Impact of Soil Microbial Biomass and Fertiliser Source on Nitrogen Use Efficiency

Keywords: ¹⁵N, animal manure, DOC long-term field experiment, mineral fertiliser, nitrogen use efficiency, soil microbial biomass.

Global population is increasing exponentially and is forecasted to be about 9 billion in 2050. During the next years fertiliser consumption also will increase as food security has to be attained. Currently, fertiliser nitrogen (N) use efficiency is on average only 50% for mineral fertiliser and even lower for animal manure. Fertiliser N which is not recovered by crops or immobilised in the soil is lost from the soil-plant system and adversely affects the environment. Hence, one of the biggest challenges in agriculture is to increase production and at the same time minimising N losses. Organic farming generally is assumed to be environmental-friendlier than conventional farming. Due to the prohibition of synthetic fertiliser, organic farming depends on organic fertilisers whose availability to crops depends on microbial mineralisation and immobilisation processes. Microbial biomass and activity is usually higher in organically than in conventionally managed cropping systems. Using the DOC long-term field experiment as a model we analysed the impact of the soil microbial biomass on N use efficiency of animal manure and mineral fertiliser and on the fate of fertiliser N not taken up by crops in an organic and a conventional cropping system. Despite higher microbial activity in the soil of the organically than the conventionally managed cropping system the fate of fertiliser N was the same in both cropping systems, as shown by similar fertiliser N use efficiency by crops and similar recovery of fertiliser-derived N in the soil. This suggests that the two cropping systems have the same potential to emit N compounds to the environment.

C Bosshard¹, A Oberson² and J Mayer¹

¹ Agroscope Reckenholz-Tänikon, Reckenholzstrasse 191, 8046 Zurich, Switzerland.

² Institute of Plant Sciences, Group of Plant Nutrition, ETH Zurich, Switzerland.

24 pages, 4 tables, 1 figure, 84 references.