But wheat yields per acre grew worse if anything as soil nutrients were depleted.

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Compost added to soil replenishes the nutrients and promotes plant growth.

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If it wasn't for fungi, plants would not be able to extract nutrients from the soil.

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Next year's crop is then planted directly into the mat, retaining more nutrients in the soil.

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Organic mulches such as wood chips, pine straw or bark have the added benefit of slowly breaking down which adds nutrients to the soil.

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As bank lending returns, and if soya prices fall, farmers will switch to crops such as maize, which offer lower returns but return nutrients to the soil.

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That means more nutrients in the soil, where it feeds food crops, and less in lakes and streams, where it feeds algae that sucks up oxygen and kills fish.

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Their modular hydroponic system -- where plants sit in a soil-free set up with nutrients delivered through irrigation channels -- can be retrofitted to just about any wall.

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The softening of the soil and the consequent release of nutrients is likely to encourage the growth of shrubs on land that is now dominated by grass, moss and lichens.

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In the hills, torrents of water washed soil away, or left it but rinsed the nutrients out of it.

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These problems include the destruction of wetlands and mangroves, the dispersion of chemicals and nutrients, and the salinisation of the soil.

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When the next food crop is planted, it benefits from the nutrients and improved physical properties of the soil that the trees have provided.

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And David Laird, of America's Department of Agriculture, showed that biochar even helped the rich soil of America's Midwest by reducing the leaching from it of a number of nutrients, including nitrate, phosphate and potassium.

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This is achieved due to its soil, which sits on a gravelly plateau where the vines have to dig deep to extract the nutrients.

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