Annual nutrient demand for the growth of autumn branch, spica and fruit in litchi

Objectives Autumn branches generally sprout after fruit harvest and act as bearing base shoot in litchi (Litchi chinensis Sonn.). Fertilizer is often applied only after the flowering and fruit setting in the practice, which is not good for the breeding of fruit bearing shoot, and might negatively impact the flowering and fruit setting of litchi. Annual nutrient requirement by annual growth of autumn branch, spica and fruit in litchi was investigated in this work to supply basis for nutrient management in litchi.Methods Feizixiao, the most widely grown litchi cultivar in China, was chosen as tested materials in this study. Autumn branches of litchi tree usually sprout twice to three times every year, and only the last sprouted branches bear fruits. Nine litchi trees (Feizixiao) were chosen to harvest for sampling treatments and each treatment with three trees. All the samples of the autumn branches, spicas and fruits were collected in the stages of last autumn branch maturing, flowering and fruit swelling, respectively. The biomass of the trees was weighed and the nutrient concentrations in different parts of the trees were determined. The nutrient accumulation and transfer through the litchi tissues were calculated.Results The biomass of the last branches and their nutrient accumulation approximately equaled to the sum of the first and the second ones. For formation of (55.27.8) kg/tree of yield, about (39.782.60) kg of autumn branches were needed to be produced, and the corresponding nutrient accumulation was N (259.528.4) g, P (28.32.6) g, K (186.519.6) g, Ca (41.69.2) g, Mg (36.14.7) g, S (12.436.1) g, Zn (316.853.4) mg, B (201.129.0) mg and Mo (1.40.3) mg. All of the N, P, K, Mg, S, Mo, 67.5% of Zn and 20.2% of B accumulated in the spicas were transferred from the last autumn branches. Ca was not efficiently taken up by the last branches and then delivered to the spica and the fruit. N, P, K, Ca and Mg accumulated in the autumn branch and the spica with the ratio of 1:0.11-0.12:0.72-0.75:0.16-0.44:0.13-0.14, and in the fruit with the ratio of 1:0.13:1.06:0.16:0.12.Conclusions Litchi tree did not absorb nutrients from last autumn branch maturing stage to early flowering stage, with the exception of Ca, Zn and B. Almost all of the N, K, Ca, Zn and S required by the fruit were newly absorbed during the fruit swelling, and partial P, Mg, B and Mo were originated from the first and the second autumn branch. Consequently, vigorous autumn branch is the key of the flowering of litchi and the base of high fruit yield. Fertilization only after the flowering or fruit setting should be avoided in litchi production. Nitrogen fertilizer should dominate in the nutrient management during the autumn branch development, and potash is preferable during the fruit swelling.