Redistribution of Soil Nutrients using Biomass

One of the advantages of using weeds/yard waste/plant material off the landscape to restore topsoil is the redistribution of soil nutrients from more productive areas to less productive areas to boost the overall productivity of the landscape.  At the Painted Pony Resort, this means material from the river bottom moved up slope onto the benches to promote new topsoil formation and plant growth.  An important step in this process is an understanding of the soil.  Different soils have different requirements and therefore different management approaches.  One step in understanding the soils is to create a soil texture map.  Since soil is composed of sand, silt, and clay, an understanding of the relative amounts of these components helps guide the restoration approach.  Below is an example of a soil texture measurement.  A 4" bore of the topsoil was recovered and thoroughly mixed.  An aliquot of mixed soil was added to vial and mixed with water and a pinch of non-foaming laundry detergent.  This was allowed to settle for 48 hrs and the relative amounts of sand, silt, and clay measured.  In this example there was 74% sand, 20% silt, and 6% clay, from a soil triangle this translates to the border between sandy loam and loamy sand.  Very little clay in the soil results in this poor outcome.  The question then becomes, how to improve the clay content?  The easiest way is to top dress with compost.  But instead of compost the estate uses a redistribution method to move biomass and nutrients around the landscape.  Unwanted plant material is collected and placed perpendicular to the dip or prevailing winds where it is allowed to decay.  During the decay process the barrier slows water across the landscape catching additional soil particles, it also catches wind born seeds, provides a micro-habitat for the subsequent growth of new plants especially grasses, and releases stored nutrients for use by germinating grasses the next season.

measuring soil texture.

topsoil restoration barriers on the estate, a redistribution of soil nutrients.

Range Restoration: Building Topsoil

The Painted Pony Resort lies in San Simon Valley between the Chiricahua Mountains and Peloncillo Mountains of southwestern New Mexico just a couple of miles from the Arizona boarder which bisects the valley.  An open valley set between towering mountains ranges a variety of people have called it home.  From early hunter gather groups to early agricultural groups such as the Mimbres and Hohokam and up to the present the valley has seen it all, from hunting to farming and most recently grazing.

Past range management decisions, beginning in the late 1800's with corporate ranching combined with changes in rainfall have resulted in a generally altered rangeland in many areas of the valley.  A decrease in grasses combined with an increase in woody shrubs, notably mesquite and creosote, have reduced the current productivity of the landscape.  A local attempt to restore and sustain the grasslands is spearheaded by the Malpai Borderlands group whose goal "is to restore and maintain the natural processes that create and protect a healthy, unfragmented landscape to support a diverse, flourishing community of human, plant and animal life in our borderlands region."  Through their efforts much of the bootheel is managed for both cattle and wildlife.  Yet there are other areas (notably public lands, state and federal) where management practices are not producing an increasingly productive landscape but rather a continuing decrease in productivity is observed (see image below).  One of the goals at the Painted Pony Resort is to increase range land productivity on the estate through the grasslands restoration project.

The estate is composed of 750 deeded acres spanning the both sides of the San Simon Riverbed, it includes 6 types of soil, and last year received about 10.75" of rain (CoCoRaHS rain network, NM-HD-17).  The ground cover varies significantly across the estate and ranges from areas denuded of grasses where erosion has eliminated the topsoil to other areas such as the riverbed where fencing has created a seed reservoir used for spreading native grass seed back onto the surrounding landscape.  After successful preliminary experiments with simple top soil restoration barriers as a tool to slow erosion and encourage new grasses these barriers were expanded in both scope and materials.  Instead of simple barriers constructed from cut weeds, mesquite from the riverbed was employed to create topsoil restoration barriers.  Mechanically removed mesquite is transported up out of the riverbed and placed in rows perpendicular to either the dip or to the prevailing winds on a scarified subsoil base.  Grass from the riverbed is then harvested and placed on the upwind (up dip) side of the mesquite barrier followed by some soil from the riverbed to reintroduce microbes and nematodes crucial to developing new topsoil.  The branches of the mesquite combined with raked grasses create micro climates on the exposed subsoil leading to new plant growth.

The result of this effort is already producing results.  As shown below the mesquite topsoil barriers have caught wind blown seed, slowed water flow and new grasses are developing along the restoration barriers.  A simple technique that can be implemented by anyone, the topsoil restoration barriers are useful tools for building new topsoil and restoring the landscape and best of all require no investment beyond time and energy.

Blowing dust on New Mexico State land, the result of poor range management decisions.

Soil map showing the boundaries of the Painted Pony Resort.

Three topsoil restoration barriers installed on the exposed subsoil, click to enlarge.

New grass along a mesquite topsoil barrier

New grass along a topsoil barrier

A topsoil restoration barrier with new grass created from road waste.

Mesquite Treatment and Rangeland Restoration

One of the goals of the grassland restoration project is to return the segment of the San Simon riverbed at the Painted Pony Resort to open grassland, creating a seed reservoir, and this means removing mesquite.  The riverbed was over run with mesquite as a result of unmanaged cattle grazing.  Cattle are a major dispersal agent in the spread of mesquite, eating and passing seeds back onto the landscape where they germinate.  Originally confined to riparian areas, mesquite has spread across the landscape in modern times.  But it is not all bad, mesquite provide forage for cattle and other native browsers, habitat for nesting birds, and most importantly they fix nitrogen in addition to holding the soil.  Mesquite can be stubborn to remove since they produce deep tap roots and mechanically removed mesquite come back quickly requiring further treatment.  A backhoe or other device that will pull the taproot out is required to completely remove the plant and prevent regrowth.  Alternatively, herbicide treatment may be used after initial removal of the above ground portions of the plant.  But tests by others with a number of different herbicides show variable results with both application timing and herbicide compound being important variables.  Because of the variable results with different herbicides a 2 prong approach was chosen for herbicide treatment.  Glyphosate (the active chemical compound found in Roundup) is available off label at 40% concentration.   This is diluted to a final concentration of 2% (found in commercially available formulations) and combined with 2,4-D at a final concentration of 0.2%.  2,4-D is a plant hormone analogue while Glyphosate interrupts amino acid synthesis.  Once absorbed both herbicides work through different mechanisms interrupting plant growth and killing the reoccurring mesquite.  Below are photographs of a mechanically removed mesquite in the riverbed treated with this combination of herbicides.  Although effective some regrowth is noted requiring a second application to finish off the mesquite.

This combination of mechanical removal followed by herbicide treatment is returning the riverbed to an open grassland while maintaining a few large single stemmed mesquites for habitat and leaving mesquite along the margins and on the uplands to provide cover, soil stabilization, and nitrogen fixation this approach shows what may be accomplished with a minimal investment.  

Untreated, 2 weeks after mechanical removal

96 hrs post herbicide treatment

10 days post herbicide treatment, residual new growth will require a second treatment