Low nitrogen losses with a new source of nitrogen for cultivation of conifer seedlings

Losses of nitrogen (N) when cultivating plants may cause a number of adverse environmental effects. N losses from conifer nurseries, for instance, may have a considerable impact on the local environment, and studies indicate that the bulk of added N is not recovered in the cultivated plants. This study was conducted to obtain insight into the causes of the low recovery and to test an alternative N fertilizer. Hence, growth of the economically important Scots pine (Pinus sylvestris (L).) seedlings and the recovery of different forms of added nitrogen (N) were investigated in a greenhouse experiment. Containerized seedlings were grown in peat for one summer, with two different N fertilizers, one organic (arginine) and one inorganic (a commercial fertilizer (CF) containing a mixture of ammonium and nitrate) each at an N concentration of 3 mM. At the end of the growth period, some seedlings were labeled with solutions containing either U-[13C6], [15N4]-arginine, (15NH4)2SO4, or K15NO3 supplied to the growth substrate. Labeled seedlings were harvested 1 h, 5 days, and 19 days after tracer addition, and the recovery of each added nitrogen source in both the seedlings and the growth substrate was measured. The retention of the three N forms during discharge of solutions from the growth substrate, peat, was tested in a separate experiment. Arginine-fed seedlings grew better and had higher needle N concentrations than the CF-fed seedlings. Isotopic data showed that the arginine treatment gave significantly higher N recoveries (80%) compared to the CF treatment (50%). The low recovery of N in the CF treatment was largely due to very low recovery (30%) of NO3- -N. The retention of the different N forms during discharge of solutions from the growth substrate was highest for arginine, somewhat lower for NH44+, and very low for NO3-. The high rate of seedling growth and the small nitrogen losses observed when using arginine suggest that this amino acid may be an efficient and environmentally favorable N source for cultivating conifer seedlings.