S15 - Session P2 - Opportunities and limitations of bulb onion (Allium cepa L.) crop rotation systems related to upland crops in Gyeongsangnam-do Province in Korea Republic

Authors: Injong Ha *, Byeonggyu Min, Gilseog Park, Mijin Lee, Jaecheol Seo, Taeja Kim

Along with red pepper and garlic, onion is one of the main condiments used in Korea; moreover, it is gaining attention as a health functional food. Gyeongnam has the second largest onion cultivation area and yield, the first being Jeonnam, among Korean local governments, and most onion crops are cultivated in paddy fields using a rice-based cropping system. When onions are grown in paddy fields, the fresh water partially destroys soil pathogens, pests, and weed seeds during the rice growing period, and an additional advantage is the continuous and extended growth of large bulbs due to high water and nutrient retention. Conversely, the soil in paddy fields is easily acidified, and emissions of methane and other greenhouse gases may be increased. To address these problems, it is necessary to develop an onion cropping system linked to field crops. In the present study, soybean (which effectively improves soil) and sweet potato (with high revenue per unit area) field crops were selected and assessed in association with onion cropping. The medium-to-late-maturing onion variety Katamaru was sown and seeded on September 11 and planted on three later dates (October 26, November 11, and November 16). The possibility of developing a cropping system was assessed by reviewing the main cropping seasons (planting season, harvesting season, etc.), quantity, and economic feasibility (revenue) of the onion and field crops, and the appropriate time for onion planting and limits under the cropping system were studied. For most soybean varieties, the best time to sow in the southern region is early-to-mid-June, and the yield can be maintained when sowing is completed up until the end of June. The best time to harvest soybeans for short-term fermented soy sauce and tofu is mid-to-late September, whereas late September to early October is best for normal soy sauce and tofu (Rural Development Administration, 2018). Therefore, the best time to plant onions is after the harvest of soybeans. For all three treatments, the harvest time of onions was June 8, which allowed for the timely sowing of soybeans following the harvest of onions. In the southern region, the optimal cutting period for sweet potatoes is early May, and the last period possible for cutting before the harvest, i.e., cutting limit period is early July (Rural Development Administration, 2018). Given that the harvest time of all three onion planting periods was June 8, i.e., earlier than the cutting limit period but later than the optimal cutting period of sweet potatoes, the use of onion varieties with earlier harvest times would be advantageous for sweet potato production. The optimal number of days from cut planting to harvest is 110 days for early-ripening varieties and 120 days for late-maturing varieties (Rural Development Administration, 2018). In the present study, sweet potatoes were cut-planted after onion was harvested on June 8 and could be harvested after mid-October; thus, there was minimal overlap with the onion planting period. The crops planted on October 26 had the highest number of the yield and revenue per unit area (10a) at 10,854 kg and 3,053 thousand won, respectively, whereas those planted on November 5 had the second highest at 10,409 kg, and 2,928 thousand won, and those planted on November 16 had the third highest at 7,947 kg and 2,235 thousand won (significantly lower values than those for crops planted on November 5). Thus, the optimum time to plant onions in a soybean-linked cropping system is late October, and the planting limit period is early November. For the development of a sweet potato-linked cropping system, additional research on early onion varieties is required.