Skip to 0 minutes and 11 secondsHello. I'm [INAUDIBLE],, senior lecturer in climate and environmental science. Feeding our planet requires healthy soils to grow crops and raise animals. But if soils are managed poorly, they will degrade, and crop yields will decline. 25% of all agricultural soils worldwide are highly degraded posing a real threat to food security. To find out how to stop this degradation and maintain soil health, we first need to understand what a healthy soil looks like. Healthy soils have a light and crumbly structure. About half of their volume consists of pore space, which is the empty space between soil particles. In healthy soils, these particles are bound together with pieces of organic matter into soil crumbs called aggregates with pore spaces in between.

Skip to 1 minute and 1 secondStable aggregates stay intact, even when they're hit by raindrops or crushed by footsteps or farm equipment. Soils with a good structure act like a sponge. Water infiltrates easily and much of this water is retained in pore spaces where plants can access it. Healthy soils also teem with life. They contain large amounts of organisms, such as bacteria, fungi, insects, and earthworms. These organisms break down organic matter, like animal manure and the remains of crops, which releases nutrients for plant growth. It also produces compounds that bind soil particles into aggregates. By digging tunnels through the soil, earthworms allow air and water to infiltrate. About 1% to 6% of the weight of a healthy soil is organic matter.

Skip to 1 minute and 49 secondsSoil organic matter is important to all aspects of soil health. It contributes to soil fertility and soil structure. And by feeding microorganisms, it also promotes biological activity. Farming practices affect soil health in many ways. For instance, crop lands take nutrients from soil to grow, mostly nitrogen, phosphorus, and potassium. When crops are harvested, these nutrients are removed from the fields. And if these aren't replaced, soils will become depleted over time. To prevent this from happening, farmers can supplement nutrients by adding chemical fertilizer-- manure or compost. Compost and manure don't just add nutrients to the soil, but they also help to maintain healthy levels of organic matter. After crops are harvested, the bare soil is exposed to rain or wind.

Skip to 2 minutes and 41 secondsIf the soil is a poor structure, this may cause soil particles to be washed or blown away. In the UK, 2.2 million tons of topsoil are lost this way each year costing the economy about 45 million pounds, including 9 million pounds in lost production and reduced yields. However, farmers can protect soils by planting cover crops. These crops are not harvested, but they cover the otherwise bare soils. Moreover, they take up and recycle nutrients that might otherwise wash out of the soil. Cover crops are planted before and after the main crop and then tilled into the soil where they decompose into organic matter. Widely used cover crops includes grass species, such as perennial ryegrass, and grain crops, like wheat and oats.

Skip to 3 minutes and 30 secondsA legume cover crop, such as vetch and clover, can take nitrogen from the air and fix it into a form that plants can use, thereby adding nitrogen to the soil. If the same crop is grown over and over again, pests and diseases can build up in the soil. By changing crops between years and by including cover crops in vegetable or field crop protections, farmers can create a rich and diverse soil life that is better equipped to fight pests. Farmers use tillage, for example, plowing to break up compacted soil to incorporate organic matter and to aerate the soil. However, too much or poorly-timed tillage can destroy soil structure and reduce the soil organic matter contents.

Skip to 4 minutes and 17 secondsFor instance, driving on and tilling wet soil will cause compaction. Soil particles are pressed together leaving less pore space for air and water, which plants need to grow. Compaction also makes it difficult for water to infiltrate causing overland water flow and soil loss. However, farmers can reduce these problems by carefully timing when they till the soil or by opting for less disruptive tillage methods. Because we rely on soils to provide most of our food, soil health is vital to food security. Even though soil health is under threat, smart management will help to maintain soil health and improve food security for generations to come.

Soil - A vital ecosystem

In this video, Dr Kees Jan Van Groenigen shows what healthy soil looks like and how farmers can help soil structure and nutrients by using different cultivation methods.

In the next activity we ask you to get your boots on and get dirty, examining the soil around you.

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This video is from the free online course:

Future Food: Sustainable Food Systems for the 21st Century

University of Exeter

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