Soil Science

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Which of the following can result in significant losses of N from grazed agricultural systems?

Correct! All the above are pathways by which N can be lost from the soil. Ammonium ions can be converted to ammonia and lost by volatilisation, or be nitrified to nitrate. Nitrate may be leached from the soil or, if the soil becomes waterlogged, converted to nitrous oxide and dinitrogen gas by denitrification.

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Which one of the following plant nutrients is mainly cycled back to the soil through urine rather than dung? ?

Correct! K, like N, is mainly retuned to the soil in urine.

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Plants take up some chemical elements that are not plant nutrients, and herbivores are able to obtain essential animal nutrients by this means. Which of the following essential animal nutrient elements is not generally required by plants?

Correct! Selenium is essential for animals, but not for plants. In soils where the availability of elements such as Se is low, plant growth will not be affected, but grazing animals, and carnivores further up the food chain, may suffer deficiency symptoms.

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What effect do you think surface application of lime to an acid soil would have on N losses by ammonia volatilisation?

Correct! Lime would raise the pH of the surface soil, which would increase the conversion of ammonium ions to ammonia, and therefore tend to increase ammonia volatilisation.

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