There was a large variation of the ratio, between average needle boron content and average needle nitrogen content for the autumn of 2008, between locations and treatments (Figure 12). At both Furuberget and Hällberget, the significant difference between treatments were the same as the average boron content result (Figure 11), but at Näverberget there was a difference. There, the ratio at C area was not significantly separated from ratio at BioB and M areas. The ratio at BioB area was not significanlty different to the ratio at BioA area, both with values at around 0.2%, while C and M areas had values around 0.3%.
Figure 12: Needle boron/nitrogen ratio in the autumn of 2008. The ratio was compared between treatments and target values are marked with a dotted line. Similarities and significant differences (p<0.05) are indicated by letters for each treatment and location.
25 All ratios at C areas were higher than ratios at treated sites at Furuberget (Figure 13a). The ratios at C areas were all above the target value. Ratios for BioA, BioB and M areas were not significantly different from each other for any of the nutrient/nitrogen ratios in 2008, except the Mg/N ratio, where the ratio for M area was higher. In 2012, the ratios for P/N at BioA and BioB areas were not significantly different from each other. The K/N ratio at C area was 35 and only significantly higher than the ratio at M area, while all other treatments did not differ from each other. The three fertilized sites showed K/N ratios slightly below the target value. The Ca/N ratio at M area was around 26 and was significantly lower than the ratio at all other sites. The Mg/N ratio at M area was also lower than the ratio at the other locations, with a ratio around 7.
At Hällberget in 2008, the P/N result showed that ratio for C area was only similar to ratio at BioA area, but higher than ratios at BioB and M areas (Figure 13b). The P/N ratio for BioA area was also similar to the ratio at BioB area. The ratio at M area was significantly lower than ratio at all other treatments, with a ratio close to 9. For the three other ratios in 2008, C areas had significantly higher ratios than the other treatments. The K/N ratio at BioA area was higher than at M area with a ratio of almost 35, while the ratios at BioB and M areas were both around 30 and not significantly separated.
For both Ca/N and Mg/N ratios, BioA and BioB areas were not significantly different at close to 25 and 4 respectively, while ratio at M area was significantly lower than BioA and BioB areas, at around 20 and 3 respectively. All ratios at C areas and most ratios at fertilized sites were above the target values. In 2012, the P/N result showed that the ratio at C area was close to 10 and only significantly lower than the ratio at BioA area. The P/N ratio at BioA, BioB and M areas are all significantly different from each other. The K/N, Ca/N and Mg/N ratios at C areas were higher than the ratios at fertilized sites, and the ratio at M area was significantly higher than at BioA and BioB areas. The two latter were not significantly different from each other. The K/N ratio at M area was slightly lower than the target value, while the ratio at BioA and BioB areas were less than half the target value.
P/N, K/N and Mg/N ratios at C areas in 2008 were significantly higher than the ratios at treated sites at Näverberget (Figure 13c). The Ca/N ratio at C area was around 24 and only higher than the ratio at BioB and M areas, while BioB and M areas had ratios around 17. The ratio at BioA area was not significantly separated from the ratio of any other treatment. Most results in 2008 were similar to the results of Furuberget in 2008. In 2012, there was no significant difference between treatments for the P/N, K/N or Ca/N ratios. The Mg/N ratio at C area was higher than ratio at BioA and BioB areas, but not higher than at M area. The ratio at M area was not different from ratio at BioA or BioB area. In 2012, all K/N ratios are slightly lower than the target value.
26
Figure 12: Needle nutrient/nitrogen ratio in the autumn of 2008 and 2012 at a) Furuberget, b) Hällberget and c) Näverberget.
Each ratio was compared between treatments and target values are marked with a dotted line. Similarities and significant differences (p<0.05) are indicated by letters for each ratio and treatment.
a
b
c
27
Growth increase versus nitrogen content
The growth increase between years 2007-2012 is plotted against the needle nitrogen content measured in 2008 at Furuberget (Figure 13) and Näverberget (Figure 15). At Hällberget, the increase between years 2007-2009 was used instead, but with the same nitrogen values (Figure 14). At both Furuberget and Näverberget, the C samples were clearly separated from treated samples which in turn did not appear to be clearly separated from each other. For both these locations, the growth increase was lower when the nitrogen levels were lower. The growth result for C area at Hällberget was not separated from the other treatments, but the nitrogen concentrations were lower at C areas than at fertilized areas.
Figure 13: The growth increase between years 2007-2012 was plotted against the needle nitrogen content measured in the autumn of 2008 at Furuberget.
Figure 14: The growth increase between years 2007-2009 was plotted against the needle nitrogen content measured in the autumn of 2008 at Hällberget.
Figure 15: The growth increase between years 2007-2012 was plotted against the needle nitrogen content measured in the autumn of 2008 at Näverberget.
28
Discussion
Since the ICP analyses were performed by different people and different machines the two different years, it is hard to compare the results with each other. It is therefore easier to compare how the different treatments have affected the amount of one element at one time point and also compare the results from the different locations. Since the nitrogen analyses were performed by qualified people both times is can be assumed that these results are more comparable. There was a large difference in total nitrogen application for the M, BioA and BioB treatments at 150, ~600 and ~800 kg N/ha respectively. Because of this, it is very hard to compare the results directly. If Bio Nutrient fertilizer had been applied in 150kg N/ha just like Mineral Nutrient, then possible differences in effects on either nutrient status or tree growth could have been attributed directly to one of the treatments. Now, differences might be due to either the fertilizer or the large difference in nitrogen addition.