{"id":867,"date":"2026-05-15T07:28:23","date_gmt":"2026-05-15T07:28:23","guid":{"rendered":"https:\/\/foragebaler.com\/?p=867"},"modified":"2026-05-15T07:28:23","modified_gmt":"2026-05-15T07:28:23","slug":"pre-cut-knife-system-setup-wear-and-when-to-engage","status":"publish","type":"post","link":"https:\/\/foragebaler.com\/fr\/pre-cut-knife-system-setup-wear-and-when-to-engage\/","title":{"rendered":"Pre-Cut Knife System: Setup, Wear, and When to Engage"},"content":{"rendered":"
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<\/div>\n
Baler Cutting System Reference<\/span><\/p>\n

Pre-Cut Knife System: Setup, Wear, and When to Engage<\/h1>\n

The pre-cut knife system on a round baler is the most frequently misused feature on the machine. Many operators leave knives permanently engaged regardless of crop or end use. Others disengage them entirely after one difficult day and never re-engage. Both approaches waste either the system’s quality benefits or the machine’s full potential. This guide covers the precise conditions that determine the right engagement setting, how to set knife depth correctly, and what knife wear looks like before it becomes a problem.<\/p>\n

Engagement Decision Guide<\/a>
\nGet Knife System Support<\/a><\/div>\n<\/div>\n<\/div>\n
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What the Pre-Cut System Does \u2014 and What It Costs You to Run It Wrong<\/h2>\n

The pre-cut knife system (also called the chopper, pre-cutter, or knife bank) consists of a bank of fixed blades positioned at the pickup outlet that the crop stream passes through before entering the bale chamber. As crop flows over the knives, stems are cut to shorter lengths \u2014 typically 2 to 6 inches depending on the number of knives engaged and the knife geometry. This particle size reduction has several measurable effects: it increases bale density by allowing finer material to pack more tightly; it improves silage fermentation by exposing more cut stem surfaces to lactic acid bacteria; and it improves fiber digestibility for ruminants by reducing the physical length of the indigestible cell wall fraction.<\/p>\n

The cost of operating the system incorrectly comes from two directions. Running all knives on dry hay for an elevator market reduces the hay’s physical length \u2014 and many elevator buyers pay a premium specifically for long-stemmed hay. Running no knives on silage that will be fed to a high-producing dairy herd denies those animals the fiber length reduction that improves total mixed ration digestibility. The correct knife engagement is crop-specific, end-use-specific, and sometimes field-specific.<\/p>\n

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+10\u201318%<\/div>\n
Bale density increase from pre-cut engagement in alfalfa<\/div>\n<\/div>\n
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2\u20136 in<\/div>\n
Typical particle length produced; fewer active knives = longer particles<\/div>\n<\/div>\n
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3\u20135\u00d7<\/div>\n
Higher shear bolt consumption when knives are engaged in stony or contaminated windrows<\/div>\n<\/div>\n<\/div>\n<\/div>\n
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When to Engage and When to Disengage: The Decision Table<\/h2>\n

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The engagement decision has four inputs: crop type, end-use market, field contamination risk, and current knife condition. When any one of these inputs changes, the engagement decision should be revisited. The following table gives the baseline recommendation for the most common combinations:<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n\n\n
Crop \/ end use<\/th>\nKnives engaged?<\/th>\nHow many<\/th>\nReason<\/th>\n<\/tr>\n<\/thead>\n
Alfalfa \u2192 silage \/ haylage<\/td>\nYes<\/td>\nFull bank or 50\u201375%<\/td>\nShorter particles improve fermentation surface area, packing density, and ruminant fiber digestibility<\/td>\n<\/tr>\n
Alfalfa \u2192 dairy elevator premium<\/td>\nNo<\/td>\nFully disengaged<\/td>\nPremium elevator and Japan export buyers require long-stem physical structure; cutting reduces acceptance grade<\/td>\n<\/tr>\n
Alfalfa \u2192 beef hay, on-farm<\/td>\nOptional<\/td>\n25\u201350%<\/td>\nModest cutting improves density and ring feeding efficiency without sacrificing market value; full cutting not needed<\/td>\n<\/tr>\n
Grass hay \u2192 horse market<\/td>\nNo<\/td>\nFully disengaged<\/td>\nHorse buyers specifically reject cut hay; dust and short particles reduce palatability and can contribute to respiratory issues<\/td>\n<\/tr>\n
Wheat \/ barley straw \u2192 biomass<\/td>\nYes<\/td>\nFull bank<\/td>\nMaximum density; shorter straw packs tighter, improving bulk density in transport and combustion efficiency in boilers<\/td>\n<\/tr>\n
Straw \u2192 livestock bedding<\/td>\nOptional<\/td>\n25\u201350%<\/td>\nShort straw bedding absorbs moisture more efficiently than long; excessive cutting creates dust that affects animal respiratory health<\/td>\n<\/tr>\n
Cover crop \u2192 silage<\/td>\nPartial (4\u20136 knives)<\/td>\n50% of bank<\/td>\nFull bank creates ultra-short particles that pass through net wrap mesh before film can seal; partial engagement balances fermentation benefit vs. wrap integrity<\/td>\n<\/tr>\n
Any crop \u2014 rocky \/ stony field<\/td>\nNo<\/td>\nFully disengaged<\/td>\nRock impacts on engaged knives shatter blade edges immediately and cause shear bolt cascade failures; disengage before entering known stony sections<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n
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How Pre-Cut Knives Work Mechanically \u2014 and What That Means for Depth Setting<\/h2>\n

\"round<\/p>\n

Pre-cut knives are stationary blades mounted in a bank beneath the crop flow path. A rotor with counter-blades or ridges passes above the knife bank, creating a shearing action as crop is drawn through. The depth to which each knife extends into the crop stream \u2014 knife depth or knife protrusion \u2014 determines both cutting efficiency and shear bolt load. Knives set too shallow contact insufficient crop to cut cleanly; knives set too deep create excessive resistance that fires shear bolts unnecessarily.<\/p>\n

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Knife Depth Setting Procedure<\/div>\n
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1<\/div>\n

Disengage the PTO and remove power completely<\/strong> before any knife system access. Pre-cut knives are adjacent to the rotor, which spins at high velocity \u2014 this is a severe stored-energy hazard if PTO is inadvertently engaged during adjustment.<\/p>\n<\/div>\n

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2<\/div>\n

Locate the knife depth adjustment<\/strong> on each individual knife position. Most designs use a slotted or threaded holder that allows the knife to be raised or lowered relative to the rotor. The operator’s manual specifies the nominal protrusion distance (typically 5\u201315mm above the rotor surface for standard hay crops).<\/p>\n<\/div>\n

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3<\/div>\n

Set all engaged knives to the same protrusion depth.<\/strong> Uneven knife depths create uneven loading \u2014 the deepest-set knife fires its shear bolt first while shallower knives are still functional. The goal is simultaneous load distribution across all active knives.<\/p>\n<\/div>\n

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4<\/div>\n

Run a test pass on 5\u201310 bales and assess particle length.<\/strong> Sample the bale by pulling a handful of material from the bale face after ejection. Desired length depends on use: 3\u20134 inches for silage or high-density hay; 5\u20136 inches for on-farm beef feeding. Adjust knife depth up (more protrusion) to cut shorter; down (less protrusion) to cut longer.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

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Knife Wear: Four Indicators That Mean Replacement Is Due<\/h2>\n

Pre-cut knives are consumable items \u2014 they wear predictably and should be replaced on a schedule based on material processed, not just when they stop cutting entirely. A worn knife that still appears to cut is cutting less efficiently: higher shear bolt consumption, higher power draw, and longer particles than the same knife when new. The four indicators that replacement is approaching:<\/p>\n

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1<\/div>\n
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Visible edge rounding<\/div>\n

Run your thumbnail along the knife edge. A sharp knife has a distinct edge that catches the thumbnail. A worn knife feels smooth and rounded \u2014 the cutting edge has been abraded away. Any knife where the edge feels uniformly smooth should be replaced or resharpened before the next baling session.<\/p>\n<\/div>\n<\/div>\n

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2<\/div>\n
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Increased shear bolt consumption at same knife depth<\/div>\n

A dull knife does not shear crop cleanly \u2014 it pushes and compresses rather than cutting, requiring more force to process the same crop volume. If your shear bolt consumption increases noticeably from one season to the next at the same settings, dull knives are the most common cause. Compare bale count per shear bolt across seasons to detect the trend before it becomes acute.<\/p>\n<\/div>\n<\/div>\n

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3<\/div>\n
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Particle length longer than set depth should produce<\/div>\n

If the bale sample shows particles consistently longer than the knife depth setting should produce \u2014 particles 6\u20138 inches when knife depth targets 3\u20134 inches \u2014 the knives are deflecting under load rather than cutting. This indicates wear beyond the point where additional protrusion depth can compensate. Replace the knife set.<\/p>\n<\/div>\n<\/div>\n

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4<\/div>\n
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Chipping or visible edge damage<\/div>\n

Any knife with a chipped cutting edge \u2014 caused by rock contact or metal object impact \u2014 should be replaced immediately regardless of overall wear level. A chipped edge creates an irregular shearing geometry that both reduces cut quality and creates a stress concentration point that can fracture further under normal cutting loads.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

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Shear Bolt Management: Understanding Cascade Failures<\/h2>\n

Shear bolts in the pre-cut knife system are the overload protection mechanism \u2014 they break before the knife mounting hardware, rotor, or gearbox is damaged by a rock or dense object impact. A single shear bolt event is normal and expected in any field with modest debris. A cascade failure \u2014 multiple shear bolts firing in rapid succession on the same day \u2014 indicates a systematic problem rather than isolated impacts.<\/p>\n

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Normal shear bolt rate<\/div>\n

1\u20133 shear bolt events per 100 bales in clean, established hay fields without unusual debris. At this rate, keep 15\u201320 pre-cut shear bolts in the tractor cab at all times. Each event is an isolated rock or dense stem cluster \u2014 replace and continue without adjusting knife depth.<\/p>\n<\/div>\n

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Elevated rate (3\u20138 per 100 bales)<\/div>\n

Check: are you in a rocky field section? Is knife depth set too aggressively for this crop density? Are the knives dull (see Indicator 2 above)? Reduce knife depth by 3\u20135mm and retest. If the rate drops, knife depth was the cause. If rate stays elevated, field debris is the cause \u2014 consider partial knife disengagement in that field section.<\/p>\n<\/div>\n

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Cascade failure (3+ bolts in 5 bales)<\/div>\n

Stop and inspect. Cascade failures are almost always caused by: a dense object lodged in the crop path that is being recycled; a wrong-spec shear bolt installed (lower grade than OEM specification fires at lower force); or a knife that has cracked and is now catching the rotor on each revolution. Each repeated firing increases the risk of rotor or mounting hardware damage.<\/p>\n<\/div>\n<\/div>\n

Critical: only use OEM-specification shear bolts.<\/strong> Using a higher-grade bolt than specified does not provide better protection \u2014 a grade 8 bolt where a grade 5 is specified will not break under the overload load, transferring the full impact force to the knife mounting hardware and rotor. The shear bolt is designed to be the weakest link in the system; substituting a stronger bolt defeats the entire purpose of the overload protection design.<\/div>\n<\/div>\n
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Partial Knife Engagement: Why Half the Bank Often Outperforms All or Nothing<\/h2>\n

The option to engage only a subset of the knife bank \u2014 25%, 50%, or 75% of available knives rather than all or none \u2014 is underused by most operators. Partial engagement allows precise control over particle length, power draw, and shear bolt consumption that binary all-or-nothing switching cannot achieve. The spacing of the active knives determines the cutting frequency \u2014 with every other knife active, you produce approximately twice the particle length as with all knives active at the same depth setting.<\/p>\n

The partial engagement approach is particularly effective for: on-farm beef hay where some density improvement is valuable but full-length fiber is still preferred; first-cut alfalfa with heavy windrows where full knife engagement at maximum depth creates excessive HP demand; and any field transitioning between rocky and clean sections where a quick partial disengage on the headland avoids the rock exposure while maintaining cutting in the clean center sections. For the interaction between pre-cut knife engagement and pickup system performance \u2014 specifically how knife particle size affects crop flow through the pickup transition zone \u2014 the pickup system guide<\/a> covers the crop flow path upstream of the knife bank. For diagnosing knife system symptoms that appear as operational problems during baling, see the guide de d\u00e9pannage des presses \u00e0 balles<\/a>. The rotor drive shaft specifications and gearbox torque ratings that determine the maximum knife loading the drive system can sustain are covered in sp\u00e9cifications des composants de la bo\u00eete de vitesses agricole et de la prise de force<\/a>.<\/p>\n<\/div>\n

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Pre-Season Knife System Checklist<\/h2>\n

\"foragebaler.com<\/p>\n

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All knife edges<\/div>\n
Thumbnail test each knife; replace any knife with rounded, smooth, or chipped edge. Inspect for micro-cracks at blade base \u2014 a crack at the base can cause sudden fracture under normal load.<\/div>\n<\/div>\n
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Knife depth settings<\/div>\n
Verify all active knives are set to the same protrusion depth with a ruler or depth gauge. Measure each position and adjust any that deviate more than 2mm from the target depth.<\/div>\n<\/div>\n
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All shear bolts<\/div>\n
Confirm all shear bolts are OEM-specification grade and fully installed. Check that none have partially sheared from the previous season’s operation without being noticed. Stock 20+ OEM-spec shear bolts in the tractor cab before season start.<\/div>\n<\/div>\n
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Knife holder hardware<\/div>\n
Inspect all knife mounting hardware for wear elongation of the bolt hole or cracks in the knife holder casting. A holder with an elongated mounting slot allows knife vibration that accelerates edge wear and shear bolt consumption.<\/div>\n<\/div>\n
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Engagement mechanism<\/div>\n
Test the knife engagement\/disengagement mechanism with PTO off \u2014 confirm all knives engage and disengage cleanly from their parked position. A knife that sticks partially engaged will fire its shear bolt on the first bale of operation.<\/div>\n<\/div>\n<\/div>\n<\/div>\n
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Pre-Cut Knife System FAQs<\/h2>\n
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\nWill engaging the pre-cut knives significantly reduce baler throughput or ground speed?+<\/span><\/summary>\n
Yes \u2014 the pre-cut system adds HP demand to the baling operation. A fully engaged knife bank at recommended depth typically adds 8\u201315% HP requirement compared to the same baler with knives disengaged. In a heavy first-cut alfalfa windrow where the baler is already operating near maximum HP capacity, this additional demand can cause engine lug events that force reduced ground speed. The practical approach: if your tractor has adequate HP reserve for the knife system (check: does PTO RPM remain above 500 RPM during peak chamber loading with knives engaged?), you can maintain full baling speed. If PTO RPM drops significantly under load with knives engaged, reduce either knife depth or ground speed by 10\u201315% to restore engine reserve margin.<\/div>\n<\/details>\n
\nCan I sharpen pre-cut knives rather than replacing them?+<\/span><\/summary>\n
Yes \u2014 pre-cut knives can typically be resharpened 2\u20133 times before they reach minimum usable thickness. Resharpening is done on a bench or angle grinder by restoring the original bevel angle on the cutting edge face. Do not grind the flat back face \u2014 grind only the beveled cutting face to maintain the original edge geometry. After resharpening, all active knives should be resharpened to the same edge profile to maintain consistent cutting across the full knife bank. Keep the knife cool during grinding to avoid drawing the temper from the steel \u2014 grinding with excessive heat creates a soft zone behind the edge that dulls more rapidly than the original heat-treated steel. Wet grinding or using short grinding bursts with cooling intervals between passes prevents heat buildup.<\/div>\n<\/details>\n
\nMy shear bolt breaks but no rock or object impact is apparent. What else causes shear bolt failure?+<\/span><\/summary>\n
Several non-rock causes trigger shear bolt failures in pre-cut systems: (1) knife depth set too aggressively for crop density \u2014 the accumulated load from cutting through a particularly dense section of windrow exceeds the shear bolt’s rated load even without a discrete impact; (2) incorrect-spec replacement bolt (a lower-grade bolt fires at lower force than OEM design); (3) dull knife that requires more force to cut the same crop volume as a sharp knife \u2014 sometimes doubling the instantaneous load peak; (4) a partially disengaged knife that is catching the rotor edge rather than the cutting surface, creating impact rather than shear loading; and (5) drive system alignment issue \u2014 a rotor that is not running concentric with the knife bank creates a periodic load spike each revolution that fires bolts at predictable intervals regardless of crop density.<\/div>\n<\/details>\n
\nDoes pre-cutting hay reduce its shelf life in outdoor storage?+<\/span><\/summary>\n
Slightly \u2014 but the effect is modest in well-formed bales. The concern is that shorter cut particles pack more densely, leaving less air void space in the bale structure. This increased density has two opposing effects on outdoor storage: it reduces the bale’s surface-to-volume ratio (good \u2014 proportionally less surface is exposed to weathering per ton), but it also reduces the bale’s ability to shed water from the curved surface (the tighter outer layer acts more like a flat surface, reducing runoff). Net effect over a 6-month outdoor storage period is approximately 1\u20132% higher DM loss in pre-cut bales compared to long-fiber bales in the same storage conditions. For most on-farm uses this difference is not significant. For commercial hay stored 6\u201312 months outdoors in wet climates, consider covered storage for pre-cut bales to eliminate this modest additional weathering risk.<\/div>\n<\/details>\n
\nCan I install a pre-cut knife system on a baler that did not come with one?+<\/span><\/summary>\n
For balers from manufacturers that offer the pre-cut system as an optional accessory on that model, a factory retrofit kit is typically available and can be installed with basic mechanical skills. For balers from manufacturers that do not offer a pre-cut option, or for models where the pickup-to-chamber geometry is not compatible with a knife bank, aftermarket knife systems are available from third-party manufacturers \u2014 but compatibility, mounting geometry, and shear bolt specification must all be confirmed before purchase. Adding a knife bank to a baler designed without one requires careful attention to: crop flow path clearance (the knife bank must not create a restriction that jams in heavy windrow conditions); rotor clearance (counter-blade geometry must match the rotor surface on that specific model); and drive system capacity (confirm the main gearbox and PTO shaft can sustain the additional HP demand). Contact the baler manufacturer’s technical support before purchasing any aftermarket knife system for compatibility confirmation.<\/div>\n<\/details>\n
\nHow does knife engagement affect bale net wrap performance?+<\/span><\/summary>\n
Pre-cut engagement at standard depth (3\u20136 inches particle length) has no meaningful effect on net wrap performance. However, full knife engagement at maximum depth producing very short particles (1\u20132 inches) can create a bale surface that is finer than standard net wrap mesh openings \u2014 fine particles can protrude through net wrap diamond mesh during the wrap cycle, creating small punctures and reducing the wrap’s structural integrity. This is most relevant for silage bales where the net wrap under-layer must maintain its structural integrity during film wrapping. For silage baling with the full knife bank engaged, consider using a finer-mesh net wrap specification (ask supplier for mesh opening size) or reducing knife engagement to 50% of the bank to limit the ultra-short particle fraction in the outer bale layer.<\/div>\n<\/details>\n<\/div>\n<\/div>\n
\"foragebaler.com<\/p>\n

Get Knife System Specifications and Setup Support<\/h3>\n

Knife bank configuration, individual knife depth specification, and OEM shear bolt grade documented with every baler that includes the pre-cut system. Tell us your primary crop and end-use market \u2014 we confirm the right engagement setting before delivery.<\/p>\n

Get Knife System Support<\/a><\/p>\n<\/div>\n

\u00c9diteur : Cxm<\/p>\n<\/div>","protected":false},"excerpt":{"rendered":"

Baler Cutting System Reference Pre-Cut Knife System: Setup, Wear, and When to Engage The pre-cut knife system on a round baler is the most frequently misused feature on the machine. Many operators leave knives permanently engaged regardless of crop or end use. Others disengage them entirely after one difficult day and never re-engage. Both approaches […]<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[28],"tags":[],"class_list":["post-867","post","type-post","status-publish","format-standard","hentry","category-forage-baler"],"_links":{"self":[{"href":"https:\/\/foragebaler.com\/fr\/wp-json\/wp\/v2\/posts\/867","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/foragebaler.com\/fr\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/foragebaler.com\/fr\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/foragebaler.com\/fr\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/foragebaler.com\/fr\/wp-json\/wp\/v2\/comments?post=867"}],"version-history":[{"count":2,"href":"https:\/\/foragebaler.com\/fr\/wp-json\/wp\/v2\/posts\/867\/revisions"}],"predecessor-version":[{"id":869,"href":"https:\/\/foragebaler.com\/fr\/wp-json\/wp\/v2\/posts\/867\/revisions\/869"}],"wp:attachment":[{"href":"https:\/\/foragebaler.com\/fr\/wp-json\/wp\/v2\/media?parent=867"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/foragebaler.com\/fr\/wp-json\/wp\/v2\/categories?post=867"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/foragebaler.com\/fr\/wp-json\/wp\/v2\/tags?post=867"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}