供氮方式及水平对米老排苗期生长动态的影响1）

为探索不同施肥方式及施用量对米老排（ Mytilaria laosensis Lecomte）苗期生长动态的影响，确定其苗期施肥的最佳供氮方式及水平，采用等量施肥（C）、阶段递增施肥（A）和修正指数施肥（ME）3种方式，以0 mg·株－1为对照，分别设置50、100、200、400、600 mg·株－15个氮素水平开展米老排幼苗盆栽试验。结果表明：3种方式下中低剂量施肥有利于米老排后期生物量积累，高剂量施肥导致其积累停滞或下降。低剂量修正指数施肥（50 ME和100 ME），苗高在整个试验期间保持“J”型高速增长状态，地径呈直线式生长；其他处理苗木在苗高、地径生长和生物量积累上均因后期施肥不足或肥料积累而较前期生长有不同程度减缓。此外，所有施肥处理在不同程度上提高了收获时米老排的苗高、地径和总生物量，其中100 C的苗高达到最大（44．4 cm），是对照的259．0％；200 C的苗木地径（3．92 mm）、生物量（4．75 g·株－1）均为最大，分别是对照的142．5％、360．6％；200 C的质量指数最大，其次是100 ME和50 ME。综合上述形态指标评价研究结果得出，米老排苗期最佳供氮方式为等量施肥法，最佳供氮水平为200 mg·株－1。

Effects of Different Nitrogen Loading Regimes and Levels on Growth Dynamic of Mytilaria laosensis Seedlings

A fertilization trial under three nitrogen loading regimes including conventional ( C) , phase-additional ( A) and modi-fied-exponential regime (ME) was conducted with five nitrogen levels (0, 50, 100, 200, 400 and 600 mg· seedling-1), 0 mg· seedling-1 severing as the control to study the effects on growth dynamic of Mytilaria laosensis seedlings and deter-mine the optimal nitrogen loading regime and amount .The fertilization of low doses under three regimes benefited the bio-mass accumulation for M.laosensis in late growth season, while retardation or decline of biomass accumulation was caused by fertilizing of high dose .Seedlings treated with 50 ME and 100 ME remained rapid height growth during the whole experi-ment, showing a “J” shape growth curve , and diameter was on a linear growth curve .Seedlings with residual treatments were observed and decreased in seedling height , ground diameter and total biomass accumulation due to insufficient or ex-cess fertilization compared with the early stage .In addition , fertilization treatments improved all the measurement parame-ters of seedlings at harvest , of which seedlings height treated with 100 C reached the maximum of 44.4 cm and was 259.0%of the control, and the maximum ground diameter (3.92 mm) and biomass (19.00 g· seedling-1) of 200 C were 142.5%and 360.6%of the control , respectively .Seedling of 200 C reached the highest in the quality index , followed by 100 ME and 50 ME.By a comprehensive evaluation of morphological indices , the optimal nitrogen loading regime and amount was 200 mg· seedling-1 under conventional fertilization .