{"id":790,"date":"2026-05-28T06:37:51","date_gmt":"2026-05-28T06:37:51","guid":{"rendered":"https:\/\/rock-crusher-tractor.com\/?p=790"},"modified":"2026-05-28T06:37:51","modified_gmt":"2026-05-28T06:37:51","slug":"korean-onion-stone-clearing-thor-ep-ew-4000-decision-guide","status":"publish","type":"post","link":"https:\/\/rock-crusher-tractor.com\/de\/korean-onion-stone-clearing-thor-ep-ew-4000-decision-guide\/","title":{"rendered":"Koreanische Zwiebelproduktion und Steinr\u00e4umung \u2013 THOR 2.4- und EP-EW-4000-Entscheidungsleitfaden f\u00fcr Allium-Anbaugebiete in Gyeongnam"},"content":{"rendered":"
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Korean Onion Production and Stone Clearing \u2014 THOR 2.4 vs EP-EW-4000 Decision Guide for Gyeongnam and Gangwon Allium Fields<\/h1>\n

Korean onion bulbs develop at only 5\u201312 cm depth \u2014 shallower than any other major crop in the Watanabe system. The stone clearing requirement is not less stringent, but the machine decision genuinely differs from potato and garlic.<\/p>\n

Onion Field Stone Clearing Enquiry<\/a><\/p>\n<\/div>\n<\/div>\n

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Korean onion production \u2014 concentrated in South Gyeongsang Province (Changnyeong-gun, Hapcheon-gun, Miryang) and extending to some Gangwon highland sites \u2014 is the third major allium crop in Korea after garlic and spring onion. Annual Korean onion production exceeds 900,000 tonnes, with Gyeongnam producing approximately 60% of the national total. Stone management for Korean onion has a unique characteristic that separates it from garlic and potato: the onion bulb develops at very shallow depth (5\u201312 cm), meaning the stone sensitivity is not primarily about bulb contact during development but about the mechanical harvest undercutter bar that must pass cleanly below the bulb zone.<\/p>\n

This distinction produces a genuine machine decision that does not exist for potato or garlic \u2014 on established Korean onion fields where the stone population consists primarily of surface and near-surface frost-heave re-emergents, the EP-EW-4000 rock rake can often handle the stone management requirement without THOR 2.4 deployment. This article defines exactly when each machine is the correct choice, covers the Korean onion variety calendar and its stone management integration, explains the undercutter bar stone sensitivity mechanism, and presents the garlic-onion-potato mixed farm utilisation case for the THOR 2.4 investment.<\/p>\n

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Onion Bulb Development and Stone Sensitivity \u2014 Shallower But Not Simpler<\/h2>\n

\"THOR<\/p>\n

Korean onion bulbs (both yellow and white types) develop primarily from a thickened basal plate at 5\u201312 cm below the soil surface. The wrapper leaf layers form from the outside as the bulb expands laterally \u2014 the largest diameter of a mature Korean onion bulb is typically 7\u201310 cm, meaning the bulb occupies the soil volume from approximately 3 cm below surface to 12 cm below surface at full maturity. This shallow development zone creates a specific pattern of stone sensitivity:<\/p>\n

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Low direct bulb-stone contact risk during development<\/p>\n

Because Korean onion bulbs develop primarily in the upper 12 cm of the soil profile \u2014 expanding laterally in the fine-tilth zone rather than deepening \u2014 they are less likely to encounter deep-seated stones that a THOR 2.4 would fragment below 15 cm depth. The lateral bulb expansion happens in the same surface zone that annual frost-heave maintenance with the EP-EW-4000 addresses. For this reason, an onion field that has had good EP-EW-4000 surface clearance has lower direct bulb-stone contact risk than an equivalent potato field would have without THOR clearance.<\/p>\n<\/div>\n

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High undercutter bar sensitivity at harvest \u2014 the critical stone risk<\/p>\n

Korean onion mechanical harvest uses an undercutter bar (a horizontal blade that passes horizontally below the bulbs at 5\u20138 cm depth) to sever the roots and lift the bulb string clear of the soil. This undercutter bar must travel cleanly through the top 8\u201310 cm of soil in a continuous horizontal plane. A stone at 6\u20138 cm depth in the bar’s path deflects the bar upward \u2014 either causing the bar to contact and bruise the base of bulbs above the deflection point, or causing the bar to ride up and miss bulbs entirely, leaving them in the ground. Stone sensitivity for onion harvest is therefore most critical in the 5\u201312 cm depth zone \u2014 the undercutter operating depth \u2014 not the full 20\u201325 cm profile that potato and garlic require.<\/p>\n<\/div>\n<\/div>\n

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The Machine Decision \u2014 When THOR 2.4 Is Needed and When EP-EW-4000 Is Sufficient<\/h2>\n

This decision is the unique analytical contribution of this article \u2014 for no other crop in the Watanabe system does the EP-EW-4000 have a genuine case as the primary stone management machine rather than a supplementary final-sweep tool. The decision is based on the depth distribution of the stone population:<\/p>\n

\n\n\n\n\n\n\n\n\n
Feldbedingungen<\/th>\nCorrect machine<\/th>\nArgumentation<\/th>\n<\/tr>\n<\/thead>\n
Established cleared field \u2014 only annual frost-heave re-emergents on surface (0\u201315 cm)<\/td>\nEP-EW-4000<\/td>\nSurface collection sufficient \u2014 no deep stone population remains from prior THOR clearance. EP-EW-4000 collects all stones above the 40 Kg threshold from the 0\u20138 cm zone. Undercutter bar path is clear.<\/td>\n<\/tr>\n
Established field \u2014 light frost heave but confirmed stones at 10\u201315 cm from soil probe<\/td>\nEvaluate: EP-EW-4000 + hand clear, or shallow THOR<\/td>\nEP-EW-4000 handles surface; THOR at 15 cm depth handles the undercutter zone stones. Walk the field and count stones in the 5\u201312 cm zone by hand probing before deciding.<\/td>\n<\/tr>\n
Previously un-cleared field or new land \u2014 stones at all depths including 5\u201315 cm undercutter zone<\/td>\nTHOR 2.4 (15\u201318 cm depth)<\/td>\nSubsurface stone population in the undercutter zone cannot be addressed by EP-EW-4000 alone. THOR 2.4 at 15\u201318 cm fragments stones in the critical harvest depth zone. CT-2100 collects output.<\/td>\n<\/tr>\n
New land \u2014 heavy stone population at all depths<\/td>\nTHOR 2.4 (two-pass, 18 cm)<\/td>\nSame two-pass new land protocol as potato, but 18 cm depth maximum (onion bulb zone only). New land brings high stone density to the undercutter zone that requires full THOR fragmentation protocol.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
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The field probe test \u2014 15 minutes that determines the machine choice<\/p>\n

Walk the field in August\u2013September (before autumn onion preparation) carrying a steel probe rod. Push the rod to 15 cm depth at 20-point grid across the field. Count the number of probe positions where resistance is encountered between 5 cm and 12 cm depth \u2014 stones in this zone are in the undercutter bar path. If more than 4 of 20 probe positions show resistance in the 5\u201312 cm range: deploy THOR 2.4 at 15\u201318 cm depth. If fewer than 4 of 20: EP-EW-4000 surface clearance is sufficient. This test takes approximately 15 minutes across a 1 ha field and prevents the most common Korean onion stone management error \u2014 using EP-EW-4000 on a field that still has significant subsurface stone presence in the undercutter zone.<\/p>\n<\/div>\n

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Korean Onion Varieties and Growing Calendar \u2014 Stone Management Timing<\/h2>\n

\"CT-2100<\/p>\n

Korean onion production uses two main planting systems \u2014 autumn planting (overwinter) and spring transplanting \u2014 with significantly different stone management timing implications for each:<\/p>\n

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Changnyeong Yellow Onion (Gyeongnam dominant)<\/p>\n

Autumn seedling transplant \u2014 primary type<\/p>\n