{"id":1189,"date":"2026-09-08T08:22:48","date_gmt":"2026-09-08T08:22:48","guid":{"rendered":"https:\/\/rock-crusher-tractor.com\/?p=1189"},"modified":"2026-09-08T08:22:48","modified_gmt":"2026-09-08T08:22:48","slug":"potato-digger-blockage-clay-soil-causes-and-fixes","status":"publish","type":"post","link":"https:\/\/rock-crusher-tractor.com\/it\/potato-digger-blockage-clay-soil-causes-and-fixes\/","title":{"rendered":"Ostruzione della scavapatate in un terreno argilloso: cause e soluzioni"},"content":{"rendered":"
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PROBLEM AND SOLUTION \u2014 CLAY SOIL<\/span><\/div>\n

Ostruzione della scavapatate in un terreno argilloso: cause e soluzioni<\/h1>\n

Clay blockage is not a machine fault. It is the wrong combination of soil moisture, chain speed, and forward speed for a soil type that has different rules from sandy loam. Getting those three settings right \u2014 in the right order \u2014 stops the blockage before the shear bolt decides for you.<\/p>\n

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3\u20135 dry days<\/div>\n
After rain \u2014 before clay harvest<\/div>\n<\/div>\n
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Speed first<\/div>\n
Reduce forward \u2014 not just chain<\/div>\n<\/div>\n
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Ball test<\/div>\n
Field soil moisture check<\/div>\n<\/div>\n<\/div>\n

Clay Soil Guidance<\/a><\/p>\n<\/div>\n<\/div>\n<\/div>\n

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A potato digger that works flawlessly in sandy loam can become completely unmanageable in clay \u2014 not because anything has broken, but because clay soil’s physical and chemical properties create a completely different interaction with the elevator chain than any other soil type. Farmers who discover this mid-harvest, with a blocked elevator chain, a severed shear bolt, and a trailer half-filled with clay-covered potatoes that cannot get to the field, face one of the most frustrating and expensive single machinery problems in the potato calendar. Understanding why clay blocks and what changes \u2014 in the machine, in the soil, and in the timing \u2014 prevent it from blocking is the knowledge that separates a harvested crop from a crisis.<\/p>\n

This guide works through the clay blockage mechanism from first principles, identifies the six most common specific causes, and provides a priority-ordered set of fixes \u2014 from the immediate adjustments that can change the situation in the next 100 metres of travel to the pre-season decisions that determine whether the field is harvested that day at all.<\/p>\n

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How Clay Soil Creates Elevator Blockage \u2014 The Chemistry of Adhesion<\/h2>\n

\"potato<\/p>\n

Clay blockage is not simply a matter of too much soil arriving on the chain. It is a different type of soil-chain interaction driven by clay’s unique physical properties. Clay minerals are phyllosilicates \u2014 sheet-structured aluminium silicate compounds (kaolinite, illite, smectite) whose particle geometry is plate-shaped rather than spherical. These plates have electrochemical charges on their surfaces and edges that create both inter-particle attraction (clay particles stick to each other) and adhesion to other charged surfaces \u2014 including steel. When wet clay contacts a steel elevator rod, some of the clay particles adhere electrostatically rather than sliding off under gravity. As the chain carries these adhered clay particles forward, more clay contacts the adhered layer, building up a film that eventually spans the gap between adjacent rods. This is the “soil bridge” or “arch” that creates blockage: once a clay film spans a rod gap, further clay cannot pass through the gap, and instead presses against the bridge from behind. Within a few seconds, a multi-rod clay arch forms that the chain cannot pull through \u2014 the chain drive system stalls, and either the shear bolt severs to protect the gearbox or, in the absence of a correctly specified shear bolt, the chain or drive components sustain damage.<\/p>\n

This mechanism is moisture-dependent: dry clay has lower particle surface charge activity and is less adhesive to steel. As clay approaches field capacity (the moisture content at which water just fills all soil pores), adhesion to steel surfaces reaches its maximum. Above field capacity (waterlogged conditions), adhesion actually decreases slightly as the free water lubricates the clay-steel interface \u2014 but at this moisture level the clay flows rather than separates, producing a different problem (soil carry-over onto the crop) without necessarily causing a hard blockage. The practical worst case for elevator blockage is clay at approximately 80\u201395% of field capacity \u2014 moist enough to be highly adhesive but not so wet as to be self-lubricating. This is the condition that typically applies in the day immediately after rainfall or in a field that drains slowly \u2014 and it is the condition that makes harvesting on that day the decision that determines whether the day is productive or a mechanical rescue operation.<\/p>\n

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Six Most Common Clay Blockage Causes \u2014 Diagnosis and Priority Order<\/h2>\n
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1<\/div>\n
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Harvesting at too-high soil moisture<\/strong> \u2014 the primary cause in more than half of clay blockage events<\/p>\n

Diagnostic:<\/em> clay comes off the elevator in continuous sticky sheets rather than disaggregated fragments; rapid bridge formation within the first 10 m of entry into the field. Fix:<\/em> stop immediately; postpone harvest until soil moisture decreases (see soil moisture timing section below). No machine adjustment compensates for clay at or near field capacity.<\/p>\n<\/div>\n<\/div>\n

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2<\/div>\n
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Forward speed too fast for clay conditions<\/strong><\/p>\n

Diagnostic:<\/em> blockages occur progressively \u2014 not immediately on field entry but after 30\u201360 m, as the clay volume accumulating on the chain exceeds the chain’s clearing rate. Fix:<\/em> reduce forward speed to 1.5\u20132.5 km\/h before increasing chain speed. Delivering less clay mass per unit time is more effective than trying to move existing clay faster.<\/p>\n<\/div>\n<\/div>\n

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3<\/div>\n
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Chain speed too low for clay conditions<\/strong><\/p>\n

Diagnostic:<\/em> clay accumulating at the bottom of the chain’s return loop; bridging at the elevator entry rather than mid-elevator. Fix:<\/em> increase chain speed to minimum level that keeps clay fragments in continuous motion \u2014 but be aware that increasing chain speed also increases tuber bruise risk (see P-26). The correct balance: lowest chain speed that prevents clay bridging, combined with reduced forward speed.<\/p>\n<\/div>\n<\/div>\n

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4<\/div>\n
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Chain tension inadequate<\/strong><\/p>\n

Diagnostic:<\/em> chain sags visibly mid-span; blockage tends to start at the chain’s lowest sag point rather than uniformly across the elevator. Fix:<\/em> re-tension the chain to manufacturer’s specified sag value (typically 10\u201320 mm mid-span deflection under no load). Loose chain creates pockets where clay accumulates rather than flowing forward continuously with chain movement.<\/p>\n<\/div>\n<\/div>\n

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5<\/div>\n
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Insufficient or absent agitation bars<\/strong><\/p>\n

Diagnostic:<\/em> clay arrives at the separator end as solid intact slabs rather than fragments; soil carry-over onto the crop is high even when chain is not blocked. Fix:<\/em> ensure the elevator section carries the maximum number of agitation bars specified for heavy soil use; add additional bars if the machine’s frame allows. Note: adding agitation bars in the separator zone (where tubers are already separated from soil) increases bruise risk \u2014 target additional bars in the elevator zone only.<\/p>\n<\/div>\n<\/div>\n

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6<\/div>\n
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Share angle creating clay ball formation<\/strong><\/p>\n

Diagnostic:<\/em> large, intact clay balls (10\u201315 cm diameter) arriving on the elevator rather than a continuous flow of smaller aggregates; these balls roll along the chain rather than breaking apart, blocking the separator outlet. Fix:<\/em> check the share’s working angle relative to the soil surface \u2014 the share leading edge should be at 15\u201322\u00b0 from horizontal; lower angles create a pushing\/compressing action that forms clay balls rather than the lifting\/fracturing action that disaggregates the ridge.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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Chain Speed on Clay \u2014 The Balance Between Blockage Prevention and Tuber Bruise<\/h2>\n

\"potato<\/p>\n

The most common operator response to clay blockage is to increase chain speed \u2014 and this is sometimes the correct response. But it is the second adjustment to make, not the first, and there is a ceiling beyond which increasing chain speed creates a different quality problem without solving the blockage. The correct adjustment sequence for clay conditions is strictly ordered:<\/p>\n

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Clay Blockage \u2014 Correct Adjustment Sequence<\/div>\n
\u2460<\/span><\/p>\n
Reduce forward speed first<\/strong> \u2014 halve the speed if needed (from 4 km\/h to 2 km\/h). This immediately reduces the clay mass arriving on the chain per unit time, giving existing clay more time to process before new clay loads the elevator. This is the highest-impact, lowest-bruise-risk adjustment available.<\/div>\n<\/div>\n
\u2461<\/span><\/p>\n
Increase chain speed moderately<\/strong> \u2014 move from the lowest working setting to the middle of the operating range. Monitor tuber quality: at moderate chain speed in clay, the soil mass around tubers provides some cushioning \u2014 the bruise risk is lower than the same chain speed on sandy soil, because clay aggregates absorb some impact energy. But continued increases above middle range will increase bruise.<\/div>\n<\/div>\n
\u2462<\/span><\/p>\n
Check chain tension<\/strong> \u2014 any time conditions change (field moisture increases across the day, new field), verify that chain tension is at the specified sag value. Tension decreases as the chain warms and stretches under load; check every 2\u20133 hours in heavy clay conditions.<\/div>\n<\/div>\n
\u2463<\/span><\/p>\n
If still blocking after \u2460 \u2461 \u2462 \u2014 stop and test soil moisture<\/strong>. If the clay fails the ball test (see below), harvest should not proceed regardless of machine settings. No combination of chain speed and forward speed adjustment compensates for clay at or above field capacity.<\/div>\n<\/div>\n<\/div>\n

The fundamental tension between anti-blockage chain speed and bruise-limiting chain speed is real and cannot be fully resolved by machine settings alone when the soil is too wet. This is why soil moisture timing is discussed last in the adjustment sequence but is actually the most important decision of the day: the operator who checks soil moisture before entering the field avoids both blockage and excessive bruise risk simultaneously.<\/p>\n

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Agitation Bars, Anti-Clog Devices, and Hardware Modifications<\/h2>\n

Where clay conditions are a recurring feature of a field or farm \u2014 not a seasonal exception but an annual challenge \u2014 hardware modifications to the elevator system can reduce the frequency and severity of blockage events. These modifications do not substitute for correct operating settings or correct harvest timing, but they extend the range of clay conditions within which the digger can operate acceptably.<\/p>\n

Agitation bars<\/strong> are cross-bars mounted transversely on the elevator chain frame (not on the chain itself \u2014 they are fixed to the side walls or intermediate supports of the elevator section). As the chain moves, clay bridging across the rod gaps is disrupted by the fixed agitation bars, which physically shear the clay bridges before they fully span the rod spacing. Most diggers are supplied with a base agitation bar set designed for sandy-loam conditions. For heavy clay, the manufacturer’s maximum agitation bar configuration should be fitted \u2014 typically 2\u20133 additional bars added to the lower half of the elevator where clay bridges form most readily. Fitting more bars than the manufacturer specifies risks reducing clearance and creating alternative blocking points; stay within the machine’s specified range.<\/p>\n

Rubber-tip wipers<\/strong> are flexible rubber fingers or strips fitted to the underside of the elevator frame, positioned so that they contact the steel rods as they pass at the bottom of the chain’s return loop. Their function is to mechanically scrape clay that has adhered to the rod surface during the elevator pass before the rod returns to the receiving end of the chain. Without wipers, a clay film builds up progressively on the rods across the harvest day; with wipers, each rod returns to the entry point cleaned of most adhered clay. Wipers are a low-cost, retrofit modification widely used in UK heavy land potato country and are available from most agricultural engineering suppliers as aftermarket accessories.<\/p>\n

Hydraulic agitation systems<\/strong> \u2014 available on some higher-specification trailed diggers and harvesters \u2014 provide an oscillating or vibrating secondary bar arrangement that actively disrupts clay bridges at a frequency matched to the chain speed. These systems are most effective on the heaviest clay soils (Flevoland polder clay, East Anglian chalky boulder clay, West Flemish maritime clay) where static agitation bars are insufficient. They add mechanical complexity and are not necessary for moderate heavy land \u2014 but for farms that regularly harvest very heavy, moist clay, the investment in a machine with hydraulic agitation is often recovered in reduced blockage downtime within two seasons.<\/p>\n

For enquiries on potato digger configurations with heavy land agitation options<\/a>, Korea Watanabe can confirm agitation bar specifications and compatibility for each machine in the range.<\/p>\n

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Soil Moisture Timing \u2014 The Field Tests That Make the Go or No-Go Decision<\/h2>\n

\"potato<\/p>\n

No combination of machine settings produces acceptable elevator performance in clay soil at or above field capacity. The soil moisture decision \u2014 made before the tractor enters the field, not after the first blockage confirms the problem \u2014 is the single most important clay-blockage prevention measure available. Two field tests, requiring no specialist equipment, provide reliable go\/no-go moisture assessment for clay soils.<\/p>\n

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THE BALL TEST \u2014 60-Second Field Moisture Check<\/div>\n
Procedure:<\/strong> Take a handful of soil from 20\u201325 cm depth (digging depth) in the field you intend to harvest. Compress the soil firmly in your fist into a ball approximately 5 cm diameter. Drop the ball from chest height (approximately 1.3 m) onto a hard surface (boot toe, tool handle, or the ground if hard).
\nStop \u2014 too wet:<\/strong> Ball stays intact or only partially cracks \u2014 clay is adhesive and will bridge elevator rods.
\nMarginal \u2014 proceed cautiously:<\/strong> Ball cracks into 3\u20135 pieces \u2014 harvest possible with reduced forward speed and maximum agitation.
\nGo \u2014 acceptable:<\/strong> Ball shatters into 6+ fragments or crumbles completely \u2014 clay moisture is low enough for manageable elevator separation.<\/div>\n<\/div>\n
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THE SMEAR TEST \u2014 Clay Particle Adhesion Check<\/div>\n
Procedure:<\/strong> Take a small amount of the same soil sample. Rub it between thumb and forefinger with moderate pressure.
\nStop \u2014 too wet:<\/strong> Soil smears into a smooth, continuous, lustrous film without any gritty feeling \u2014 clay particles are fully dispersed and maximally adhesive.
\nMarginal:<\/strong> Smears but shows some particulate texture \u2014 proceed with caution at reduced speed.
\nGo:<\/strong> Breaks into particles when smeared, or shows clear gritty texture \u2014 clay is drier and less adhesive; acceptable conditions for digger operation.<\/div>\n<\/div>\n<\/div>\n

After significant rainfall on clay soils, the waiting period before harvest conditions become acceptable typically ranges from 3\u20135 days in warm, dry, windy conditions to 7\u201310 days in cool, overcast conditions. Penetrometer testing at 25 cm depth provides quantitative confirmation: readings above 1.0 MPa at digging depth typically indicate acceptable clay moisture for digger operation; readings below 0.8 MPa indicate high blockage risk. These thresholds vary by clay type and should be calibrated against actual harvest experience on each specific field for the first season, then used as the site-specific threshold in subsequent years.<\/p>\n

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Domande frequenti<\/h2>\n
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\n\u25b6<\/span>The digger works fine for the first two hours on clay then starts blocking every 20 minutes \u2014 what is causing the pattern?<\/summary>\n

This time-progressive pattern is one of the most common clay blockage presentations and has three possible causes operating simultaneously. First: chain tension decreases as the chain warms and stretches slightly under load \u2014 a chain that is correctly tensioned at the start of the day can be 5\u201310 mm loose by mid-morning, creating the slack that allows clay accumulation. Check and re-tension every 2\u20133 hours in clay conditions. Second: soil moisture in the field is not uniform \u2014 the low-lying or north-facing areas that were still moist at the start of the day become the areas where the digger reaches after the first two hours’ progress. The moisture variation across a clay field can be significant enough to take conditions from acceptable to problematic within a single field. Third: the digger’s agitation bars and wipers accumulate their own clay build-up during the first two hours, reducing their effectiveness progressively. Stop at the two-hour mark, check the bar and wiper condition, clear any clay from the bar faces, and re-tension the chain before continuing.<\/p>\n<\/details>\n

\n\u25b6<\/span>Should I increase chain speed or decrease forward speed when clay starts building on the elevator \u2014 which is more effective?<\/summary>\n

Decrease forward speed first \u2014 this is consistently more effective as a first response. The reason: increasing chain speed moves clay that is already on the elevator faster, but does not reduce the rate of new clay arriving. If the rate of clay arrival exceeds the chain’s clearing rate, increasing chain speed only delays the blockage event rather than preventing it. Reducing forward speed directly reduces the rate of arrival \u2014 delivering less clay per unit time gives the existing chain capacity and speed adequate time to process the load before the next batch arrives. In practice, halving forward speed (from 4 km\/h to 2 km\/h) typically doubles the chain’s available processing time per unit of clay delivered, which is the equivalent of doubling chain speed without the tuber bruise penalty. Once forward speed is at the minimum practical level (typically 1.5\u20132 km\/h \u2014 slower creates other problems including ridge collapse and uneven digging), a moderate chain speed increase is the correct second adjustment.<\/p>\n<\/details>\n

\n\u25b6<\/span>Does a riddle frame separator perform better or worse than star wheels in clay blockage conditions?<\/summary>\n

Star wheels perform better in clay for the separator function (final separation of adhered clay from tubers) because their active rotation physically breaks clay aggregates that have survived the elevator. However, the blockage problem on clay occurs primarily in the elevator section \u2014 before the separator \u2014 where neither star wheels nor riddle frames are present. The separator type is therefore secondary to the elevator design for clay blockage prevention: a machine with excellent star wheel separation can still block in the elevator section if the clay is too wet. The elevator design \u2014 rod spacing, agitation bar number and position, chain speed range \u2014 is the relevant specification for clay blockage tolerance. For separator selection on clay soils, star wheels are strongly preferred for the separation quality reason; for elevator design, the relevant specifications are rod spacing (wider = less bridging risk; 30\u201335 mm preferred for heavy clay) and agitation bar provision.<\/p>\n<\/details>\n

\n\u25b6<\/span>Can a stone management programme reduce clay blockage as well as stone damage?<\/summary>\n

Not directly \u2014 stone management removes stones from the soil profile but does not change the clay mineral content or moisture behaviour of the clay fraction. However, there is an indirect connection: on soils that are both clay-heavy and stony (some Scottish black soils, chalky boulder clay in East Anglia, some Midlands clay fields with periglacial stone), the stones in the elevator stream act as natural agitation agents \u2014 tumbling against clay aggregates on the chain and helping break them apart. Removing all stones through an aggressive stone clearance programme on such soils can, paradoxically, slightly reduce natural agitation and increase pure clay blockage tendency, because the agitation contribution of the stones is eliminated. In practice this effect is small compared to the machinery damage and safety benefits of stone removal, and the solution \u2014 fitting additional agitation bars after stone clearance on clay fields \u2014 is straightforward. The recommendation: proceed with stone clearance on any soil type where stone density warrants it, then assess agitation bar configuration in the first post-clearance harvest season and add bars if clay separation performance has declined.<\/p>\n<\/details>\n

\n\u25b6<\/span>Is there a shear bolt specification guidance for clay soil to prevent chain damage when blockage does occur?<\/summary>\n

Yes \u2014 the shear bolt (or shear pin) fitted in the digger’s PTO drive line is specifically designed to fail before the chain, gearbox, or drive shaft sustains damage when a blockage occurs. The shear bolt’s failure torque must be correctly specified: too strong, and the chain or gearbox is damaged before the shear bolt fails; too weak, and it fails unnecessarily under normal heavy-soil operating loads (not just blockage events). Most manufacturers specify shear bolt grade and diameter for standard soil conditions, and a separate specification for heavy clay\/high-torque conditions. In clay country, fitting the manufacturer’s heavy-soil shear bolt specification \u2014 not a generic substitute \u2014 is strongly recommended, because the clay blockage event produces a torque spike that can be significantly above normal operation but below the chain’s damage threshold; the correctly specified bolt will intercept this event. Carrying a stock of the correct shear bolt (and the tools to replace it in the field within 5 minutes) is standard practice for any UK or Belgian clay-country potato operation \u2014 budget for 2\u20133 shear bolt events per harvest season on heavy clay.<\/p>\n<\/details>\n<\/div>\n

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Clay Blockage on Your Farm?<\/p>\n

Share your soil type, clay fraction estimate, current agitation bar configuration, and typical harvest moisture. Korea Watanabe will confirm the correct agitation specification and chain settings for your scavapatate<\/a> on heavy land.<\/p>\n

Corea Watanabe Rock Crusher Tractor Co., Ltd. \u2014 Ansan-si, Gyeonggi-do<\/p>\n<\/div>\n

Heavy Land Technical Support<\/a><\/div>\n<\/div>\n<\/div>\n

Redattore: Cxm<\/p>\n<\/div>","protected":false},"excerpt":{"rendered":"

PROBLEM AND SOLUTION \u2014 CLAY SOIL Potato Digger Blockage Clay Soil \u2014 Causes and Fixes Clay blockage is not a machine fault. It is the wrong combination of soil moisture, chain speed, and forward speed for a soil type that has different rules from sandy loam. Getting those three settings right \u2014 in the right […]<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[31],"tags":[],"class_list":["post-1189","post","type-post","status-publish","format-standard","hentry","category-application-and-technical-guid"],"_links":{"self":[{"href":"https:\/\/rock-crusher-tractor.com\/it\/wp-json\/wp\/v2\/posts\/1189","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/rock-crusher-tractor.com\/it\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rock-crusher-tractor.com\/it\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rock-crusher-tractor.com\/it\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/rock-crusher-tractor.com\/it\/wp-json\/wp\/v2\/comments?post=1189"}],"version-history":[{"count":1,"href":"https:\/\/rock-crusher-tractor.com\/it\/wp-json\/wp\/v2\/posts\/1189\/revisions"}],"predecessor-version":[{"id":1193,"href":"https:\/\/rock-crusher-tractor.com\/it\/wp-json\/wp\/v2\/posts\/1189\/revisions\/1193"}],"wp:attachment":[{"href":"https:\/\/rock-crusher-tractor.com\/it\/wp-json\/wp\/v2\/media?parent=1189"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rock-crusher-tractor.com\/it\/wp-json\/wp\/v2\/categories?post=1189"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rock-crusher-tractor.com\/it\/wp-json\/wp\/v2\/tags?post=1189"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}