Response of cone yield in clonal seed orchard of Larix kaempferi to long-term nitrogen, phosphorus and potassium formula fertilization

  Objective  This paper aims to reveal the effects of different proportions of nitrogen (N), phosphorus (P) and potassium (K) fertilization on the cone yield of Larix kaempferi seed orchard and the consequent of long-term continuous fertilization, and provide a basis for the management of larch seed orchard.

  Method  The ramets of normal seed bearing clones in L. kaempferi seed orchard built in 1989 were taken as the object, using randomized block trial design, the most suitable fertilization proportions affecting their cone yields were profiled by conducting comparative tests for three consecutive years from 2008, with the fertilization level of 2.5 kg/plant, using three kinds of formula fertilizers with a combination of nitrogen, phosphorus and potassium. The effect of long-term (8 years) continuous fertilization on cone yield was analyzed with three fertilization levels in 8 years (2.5, 5.0, 7.5 kg/plant) under the most suitable fertilization proportion from 2011.

  Result  (1) Fertilization with different proportions can significantly increase the yield of cones with significant differences (P < 0.05). Among them, N₁P₂K₁ was the best proportion, having the highest cone yield of mother plant, reaching (97.63 ± 0.87) kg/plant , which was higher than control, N₁P₂K₁ and N₁P₁K₂ by 18.15%, 3.17% and 2.63%, respectively. (2) The annual and total output of cones with continuous fertilization in 8 years were significantly higher than control (P < 0.05) after long-term fertilization with the best proportion N₁P₂K₁ for 8 consecutive years. And the cone yield of the fertilized mother plant was different under three levels of treatment. The effect of fertilization at the level of 2.5 kg/plant was the best, having cumulative yield of cones, reaching (267.43 ± 5.15) kg/plant, which was higher than control, the level of 5.0 kg/plant and 7.5 kg/plant by 52.93%, 3.06% and 5.70%, respectively. (3) Continuous fertilization would significantly increase the yield of cones in non-fruited years (or a very small amount) to the level of small-fruited or average years (20.93−34.22 kg/plant), and shorten the interval between big and small years, resulting in the phenomenon of successive fruiting, but it had a little effect on large-fruited years.

  Conclusion  Fertilization with proportion N₁P₂K₁ (0.46∶0.24∶0.52) can effectively increase the yield of cones, the consequent of long-term continuous fertilization is significant, and the suitable fertilization amount is 2.5 kg/plant.