The Importance Of The Nitrogen Cycle

1.INTRODUCTION

The nitrogen cycle is one of the most important nutrient cycles found in terrestrial ecosystems. The element nitrogen plays a special role for the yield and quality formation of forage cultivationbreeding in agriculture. Large quantities of nitrogen are fixed by plants in form of ammonium or nitrate ions for their own growth. Crop nitrogen is then an essential feed component for animal growth and development in form of protein nitrogen. After animals’ digestion nitrogen can be detected in certain amounts in the products like milk or meat, but the major portion is excreted in the feces. These nutrients are again important for plant growth and are provided as slurry for fertilization (ROTZ, 2004). The efficiency of nitrogen-utilization

A large proportion of this excreted nitrogen quickly converts to ammonia, which rapidly evaporates into the atmosphere. This volatilization begins soon after the excretion takes process during fertilizer and all processing steps until the slurry nutrients are incorporated into the soil (ROTZ, 2004). Nitrogen losses occur in liquid form mainly as nitrate and downstream as ammonium, and gaseous form of ammonia, elemental nitrogen, nitrous oxide and nitrogen oxides (MENGEL, 1991; AHLGRIMM, 1997). Therefore nitrogen emittes into the atmosphere, flows into ground and surface waters and is washed out (DE VRIES, 2001). At the watercourses agricultural use forms about 46% of t he losses (WERNER, 1990). Currently the leaching into ground waters is the main problem. For the protection of drinking water the European Union applies a limit of 50 mg NO3/l (EU Nitrate Directive 91/676 / EEC). Even values of 50 mg NO3/l are harmful to health, especially for infants and children (DI and CAMERON, 2002). During storage nitrogen losses of almost 70% can occur. These losses are particularly volatile nitrogen oxides and ammonia, which escape into the atmosphere. Atmospheric ammonia emissions affect fertilization, acidification, eutrophication and the entire ecosystem (NRC, 2003). Microbial processes of nitrification and denitrification also emit

Ryan et al stated that this is a result that contradict other papers.

If the animals are 224 days per year outside, there is a nitrogen use efficiency of 27,9 % and if the animals are 297 days per year outside, the nitrogen use efficiency is a little bit higher with 28,8 %. These figures refer to the whole farm gate.

If we take a look at the nitrogen balance, the same result is given. When the grazing season is shorter, one cow has an nitrogen use efficiency of 24,6 %. With longer grazing season the efficiency gets higher to 25,1 %.

On some of the different types of nitrogen lost the grazing length has no influence. The amount of nitrogen in feces, urine and the emissions over ammonia are nearly the