Effect Of Agronomic Practices And Environmental Stress On The Growing Characteristics And Biomass Quality Of Switchgrass

Biomass energy is considered to be an ideal renewable alternative energy, and herbaceous energy crops as an important biomass resources, became research hot spot all over the world. According to foreign researchers reports, agronomic practices had significant influences on biomass production and biomass quality of herbaceous crops, however, these had not been systematically discussed. Experiments were carried out by this study on the effect of agronomic practices such as irrigation, fertilization, planting density, harvest time, and environmental stress on biomass production and biomass quality of switchgrass. The main conclusions are as follows:1. Under different agronomic practices, biomass production of switchgrass reached the maximum production potential in the third growing season. In the second growing season, with the proceeding of the growth period, biomass yield showed a gradually reducing trend after the maximum and biomass quality was improved as significantly reduced ash, water and undesirable components such as K and Cl in biomass, increased lignocelluloses contents; the nutrient element content such as nitrogen, phosphorus, potassium were also declined which could save fertilizer inputs and lower the biomass production costs.2. The biomass quality of switchgrass were studied systematically by using analytic hierarchy process and the indices of biomass high yield and quality were synthetically evaluated. It is concluded that the best agronomic practice combination for high yield and high quality was harvesting by the end of November, no irrigation (rainfed), no extra fertilization, and planting density of 0.8m x 0.8m; the best agronomic practice combination for optimal quality was no irrigation, nitrogen application rate of 112.8kg·ha^-1, and planting density of 0.8m x 0.6m.3. Switchgrass in vegetative period had relatively strong drought resistance and salt resistance. When soil relative water content was under 40%, it still could grow normally. The impact of different saline types on the growth of switchgrass in sequence from serious to light was as NaCl>Na₂SO₄>NaHCO₃; the appropriate concentrations of soil NaCl, Na2SO4 and NaHCO3 for normal switchgrass growth were 0.40%,0.60%, 0.80%, respectively. 4. There were significant differences between the water using efficiency of switchgrass under different soil water spatial distribution pattern and the corresponding root distribution characteristics showed up. Taking good soil water conditions in 0-180cm soil layers as CK, during the first and second growing seasons, when less available soil water occurred in soil layers of 0-180cm, the surface irrigation condition resulted in the highest water using efficiency of switchgrass and effectively promoted the root growth downwards; when less available soil water occurred in soil layers of 0-120cm and good water condition in 120-180cm soil layer, the water using efficiency of switchgrass were second and root growth downwards was promoted but the root biomass was significantly reduced. However, the root-shoot ratio of switchgrass was not significantly different among different water spatial distribution pattern in comparison with CK in the second growing season.5. The responses of switchgrass root distribution characteristics and biomass quality to saline types were significantly different. The impact of saline type on root biomass in sequence from serious to light was as NaCl>Na₂SO₄ >NaHCO₃, the corresponding gravity center of root biomass were 38cm, 23cm, and 18cm respectively while 50cm for CK. Under NaCl condition, the ash content in biomass was increased significantly; under Na2SO4 conditione, the biomass sulfur content was increased and fiber content significantly decreased, i.e. the biomass quality was reduced; under NaHCO₃ condition, the biomass potassium content was significantly decreased indicating a significant improvement of biomass quality.