Sustainable Agriculture: Innovations for Cycling Matter and Using Energy Wisely

Remember from Grade 7

In Grade 7 you learned about monocultures, crop rotation, cover crops and runoff. In Grade 9 you will explain these and newer innovations using the two big ideas of this unit: how matter cycles and how energy flows. The curriculum asks you to explain how sustainable practices related to these processes can be applied in agricultural innovations.

Let's start at the grocery store

Every item in a grocery cart started on a farm. Each harvest removes nutrients from the field: nitrogen, phosphorus and potassium leave in the grain, vegetables or milk. If those nutrients are not replaced, the soil runs down. But if too much fertilizer is added, the extra washes into lakes (Lesson 9) or escapes as nitrous oxide (Lesson 10). Farming sustainably means managing the cycles carefully, a bit like balancing a budget.

The farm as an agroecosystem

Matter cycles on a farm:

• Crops take up nutrients and CO₂; harvest carries nutrients off the farm.
• Manure, crop residue and compost return nutrients and carbon to soil.
• Fertilizer adds nutrients from outside (from factories that fix nitrogen and mines that supply phosphate and potash).
• Losses: runoff and erosion carry nutrients to water; denitrification and fertilizer use release N₂O; ploughing speeds up decomposition and releases soil carbon as CO₂.

Energy flow on a farm:

• Sunlight powers the crops (photosynthesis).
• Fossil fuel energy runs tractors, dryers and greenhouse heaters, and is used to make fertilizer.
• Feeding crops to animals adds a trophic level, so about 90% of the energy is lost (Lesson 2).

Innovations that keep matter cycling

1. 4R Nutrient Stewardship: the right fertilizer, at the right rate, at the right time (when crops need it, not before a heavy rain), in the right place (near roots). Less waste, less runoff.
2. Precision agriculture: soil tests, yield maps, drones and satellite images show which parts of a field need more or less. GPS-guided machines change their rate automatically. Computer programs, including artificial intelligence (AI) systems, can analyse images to spot weeds, disease or nutrient shortages early.
3. Cover crops: after harvest, crops like cereal rye, clover or radish keep roots in the soil over winter. They hold soil and nutrients, add organic matter, and (if legumes) fix nitrogen.
4. No-till and reduced tillage: leaving crop residue on the surface protects soil from erosion and keeps more carbon in the soil.
5. Crop rotation and intercropping: alternating legumes such as soybeans with corn adds nitrogen naturally and breaks pest cycles, like the Three Sisters (Lesson 14).
6. Buffer strips and constructed wetlands: strips of grass, shrubs or trees along streams trap soil and nutrients before they reach water.
7. Anaerobic digesters: microbes break down manure or food waste in sealed tanks. The methane is captured and burned for electricity or heat (instead of escaping as a greenhouse gas), and the leftover digestate is a fertilizer. Some Ontario farms use digesters.
8. Aquaponics: fish waste (rich in ammonia) is converted by nitrifying bacteria into nitrate that plants absorb, cleaning the water for the fish: the nitrogen cycle in a box.

Innovations that use energy wisely

• Eating lower on the food chain: a field of grain or beans feeds far more people when eaten directly than when fed to animals first. This doesn't mean everyone must stop eating meat, but plant-rich diets and less food waste use energy more efficiently.
• Reducing livestock methane: better feed, and feed additives that reduce the methane cattle produce, along with digesters for manure.
• Efficient greenhouses: Ontario has a large greenhouse industry, especially around Leamington. Greenhouses can use energy-saving curtains, LED lighting and heat recovery, and some add CO₂ to boost photosynthesis.
• Renewable energy on farms: solar panels, and biogas from digesters.
• Integrated pest management: encouraging natural predators (ladybugs, parasitic wasps, birds) uses the food web to control pests, so fewer pesticides are needed.
• Reducing food waste: a large share of food produced is never eaten. Wasted food wastes all the energy, water and nutrients used to grow it; composting at least returns the nutrients to soil.