The effect of fertilizer nitrogen immobilization its release and soil nitrogen mineralization on grass yield of permanent swards in cool temperatures
Miki, N.; Takao, K.; Nishimune, A.
Bulletin of Hokkaido Prefectural Agricultural Experiment Stations 56: 39-50
Field and pot experiments which used an air conditioned room were conducted in order to determine the effect of fertilizer nitrogen immunobilization and it's release and soil nitrogen mineralization on grass yield of permanent swards in cool temperatures. These experiments were carried out in 5 swards in the pot experiment and 10 swards in the field experiment which were established in different years, and used 15N-labelled nitrogen in form of ammonium sulfate. The results obtained are summarized as follows: 1) Grass yield of old permanent swards which have been used for more than 7 or 8 years were obviously lower than 3 year old sward in cool temperature (less than 20-30 percent of the mean accumulated temperature) at 2nd and 3rd growth periods. 2) These resulted from the fate of fertilizer nitrogen and the amount of soil nitrogen supply were lower in old permanent swards than those in the 3 year old sward in both fields and pot experiments. 3) In the incubation experiment, the amount of immobilized fertilizer nitrogen in surface layer soil of the old permanent sward was larger than it of the 3 year old sward. Furthermore, in the old permanent sward, a release speed of immobilized fertilizer nitrogen was slower than the 3 year old sward in cool temperatures. It needed about 300-400.degree. C (accumulated temperature) in the 3 year old sward and more than about 500.degree. C in the old permanent sward. 4) The amount of mineralized soil nitrogen in the surface layer soil of the old permanent sward was affected strongly by temperature, in low temperature, it was lower in the old permanent sward than it was in the 3 year old sward. From these results, it was concluded that one of the reason which are responsible for the low grass yield of old permanent swards in cool temperature at 2nd and 3rd growth periods is a small supply of both fertilizer and soil nitrogen.