LAND IMPRINTING METHODS (page 3) Prepared for Discovery Park, Safford, Arizona, by Ted St. John, Ph.D. Construction of the Land Imprinter A   number   of   land   imprinters   are   in   use   in Arizona   and   California,   but   at   the   time   of   this writing   there   is   no   manufacturer   in   routine   production.   Several   machine   shops   have constructed   land   imprinters,   as   have   individuals   with   the   facilities   and   skills   to   cut, handle, and weld large pieces of metal. Detailed   specifications   for   the   construction   of   a   land   imprinter,   including   diagrams   and measurements,   are   available   from   the   Imprinting   Foundation.   The   specifications   have also   been   posted   at   www.mycorrhiza.org   ,   where   they   can   be   downloaded   in   PDF format. Imprinters   constructed   to   date   have   cost   between   $6000   and   $15,000,   depending   on the   size   and   complexity,   and   whether   the   owner   did   part   of   the   construction.   Several contractors   in   California   and   elsewhere   own   imprinters   and   will   undertake   imprinting work   within   a   reasonable   distance   of   their   base   of   operations.   Discovery   Park   has   an older   style   land   imprinter,   and   parts   of   several   others,   that   are   available   for   loan   to qualified agencies and individuals. The land imprinter includes several subsystems: the frame, the roller, the ballast, and the material delivery mechanisms:                                                   Frame:    A   substantial   metal   frame   holds   the   other   components   in   their   proper   spatial relationships,   and   provides   a   means   for   a   tractor   to   tow   the   assembly.   The   tow   bar   is detachable   for   transport,   and   may   be   attached   to   either   end   of   the   symmetrical   frame. By   providing   the   ability   to   tow   the   unit   in   either   direction,   the   operator   may   distribute wear   on   both   the   front   and   back   surfaces   of   the   metal   teeth,   extending   the   life   of   the roller. Roller:   The   roller   consists   of   a   cylinder   20   to   24   inches   in   diameter.   Larger   rollers   used in   the   past   proved   very   difficult   to   transport.   Rollers   smaller   than   20   inches   often   slide rather   than   roll   in   wet   soil,   and   tend   to   round   the   tops   of   the   ridges.   The   length   of   the roller   is   usually   limited   to   eight   feet,   since   longer   rollers   leave   large   patches   of   flat ground   when   one   end   rides   up   on   a   rock.   There   is   no   theoretical   limit   to   the   width   on level,   stone-free   ground,   but   it   is   generally   preferable   to   gang   several   rollers   rather than construct a single very long roller. The    teeth    of    the    imprinter    push    soil    both    forward    and    backward,    into    the    cavity between   the   teeth.   Most   imprinter   teeth   are   6"   or   8"   on   a   side,   resulting   in   troughs 41/4"   or   55/8"   deep. As   with   all   aspects   of   equipment   design,   there   are   trade-offs   with tooth   size.   Larger   teeth   may   be   necessary   to   cut   through   accumulated   vegetation,   or smaller teeth may be needed for higher plant density. Tooth   shape   is   another   variable   in   imprinter   design.   Teeth   wider   than   90   °   have   trouble cutting   into   the   soil.   Teeth   narrower   than   90   °   may   bury   the   seed   too   deep.   However, narrower   angles   are   appropriate   on   steep   slopes   or   in   very   hard   soil.   The   most   current tooth   design   is   a   tooth   with   a   90   °   angle   but   the   legs   pressed   inward   to   give   a   narrow base.   This   design   penetrates   the   soil   well   yet   maintains   the   advantages   of   tooth height. The   apex   of   the   angle   may   in   some   cases   be   offset   to   the   rear,   giving   a   "saw   tooth" pattern.   Saw   tooth   patterns   work   well   on   steep   slopes,   but   the   long   side   must   always be   oriented   upslope   to   hold   water.   Imprinters   with   saw   tooth   patterns   are   not   reversible to   distribute   tooth   wear,   and   have   been   replaced   by   symmetrical   teeth   with   narrow bases. Imprinter   teeth   are   ideally   10"   in   length,   since   longer   teeth   can   lead   to   depressions   that accumulate    too    much    water    and    contribute    to    erosion.    The    imprinter    should    be designed   so   that   the   ends   of   the   teeth   are   separated   by   two   inches,   leaving   a   dam between impressions to prevent movement of water. The   teeth   are   arranged   in   rings   around   the   drum.   The   rings   are   12"   wide,   counting   the 10"   tooth   length   and   2"   between   rings,   to   give   a   water-confining   wall   between   imprints. Adjacent   rings   are   offset   by   one   half   the   width   of   a   tooth,   so   that   the   depressions   left by the roller are staggered. Ballast:    Ballast   tanks   are   balanced   over   the   roller,   to   help   maintain   a   center   of   gravity directly    over    the    axle.    They    are    filled    with    water    and    have    a    provision    for    easy drainage.   They   should   have   sufficient   capacity   that   the   total   weight   over   the   axle   can be   varied   from   500   to   1000   lb.   per   foot   of   roller   length.   I.e.,   an   imprinter   with   an   eight- foot roller should be adjustable from two to four tons in weight. Older   style   imprinters   with   a   very   large   diameter   roller   used   the   roller   itself   to   hold water   or   a   mixture   of   soil   and   water.   Newer   imprinters   use   tanks   both   in   front   of   and behind   the   roller   to   hold   water.   Other   systems   have   used   boxes   full   of   bricks,   or   trays that   could   accommodate   large   metal   castings   or   old   engine   blocks.   Newer   imprinters require   less   weight   than   the   old   style   with   large   rollers.   The   smaller   diameter   rollers with   staggered   rings   of   teeth   mean   that   fewer   teeth   contact   the   ground   at   any   one time.   This   means   that   the   weight   is   distributed   among   fewer   teeth,   and   less   weight   is required to achieve the same quality of imprint. Material   delivery :   Seeds   and   mycorrhizal   inoculum   are   delivered   from   bins   onto   the surface   of   the   roller,   where   they   are   pressed   into   contact   with   the   soil,   or   incorporated a   short   distance   into   the   soil.   The   bins   are   often   fertilizer   or   seed   boxes   purchased from   agricultural   equipment   manufacturers.   The   seed   and   inoculum   boxes   may   be manufactured   according   to   the   construction   specifications   available   from   the   Imprinting Foundation.   The   agitator   and   drive   mechanisms   in   that   design   are   elegant   in   their simplicity,   and   have   proven   more   effective   and   reliable   than   many   of   the   complex commercial designs. If   mycorrhizal   inoculum   is   fed   from   a   separate   supply   it   may   be   injected   in   lines   into   the ground   through   hollow   shanks,   or   dropped   through   tubes   behind   a   series   of   small ripping   teeth   or   disks.   In   most   cases   the   inoculum   is   mixed   with   the   seed.   Although some   of   the   inoculum   does   not   get   properly   incorporated   when   it   is   mixed   with   the seed,   the   wasted   inoculum   has   turned   out   to   be   a   fair   trade   for   the   extra   labor   that   was required to clean and maintain a separate delivery system.