Dr. Joy Agnew, PEng, Prairie Agricultural Machinery Institute
Interest in the practice of planting two different crops on the same land, or intercropping, is growing exponentially. Despite more complications during seeding, separation and storage producers are looking at intercropping to improve soil health, ease crop harvesting and to diversify risk.
In my own province of Saskatchewan, producers expect to seed around 30,000 acres of intercrops this year, which is modest, but demand for more information is evident. Intercropping workshops fill up quickly and I field an average of one inquiry a week on this topic.
Intercropping makes sense for pulse growers. During harvest, these crops have a tendency to lay flat when grown as a monocrop. Not only does this pose yield challenges, but you also face the risk of picking up rocks and damaging your machinery. In combination with other crops like canola or flax, the oilseed crops form a stand for peas, soybeans, lentils and chickpeas to grow.
The Prairie Agricultural Machinery Institute (PAMI) conducts research and development for agricultural technology. There is a lot of science yet to discover on the topic of intercropping, but we can also draw implications from our past research in grain processing and storage and apply it to this emerging technique.
SEPARATION AND CLEANING
The difference in the size of the seeds drives the ease with which grains are separated and cleaned. One can use a variety of technologies:
- Gravity tables use a tilted, vibrating table to separate grains based on seed size and weight. The capacity is 400 to 1,400 bu/hr.
- Offering efficiencies of up to 13,000 bu/hr are rotary grain cleaners, which also rely on difference of seed
- Air separators or aspirators operate on different densities of seeds with a capacity between gravity tables and rotary grain
- Flat sieves and screens offer varying capacity and also rely on differences in seed size but may also use air streams to remove
- Other technologies include the centrifuge-like spiral separators, indent cylinder machines and colour/seed property separators.
With the hundreds of combinations of grains available through intercropping, it is a science and there is no definitive optimal technology.
Beyond seed size, shape and density, one must consider different variables in their choices including dockage level and seed-mix ratio in making technology choices. In most circumstances, combining technologies may be appropriate.
It’s also important to note that these cleaning technologies were designed primarily to remove dockage from a single grain and not for separating two (or more) different grains. Increased efficiencies in separation may become available with specially designed equipment, but the need for these technologies needs to be established first.
STORAGE
Producers typically only store intercrops together until they have an opportunity to separate them – a matter of weeks to a few months. This timeframe poses little risk to quality, but, over longer periods, spoilage can result from separation becomes as much an art as temperature fluctuations and moisture migration.
The impacts of moisture and temperature can be managed by blowing some air through the grain. Aeration, or cooling of grain, requires an airflow rate of about 0.1–0.2 cfm/bu. Moisture can be removed from grain using natural air drying with an airflow rate of 1–2 cfm/bu.
Managing aeration and natural air drying with mixed grains involves careful attention to the airflow rate and uniformity of airflow. This requires an understanding of how air conditions will affect grain conditions and can be tricky because of seed segregation – typically larger kernels roll to the outside of the bin while the smaller ones stay in the middle.
Layers and areas of concentration may result in poor uniformity of airflow. In some areas, you get increased resistance and in others you get preferential airflow. Where you have pockets of grain with a significantly different level of humidity compared to the surrounding grain, issues may arise due to the formation of hot spots.
To detect the potential for spoilage and to know when to begin aeration or natural air drying, one can again turn to technology:
- Cable-mounted temperature and moisture sensors (e.g. OPI and Bin-Sense®) may be connected to fan control systems, but note that moisture sensors based on equilibrium moisture content (EMC) may not be effective for intercrops.
- Bin EMC forecasts (i.e. BINcast®) use weather advisories to inform a producer’s choices about when to run fans, but also rely on EMC equations that are not valid for intercrops.
- With aeration controller systems, fans run only when cooling will be achieved or maintained and are based only on temperature differential between air and
As intercropping science emerges, there are important questions and problems to resolve. Although we have significant data on the safe storage of monocrops, there are hundreds of possible combinations for intercrops where the assumptions do not necessarily apply. As a result, the impact of airflow resistance changes and particle size segregation on storage risk is unknown. We also have yet to study the impacts of moisture equilibration and the effects of air conditions on grain quality.
In 2018, PAMI is undertaking an evaluation of intercropping knowledge and research with a machinery-based focus. Alongside a literature review, we will be assessing the feasibility and practicality of using existing equipment for seeding, harvesting, separating and handling intercrops.
We would also like to learn from intercropping early adopters. If you have experience with intercropping seeding, harvesting, processing and storage, PAMI would appreciate hearing from you.