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Nutrient loading helps Lutz seedling establishment in Iceland

Datum: 2012.02.28

Forestry in Iceland increased dramatically during the years 1990 – 2007, counting more than 5 million seedlings per year after 2003. With increased afforestation the surveillance of new plantings has increased and many of those have revealed high mortality of newly planted seedlings.

Harsh establishment conditions for Icelandic seedlings. Photo: R. Jónsdóttir

Low atmospheric deposition of nitrogen and slow decomposition caused by the cold climate is believed to be one of the major limiting factors of plantation establishment in Iceland.

In both foreign and Icelandic studies high internal nutrient status of seedlings has shown increased growth in newly planted seedlings and, in some cases, their survival. Therefore the aim of this study was to investigate the effects of nutrient loading in Lutz spruce seedlings (Picea x lutzii Littl.) during nursery rotation and on subsequent growth and survival in field.

Nutrient loading can be explained as luxury consumption of nitrogen in plants. This can occur in nature when the availability of N is abundant or when supply exceeds the capacity of plants to utilize N for growth. Nutrient loading in the nursery utilizes this ability of plants by inducing excessive consumption of nutrients towards the end of nursery cultivation when seedlings have stopped shoot elongation. The accumulated N can be stored and used later to support new growth.

One year old Lutz spruce seedlings were nutrient loaded using four fertilization regimes (four treatments) receiving in total 0, 7.8, 22.2 and 31.4 g N/m2 over a period of eight weeks (6th august – 27th September). The total biomass of loaded seedlings was similar to unloaded seedlings after the nursery culture, but the increase in N from the nutrient loading was 29%, 41% and 48% for loaded treatments. A delay in accumulation of frost hardiness during the autumn was not detected. The results from the nursery rotation show that nutrient loading in Lutz spruce is possible, late in season, without causing bud break or delay in accumulation of frost hardiness.

To investigate if the internal N status of the seedlings affected growth, survival and N content after one growing season in field, the seedlings were planted at two field trials (A and B), with or without field fertilizer. After one growing season loaded plants showed more growth with increased loading and the fertilized plants grew better than unfertilized (fig 1).

Fig. 1. Average (±SE) dry weight of biomass above ground for Lutz spruce seedlings exposed to different nutrient loading treatments and planted in the spring with (filled bars) or without (empty bars) field fertilization at sites A and B. Different letters above the bars indicate significant differences between loading treatments at each site.

Fig. 2. The colour of unfertilized (left) treatments compared with fertilized (right) indicated nutrient deficiency. Photo: R. Jónsdóttir

This was also the case concerning N content after one growing season. The N content in loaded treatments was more than in unloaded but fertilized treatments had the most N content. The importance of fertilization at planting was well demonstrated in the study. The colour and N content of unfertilized treatments, compared with fertilized, indicated nutrient deficiency (fig. 2).

Survival was not affected by the nutrient loading after the first growing season, but fertilizing significantly decreased the damage caused by Otiorhynchus larvae in heath land. It was concluded that loading might provide an additional input for faster plantation establishment during the first crucial growing season after planting. Additional observations will be made after three growing seasons in field to investigate if nutrient loading will increase long term survival rates.

The author Rakel J. Jónsdóttir works at Norðurlandsskógar, an afforestation project in Northern Iceland. The study was carried out as a master thesis at the Swedish University of Agricultural Science (SLU), with support from NordGen and others. The title of the thesis was “Effects of nutrient loading in Lutz spruce seedlings (Picea x lutzii Littl.) during nursery rotation and on subsequent growth in field”.

The whole master thesis can be found here: http://stud.epsilon.slu.se/3206/1/Jonsdotter_R_110902.pdf