Improving Seed Spacing Uniformity of Precision Vegetable Planters

Abstract

ABSTRACT. Equidistant, uniform seed placement is important in lettuce productionlthough vegetable seeds are typically sown with precision planters, seed placement uniformity is surprisingly poor. Research studies with raw and pelleted seeds have shown that typically, only about two-thirds of the seeds planted with precision planters are placed within 3.8 cm of the target spacing (Kachman and Smith, 1995;Parish and Bracy, 1998;Bracy et al., 1999;Panning et al., 2000;Bracy and Parish, 2003). This level of precision can be problematic for crops such as iceberg and romaine lettuce (Latuca sativa L.) where seed is typically densely sown at roughly 5 cm spacing to ensure adequate stand establishment. Following germination, the crop is thinned to the desired final plant spacing of 20 to 30 cm to optimize head size and quality. Conventionally, this task is performed manually by workers equipped with hand hoes. When plants are spaced close together, extra time and care is required to remove the excess seedlings without injuring the "saved" crop plant. In 2012, automated machines for thinning lettuce were commercialized (Siemens, 2014). These machines utilize a camera-based machine vision system to detect plants and an herbicidal spray to thin unwanted seedlings. Their adoption has been limited, however, due in part to poor performance when plants are irregularly spaced. One problem is that the image processing algorithms used by these machines cannot identify individual seedlings without visible separation between leaves on adjacent plants. Thus, when closely spaced plants have overlapping leaves, the system identifies the two plants as a single plant and both seedlings are left in field. This results in increased labor costs during the subsequent hand weeding operation where weeds and any remaining closely spaced crop plants are removed.A further drawback of closely spaced plants is the risk of herbicidal spray drifting onto the saved crop plant. Typically, a buffer distance of at least 1.0 cm is required between leaf edges of adjacent plants to prevent crop injury. Since lettuce is thinned when plants are about 2.0 cm in diameter, plant spacing must be greater than 3.0 cm in order for automated machines to operate properly.In lettuce production, the two most common types of precision planters used are belt and vacuum planters. The basic design of these planters hasn't changed significantly

Investigation of the performance of a cylindrical hopper and metering device of a carrot seeder

“…A box that mimicked the real plant bed for carrot seed production was used with a dimension of 1000.0 cm long, 75.0 cm wide and 14.0 cm high. The surface of the box was coated with grease to avoid the seed bouncing when it falls from the metering cylinder as described elsewhere 6 , 12 . The field evaluation was conducted in an upland soil condition prepared by manual tilling to form a raised seedbed.…”

“…Additionally, too many carrot seeds planted in a hill would require extensive thinning 9 . This thinning operation is difficult to perform manually and entails added labor and cost 6 . This can also cause root damage to the remaining plant in a hill due to uprooting of nearby plants.…”