笔者通过对3年生的杉木低产林幼林进行施磷肥试验，试图研究杉木低产林幼林生长量与磷肥施肥量之间的回归关系。结果表明：杉木低产林幼林生长量与磷肥施肥量之间的关系符合一元二次抛物线方程，反应曲线为典型凸形曲线，即生长量各指标均存在1个峰值。峰值以前，生长量各指标随着磷肥施肥量的增加而上升；峰值以后，生长量各指标随着磷肥施肥量的增加而下降。根据回归模型方程式求解，得到树高、地径生长量最大时对应的磷肥施肥量分别为0.098 kg、0.100 kg，对应的最高理论树高、地径分别为1.48 m、3.15 cm，分别较对照提高了49.5%、37.6%。

To reveal the regression effect between the sapling increment and the rate of P application, an experiment of phosphorus fertilizer was conducted in 3a low-yield young Cunninghamia lanceolata forest. The conclusions have been showed as follows: a parabolic trend equation was efficiently affected the relationship between the increment and the application amount, which showed a typical convex curve and one peak each index of increment reflected. Each index of increment rose with the increase of P fertilizer amount before the crest, and turned to degradation with the increasing of fertilizer application after the peak. According to the results, 0.098kg and 0.100kg per tree of P fertilizers were applied to trees which average height and base diameter was corresponded to the maximum respectively, the greatest height and base diameter in theory were 1.48m and 3.15cm, and respectively increased by 49.5% and 37.6% were compared to the comparison’s.