Rather than rotating corn planting with soybeans to replace soil nitrogen, many farmers are planting corn year after year and adding large amounts of nitrogen fertilizer.

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Companions or beneficial plants are included to attract insects for natural pest management while some plants are soil amenders providing nitrogen and mulch.

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He acknowledged that any soil used to grow nitrogen-fixing plants or were fertilised for agricultural reasons would result in an increase in gases involved in the formation of ozone.

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Researchers at Kansas State University are creating precise maps of nitrogen deficiencies in soil to help farmers apply fertilizer where it is needed most.

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Conventional farming methods using conventional fertilisers are adding active nitrogen to the soil, which tends to move to other places - lakes, rivers, seas, the air.

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The only way to increase yield was to find a way of supplying extra nitrogen, phosphorus and potassium to the soil.

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Embrapa scientists also bred varieties of rhizobium, a bacterium that helps fix nitrogen in legumes and which works especially well in the soil of the cerrado, reducing the need for fertilisers.

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