Land Imprinting Methods (page 4) Prepared for Discovery Park, Safford, Arizona, by Ted St. John, Ph.D.   Other   designs:   Most   of   the   people   who   have   built their   own   imprinters   have   introduced   variations   on   the   basic   design,   either   to   reduce construction   costs   or   to   add   what   the   builders   considered   to   be   improvements.   In most   cases   these   have   not   worked   out   well.   Examples   include   a   roller   so   small   that   it slides   rather   than   rolls   when   the   ground   is   wet,   a   unique   tooth   design   that   leaves more    flat    ground    than    imprinted    area,    and    a    frame    of    light    design    that    cannot accommodate   enough   weight   to   properly   imprint   hard   soils.   Other   "improvements" have   included   low-cost   bearings   on   the   roller   that   resulted   in   immediate   breakage, and   a   drive   mechanism   for   a   seed   bin   agitator   that   was   so   complex   that   the   operator spent   more   time   repairing   than   using   it.   Most   of   the   mistakes   have   resulted   from   a misunderstanding   of   the   reasons   for   the   original   design,   or   a   lack   of   experience   in field   operation   with   the   stock   version.   In   general,   it   is   better   to   reserve   modifications to   the   imprinter's   design   until   after   one   has   accumulated   some   experience   with   the basic model. Dr.   Bob   Dixon   has   continually   improved   the   imprinter   over   the   years,   and   the   most recent    models    bear    only    limited    resemblance    to    the    earliest    versions.   A    recent variation   includes   a   design   that   clamps   onto   the   blade   of   a   bulldozer,   with   the   weight provided   by   the   tractor's   hydraulic   system   rather   than   ballast.   This   version   can   climb steep   slopes,   limited   only   by   the   angle   at   which   the   bulldozer   can   apply   downward pressure   to   the   roller.   It   can   also   be   clamped   on   a   rear   toolbar,   again   with   the   weight provided   by   the   tractor's   hydraulics.   This   style   is   lighter   than   the   tow   style,   and   thus less   expensive   to   build   and   easier   to   transport.   However   it   does   not   perform   as   well on rough ground where the independent swiveling of the tow model is an advantage. Use of the Land Imprinter The   imprinter   is   adjusted   for   conditions   at   each   project,   with   the   loading   of   the   ballast tanks    the    primary    adjustment.    Most    soil    conditions    may    be    met    by    loading    the machine   to   a   total   weight   between   500   and   1000   lb   per   foot   of   roller   length.   The exceptions   are   very   heavy   clay   soils,   which   may   be   too   hard   to   imprint   when   dry,   and very sandy soils, which do not hold the imprint shape very well. The   desired   imprints   have   smooth   walls   with   the   seeds   firmly   pressed   into   the   soil. The   soil   surface   is   occupied   fully   by   depressions,   ridges,   and   walls   between   the imprints.   The   bottoms   of   the   depressions   and   the   tops   of   the   ridges   are   sharp   rather than   rounded.   If   the   soil   is   left   with   a   rolling   series   of   indistinct   depressions,   with   the walls   consisting   of   loose   clods   rather   than   smooth   soil,   the   soil   was   too   hard   or   the imprinter was not weighted properly. The   smooth,   well-firmed   walls   of   a   good   imprint   leave   the   seeds   firmed   into   the   soil so   that   capillarity   can   re-wet   the   seeds   from   the   moisture   that   collects   at   the   base   of each   impression.   Enhanced   capillary   re-wetting   accounts   for   much   of   the   advantage of imprinting over other seeding methods. If   the   soil   is   too   hard   for   good   imprints,   it   needs   moisture   or   mechanical   ripping. About   one   half   inch   of   rain   prepares   most   soils   for   imprinting.   One   half   inch   of   water moistens   a   sand   to   about   a   foot   and   a   clay   to   three   or   four   inches,   usually   enough   for good   imprints.   Sandy   soil   may   be   imprinted   immediately   after   a   rain,   but   clay   soil should be allowed to dry a few hours so it will not stick to the roller. Ripping   is   the   method   of   last   resort   because   it   damages   whatever   structure   the   soil may    have.    Ripping    shanks    may    be    spaced    twelve    to    eighteen    inches    apart, depending   upon   the   configuration   of   the   tool   bar.   Wide   spacing   is   usually   satisfactory in   hard   soils,   which   tend   to   break   apart   between   the   ripping   shanks.   Disking   and tilling are even more harmful to soil structure than ripping, and should be avoided. The   imprinter   can   make   organic   debris   and   even   living   plants   into   beneficial   mulch, but   a   large   accumulation   of   weeds   or   brush   can   prevent   successful   imprinting.   Brittle woody   material   is   less   troublesome   than   tough,   ropy   weeds.   Large   imprinting   teeth (8x8"),   or   those   with   a   sharp   angle,   work   best   in   heavy   vegetation.   Shrubs   and perennial   grasses   usually   recover   well   after   imprinting,   allowing   the   use   of   imprinting to improve partially degraded native vegetation. During    imprinting    the    soil    must    be    compacted    enough    to    assure    good    capillary movement   of   moisture,   but   loose   enough   to   allow   root   growth.   It   is   important   not   to load the imprinter any more heavily than necessary for the soil conditions. The   plants   used   in   the   imprinting   seed   mix   represent   the   desired   flora,   but   must   also include   species   that   have   important   roles   in   the   process   of   rehabilitating   the   land. Roles    played    by    the    plant    species    include    soil    protection,    weed    suppression, sheltering   of   more   vulnerable   plant   species,   and   building   the   network   of   mycorrhizal fungi. The    best    "weed    beaters"    are    generally    fast    growing    natives    that    are    good mycorrhizal    hosts.    In    many    cases    these    are    short-lived    perennial    grasses    and composites.    Most    of    these    plants    are    intermediate    in    succession    between    the pioneer    and    the    late    successional    (climax)    species.    These    tend    to    be    good    at building   the   network   of   mycorrhizal   fungi   in   the   soil,   which   protects   against   erosion, suppresses   weeds,   and   lays   the   foundation   for   growth   of   the   final   suite   of   late successional plant species. The   late   successional   species   are   often   left   out   of   the   seed   mix.   Conditions   at   the time    of    seed    application    are    rarely    suitable,    and    these    species    tend    to    require pretreatment   of   seeds   for   good   germination.   They   will   often   find   their   way   to   the   site in   later   years   when   the   original   vegetation   becomes   inviting   to   birds   and   mammals. They may also be planted from containers when conditions become favorable. Mid-   and   late-seral   species   are   also   included,   but   will   fail   without   the   protective   and soil-building   actions   of   the   nurse   crops.   Late-successional   species   are   rarely   good competitors   against   an   established   weed   population.   The   worse   the   potential   weed problem, the "weedier" the seed mix species must be. The    seeds    should    represent    a    diversity    of    suitable    plant    species,    since    higher diversity   plant   communities   better   resist   destructive   forces,   and   are   better   habitat   for most   kinds   of   wildlife.   On   large   land   areas   the   seeds   that   make   up   the   bulk   of   the   mix should be relatively inexpensive, should germinate without elaborate pre-treatment, and should stand up well to storage and mechanical handling. There   is   no   hard   rule   for   determining   the   amount   of   seed   to   apply,   but   the   total amount   often   lies   between   10   and   20   lb.   per   acre.   It   is   best   to   determine   from   the seed   supplier   or   by   testing   the   number   of   seeds   per   pound,   the   fraction   of   seeds   that will   germinate,   and   the   proportion   of   the   bulk   seed   mix   that   consists   of   seeds   rather than   chaff   or   other   materials.   This   pure,   live   seed   (PLS)   count   is   used   to   determine the   number,   rather   than   the   weight   of   seeds   per   acre.   For   land   imprinting,   about   250 PLS   per   square   yard   of   ground   surface,   all   species   combined,   gives   a   good   general guideline. Seed   for   use   in   the   imprinter   is   mixed   with   wheat   bran   to   prevent   sorting   by   size. Bran   is   available   from   feed   dealers,   and   the   most   desirable   type   is   "red   flaky   wheat bran".   The   mixing   ratio   with   seeds,   or   with   seeds   and   granular   mycorrhizal   inoculum, is   usually   1:1   by   volume.   If   the   seed   is   "trashy,"   it   will   be   necessary   to   agitate   it vigorously   to   thoroughly   mix   the   bran   and   the   seed. Any   mycorrhizal   inoculum   should be   added   after   hammer   mill   treatment,   although   it   can   withstand   gentler   forms   of agitation. If   the   soil   is   devoid   of   native   mycorrhizal   fungi,   as   would   be   the   case   on   eroded, graded,   or   overgrazed   land,   the   project   must   be   inoculated   at   planting,   or   all   plant species   must   be   non-hosts.   That   is,   the   seed   mix   must   be   limited   to   the   species   that do    not    need    the    mycorrhizal    symbiosis.    The    most    widely    used    examples    are members   of   the   genus   Atriplex.   A   few   other   species   can   survive   without   symbionts, and these are generally recognizable as the weediest among the natives. The    regular    pattern    of    depressions    left    by    the    land    imprinter    suggests    that    the resulting   vegetation   will   resemble   an   orchard   more   than   a   wildland. This   turns   out   not to   be   the   case.   Plant   species   sort   themselves   by   their   requirements   for   such   spatially diverse   factors   as   soil   chemistry,   depth,   or   texture,   position   on   the   slope,   and   local moisture   conditions.   Within   three   to   five   years   the   great   majority   of   imprinting   sites have   looked   very   much   like   natural   vegetation,   with   little   sign   of   the   original   rows, and plant species forming local single species patches.