Using Plants Sustainably: Crop Rotation, Seed Saving and the Three Sisters

Feeding people without wearing out the land

A field can grow corn year after year, but soon yields fall, pests build up, and the soil washes away. Every society that depends on plants has had to solve the same problem: how do we take food, fibre and medicine from the land and still leave it healthy for our grandchildren? The curriculum asks you to evaluate how different societies have answered that question, including crop rotation, seed saving and traditional corn production.

Crop rotation

Growing the same crop in the same field every year (continuous monoculture) causes problems:

• The crop takes the same nutrients from the soil every year, so they run low.
• Pests and diseases that attack that crop build up in the soil, because their food is always there.
• Weeds adapted to that crop multiply.

Crop rotation changes the crop each year in a planned order. Rotations have a long history: medieval European farmers used a three-field system, and 18th-century English farmers rotated wheat, turnips, barley and clover. A common rotation in Ontario today is corn, then soybeans, then winter wheat, often with a cover crop such as red clover planted with the wheat.

Why it works:

• Legumes (soybeans, clover, alfalfa, peas) fix nitrogen, so the next crop needs less fertilizer.
• A pest that feeds on corn starves when the field is in soybeans the next year.
• Crops with different root depths use nutrients from different soil layers.
• Cover crops keep roots in the soil over winter, which prevents erosion, adds organic matter and feeds soil organisms. Reduced tillage (no-till) leaves crop residue on the surface, which also protects soil.

Seed saving and seed banks

For thousands of years, farmers saved the best seeds from each harvest to plant the next year. Over many generations this produced thousands of local varieties adapted to their own soils and climates, carrying a huge store of genetic diversity.

Today, many farmers buy F1 hybrid seed each year. Hybrids are crosses of two parent lines and are often very uniform and high-yielding, but seeds saved from them don't grow true: the next generation is a mixed bag. Open-pollinated and heirloom varieties do grow true when their seeds are saved (as long as they aren't cross-pollinated by another variety).

Why saving seeds matters:

• Genetic diversity is insurance. A variety that seems unimportant today might carry a gene for resistance to a future disease or tolerance of drought (remember the bananas in Lesson 11).
• Seed banks store seeds at low temperature and humidity for decades. Canada's national seed bank, Plant Gene Resources of Canada, is in Saskatoon. The Svalbard Global Seed Vault in Norway holds backup copies of seeds from gene banks around the world.
• Community seed libraries and groups such as Seeds of Diversity Canada help gardeners save and share local varieties.
• Many First Nations communities are also working to bring back and protect their own traditional seeds, such as heritage varieties of corn and beans.

The Three Sisters

Many Haudenosaunee communities, and other Indigenous nations across North America, grow corn, beans and squash together. In Haudenosaunee teachings these crops are the Three Sisters, and they are central to culture and ceremony as well as to food. The crops are often planted together in small mounds:

• Corn grows tall and gives the beans a pole to climb.
• Beans climb the corn and, through bacteria in their root nodules, fix nitrogen, which helps keep the soil fertile over the years.
• Squash spreads big, prickly leaves over the ground that shade the soil, keep it moist, slow erosion and crowd out weeds.

The three foods also fit together nutritionally: corn is rich in starch; beans add protein, including the amino acid lysine that corn is low in; squash adds vitamins and its seeds add oils. This is a polyculture: several crops sharing space and helping each other, unlike a monoculture.

Other practices of First Nations, Métis and Inuit communities also link plant use to care for the land, for example: harvesting manoomin (wild rice) by canoe in a way that leaves grains to fall back into the water and reseed the beds; harvesting only part of a patch of medicine plants or berries so the plants recover; and, in some regions, carefully controlled cultural burning to renew prairies and berry patches. These practices are based on knowledge refined over many generations and grounded in values of respect and responsibility toward the land.

Evaluating a practice

To evaluate a practice, look at both sides:

• Benefits to people: yield, nutrition, cost, labour, income, culture.
• Effects on the environment: soil health, water quality, biodiversity, fertilizer and pesticide use, energy use.
• Limits: some practices take more labour or knowledge, or are harder to use with large machines. A Three Sisters garden is hard to harvest with a combine, for example, while a large corn monoculture is easy to harvest but costly to the soil.

Good sources for your research include government agricultural departments (such as OMAFA, Ontario's agriculture ministry, or Agriculture and Agri-Food Canada), university research, and sources written by or with Indigenous communities about their own practices.