Written by Linden Schneider
Robust monsoon predicted. On Wednesday April 11th folks gathered to learn and teach about soil health at the NMAA teaching farm in Chamisal. This drought year is the perfect time to think about soil health; most of the water we will receive will be from the intense monsoon rains. Almost all climate models are predicting a robust monsoon season and this comes with particular challenges for our soils and plants. When this intense, heavy rain falls we want it to penetrate deep into our soils, feeding the plant roots, and recharging our aquifers. Having healthy soils with lots of organic matter, good structure, and a covered soil surface will help us keep the little water we will get ( See Figure 1).
Diversity. Acequia irrigation systems require us to have community consciousness making both our plant and human communities robust in times of change. In the workshop we heard about the many unique soils and farming goals all the participants had. A diversity in farming perspectives, techniques, management and adaptation plans are absolutely necessary for resilience. The same goes for soils! A diversity of life and components within soils makes them healthier and more resilient!
Time and change. The beautiful rich topsoil on the Chamisal farm is some of the best in the state for growing food. It takes about 500 years for one inch of that soil to form. However, the degradation of soil health through intensive agricultural practices such as over tilling or over grazing can happen in a season or two! Restoring soils to their previously healthy state can take decades if it is possible at all. Soil degradation destroys the ability of soils to capture and store water (see Figure 2).
New Mexico Soils. Not only is New Mexico’s seasonal weather pattern unique, but so are the soils themselves. At the bottom of this article you will find resources specific for our New Mexico soils as most other farming and gardening literature is meant for eastern or coastal soils and climates.
New Mexico Soil Health Indicators. There are a few key factors to consider when thinking about the health of our New Mexico soils:
- Soil texture- This is the ratio of the three soil particle sizes to one another: sand, silt, and clay. Knowing your soil texture will help you determine things like
- A. Will water runoff or infiltrate?
- B. Will nutrients stick to the soil particles, making then available to plants or will they run off?
- C. Will tillage greatly deteriorate the soil structure or can the soils stand up to light tillage?
At the bottom of this article is a reference to a chart to help you determine your soil texture by feeling damp soils with your hand.
- Soil structure (aggregation)- This is how the particles (the sand, silt, and clay) that make up the texture, along with organic matter, all stick together. Knowing about your soils aggregation helps you understand how stable your soil will be when it comes in contact with water:
- Low aggregation- formation of soil crusts and water runoff
- High aggregation- water infiltration and storage, oxygen infiltration (good for healthy roots)
The biggest threat to high soil aggregation is tillage (see Figure 2), the more we till the more we break up the structure of the soil. It is very hard to increase aggregation, but you can do so by adding organic matter like compost or manure. Figure 1 and Figure 2
- Organic Matter content- This is how much organic (plant, animal, microbial) material we have in our soils and it is important for aggregation and holding and supplying water and nutrients. You can get a rough idea of this by looking at soil color, if it is a beautiful dark brown, you know you have high organic matter (see Figure 2, 2 soils on the right). In New Mexico we have some very beautiful soil colors: yellow, red, light brown…however all these colors indicate very low organic matter.
4. pH- This is the main descriptor of the chemistry of your soil. Knowing the pH of your soil will tell you things like what plants you can grow and the availability of nutrients to your plants. In New Mexico we have neutral to high pH soils, this means:
- We have limited availability of the essential nutrients phosphorus, potassium, iron and manganese
- We have a hard time growing plants like blueberries and blackberries.
We can change the pH of our soil slightly by adding elemental sulfur usually sold as ‘Soil Acidifier’, but this takes a lot of monetary investment. Instead we can choose to add phosphorus rich amendments like chicken pellets and grow crops tolerant of our high pH soils like carrots, cauliflower, corn, garlic, lettuce, winter squash and peppers.
Soil Health Tests. Some of the workshop participants had their soil’s health tested. Here are a few pointers on things that you should make sure the testing lab does for you:
- For testing phosphorus make sure you get the Olsen Test: this will tell you about how much phosphorus is available to your plants at a pH relevant to your soil
- Make sure they give you the sodium adsorption ratio: this will; tell you about the stability of your soil aggregates when watered.
- The results that you receive can be difficult and frustrating to interpret, contact your local NRCS office for help: https://goo.gl/sgD1Yr
- Lastly, if you plan on applying your own compost or manure to the soil as an amendment get that tested too.
Soil Texture by Feel https://goo.gl/KZPp9C
NRCS Soil Health https://goo.gl/DkQAK5
USDA WebSoilSurvey https://goo.gl/4cLgtT
NMSU Western soils http://westernsoil.nmsu.edu/
Soil Slaking Test https://goo.gl/6hksGG
Linden Schneider, author of this article: firstname.lastname@example.org