College of Animal Sciences
Hangzhou, Zhejiang, China
NUMBER AND LENGTH OF BRANCHES AND SHOOTS
Investigations have shown that in Zhejiang and Jiangsu Provinces, when the number of branches and shoots is below 75 000/ha, the annual leaf yield is about 15 tonnes; between 90 000 and 150 000, the yield is 22.5-37.5 tonnes; but above 150 000, the yield will decrease. The ideal number is between 100 000 and 120 000.
High-yield mulberry plantations have a good colonial structure starting with a planting density of 12 000-15 000 plants/ha, the number of crowns at 37 500-45 000; the number of branches and shoots at 105 000-120 000 and the total length of the branches at 150 000-180 000 m per ha (the average length of a branch or shoot is about 1.4 m). Some high-yield plantations have a density at 22 500-30 000 trees/ha with four branches and shoots per tree, for a total of branches/shoots.
Apart from their numbers, the length and diameter of branches and shoots are also directly related to leaf yield.
When a new mulberry field is established, high-yield and superior quality varieties, adaptable to the local environment, should be used. Among the Husang varieties, Heyebai is a high-yield variety widely cultivated in Zhejiang and Jiangsu Provinces.
There is a direct positive relationship between fertilizer dosage and quantity and quality of mulberry leaves. However, there is a reduction in the incremental response to fertilizer application as the dose increases.
High-yield mulberry plantations require a plentiful supply of fertilizers (N 1 100 kg; P2O5, 345-450 kg; K2O, 375-525 kg/ha/year) and water. Timing and application method should be adequate to obtain maximum response.
PLANT SHAPE AND AGE
Under similar conditions, low-trunk trees can be formed in a short period, and their leaf yields are higher than and medium-trunk trees, which take longer to develop. Harvest index and leaf yield of trees are low because of the high proportion of the non-assimilating organs. Since the 1970s, many high-yield plantations with low-trunk or trunkless mulberry trees have been established in China. The varieties planted have good characteristics, such as fast growth and high harvest index, but the highly productive life is shorter compared with high and medium-trunk trees.
Compared with mature trees, both young and old trees have a lower leaf yield. Young trees need to form structural organs, and old trees have lost physiological capacity. Therefore, attempts should be made to develop plants quickly and to lengthen the high-yield period as much as possible.
Apart from the above factors, mulberry leaf yield is also related to methods and frequency of harvesting, as well as to crop management.