Development and Evaluation of a Ridge-forming Direct Seeder for Double Cropping in Warm Regions

<p>The developed machine was installed behind the tractor and the tire marks were leveled at the ridge-forming supporting unit. The seeding ridges, with a hard surface and trapezoidal cross-sections, were formed by ridge-forming unit for preventing water leakage in the field. In addition, sowing was done on top of the ridges by the direct-seeding unit, the seed-feeding unit, and the soil-covering compaction unit. The structure was designed to avoid moisture damage, due to rainfall and water stagnation, during the early stages of growth. This machine also supports sowing of soybean and wheat, in addition to rice, using the following settings: working width = 210 cm, row spacing = 30 cm, number of rows = 7, applicable tractor output = 40–60 PS (29.4–44.1 kW). During the field tests in the gray lowland soil field (Tamana City, Kumamoto Prefecture), there was a rainfall of 214 mm for 2 weeks until the day before sowing and the soil moisture content was 42% (Liquidity index = 0.4), which was 10% higher than the plastic limit (32%), causing soil sticking. However, the seeder was efficient in sowing in the sticky soil. The work efficiency of the developed machinery was 12 min/10a in a field area of 60–72 a at a work speed of 3.5 km/h. The workable precipitation was defined as ≤ 7 mm on the day of sowing, ≤ 29 mm one day before sowing, and ≤ 48 mm, two days before sowing. The relationship between the direct-seeding tests and rainfall (2015–2021) was considered to estimate the optimum sowing time for each crop. The average possible number days for 10 years (2012–2021) were estimated to be 24 for rice, 22 for soybean, and 26 for wheat and barley. Based on the work efficiency of the ridge-forming direct seeder, the workable area for each crop was calculated to be 67 ha for rice, 61 ha for soybean, and 73 ha for wheat and barley. Furthermore, in a cultivated area of 50 ha (land use rate: 200%, crop conversion rate: 40%) in Kyushu, the total cost for cultivating 60 kg of general-purpose rice using a ridge-forming direct seeder was 39% lower than that using conventional methods.</p>