Foraging ahead with intercropping

Trials look at which crop combinations are the most productive, beneficial to the soil and reduce insects and disease risks

Einstein said no two objects can occupy the same spot at the same time, but he didn’t forbid them from being really close.

In agriculture, it’s called intercropping.

Intercropping is a complicated system in which two or more plant species occupy the same field at the same time. Biodiversity in the field provides a certain degree of protection against a range of pests, but it’s generally considered to be impractical.

In modern agriculture, farmers plant only one crop at a time in any given field. Monoculture is obviously the most convenient and practical way to grow field crops, but the crop is more vulnerable.

As well, monoculture farming depends on expensive crop protection products to ward off weeds and diseases, says plant scientist Ann Bybee-Finley, a PhD student at Cornell University.

“For example, if one plant gets a disease, the others are likely to catch it,” she said.

Bybee-Finley said a bad drought in her home state of West Virginia in 2012 motivated her to delve into intercropping.

“The stories of crop failure made me want to understand how to make farming practices more resilient, especially as climate change makes extreme weather events more frequent,” she said.

“Agricultural science is just beginning to look beyond the simplified strategy of planting only one crop per rotation. Intercropping reduces risk of insects and disease. The invaders have a tougher time finding enough of the host plant of one species concentrated in one spot.

“Diversity begets diversity. It gives farmers more options if one of their crops fails. It’s like a diversified stock portfolio. Plant diversity (on the field) leads to more diversity below ground, too.”

Bybee-Finley concentrated on a simplified intercropping system with two grasses — pearl millet and sorghum — and two legumes — cowpea and sunn hemp.

The grasses add organic matter to soil that has been depleted by years of farming. Legume roots release nitrogen when they decompose.

From a practical point of view, these forages are a source of livestock feed, thus providing farmers with cash income as another incentive to put them into their rotations.

She said her intercropping experiment is designed for forages rather than for cereal or oilseed crops.

“In the area around Washington, D.C., where we did some of the trials, the legumes performed well, but when we took the trials further north up into Vermont, the legumes did not do well,” she said.

“I can imagine that where you are, located north of North Dakota and north of Montana, you’ll have a difficult time finding cold-hardy legumes that produce as much biomass as you need to justify the planting.

“Legumes generally just don’t produce enough biomass. If you intercrop legumes with grass species, it should give you good yield stability over time. One year millet does better, then the next year sorghum, Sudan grass does better.”

However, legumes are a necessary part of the intercropping mix.

Bybee-Finley said farmers and researchers should apply more pressure on seed companies to develop cold hardy legumes. They should lobby the breeders who are applying for funding to ask for winter peas and winter lentils.

She said species that grow at a similar rate didn’t compete for space and resources as much as plants that grew at different rates did, which meant they were more productive.

Her next step is to determine which plant combinations are best as livestock feed. Experiments like this one, with so many variables, always yield a complex set of conclusions.

“When you’re looking at an entire system, it makes it harder to have an immediate take-away,” she said.

“There’s so many unexplored avenues and questions to ask. Which species should I plant together? And how many of each? I’m sure there’s a sweet spot.”

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