1. Effects of a raised water table on greenhouse gas emissions and celery yield from agricultural peat under climate warming conditions
Magdalena Matysek¹, Steven Banwart², Jonathan Leake¹, Donatella Zona¹
Department of Animal and Plant Sciences, University of Sheffield, UK University of Leeds, UK
Background
40% of peatlands in the UK have been drained for agricultural use.
Cultivation of peat soil requires drainage as most crops are intolerant of root-zone anoxia: this leads to creation of oxic conditions in which organic matter becomes vulnerable to mineralisation by aerobic microorganisms.
The position of the water table is credited to be of key importance in determining the rate of mineralisation of organic matter: its lowering is expected to increase the flux of CO2 and decrease emissions of CH4.
There is a lack of studies which attempt to find water table level that strikes a balance between crop yield and greenhouse gas production.
Rising temperatures should accelerate the rate of organic matter mineralisation, which is expected to lead to higher emissions of greenhouse gases as well as enhanced plant growth due to better availability of nutrients.
3. Results
Wet aboveground biomass was significantly lower in the -30 cm water table treatment by 19%. The elevated (+5°C) temperature had no significant effect on wet aboveground yield (Figure 1).
Mean soil respiration from the elevated temperature treatment was significantly higher by 25%. Mean soil respiration was significantly higher by 31% from the -50 cm water table treatment (Figure 2).
Mean CH4 emissions were unaffected by the temperature and water table treatments (Figure 3). *
2. Research design
64 peat soil cores (Picture 1) were taken from a field in Methwold Hythe, Norfolk, UK (Map 1).
The experiment lasted 11 weeks. To simulate the conditions in field, the temperature was being raised each week from the base temperature of 17°C
(22°C in the elevated temperature treatment) until it reached 20°C (25°C in the elevated temperature treatment) in week 6.
The treatments administered were:
- Water table at two levels: -30 cm and -50 cm
- Temperature at two levels: ambient and elevated (+5°C)
- Planting and no planting
CO2 and CH4 measurements were taken once a week with an LGR Ultra Portable Gas Analyser.
At the end of the experiment, celery plants were harvested, dried at 80°C and weighed.
Statistical analysis was performed in R Studio with the use of linear and linear mixed effects models.
Linear mixed effects models were run using the lme4 package. *
Map 1 *
Figure 1
Figure 2
Figure 3
Picture 1
4. Conclusions
Lower wet aboveground biomass from the -30 cm water table treatment suggests that nutrient limitation was present: the -50 cm water table level facilitated root expansion, which allowed for better nutrient mining.
Higher CO2 emissions from the elevated temperature treatment point to increased rates of organic matter oxidation by soil microorganisms. Higher CO2 emissions from the -50 cm water table treatment suggest that a large portion of microbial decomposition occurred in the zone between -30 cm and -50 cm.
The lack of effect of the water table rise on CH4 emissions indicates that a water table of -30 cm was enough for complete oxidation of methane. A higher temperature might have affected methanotrophic and methanogenic microbial communitiesto to the same extent.
Raising the water table to -30 cm would reduce C loss from temperate peats used in horticulture. A +5°C warming is likely to increase summer peat CO2 emissions.
Acknowledgements:
I would like to thank Simon Benson (University of Leicester), Irene Johnson (University of Sheffield), Jörg Kaduk (University of Leicester), Owen Hayman (University of Sheffield), Samuel Musarika, Susan Page (University of Leicester) and Alan Smalley (University of Sheffield).
This research was funded by the Grantham Centre for Sustainable Futures.