Ecosystem response to fertilizer application in grasslands: what can tell us long-term experiments?

Eingeladen durch Dr. Camilla Wellstein, Biogeography.

Organic as well as mineral fertilizers were used for centuries to improve quantity and quality of forage produced on permanent grassland. In many regions, application of organic fertilizers on farm land resulted in creation or in enlargement of oligotrophic plant communities highly valuated by nature conservation today. Industrial production of synthetic fertilizers started in the middle of the 19th century and since that time, long-term fertilizer experiments were established. Ten grassland experiments at least 40 years old are still running in Austria, Czech Republic, Germany, Great Britain, Poland and Slovakia.
Our findings demonstrate that short and long-term effects of fertilizer application on plant species composition differ substantially. In contrast, short-term experiments cannot to be used to predict long-term effects. On oligotrophic soils, highly productive species supported by short-term N fertilizer application can completely disappear under long-term N application whilst other nutrients such as P become limiting. Under P limiting conditions, species characteristic for low productive grasslands (sedges, short grasses and some orchids) can survive even under long-term N application. It is more likely that enhanced P soil content causes species loss than N enrichment. Residual effect of fertilizer application differs substantially among individual types of grassland and nutrients applied. Decades long after-effects of Ca and P application were revealed in alpine grasslands under extreme soil and weather conditions decelerating mineralization of organic matter. In extreme cases, resilience of the plant community after long-term fertilizer application can take more than several decades. Changes in plant species composition may even be irreversible. At lower altitudes with less extreme soil and climatic conditions, residual effect of fertilizer application is generally substantially shorter. From the comparison of long-term vs short-term nutritional effects, it was concluded that long-term fertilizer experiments are irreplaceable as many existing models and predictions can be validated only by means of long-term manipulation of plant communities and their continuous observation and documentation.
In conclusion, I will give examples of how to apply forward-looking grassland research on existing long-term experiments and explain the extraordinary value that is provided by plant-soil-environment equilibrium.

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