Effect of different elements on the occurrence of exposed kernel of walnut in Xinjiang

Abstract: 【Objective】The phenomenon of exposed kernel is very common with two main walnut cultivars‘Wen185'and‘Xinxin2'in Xinjiang, which affects both the appearance quality and the market price greatly. In order to reduce kernel exposure rate and improve appearance quality, the different mineral elements were applied to two walnut varieties respectively.【Methods】In the shell-hardening period, the elements N, P, K, Zn, Ca and Mg elements were applied to two walnut varieties, respectively, and after the fruit matured and the nuts naturally dried, the nut indexes were measured separately, which included the numbers of exposed kernel, the average nut weight, the kernel weight, the shell thickness, the kernel percentage and so on, to study the effect of different elements on nut quality.【Results】There was a significant effect of different elements on the quality with two walnut varieties. Among them, K, Ca and Mg could improve the average nut weight of‘Wen185'significantly, with the single nut weight reaching 13.76-14.43 g, increasing by 6.50%-11.69%. There was no significant difference in average nut weight between N and Zn treatments, but P element could reduce the average nut weight with‘Wen185'. The kernel weight of‘Wen185'could significantly increase by 8.09%, compared to that of Control with the treatment of K element. However, the difference was not significant between N, P, Zn, Ca and Mg elements as well as control. Spraying with K, Ca and Mg elements all could improve theshell thickness with‘Wen185'and reduce the exposed kernel rate significantly, with the exposed kernel rates decreasing from 28.00% (control) to 0.05%. Spraying with N, P, K, Zn, Ca and Mg elements could improve the average nut weight of‘Xinxin2'significantly, and the single nut weight with the treatment of Mg element was higher than that with the treatments with N, P and Ca significantly, but the difference was not significant between Mg as well as K and Zn. Spraying with N, P, K and Zn elements could improve the kernel weight of‘Xinxin2'significantly, increasing by 5.11%-9.16%. Spraying with six elements could increase the shell thickness of‘Xinxin2'significantly and reduce exposed kernel rate of‘Xinxin2'significantly, and the effect of spraying with N, K, Zn, Ca and Mg elements on increasing the shell thickness was significantly better than that with P element. The effect of Mg element on reducing exposed kernel rate was significantly higher than that of N and P elements. The shell thickness was different in the same azimuth under different processing methods, spraying with P, K, Zn, Ca and Mg elements could improve the shell thickness with‘Wen185', among which K and Ca element treatments were more obvious, the maximum shell thickness could increase by 42.86%. Spraying with N, P, K, Zn, Ca and Mg elements could improve the shell thickness with‘Xinxin2', which reduced the exposed kernel rate, and the effect of spraying with Zn and Mg elements was obvious particularly, with the shell thickness increasing by 162.50%. The shell thickness of nuts from the upper canopy was significantly higher than those from the lower canopy. The shell inside the crown of the tree was the thinnest and the occurrence of exposed kernel was the most grievous. The distribution of exposed kernel rate on a canopy showed in an ascending order: eastern>southern>western>northern and inner canopies.【Conclusion】The occurrence of exposed kernel was serious in Xinjiang walnuts, which was commonly affected by the variety characteristics, fertilizers and light conditions. Except for strengthening pruning management in production, some elements should also be sprayed, such as K (0.3% K₂ SO₄) , Ca [0.5%Ca (NO₃) ₂], and Mg [1% MgSO₄· 7 H₂ O] respectively to improve the nut weight, kernel weight, shell thickness, and reduce the exposed kernel rate significantly, so as to improve the yield and quality.