Trends in Dataset
To follow trends in both soils we used bar graphs to show changes in gas flux from all treatments. Non-tilled/unfertilized plots were considered to be control plots. As the figure 1 shows the highest CO2 emissions are from tilled-fertilized plots and the lowest are from non-tilled/unfertilized (control). What is attracting attention here is that gas emissions from all treatments increase drastically in July and decrease significantly in August. Maybe because of changes in temperature and precipitation.
Figure 1: Gas flux measurements from Chernozemic soil
Breton showed the same trend for all treatments from June to August. Like Ellerslie, CO2 emissions from non-tilled/unfertilized (control) were the lowest and from tilled/fertilized were the highest. Generally fertilization increased CO2 emissions from soil for both sites, but with a little difference. By comparison of both non-tilled/fertilized and tilled-unfertilized in both Chernozemic and Luvisolic soils we see that fertilization has a greater impact on CO2 emission from a Luvisolic soil. One reason for that is luvisolic soils are poor in organic matter, so fertilization has a more significant impact in terms of tillage operations. Also, CO2 emissions for all treatments from Ellerslie were higher than Breton because of difference in organic material content between Chernosemic and Luvisolic soils.
Figure 2: CO2 flux measurements from Luvisolic soil
ANOVA
Since data from both locations were normal and homoscedastic we chose to use ANOVA for our analysis. A two way (multi-factor) ANOVA was used to compare treatment levels.
Results of ANOVA for location, month, treatment, and their interactions are represented in table 1. By looking at this table it can be concluded that there is significant difference in gas flux measurements between two sites and at least between two months and two treatments. ANOVA showed a significant difference between measurements but it didn't say what two measurements were significantly different. So Tukey pairwise comparisons between months and treatments and also the interactions were done.
Results of ANOVA for location, month, treatment, and their interactions are represented in table 1. By looking at this table it can be concluded that there is significant difference in gas flux measurements between two sites and at least between two months and two treatments. ANOVA showed a significant difference between measurements but it didn't say what two measurements were significantly different. So Tukey pairwise comparisons between months and treatments and also the interactions were done.
Table 1: ANOVA table showing significant difference between measurements from two locations, months, treatments
Table 2 shows that some of treatment levels in Ellerslie and Breton have significant difference according to their adjusted p-value. In Ellerslie the only significant difference is seen between control and tilled/fertilized treatments. In Breton the difference between control/nontilled-fertilized, control/tilled-fertilized and tilled-fertillized/untilled-fertillized is highly significant. Obviously, the control and tilled-unfertillized plots in Breton and Ellerslie are showing significant difference.
Table 2: Tukey pairwise comparison between treatment levels in both sites
Table 3 is indicative of highly significance in difference between most of the months. Only measurements in Breton in July and August and also in June between Ellerslie and Breton are not significantly different.
Table 2: Tukey pairwise comparisons between months in both sites
Conclusion
According to the results yielded from ANOVA and pairwise comparisons it can be inferred that CO2 emissions from rich organic matter soils in Ellerslie are higher than poor organic matter soils in Breton. In both soils tillage along with fertilization increased CO2 emissions from both sites but in Breton fertilization itself showed higher degrees of gas flux. This conclusion is interesting because in soils which organic materials are so low such as Luvisolic soils; farmers should be more careful about the amounts of fertilizers they're using because it will increase the CO2 flux in those soils drastically. By doing only tillage in both soils the CO2 emissions were higher in Chernozemic soils rather than Luvisols because they were already rich in organic matter. Another result is indicative of this conclusion that without even having tillage and fertilization the gas flux was higher in Ellerslie. So presence of high amounts of organic matter in soil, per se can elevate CO2 emissions.
Following the results; it gets more clear that CO2 flux really increases from June to July and decreases from July to August in both sites except in Breton from July to August. So environmental factors such as precipitation, and temperature have effect on CO2 emissions because they aren't constant in the sequence of months during the growing season.
So our conclusions satisfied most our expectations and the final inferences are listed below:
1- Tillage reversal (doing tillage after a long period of no-till management) increases CO2 emissions from both Chernozemic and Luvisolic soils
2- Fertilization mostly increases CO2 emissions in soils which are poor in organic matter but it will exacerbate CO2 emissions from rich organic matter soils if used along with tillage.
3- Tillage reversal causes greater CO2 emissions from organic matter-rich Chernozemic soils than that from relatively organic matter poor Luvisolic soils.
Following the results; it gets more clear that CO2 flux really increases from June to July and decreases from July to August in both sites except in Breton from July to August. So environmental factors such as precipitation, and temperature have effect on CO2 emissions because they aren't constant in the sequence of months during the growing season.
So our conclusions satisfied most our expectations and the final inferences are listed below:
1- Tillage reversal (doing tillage after a long period of no-till management) increases CO2 emissions from both Chernozemic and Luvisolic soils
2- Fertilization mostly increases CO2 emissions in soils which are poor in organic matter but it will exacerbate CO2 emissions from rich organic matter soils if used along with tillage.
3- Tillage reversal causes greater CO2 emissions from organic matter-rich Chernozemic soils than that from relatively organic matter poor Luvisolic soils.
Disclaimer: All datasets, events and parameters have been manipulated and/or randomly generated.