FRICK, H.1,2, OBERSON, A.2, FROSSARD, E.2, WETTSTEIN, H.-R.3, BÜNEMANN, E. K.1,
1 Department of Soil Science, Research Institute of Organic Agriculture (FiBL), Switzerland; 2 Institute of Agricultural
Sciences, ETH Zurich, Switzerland; 3 Agrovet-Strickhof, ETH Zurich, Switzerland
INTRODUCTION
Animal manure is suspected to be a major source of nitrate leaching due to its variable N concentration and availability and the resulting difficulties in synchronizing crop N-demand and N-supply. In order to gain a better understanding of the fate of N from fertilizers in the soil-plant-system, N-uptake by the crop, residual N in the soil as well as losses via nitrate leaching and ammonia volatilization after the application of mineral fertilizer or animal slurry will be assessed and compared in a field study over a period of 2.5 years.
Thereby, we will use 15N-labelling approaches to address the following questions: i) how much N is lost
from animal manure by leaching, and ii) how to improve N use efficiency of animal manure and reduce leaching risk?
MATERIAL AND METHODS
Production of 15N-labelled cattle manure
15N-labelled manure will be produced shortly by feeding a young cattle with 15N-labelled ryegrass hay
(Lolium multiflorum) over 10 days. Thereby, urine and faeces will be collected separately allowing for
detailed analysis of 15N enrichment in the different components and their respective mineralization
potential in a column trial.
For the further experiments, urine and faeces will be mixed relative to their respective excretion amounts. Parts of the resulting slurry will be anaerobically digested following standard procedures for biogas production, or mixed with amendments such as biochar or nitrification inhibitors, respectively. Potential differences in leaching losses and nitrogen use efficiency of the processed manures will be assessed in column experiments.
Microplot field study
During the cropping season of 2018, we will apply the 15N-labelled cattle slurry to microplots in a similar
design as suggested by Jokela and Randall (1987), in amount and timing according to common agricultural practice. Thereby, our microplot study will be integrated with an on-farm trial in the canton Solothurn, Switzerland, focusing on different management strategies to prevent nitrate leaching.
Furthermore, we will establish microplots with either 15N-labelled mineral fertilizer, or without any N
fertilization as a control treatment with four replicates and on two different field sites, respectively (i.e. 24 microplots in total). In the subsequent years, microplots will be fertilized together with the surrounding fields with non-labelled fertilizers according to farmer`s practice.
Plant and soil (at least up to 90 cm depth) will be sampled upon harvest of each crop. Nitrate leaching will be assessed via so-called self-integrating accumulators (SIAs) (Bischoff, 2007), a method which
allows for measuring cumulative NO3-losses per area per cropping season. It is based on cylinders filled
with an ion exchange resin that will be installed underneath the undisturbed soil profile of the microplots in 100 cm depth and exchanged after the harvest of each crop. Additionally, losses via ammonia volatilization upon manure application in the field will be measured via acid traps for at least
will allow to trace the fate of the labelled fertilizer components and to establish a soil-system N- balance including leaching losses.
Source identification of nitrate in drainage water via natural abundance of 18O/15N
In addition to the above described microplot study, the natural abundance of 18O/15N in drainage
water, sampled with both suction cups and SIAs under five fields in the same region, will be assessed in order to identify sources of nitrate in agricultural drainage water (Stoewer, 2016).
RESULTS AND DISCUSSION
The 15N-labelled ryegrass hay has been produced both, in a greenhouse and on a field site by fertilizing
ryegrass with 15N-ammoniumnitrate and will be fed to a young cattle in February 2018. By June 2018,
we expect to have first results on the manure properties. For the field and column studies we hypothesize that i) nitrate in the groundwater has variable sources, ii) cattle slurry contributes considerably to nitrate leaching, but that iii) anaerobic digestion or manure amendments will increase N use efficiency, thus, reduce nitrate leaching from cattle slurry.
With this study we expect to gain valuable insights into the sources of nitrate in agricultural drainage water as well as the fate of nitrogen from cattle manure in the environment over several years, helping to develop strategies to optimize N use efficiency.
Acknowledgements The research project “NitroGäu“ receives financial support from the Swiss Federal Office of Agriculture and the canton of Solothurn.
REFERENCES
BISCHOFF, W.-A. 2007. Development and applications of the self-integrating accumulators: A method to quantify the leaching losses of environmentally relevant substances. PhD thesis, TU Berlin. JOKELA, W. & RANDALL, G. 1987. A nitrogen-15 microplot design for measuring plant and soil
recovery of fertilizer nitrogen applied to corn. Agronomy journal, 79, 322-325.
STOEWER, M. M. 2016. Vulnerability assessment of nitrate leaching on the regional scale using isotope techniques. Dissertation, Albert-Ludwigs-Universität Freiburg, 2015.
HIGH WATER TABLES DURING WINTER HAVE NO IMPACT ON WINTER WHEAT NITROGEN UPTAKE