Efficiency of Prolonged-Release Mineral Fertilizers when Growing Scots Pine Seedlings with Closed Root Systems in Cell Packs

In Russia, given the observed trend of increasing demand for growing high-quality planting material of year-old Scots pine (Pinus sylvestris L.) seedlings with a closed root system, an increase in the planned share of them planted during reforestation up to at least 30% of the total volume comes off as natural. The objective of the study is to analyse starter mineral treatment via the means of prolonged-release fertilizers and to assess their effectiveness for growing year-old seedlings of P. sylvestris as regards their development rate and changes in their taxation and biometric indicators. The methods used were agrochemical analysis of soil, manual biometric counting of seedlings and statistical analysis. The object of the study is starter mineral treatment introduced into the cell packs (cassettes) with wet high-moor peat of high acidity. Starter mineral treatment using urea capsules allows achieving 98% seed germination, reducing the rate of calendar development of year-old P. sylvestris seedlings from the seeds of the XI forest seed region until they reach standard parameters with less thinning. Growing P. sylvestris seedlings with the introduction of potassium monophosphate, phosphate rock, encapsulated urea in doses of 0.0369, 3.7647, 0.1159 kg/m3, respectively, allows seedlings to reach the largest root collar diameter of up to 2.2 ± 0.4 mm before the age of one year. The use of encapsulated urea with hydroquinone for a total dose of 0.1162 kg/m3 stimulates the growth of seedlings in stem height the most, reaching 17.9 ± 1.4 cm. In the experimental variants, unlike in the control with “Aquarin 5” fertiliser and a 0.5 cm layer of pine sawdust, the formation of verticils was noted. The experimental variant using urea capsules is the most effective variant of starter application of mineral treatments. It allows to reach a stem height of 16.8 ± 1.4 cm and a root collar diameter of 2.2 ± 0.4 mm with the lowest thinning percentage equal to 16.7% of the control, up to 38.3%, after their random sampling for agrochemical analysis and removal of dead seedlings.