The effect of wet coffee processing in water quality in streams and rivers of Jimma Zone, South Western Ethiopia

Abstract

Schematic representations of the nitrogen cycle often make it look as if the nitrogen undergoes simple chemical reactions to change from one form to another. However, while many chemical reactions do take place in the soil, the nitrogen conversions occur primarily through the action of soil organisms. The most common form of nitrogen is ammonium (NH 4 +), and is found in the excretions of most larger organisms. This is quickly consumed by plants, fungi and special bacteria (nitrifying bacteria). Their excrement contains nitrogen first in the form of nitrite (NO 2 -), which is then consumed by other bacteria who excrete nitrogen in the form of nitrate (NO 3 -). This is the preferred form of nitrogen for grasses and most row crops. It is not surprising then that most grassland soils are dominated by bacteria. Most of our agricultural crops are grasses (grains, forage grasses) and grassland plants. These plants are accustomed to, and will be healthiest in, soils high in humus. Because the metabolic activity in the soil is highest during the most active growth period of plants (highest temperatures), the nitrogen will become available to plants just as it is required, so supply and demand are in perfect balance. Soils that are low in oxygen (due to water logging, compaction, etc) contain a large number of (facultative) anaerobic bacteria (those that can exist without oxygen = denitrifying bacteria). These will take much of the excess nitrate (NO 3 -) and convert it to gaseous forms of nitrogen (N 2 or N 2 O) and oxygen. This supplies the soil with badly needed oxygen, and supplies the nitrogen fixing bacteria in this air-starved environment with nitrogen (N 2). Any excess returns to the air as nitrogen gas (N 2 O). Of course in all situations some of the nitrogen will be leached to deeper levels of the soil and into the waterways, where it feeds other organisms.