Effects of loading capacity on tree nutrition, growth and fruit quality in Xinxin 2 walnut

Abstract:【Objective】This experiment was conducted to study the effects of different ratios of com- pound leaves to fruits on the nutritional storage and fruit quality of Xinxin 2 walnut. The aim was to ex- plore the suitable loading capacity of Xinxin 2 walnut variety in production, and to provide theoretical basis for efficient and high-yield cultivation of Xinxin 2 walnut.【Methods】Five treatments were set ac- cording to the ratio of the number of compound leaves to the number of fruits on the fruiting branches (1∶1, 2∶1, 3∶1, 4∶1 and 5∶1). At the same time, the CK (control) was set. The fruit and compound leaves of the whole walnut tree were extirpated according to different loading capacity settings. The changes of N, P, K nutrient storage in leaves, current shoots and root system and fruit quality were measured under different loading capacity.【Results】The results showed that with the decrease of fruit loading capacity, the leaf P and K mass fractions increased correspondingly. At the same time, the leaf P and K mass frac- tions with the treatment of 5∶1 were all significantly higher than those of other treatments, which reached 2.48 g · kg- 1 and 13.30 g · kg- 1, respectively. The N mass fraction, leaf area, and dry and fresh weight per 100 leaves reached the peak value when the ratio of compound leaves to fruit was 4∶1, which were 9.48%, 49.54%, 23.48% and 14.13% higher than those of CK, respectively. There was no significant difference in leaf chlorophyll contents among 4∶1, 3∶1, 5∶1 and 2∶1 treatments, but they were all significantly higher than CK and 1∶1 treatment. However, with the decrease of fruit loading ca- pacity, there was no significant difference in the ratio of length to width and the ratio of dry weight to fresh weight per 100 leaves. The annual growth, N, P and K mass fractions and total polysaccharide con- tent in current shoots all gradually increased with the decrease of loading capacity. And the annual growth of current shoots reached 9.40 cm and 9.34 cm with 4∶1 and 5∶1 treatments, which were 31.28% and 30.45% higher than those of CK, respectively, and there was no significant difference be- tween the two treatments. The P mass fractions with 4∶1 and 5∶1 treatments were not significantly dif- ferent. The N mass fraction (11.20 g·kg-1), K mass fraction (5.45 g·kg-1) and total polysaccharide con- tent (82.00 g·kg-1) in current shoots with 5∶1 treatment were all significantly higher than those with oth- er treatments. The results showed that the single fruit weight, kernel percent, protein and vitamin E con- tents significantly increased with reducing the loading capacity. The single fruit weight increased by 21.62%, the protein increased by 9.64%, and the vitamin E content increased by 11.11%, compared to CK. However, the fat content in nuts decreased gradually with the decrease of loading capacity, and there was a positive correlation between them. With the change of loading capacity, the quality of walnut kernel was not significantly different among the treatments. The root trait was affected significantly by different ratios of compound leaves to fruits. The annual root growth, N, P and K mass fractions and invert sugar content in new roots all increased gradually with the decrease of loading capacity, and reached the maximum when the ratio of compound leaves to fruit achieved 4∶1. At the same time, the annual root growth per cubic meter reached 89.06 cm, the N mass fraction reached 12.40 g · kg- 1, the P mass fraction reached 1.74 g·kg-1, the K mass fraction reached 3.88 g·kg-1, and the total polysaccharide content reached 90.00 g·kg-1, which were 19.02%, 49.40%, 89.13%, 12.14% and 21.62% higher than those with CK, respectively【. Conclusion】The N, P and K mass fractions and total polysaccharide con- tent in new root and current shoots all increased gradually with the decrease of loading capacity. Consid- ering the factors of fruit quality and nutritional storage balance, the tree nutritional status and fruit quali- ty of Xinxin 2 walnut were better when the ratio of compound leaves to fruit was adjusted to 4∶1, which could be regarded as the suitable loading capacity of Xinxin 2 walnut in production.