An ASABE – CSBE/ASABE Joint Meeting Presentation
Paper Number: 141899456
Greenhouse Gas Emissions from Drip Irrigated Fields K. P. Edwards1, C. A. Madramootoo1, J. K. Whalen2, V. I. Adamchuk2, A.S. Mat Su1, H. Benslim2 Written for presentation at the 2014 ASABE and CSBE/SCGAB Annual International Meeting Sponsored by ASABE Montreal, Quebec Canada July 13 – 16, 2014 Abstract. Irrigation practices change the soil moisture in agricultural fields, and in turn influence the emissions of greenhouse gases. A two year field study was conducted to assess the emissions of CO2, and N2O from surface drip and subsurface drip irrigated tomato fields in Southwestern Ontario, Canada. Gas fluxes were obtained through the static chamber method, taking samples every 15 minutes over a one hour time period. Soil moisture and temperature were measured and used to interpret the gas emissions. A peak mean N2O flux at 405 µg m-2 h-1 was observed in the surface drip irrigation treatment on 8 July 2013, following a rainfall event. Most N2O fluxes which occurred during the growing season were around 50 µg N2O-N m-2 h-1 in both treatments. Both the lowest CO2 mean treatment fluxes (12 mg m-2 h-1) and highest (120 mg m-2 h-1) were observed in the surface drip irrigation plots. Seasonal emissions of CO2 were significantly greater in surface drip plots than subsurface drip plots in 2013, but not in 2012, and this is likely attributed to soil temperature differences. Generally, there was no significant difference in soil moisture between the types of drip system. Consequently, there were only a few days which showed significant differences between treatments for the gas fluxes throughout the two growing seasons. Overall, neither subsurface drip irrigation nor surface drip irrigation has a major effect on the emissions of greenhouse gases from the tomato fields in this study. . Keywords. Carbon dioxide, nitrous oxide, flux, surface drip irrigation, subsurface drip irrigation/
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Department of Bioresource Engineering and Department of Natural Resource Sciences, McGill University, SainteAnne-de-Bellevue, Quebec, Canada,. Corresponding author: Kerri Edwards, Department of Bioresource Engineering, Macdonald Campus of McGill University, 21, 111 Lakeshore Rd, Sainte-Anne-de-Bellevue, Quebec, H9X 3V9; phone: 519-546-8322; e-mail:
[email protected]
Introduction Soil moisture is a known driver of emissions of N2O and CO2 to varying degrees. Many studies have shown that an increase in soil moisture increases N2O emissions from soils (Schaufler et al., 2010; Lee et al., 2009; Gregorich et al., 2005; Smith et al., 2003; Ball et al., 1999). Irrigation causes increases in GHG emissions from fields by increasing the soil moisture. Drip irrigation, which provides water directly to the soil in smaller quantities over a longer period of time of application, has reduced emissions from furrow irrigated crops. Surface drip irrigation N2O emissions are up to 70% lower than those observed from furrow irrigation in melon crops (Sánchez-Martín et al., 2008). Kallenbrach et al. (2010), in a study out of California, found N2O emissions in the growing season from subsurface drip irrigation to be half of those from furrow irrigated tomatoes. Differences between furrow and subsurface irrigation likely resulted from the high denitrification rates caused by furrow irrigation. Conversely, CO2 emissions from furrow and subsurface drip irrigation were similar with no significant difference (Kallenbrach et al., 2010). A comparison has not been made between the emissions from surface drip irrigation and subsurface drip irrigation. The objective of this study is to compare N2O and CO2 emissions between tomato fields with subsurface drip irrigation and surface drip irrigation.
Methods Site Description The research site is located in Leamington, Ontario, Canada on Palichuk Farms (Latitude 42° 5’ N, Longitude 82° 34’ W). Two different fields were used in the experiment since the tomatoes were in rotation with other crops. In 2012, an 8 ha field was used, and in 2013, an adjacent field of 10 ha was used. At both field sites, the soil is a loamy sand (82.0% sand, 9.2% silt, 8.8% clay in 2012; and 81.2% sand, 10.5% silt, 8.3% clay in 2013). In 2012, rainfall over the growing season totaled 46 mm less than the 30 year average, and in 2013, rainfall was 53 mm higher than the 30 year average from the Weather Network station in Kingsville, Ontario (Farmzone, 2013). Processing tomatoes (Heinz 9553) were transplanted on May 22nd and 23rd, 2012 and on May 29th, 2013 into the respective fields at a density of 32 500 plants/ha. The tomatoes were double row planted at a spacing of 42 cm between rows, on 1.5 m raised beds. Harvest occurred on September 7th and September 14th in 2012, and September 13th and September 17th in 2013, for the surface drip irrigation and subsurface drip irrigation plots, respectively. Experimental Design The experiment was designed to compare GHG emissions between surface drip irrigation and subsurface drip irrigation. Five replicate static gas chambers, 25 m apart, were used in each treatment. The plots were located 6 beds apart (10.5 m) from each other, and chambers were parallel to one another between the plots. In 2012, three rows of each type of irrigation were used in order to separate the two treatments. In 2013, due to unfavourable spring conditions, the drip tape was not buried into the ground for any of the rows, but instead was buried beneath the chambers. The same field layout was used during both years, though the plot locations differed between two fields. Irrigation In 2012, the surface drip irrigation tape was laid in the field on June 14th, with the subsurface drip tape already present in the field from previous years. In 2013, the whole field was outfitted with surface drip irrigation on June 25th and the drip tape for the subsurface drip irrigation plot area was buried to the same depth as in 2012, on July 4th. The drip tape for both years was a 1.6 cm NetafimTM tape through which the water flows at 189 litres/min/ha at a pressure of 103.4 kPa. The distance between emitters is 0.30 m. Consistent irrigation began on July 1st and continued until August 18th, 2012. Irrigation was run for three hours a day, unless rainfall had occurred. There were 37 days within that 48 day time period when the fields were irrigated. In the 2013 growing season. Irrigation was run for two days in July, on July 15th and July 27th. Then
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[email protected] or 269-932-7004 (2950 Niles Road, St. Joseph, MI 49085-9659 USA). 2014 ASABE – CSBE/SCGAB Annual International Meeting Paper
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more consistent irrigation began on August 10th continuing to September 9th, with a few breaks due to rain. In 2013, there was a total of 24 days of irrigation. N2O and CO2 Sampling A static vented non-flow through chamber technique was used for GHG sampling (Livingston & Hutchinson, 1995). The gas was extracted to exetainers every 15 min for the course of one hour, totally 5 samples. Samples were sent to McGill University for analysis with a gas chromatograph 450-GC System (Bruker corp., Bremen, Germany). A FID (flame ionization detector, set at 300°C) was used for CO2 measurement and an ECD (Electron capture detector, set at 350°C) was used for N2O measurement. The greenhouse gas concentrations were calculated as outlined by Livingston & Hutchinson (1995). Data where the CO2 was below 300 ppm was removed from the analysis. As well, due to some septa problems in 2013, any data below a value of 0.15 ppm N2O was removed as it can’t be verified. The change in gas concentration with change in time was determined by taking ten slopes (all of the different ones from the five sampling points). The median of these ten slopes gave the best estimation of the overall change that would have occurred over the hour period, while taking out any outliers which may have occurred (Mat Su et al., 2013). On days where the CO2 flux was zero or a negative value was produced using the ten slope method, this particular flux was removed as it would not have occurred in the field. Based on the fact that there was likely an error somewhere between sampling and the ten flux calculations, both CO2 and N2O data were removed. The mean flux calculated from the five chambers on each plot was calculated to compare treatments. Soil Moisture and Soil Temperature Measurements The soil temperature at each of the chambers were recorded with the Checktemp®1 temperature probe once per sampling time per plot (HANNA Instruments Inc., Woonsocket, RI). Soil moisture was also recorded. At each chamber, four soil moisture readings were taken with a ML2x ThetaProbe (Delta-T Devices Ltd, Cambridge, England), one from each side of the chamber (on the outside) which were averaged together for an estimate of the soil moisture within the chamber. This was done at each chamber once per plot. Statistical Anaylsis In order to compare the fluxes from the subsurface and surface drip irrigation, a paired t-test was used to test the means from the five chambers of each treatment for CO2 and N2O on every sampling date. Significance was determined at the p = 0.05 level.
Results and Discussion Soil Temperature and Soil Moisture Differences in the two types of irrigation plots in terms of soil temperature revealed that the surface irrigated plots were consistently 1 to 2°C higher than the subsurface drip irrigated plots. Soil temperatures over both season ranged between 10 and 30°C. The average soil moisture between the plots did not vary greatly, and were mainly between 15 and 20 % volumetric water content. Both treatments tended to show similar average soil moistures ranging between, although generally the recorded soil moisture was greater in the surface drip irrigation plots. This is likely due to the shallow depth of the subsurface drip tape and the amount of capillary rise occurring (Jaria & Madramootoo, 2013).
N2O Most values during irrigation in both years were between 0 – 50 µg N2O-N m-2 h-1, seen in Figure 1 and were at the lower end of flux values compared to peaks which followed rainfall events. The N2O flux values observed over the two years are similar to the fluxes observed by Kallenbach et al. (2010) for subsurface drip irrigated tomatoes, where most of their observed fluxes in the growing season were below 50 µg N2O-N m-2 h-1, but had peaks of up to 450 µg N2O-N m-2 h-1. Only two days showed a significant difference (p= 0.05) between the two treatments for the N2O fluxes in 2012. The first day, after the harvest, was likely attributed to the differences in harvesting dates of the two plots and the resultant flush of emissions being different. On the final sampling date of October 15th 2012, the surface drip plot had significantly greater fluxes than the subsurface drip plot. Although the surface drip plot exhibited a 2014 ASABE – CSBE/SCGAB Annual International Meeting Paper
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significantly higher soil moisture, there were other times throughout the season where this occurred, but no significant difference in the fluxes was noted. In 2013, only one day, May 23rd, showed a significant difference between fluxes from the two treatments. This was the sampling prior to planting. During the sampling of the subsurface drip irrigation plot, and before sampling of the surface drip irrigation plot, the crop producer fertilized the surface drip irrigated plot. Although the machinery was lifted to accommodate the chambers, the solid fertilizer placed in the area of the chamber shortly before sampling the surface drip plot could have accounted for the significant difference in fluxes between the two sites. In both years, the soil moisture between the two plots were similar. This could be the main reason we do not see significant differences between the irrigation treatments. Another potential reason for lack of significant differences in fluxes, on most days, could be the high variability of the micro-organism populations which can change the fluxes within a small area, creating high variability in the fluxes recorded from each of the chambers regardless of treatment (Gregorich et al., 2005).
N2O flux (ug N2O‐N m‐2 h‐1)
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Date Figure 1. Nitrous oxide fluxes in 2012 and 2013 from subsurface drip irrigation and surface drip irrigation treatments
CO2 In both years, the peak fluxes occurred in the middle of July with fluxes reaching around 120 mg m-2 h-1 (see Figure 2). The results observed over these two years are similar to the CO2 fluxes observed in tomato fields by Kallenbach et al. (2010) and Burger et al. (2005). Kallenbach et al. (2010) observed some peaks of CO2 reaching over 200 mg CO2-C m-2 h-1, which is higher than any observed on this field, likely due to the warmer temperatures which occur in California as opposed to Ontario. 2014 ASABE – CSBE/SCGAB Annual International Meeting Paper
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Only one date in 2012, the last sampling date, showed a significant difference between the fluxes from the two treatments. In this case, the surface drip irrigation plot had significantly larger fluxes than the subsurface drip irrigation plot, which was consistent with N2O observation. The main reason for the significant difference on this date was the consistency of the fluxes from the five chambers in each plot. This is not seen in most of the season, and the fluxes on this date are some of the lowest fluxes overall, as seen in Figure 4. In 2013, there were five days where a significant difference in the CO2 fluxes between the treatment plots occurred. In all five cases, the fluxes from the surface drip irrigation plot were significantly higher than those from the subsurface drip irrigation plot, with three of them occurring during the irrigation period. The five days were: June 19th, July 24th, August 14th, August 21st, and August 29th. The change in soil temperature between the two plots over these dates is higher than most of the other days in the season, which is likely the cause of the increased fluxes. These days show some of the highest temperature changes, with most being greater than 1°C, likely leading to the significant difference in CO2. Other studies have shown that soil temperature has a stronger relationship with CO2 than soil moisture (Schaufler et al., 2010; Kallenbach et al., 2010; Lessard et al., 1993). Hence soil temperature is the likely reason for the difference in fluxes between the two plots, as opposed to the irrigation treatment. 160
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Figure 2. Carbon dioxide fluxes in 2012 and 2013 from subsurface drip irrigation and surface drip irrigation treatments
2014 ASABE – CSBE/SCGAB Annual International Meeting Paper
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Conclusions Overall difference in fluxes of N2O and CO2 were found to be quite small between the subsurface drip irrigation and surface drip irrigation treatments. Some significant differences occurred in CO2 fluxes and are likely attributed to the differences in soil temperature, rather than to the different irrigation practices. Mean N2O fluxes and emissions were fairly consistent during the irrigation periods, between the surface drip irrigated plots and the subsurface drip irrigated plots. In conclusion the use of either subsurface drip irrigation or surface drip irrigation in tomato fields doesn’t have a significant effect on the emissions of N2O and CO2. Acknowledgements This project would not have been possible without funding and support of Agriculture and Agri-Food Canada. A special thanks also to Wayne Palichuk for the use of his farm and irrigation systems, and for his co-operation in allowing us to install the equipment and instrumentation in his fields. Finally I would like to thank Eduardo Ganem Cuendo whose help as the project coordinator was invaluable.
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