Influence of high planting density herbal cultivating on yield and quality of whole-plant mulberry (Morus alba)

In order to select the optimum planting density of forage mulberry (Morus alba), a planting density experiment in a randomized complete block design was carried out over three years in Northeast Sichuan, South China, using a forage mulberry cultivar ('teyou No. 2') using three planting densities (75 000, 105 000, and 135 000 plant·ha^–1). The above-ground biomass productivity, agronomic characteristics, and feeding value of the whole-plant forage mulberry were evaluated. Results showed that the biomass yield of forage mulberry, including stems and leaves, increased with planting year. Planting density had a significant effect (P < 0.05) on the biomass yield of forage mulberry. The highest yield was obtained under 105 000 plants·ha ^–1 in the same year. The above-ground biomass increased with increasing leaf content, and the stem-leaf ratio remained constant regardless of initial planting density. Plant height and total branch number increased at first, and then decreased slightly with increasing density. The ranges of plant height and total branch number across the three densities were 75.33～77.00 cm and 11.67～12.33, respectively. The main stem diameter and leaf number per stem decreased with increasing density, and the ranges of these two traits across the three densities were 0.64～0.75 cm and 11.67～12.67, respectively. A significant effect of plant density on feeding value was observed. The crude protein (CP) and ether extract (EE) content of the whole plant increased at first, then decreased with increasing density. The CP and EE contents, which were both highest at 105 000 plant·ha^–1, measured in at 16.60% and 3.67% at this density, respectively. The NDF (neutral detergent fiber) and ADF (acid detergent fiber) contents gradually increased with increasing density, with minimums of 42.84% and 30.18% at 75 000 plant·ha^–1, respectively. The crude ash content gradually increased with increasing density, and peaked at 8.69% at 135 000 plants·ha^–1. The relative feeding value of the whole forage mulberry plant under the three densities ranged from 128.19 to 141.93, demonstrating that the forage mulberry is an excellent food source with a good feeding value at high planting densities. In summary, the optimum cultivation density of forage mulberry for whole-plant harvesting is 105 000 plants·ha^–1 in Northeastern Sichuan.