LAND IMPRINTING METHODS Prepared for Discovery Park, Safford, Arizona, by Ted St. John, Ph.D. THE NEED FOR IMPRINTING  Seed   is   far   less   expensive   than   container   planting   in   most   re-vegetation   situations,   and is   the   only   available   option   on   the   great   majority   of   very   large-scale   projects.   Since simple   broadcasting   of   seed   is   unreliable,   ecologists   and   rangeland   scientists   have devised    seed    application    methods    that    greatly    improve    germination    and    seedling establishment. Among the most successful of these methods is land imprinting. Land imprinting is the formation by mechanical means of short, smooth-walled V-shaped   furrows   in   the   soil   surface.   Imprinting   depends   upon   a   heavy   tractor-drawn roller,   armed   with   metal   teeth,   to   form   the   furrows. The   implement   used   for   this   purpose, the   land   imprinter,   is   able   to   not   only   shape   the   soil,   but   also   apply   seed,   and   even place beneficial mycorrhizal fungi beneath the soil surface. The   imprinting   pattern   provides   improved   exchange   of   water   and   air,   erosion   protection, and   good   contact   between   seeds   and   soil. The   imprints   collect   rainwater   and   permit   it   to infiltrate,   even   if   soil   surface   conditions   make   infiltration   a   very   slow   process.   Without imprints,   rainwater   runs   off   and   collects   in   the   lowest   parts   of   the   terrain,   often   causing erosion.   Only   the   soil   under   the   depressions   becomes   charged   with   moisture,   and   only those   areas   can   meet   the   needs   of   germinating   seeds.   Land   imprinting   forces   infiltration over the entire soil area, permitting much more uniform establishment of plants. A   very   important   result   of   imprinting   is   improved   exchange   of   air   between   the   soil   and the   atmosphere.   Good   soil   aeration   encourages   the   soil   organisms   that   make   a   natural plant community possible. The   imprinting   pattern   provides   soil   heterogeneity,   required   for   successful   germination and    early    establishment    of    plants.    The    impressions    provide    "seedling    cradles," protective   depressions   similar   to   natural   "safe   sites"   that   offer   moisture,   shade,   cover from   small   herbivores,   and   other   plant   requirements.   Loose   soil,   blowing   organic   matter, and   other   material   collects   in   the   depressions   and   increases   over   time   the   effectiveness of the seedling cradles. Imprinting   is   generally   of   most   value   in   arid   environments,   although   it   has   been   used   in a variety of climates. Dr.   Bob   Dixon,   the   inventor   of   imprinting,   has   summarized   the   factors   that   make   the most   difference   in   imprinting   of   dry   land   sites:   good   seeds,   good   imprints,   and   good rains. Good   imprints:   The   most   important   single   factor   in   a   successful   imprinting   project   is properly   formed   imprints.   The   capture   of   rainfall,   the   infiltration   of   soil   moisture,   the germination   of   seeds,   and   the   trapping   of   resources   in   the   depressions   all   depend   upon the quality of the imprints. Good    seeds:    The    choice    of    seeds    for    imprinting    is    critical.    Good    seeds    not    only germinate   well,   but   also   include   the   right   plant   species.   The   characteristics   of   the selected   plant   species   must   be   compatible   with   the   project   and   must   give   a   high probability   of   success   in   project   conditions,   factors   which   are   discussed   further   in   a   later section. It is crucial that the imprinting seed mix include some aggressive, fast-growing species to serve as nurse plants. Good   rains:   Soil   moisture   is   fundamental   to   project   success.   Although   we   have   little control   over   rainfall,   we   can   time   the   imprinting   operation   for   maximum   likelihood   of success.   In   the   southwestern   United   States,   November   and   December   are   usually   the best   months   for   imprinting.   Fortunately   many   of   the   seeds   used   in   imprinting   projects have   a   long   lifespan,   and   can   last   until   a   better   rain   year   if   necessary.   Dr.   Bob   Dixon reports that some projects have appeared as long as five years after imprinting.