Growth dynamics and optimum cutting period of hybrid Broussonetia papyrifera

The dynamic change in the growth and nutrient composition of hybrid Broussonetia papyrifera under two water and fertilizer conditions in the Lanzhou area was studied. A grey relational analysis and weight assignment method were adopted for the comprehensive evaluation of plant height, yield, crude protein (CP), ash, neutral detergent fiber (NDF), and acid detergent fiber (ADF) from each of two mowing events to determine the optimal cutting period. The results showed that hybrid Broussonetia papyrifera in the high-fertility area entered the fast-growing period for plant height and yield in the third growing month. For the hybrid Broussonetia papyrifera in the low-fertility area, the time of entering the fast-growing period was one month later than that in the high-fertility area. CP content in the two fertility areas was the highest in the third growing month when the plants entered the fast-growing period and then decreased significantly (P < 0.05). In both fertility areas, the ash content showed a continual downward trend. The two fertility areas showed a significant decline in ash content by month (P < 0.05). The low-fertility area presented a highly significant decline in ash content one month earlier than that of the high-fertility area. The content of NDF and ADF exhibited the same increasing trend in the two fertility areas, and reached the highest level in the fifth growing month. The results of the grey relational analysis and weight assignment demonstrated that the comprehensive evaluation value was the highest when the hybrid Broussonetia papyrifera were cut in the second and fourth growing months under the two water and fertilizer conditions. The second and fourth growing months are suggested as the suitable cutting periods for hybrid Broussonetia papyrifera in Lanzhou.