Biosphere Contents

1. Organic Matter

An abundant supply of nitrogen in a form that plants can take up is of vital importance

One of the best understood nutrient cycles is the nitrogen cycle, and it includes the processes of biological fixation, ammonification, nitrification and denitrification. Nitrogen fixation is particularly important for plants as it transforms atmospheric nitrogen into forms that plants are able to take up from the soil. Nitrification is inhibited by low temperatures, anaerobiosis (caused, for example by waterlogging) and acid soils, and these conditions must be avoided in agricultural soils. Denitrification, the reduction of nitrates back to nitrogen gas, is stimulated by anaerobiosis (e.g. in rice paddies). In an agricultural soil the beneficial aspects of the cycle are promoted by adding inorganic fertilizers (nitrate, ammonium or urea) or organic wastes of animal or plant origin.

What are the main processes in the nitrogen cycle?