Leaching of Mineral Nitrogen and Available Phosphorus during Culture of Bareroot Larix olgensis Seedlings under Native Fertilizer Management in Northeastern China

In order to study potential contamination risk caused by leaching from bareroot seedling nursery to local ground waters, leaching of mineral nitrogen (N) and available phosphorus (P) was quantified in production of bareroot Changbai larch (Larix olgensis) seedlings, which is a common and economical tree species for afforestation and regeneration in North-eastern China. Experiment with 5 fertilization treatments: 0 (CK), 132 (T1), 326 (T2), 450 (T3), and 652 (T4) kg ha^-1 using locally purchased diammonium phosphate was (DAP) as fertilizer (18 % N, 46 % P₂O₅) was conducted under native management on early April, 2009, followed by 2 investigations on July 2 and September 21, 2009 respectively. Significant leaching of both N and P, on 2 investigating dates, across 3 soil layers, under different fertilization treatments was found respectively. Approximately 460 to 630 ka ha^-1 mineral N and 510 to 800 ka ha^-1 available P was leached respectively to soil layers beneath 20 cm in depth, and totally leaching amount rose with the increment of fertilizer doses. Result of nutrient uptake efficiency (NUE) concerning nutrient content in basal soil and fertilizer showed that until September 21 only 15 to 25 % N and 1.5 to 4 % P approximately was absorbed by seedlings. Consequently, treatment T1 with 23.76 kg N ha^-1 and 60.72 kg P ha^-1 applied was concluded to be recommended in its relatively better impacts on leaching reducing, but local fertilizer protocal was essentially suggested to be improved as well.