral and water super highways. Scientific research has shown the ability of certain plant species to transfer nutrients including simple carbohydrates, sugars and other minerals from plant to plant. The question remains whether or not plants can signal production of fungicidal/insecticidal molecules across species, from one crop to the other, and whether plants can also transfer nutrients across plant species through mycorrhizae networks.

This type of research is extremely difficult to conduct in the field as the variables are so great, it is hard to isolate, observe and quantify the amount of plant to plant interaction. To date, we have no scientifically conclusive evidence of this occurring in intercropping, but it hasn’t stopped producers from experimenting.

Testimony and anecdotes from producers that have intercropped pulses with cereals, or canola, have spoken of perceived benefits. Some of these suggested benefits of intercropping include:

  • Decreased weed competition and in some instances, no need for herbicide application;
  • Increased standability resulting in easier harvest of peas/lentils when intercropped with canola or other vertical structured canopies such as cereals and flax;
  • Risk management in the form of one of the two crops yielding well given environmental conditions or lack of moisture (ie. Canola yields well in higher moisture seasons and peas better when moisture is limited.);
  • Decreased disease pressure often resulting in no need for fungicide application; and
  • Increased net return per acre or higher contribution margins due to decreased input costs should there be no fungicide and herbicide application.

There is currently no scientific research to support these claims, however, producers who have intercropped speak of these benefits. There are also many logistical challenges of intercropping. These may include:

  • The difficulty of seeding two crops and ensuring soil-seed contact, appropriate depths and seedbed for both species;
  • The incompatibility of herbicide options between crops;
  • Timing of harvest to reduce shatter loss or premature harvest of immature seeds;
  • Difficulty combining and having appropriate settings to retain both seed sizes without throwing over; and
  • Challenges separating or cleaning the two crops after harvest.

When reviewing all of the scientific literature, the jury is still out on whether there is improved yield through improved water, nutrient and light use efficiency. Scientists have not yet determined for certain that this is the case. Whether or not intercropping reduces the need for herbicides, insecticides or fungicides has not been proven. The logistical challenges of seeding, selecting compatible herbicide options, timing harvest and separating crops after harvest remain large obstacles for more producers to try intercropping.

The only way for certain to know if intercropping has any additional benefit is by knowing your costs of production and your net return per acre. Perhaps the jury has not yet finished deliberating on the scientific arguments, however, should you be able to reduce risk through lower costs of production, and increase your net return per acre, intercropping may still pay dividends on your operation.

Before embarking on an intercropping adventure, be sure to speak to those with experience, sort out herbicide options for crops beforehand, and ensure that you have the time to sort out the logistical challenges of harvest and subsequent cleaning. Intercropping is a practice where producers are pioneering old techniques in a low input cost environment in order to improve returns per acre.

The scientific community is watching closely and will continue to assess the perceived benefits, when possible, to confirm or debunk the many hypotheses that intercropping has been suggested to offer producers.