Development of sustainable cultivation system in forage sorghum (Sorghum bicolor Moench)

To establish cultivation systems that overcome problems of forage sorghum and reduce energy input, we performed a series of tests on cultivation and silage making. 1. Weed Control by Dense Broadcasting Cutivation in Forage Sorghum (Sorghum bicolor Moench) Weeding measures are an important issue for forage sorghum because it is inferior to corn in early growth and there are not many different kinds of herbicides applicable to sorghum. Since the concern about organic animal products and environmental problem is increasing, cultivation without herbicide application is needed. Therefore, research was conducted on seeding rate for cultural weed control in the dense broadcasting of forage sorghum. Test samples were 'Hazuki' for sorghum and 'HSK-1' for sudangrass. Seeding rate was 2 kg, 5 kg, and 8 kg per 10a for sorghum and 4 kg per 10a for sudangrass. Hazuki grew shorter in plant length, smaller in culm diameter, and more in the number of tillers in both weeded and non-weeded plots as seeding rate increased. The amount of weed at the harvest time in plots without herbicide application was large when the number of sorghum tillers was small but decreased with the increase in the number of tillers. Dry matter yield gradually increased as the number of tillers increased. The optimum number of tillers (the number of individual plants) was determined to be about 200/square m considering the amount of weed and the dry matter yield of sorghum. From the above, broadcast cultivation of forage sorghum without herbicide application was found to be practicable regardless of sowing time by seeding 8 kg 10/a, which secures the number of tillers. 2. Effects of Post-seeding Rotary Tilling and Soil Packing on the Emergence of Densely Brordcasted Forage Sorghum (Sorghum bicolor Moench) Broadcast seeding of forage sorghum (Sorghum bicolor Moench) often experiences unsatisfactory emergence and establishment of seedlings. This study evaluated post-seeding rotary tilling and soil packing as management practices to improve emergence and establishment of densely broadcasted forage sorghum 'Hazuki'. Shallow tilling to a depth of about 5 cm resulted in high seedling emergence rates (> 60%), regardless of application or intensity of soil packing. Without tilling, although seedling emergence rates were low when no or light soil packing was applied (20-45%), the rates exceeded 60% when the soil was intermediately or firmly packed after seeding. Deep tilling to a depth of about 15 cm suppressed seedling emergence (mostly 30-40%) particularly when combined with soil packing. The results show that shallow rotary tilling or no tilling followed by intermediate or intense soil packing is recommended as post-seeding management for stable high seedling emergence of broadcasted forage sorghum. 3. Effects of the Omission of Rotary Tilling after Rye Harvest on the Growth and Yield of Densely Broadcasted Sorghum We evaluated sorghum broadcasting and dense sowing without rotary tilling in spring, which is the busiest season for farm work. The sorghum variety 'Hatsuki' was used in this study. Sorghum was seeded on soil without rotary tilling after rye harvest, and covered with soil by rotary-shallow-tilling or disk-harrow-topsoil-cutting method. We examined the effects of these methods and conventional cultivation on the growth and yield of sorghum. As a result, the emergence, growth, and yield of sorghum by both rotary-shallow-tilling and disk-harrow-topsoil cutting methods without rotary tilling were similar to those by conventional cultivation. However, the initial growth by the disk-harrow-topsoil-cutting method was slightly lower than that by the rotary-shallow-tilling method. The working time required for cultivation by the rotary-shallow-tilling and disk-harrow-topsoil-cutting methods without rotary tilling was reduced to 47% and 42% of conventional cultivation, respectively. These results suggested that the rotary-shallow-tilling and disk-harrow-topsoil cutting methods were useful for the covering with soil after seeding in the dense broadcasting of sorghum without rotary tilling after rye harvest. 4. Fermentative Quality of Round Bale Silage Made from Densely Planted Forage Sorghum (Sorghum bicolor Moench) Using a Fail-type Harvester Round bale silages were made from densely planted forage sorghum using 4 different methods. In the first method (no wilting), forage was cut by a flail-type harvester and immediately ensiled without wilting. In the second method (natural wilting), forage was cut by a flail-type harvester and ensiled after 24-hour wilting without tedding. In the third method (promoted wilting), forage was cut by a flail-type harvester and ensiled after 24-hour wilting accompanied by 2 teddings. In the fourth method (conventional method), forage was cut by a rotary mower and ensiled by a cutting round baler after 24-hour wilting with 2 teddings. The moisture content of the silage material was the lowest in promoted wilting, followed by natural wilting and conventional method. The bale density was similar among the 4 methods. Silages made by the 3 methods using a flail-type harvester showed lower pH values and higher lactic acid contents than that made by the conventional method. The results show that silages with good quality and enhanced lactic acid fermentation can be made from densely planted forage sorghum by using a flail-type harvester. 6. New Low-input Type Cultivation Systems Using cv. Hazuki with High Digestibility As new systems using sorghum 'Hazuki', 'dense broadcasting of sorghum without herbicides application' and 'dense broadcasting of sorghum with no-rotary-tilling after rye harvesting' were evaluated in terms of management and estimated energy efficiency. The work time (h 10/a) and TDN yield (kg /h) expressed as percentages to those in standard cultivation were 91-97% and 112-119%, respectively, for 'dense broadcasting of sorghum without herbicides application' and 81-85% and 121-127%, respectively, for 'dense broadcasting of sorghum with no-rotary-tilling after rye harvesting'. The direct energy input (MJ 10/a) expressed as a percentage to that in standard cultivation was 91-98% for 'dense broadcasting of sorghum without herbicides application' and 83% for 'dense broadcasting of sorghum with no-rotary-tilling after rye harvesting'. These results suggest that the new cultivation systems reduce production costs, work time, and energy input compared with conventional cultivation system.