| To develop prataculture in arable land is an effective approach to promote ternary planting structure of the food, economic and forage crops coordinated development, which is to achieve mordemization of animal husbandry in China. The lower farming region of the Yangtze River located in subtropical zone, which lead to abundant rain and sufficient heat,and there is a great potential for partaculture development in arable region. But this region is typical binary plating pattern of rice and cash crops, and there is lack of suitable varieties and cultivation techniques with forage production. In addition, hay production was limited by higher temperature and more precipitation, ensiling becomes an important approach to ensure the supply of annual crude feed. To select silage crops adapting local ecological environment and to research supporting high yield cultivation and utilization techniques,which has a significant impact on sustainable development for planting grass and raising livestock in the lower farming region of the Yangtze River.Sweet sorghum (Sorghum bicolor) is a C4 crop with strong resistance and wide adaptability, and is an excellent forage crop with high biomass and regeneration. In the lower farming region of the Yangtze River, sweet sorghum is sporadic planting as a stimulant crop. Whether or not the sweet sorghum can be used as silage crops for cultivation and utilization in this region used its excellent traits. There are few related reports in China and abroad. This experiment was conducted to determine the difference between sweet sorghum (cv. Hunnigreen) and corn silage in dry matter production performance, nutritional value, silage quliaty and utilization value, demonstrate the feasibility of sweet sorghum as silage crop in the lower farming region of the Yangtze River. In addition, the effects of nitrogen fertilizer and cutting frequency on sweet sorghum was analysed through field and laboratory techniques, including production performance,nitrogen utilization, photosynthesis, nutritional value, silage quality and in vitro fermentation gas-production. The study presented the suitable cultivation and utilization techniques of sweet sorghum as a silage corp for high yield and good quality in agricultural areas in the lower farming region of the Yangtze River, The main results were summarized as follows:1. Sweet sorghum has higher yield of dry matter, crude protein and digestible dry matter than that of corn silage under farmland ecological conditions in the lower farming region of the Yangtze River, and three average value were 1.54, 1.47 and 1.73 times with corn silage. Sweet sorghm was comparable and more stable for nutirive value and silage fermentation quality than corn silage. Therefore, there was great potential of sweet sorghum can be used as silage crop in the lower farming region of the Yangtze River.2. The nitrogen experiment of two consecutive years results showed that the suitable application rate of nitrogen was 200 to 400 kg N·ha-1 in the lower farming region of the Yangtze River. The higher dry matter (DM) yield, utilization rate of nitrogen and lower nitrogen loss were displayed at N rate. Multiple regression and path analysis showed that the plant height was the important factor on dry matter yield with N rate independent, while stem/leaf ratio (S/L ratio) and LAI made different contributions to dry matter yield under different N level. The direct effect of S/L ratio and LAI on DM yield were the maximum(P=0.925) and the minimum (P=0.612), respectively, under lower N level (0, 100 kg N·ha-1).LAI has positive direct effect (P=0.797) on DM yield under medium N level (200, 300 kg N·ha-1), which was lower than the effect of plant height, but was negative direct effect(P=-0.040) on DM yield under higher N level (400, 500 kg N·ha-1). Effect of S/L ratio on DM yield decreased with N rate increasing. The results showed that reasonable density was more critical for higher DM yield of sweet sorghum under the higher nitrogen rate, when the nitrogen rate was lower, the effect of harvest time was more prominent when making a trade off between yield and quality.3. Nitrogen fertilizer and cutting frequency had significant effects on photosynthesis of sweet sorghum. The net photosynthesis rate (Pn) increased with increasing of nitrogen fertilizer rate and cutting frequency, and the maximum Pn was at the treatment of 300 kg N·ha-1 and three-cutting time. Apparent quantum yield (AQY), light saturation point (LSP)and carboxylation efficiency (CE) of sweet sorghum reached the maximum value at the same treatment. The results showed that higher application nitrogen rate and cutting frequency contributed to the photosynthesis, but dark respiration rate (Rd) also reached the maximum value at the same treatment, which indicated that the higher nitrogen rate and frequency cutting improved photosynthetic, but also increased the consumption of material and energy. Suitable cutting frequency and nitrogen level can greatly improve the photosynthetic capacity. Nitrate reductase activity (NRA) had increasing trend with increasing of cutting times. Two-cutting time was more conductive to the accumulation of photosynthate throughout the growing season.4. The experiment was to determine the effect of nitrogen application and cutting frequency on nutrition value and silage fermentation quality of sweet sorghum. The results showed that both CP and WSC increased with increasing of N application rate, and the maximum was at 300 kg N·ha-1 and 225 kg N·ha-1, respectively. There was no significant difference in IVDMD among different nitrogen fertilizer treatments. When nitrogen rate was greater than or equal to 225 kg N·ha-1, no significant increase in pH value and lactic acid (LA) content, butyric acid (BA) and NH3-N were significant higher than the other nitrogen treatment. The maximum of CP was at the treatment of two-cutting time, and was significantly higher than that of other cutting treatments. The maximum WSC was at the treatment of one-cutting time, IVDMD reached a maximum at three-cutting time. After ensiling, the CP content of three-cutting, two-cutting and one-cutting time were decreased by 22.5%, 9.7% and 18.3%, respectively. The nutritive value of sweet sorghum under two-cutting time was slightly inferior to that of three-cutting time, but the silage quality was higher, because of lower pH value, lowest NH3-N, higher Flieg score and the minimum loss of CP during ensiling. The BA content of two-cutting time was higher than that of three-cutting time, but there was no significant difference between two cutting treatments.Sweet sorghum of two-cutting time was suitable to be used as a silage.5. The experiment was to determine the effect of nitrogen application and cutting frequency on in vitro digestibility characteristic of sweet sorghum. The results showed that increasing nitrogen application had no significant effect on dry matter digestibility (DMD),neutral detergent fiber digestibility (NDFD) rate decreased with increasing of nitrogen rate.Gas production (GP) reached maximum at 300 kg N·ha-1, which had no significant differences with 150 kg N·ha-1 or 225 kg N·ha-1. The total volatile fatty acids (TVFA) and its components increased with the increasing of N application rate, and the maximum was at 300 kg N·ha-1, which had no significant difference with treatment of 225 kg N·ha-1,expect isobutyric acid (IBA) and isovaleric (IVA). The maximum acetic/propionic acid(A/P) was at 225 kg N·ha-1, and the CO2/CH4 (CCP) decreased with the increasing of nitrogen fertilizer rate, which showed that the increasing of nitrogen fertilizer not increased the CH4, but also increased the acetic acid (AA). DMD and NDFD increased with increasing of cutting frequency, the maximum GP decreased with increasing of cutting frequency. Increasing cutting frequency had a tendency to reduce the content of TVFA except isobutyric acid (IBA), while acetic acid (AA), A/P and CCP was the highest at the treatment of two-cutting time. There was no obvious difference about ruminal fermentation characteristics between fresh and silage forage under different nitrogen rate, which has slightly difference affecting by cutting frequency.There were no significant difference between two-cutting time and the other cutting treatments for PA content of fresh forage,while the PA content of silage under two-cutting time was significantly lower than that of one- or three-cutting treatments. The resuls showed that the ruminal fermentation type of sweet sorghum under two-cutting time tended to AA type. Base of analysis of VFA and gas production, the conclusion was that sweet sorghum, which was at 150-225 kg N·ha-1 with two-cutting time during the growth season, was more conducive to microbial fermentation.In summary,sweet sorghum can be used as a silage crop in the lower farming region of the Yangtze River, cutting two times with nitrogen application rate of 225 kg N·ha-1 was the suitable cultivaton and utilization techniques, which can bring higher DM yield and better forage quality. |
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