Fertilization Effect of Nitrogen Combination with Phosphorus on Seedling Growth of Pinus yunnanensis

In order to accelerate the seedling growth of Pinus yunnanensis, nitrogen in combination with phosphorus has been tested by using 3×3 regression design and drawing the characteristics of Latin square and random array. The results showed that the relationship between the growth increment, biomass and the amount of nitrogen, phosphorus can be described by quadratic parabola, and every growth index has a maximum value. The growth is improved as the increasing of amount of nitrogen and phosphorus in front of the maximum value, and the growth decreased as the increasing of amount of nitrogen and phosphorus in back of the maximum value. The optimum dosage and the optimum proportion of nitrogen and phosphorus under the highest growth indexes are calculated by the fertilization equations, and the highest growth indexes of height, basal diameter, root system, the biomass indexes of stem and leaves are 8.20, 0.55cm; 1.374, 0.177,2.295g respectively. And the corresponding increments are 25.3%, 29.1%, 151.6%, 21.2% and 175.2% respectively more than that of the control, and the corresponding nitrogen dosage are 0.17, 0.16, 0.20, 0.15, 0.19g per kilogram soil and the phosphorus are 097,1.04, 0.99, 0.88 and 0.99g per kilogram soil, and the corresponding proportion of nitrogen to phosphorus are 1∶5.70, 1∶643, 1∶5.03, 1∶5.88 and 1∶5.20 respectively. In which the leaf biomass was obviously improved by fertilization, but there are different response rules by varied growth indexes to different dosages and proportions of fertilizers. For example, the higher amount of nitrogen is more beneficial to the development of root system and the accumulation of leaf biomass, the higher amount of phosphorus is more helpful to the diameter and the height growth of the stems.