Study on biomass composition, fertilizer requirement and fertilizing amount in walnut

Abstract: 【Objective】Through the investigation of biomass of 1 to 12-year-old walnut tree and the de-termination of mineral element contents in different parts of a tree at 5 critical periods of fruit develop-ment, the annual fertilizer requirement of walnut tree with different ages and the fertilizer-applying ratio at critical periods of fruit development were determined, which could provide theoretical basis for preci-sion fertilization in walnut orchards.【Methods】The whole trees of different ages were discomposed in-to different parts and sampled respectively to determine the biomass composition. Using the 6-year-old walnut tree as experimental material, the contents of 10 mineral elements in 10 organs including leaf, shoot, perennial branch, trunk, fibrous root, lateral root, main root, green husk, seed shell and kernel were determined to calculate the accumulation and current year contents. The contents of mineral ele-ments in inflorescence, branch and fruit at 5 critical periods of fruit development were determined to analyze the change of mineral elements during the annual growth and development and the definite de-mand ratio of mineral elements at different development periods. Nitrogen was determined by GB 5009.5—2016 (first method), and other elements were determined by GB 5009.5—2016 (second meth-od).【Results】The biomass increased with tree age, the increasing curve of which accorded with the polynomial equationy=-0.001 4x 6+0.05x5-0.652 4x4+3.867 9x3-9.281 2x2+14.302x-6.780 8. The in-creasing curves of mineral elements in terms of different tree ages also accorded with polynomial equa-tions. The polynomial equations of nitrogen, phosphorous and potassium, which are wildly used in pro-duction, are as follows: y（N）=-0.008 7x6+0.313 9x5-4.186 8x4+25.533x3-64.556x2+121.64x-64.423（R²=0.999 8）; y（P）=-0.001 3x6+0.045 4x5-0.577 9x4+3.307 8x3-7.511x2+13.003x-6.294 9（R²=0.999 7）;y（K）=-0.005x6+0.207 8x5-3.199 4x4+21.998x3-60.511x2+125.7x-77.014（R²=0.999 8）；In the annual production cycle of walnut, the contents of mineral elements at 5 critical periods of fruit development (flowering stage, young fruit expanding stage, shell hardening stage, fat transforming stage, fruit ripen-ing stage and post ripening stage) were different. In current year’s organs, the content of K was the highest, and the contents of N and Ca were the second and third, respectively. The content ratio of K ele-ment at five periods was 1.82∶1.10∶1.17∶1.00∶1.62 with the highest content at flowering stage and the lowest content at fat transforming stage. The content ratio of N element at five periods was 2.23∶1.28∶1.30∶1.00∶1.16 with the highest content at flowering stage and the lowest content at fat transforming stage. The content ratio of Ca element at five periods was 1.15∶1.03∶1.57∶1.00∶1.13 with the highest content at shell hardening stage and the lowest content at fat transforming stage. The content ratio of Pelement at five periods was 3.16∶1.56∶1.13∶1.08∶1.00 with the highest content at flowering stage and the lowest content at fruit ripening stage. The content ratio of Mg element at five periods was 1.40∶1.05∶1.41∶1.00∶1.35 with little difference at flowering stage, shell hardening stage and fruiting ripening stage.【Conclusion】By measuring the biomass composition of walnut tree of different ages and the min-eral element contents at critical periods of fruit development, the annual increasing amount of mineral element of walnut tree of different age and the requirement of mineral element at different development periods can be determined, and the content of mineral element of walnut of different age and different critical periods of development can be obtained.