Soil Matters Resources
Created August 2020
It is helpful to understand the characteristics of the soil in which you are planting and how to manage that soil for fertility. This article refers to typical soils in the Albuquerque area of central New Mexico which is at an elevation of 5000 feet above sea level. The area has four distinct seasons, each with drying winds, intense ultraviolet radiation in the summer months, and about 9 inches of annual precipitation.
This region has been in and out of drought conditions for centuries. Irrigation water comes from the Rio Grande, private wells, and municipal water systems dependent on aquifers. The summer rainy season usually occurs in June, July, and August.
Climate influences soil characteristics. What follows below are generalizations about local soil.
More specific information may be gained from a variety of soil tests for your specific location and their interpretation. See:
NMSU: Test Your Garden Soil
Clemson Cooperative Extension Home & Garden Information Center: Soil Texture Analysis “The Jar Test”
Soil test kits are available free at the Bernalillo County Extension Office, 1510 Menaul Blvd Ext NW, Albuquerque, NM 87107, 505-243-1386. The laboratory test itself costs about $35.00. During COVID-19 restrictions the office door may be locked. Call ahead if you wish to pick up a test kit and then call again when you arrive. A staff member will open the door for you. The office is closed on weekdays from 12:00 to 12:30 pm for lunch.
Climate and Soil
Winds and low precipitation create a harsh environment which prevents residual organic matter, such as leaves, from easily decomposing. See:
NMSU: Climate in New Mexico
Thus, high desert soil often lacks organic matter. Home composting is important so that moisture is managed and organic materials easily decompose. Finished compost may be added to garden soil at regular intervals. This recycles nutrients back into the soil.
Unamended local soils are tan in color, have high alkalinity, contain mineral salts, are often sandy, and contain little organic matter. Thus they have low microbial activity and low nutrient exchange capacity in the root zone, that is, low fertility.
Soil Amending and Mulching
High desert garden soil used for growing vegetables, fruits, and berries benefits from the addition of organic matter in the form of compost, the end product of a managed decomposition process. See:
NMSU Bernalillo County Master Composters: Desert Composting Recommendations
US Composting Council: Benefits of Compost
US Composting Council: USCC Factsheet: Compost and Its Benefits
Finished sifted compost may be added to garden soil, usually in the early spring and again in the fall. One to three inches of compost may be spread in the garden area and then scratched into the soil with a tine rake. Then the whole area is sprinkled with water, which will help to activate microbial activity in the compost and in the soil. The soil ecosystem includes microorganisms, the living aspect of soil. Various microorganisms continue the decomposition of organic material to humus and assist in nutrient transfer in the root zone. Some microorganisms fix atmospheric nitrogen to a form useable by plants. All produce sticky biofilms which help with the aggregation of soil particles, thus influencing soil crumb structure and tilth. Some produce antibiotics which ward off pathogens in the root zone.
The amended area may be seeded or planted with bedding plants. Finally, the whole area may be covered with 3 to 4 inches of organic mulch which will conserve moisture by decreasing evaporation. There are many choices for mulching: straw, shredded leaves, fine wood chips, saw dust, coffee grounds, lawn clippings, and blends thereof. Unfinished compost may also be used as a mulch around perennials, in garden beds, and in sheet composting. Maintain moisture so that slow decomposition of the organic material occurs.
Irrigation devices should be placed underneath the mulch.
Due to high ultraviolet light radiation in the summer growing season, the use of garden shading devices may be considered. These will decrease sunburn of plants and evaporation of moisture. UVR increases 4% for every 1000 feet of elevation (NOAA). Shade fabric rated at 30 to 50% UV block may be used at 5000 feet. Pergolas and arbors may also be useful in decreasing UV intensity.
Cover and Green Manure Cropping
Cover cropping and green manure cropping are excellent methods of improving high desert garden soil fertility. These crops may be seeded in the early spring and again in the fall. The crop will eventually be chopped and dropped onto the soil or gently tilled into the soil as a green manure, thereby adding organic material which will, in due time, improve fertility. See:
Sheet Mulch Composting
A portion of a garden may be dedicated to sheet mulch composting in any season. Organic materials are layered directly on top of the soil. Materials that may be used are shredded leaves, shredded paper, cardboard, straw, lawn clippings, fruit drops, coffee grounds, manures, etc. Mixing green material with brown aids microbial decomposition. Moisture must be maintained in the layers at all times for decomposition to occur in a timely fashion. When layering is complete, the whole setup may be covered with four inches of straw and/or large pieces of perforated cardboard. In the spring, the finished compost may be incorporated into the soil. Residual undecomposed material may be used on top of the soil as a mulch.
Many New Mexico horticultural topics are addressed here:
NMSU Bernalillo County Extension Master Composters: Reading Materials
USDA Natural Resources Conservation Service: Soil Health
If You Have Questions
If you have questions about high desert composting and soil amending, please see Ask a Master.