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May 11th, 2009

CREATING TOP SOIL

The Tree of Life Rejuvenation Center’s core offering is a diet of organic raw vegan food as the basis for a healthy lifestyle. Creating a food production system for guests, staff and kitchen apprentices that was fresh and vital was essential to support their core program. The aspiration was to serve sustainably produced food that was made from flavorful, highly nutritious ingredients, harvested daily.

The center is located in southeastern Arizona where there are two distinct summers: one hot and dry, the other humid and tropical. Temperatures can reach as high as 105 degrees fahrenheit and the majority of rainfall occurs during summer monsoon events that generate high volumes of rain in short periods of time.  

Setting Fence Posts for the Circle Garden

Setting Fence Posts for the Circle Garden

Degraded clay soils, devoid of organic matter, lacked the spongy absorptive surface necessary to take advantage of the limited and intense summer rainfall.  Water needed time to soak in, and the lack of a spongy organic layer of topsoil meant that the soils didn’t get the time they needed to absorb the rain. Instead, the rain would sheet off the surface as it ran downslope, the loss of a precious resource.

Profile: Matrix Soils

Profile: Matrix Soils

These hard, alkaline, naturally salty soils became more and more cement-like over time, making it difficult for plants to take root , so the plant-scape had become dominated by a tough African grass (Eragrostis lehmanniana) that had been introduced to the area for rangeland restoration in 1930’s.

It was quickly determined that the critical first step to creating a food production system in this challenging climate would be to drastically improve soil quality in order to give the plants the resiliency they would need to deal with extreme climatic conditions. A normal process of soil development in the region, with the same soil matrix and in these climates would take decades at best.

To build soil rapidly we drew on knowledge of how natural systems build soil.

Layering Sheet Mulch Materials to Create Top Soil

Layering Sheet Mulch Materials to Create Top Soil

By layering aged manure, straw, and inert soil composed of sand and clay deposits from a nearby drainage, then seeding it with a large-seed mix of grasses and legumes (nitrogen fixing plants),  followed by systematic irrigation to support the green manure crop.

Cover Crop of Legumes and Grains is Well Developed in Wide Sheet Mulch Beds

Plants at Work: Green Manure Crop Helps Develop Top Soil in Sheet Mulched Beds

Bio mass from the initial green manure crop, including roots rich with rhizobium bacteria (a symbiotic nitrogen fixing bacteria that partner with legume plants) was incorporated whilst creating 4 foot wide growing beds, narrower than the original beds that were 14-16 feet wide.

The resultant 12″ of topsoil took about 2 and a half months to develop. Once this soil was established, it gained the potential to increase its own health by harnessing the natural resources available to the site, such as earthworms and native soil flora. The spongy surface of the soil allowed rainwater time to fully soak into the ground,  leaching the soil’s salt content below plant root zones and delivering liquid nitrogen (free fertilizer), a result of atmospheric chemistry, as lightning strikes and rainfall occur at the same time. img309

This was followed by a full planting including salad greens, root crops, leeks, chard, beans, beets, tomatoes, strawberries, corn, and gourds.

Main Path Leads to the Center of the Circular Garden

Main Path Leads to the Center of the Circular Garden

The center of the garden was planted to culinary and medicinal herbs as well as flowers (for people and pollinators).

In the first growing season, the garden was producing enough food to feed 15 people 3 diverse and interesting meals a day as well as 35-50 pounds of produce donated each week to the Senior Center in the community.

Within One Year the Garden is in Full Production

Within One Year the Garden is in Full Production

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