Because it is easier to correct a problem before you plant the trees than it is to diagnose and treat dying ones, which will probably be ripped out. A sad start to a tree is not a good ending.
In general, soil analysis is a measure of the physical, biological and chemical environment that a tree is going to be growing in. Is there going to be an impeding layer? Is it a waterlogged area prone to asphyxiation? A heavy soil that is going to need berming? Is it going to be too steep to harvest? These are physical properties that stand out and need to be considered.
Biological properties are harder to assess, but looking for old root channels and how healthy the previous crop grew are good indications of good biological health. How are those weeds growing?
The chemical side is often viewed from the nutritional and the toxicity angles. Trees are able to store nutrients in their various organs and have aids like mycorrhizae to help them take up some nutrients. So it's best to actually test the tree to see what their nutrient status is. Leaf analysis becomes the guide.
We do soil chemical analysis in trees primarily to identify potential toxicities. And for avocado trees, the main toxicities are high pH, salinity, sodium and chloride. Especially pH, which they like between 6 and 7. If it is corrected before the tree goes in the ground, it's relatively easy and inexpensive to correct. Once the tree is the ground, it takes a long time and energy and often it's hard to correct it without the tree dying. Like a waste of time and energy. But hey, I got the trees coming and it's time to be bold and act!! Let's plant.
And usually about a year after the tree is in the ground, the leaves start turning yellow and the canopy starts thinning. The tree was loaded up with iron in the nursery and after being in the high pH ground, it could not get enough iron and iron chlorosis set in. Well get ready to spend the next few years correcting the pH without killing the tree with sulfur or spending the rest of the tree's life messing with iron chelates. It would have been easy to apply a sufficient amount of sulfur in the planting area before planting, waiting for the sulfur to lower the pH, then planting.
Salinity, chloride and sodium are also important for testing prior to planting. Normally we think of these as chemicals that move with rainwater and irrigation. But in years when we have no rain, that doesn't happen. The light sprinklings we have can just move these salts a few inches into the ground and when trees are planted the salts migrate into the root zone. Even when berms are built and soil is scrapped into a hill, it's the surface soil that is being scrapped where all the salts are.
This situation can be compounded where there have been raspberry tunnels or flower tunnels previously and there has been no rain touch the ground the whole time the ground was covered. Or, where there was a crop with a high level of nutrients being applied and there could be levels high enough to affect the salt sensitive avocado. If you know salts are high, the soil can be leached before the trees are planted.
The effect of salt on the young trees can be almost immediate, within a week after planting. It can be dramatic and shocking.
Measuring sodium, chloride and salinity should be ongoing throughout the production years of an avocado. The status of the sodium, chloride and salinity are a reflection of how irrigation water is being managed. Is it getting enough, frequently enough? Was there enough rain to start the irrigation season without leaching?
Yeah, soil needs to be tested on a frequent basis. But the cheapest test and the easiest correction is done before planting. Do it.
Join the discussion July 23
About this Event
Three part webinar lecture series, staring speakers in industry, government, and the university system; covering the following soil health topics:
soil organic matter – interpreting soil test results – structure & function of plant roots – Mycorrhizae 101 – compost & cover crops – microalgae – biochar – FDA soil health perspectives – conservation tillage – organic production – pesticide effects – soil borne pathogens – ag engineering pest control.
PCA, CCA, and Pest Control continuing education credits requested for AZ, CA, NM, and NV.
More details to come on the CEU process.
Module 1: Defining Soil Health
8:00am - 10:30am
Soil Science PHD Student: UC Davis
Defining Soil Health in the American Southwest
Dr. Joey Blankinship
Soil Science Professor: University of Arizona
Soil Organic Matter in Desert Agriculture
Interpreting Soil Test Results
Dr. Glenn Wright
Extension Horticulturalist: University of Arizona
Structure and Function of Plant Roots
Director of R&D: Mycorrhizal Applications LLC
Module 2: Practices to Improve Soil Health
10:30am - 3:00pm
Dr. David Johnson
Adjunct Professor: New Mexico State University
Composting and Cover Crops
Dr. Kristine Nichols
Research Director: MyLand Company
The Role of Microalgae in Soil Health
Dr. Catherine Brewer
Assistant Professor: New Mexico State University
Biochar Production and Application Methods
Dr. Ataullah Khan
Senior Research Scientist: InnoTech Alberta
Biochar Application Development
Consultant: BioAg Product Strategies
Alternative Soil Amendments for Soil Restoration and Sustainability
Dr. David Ingram
Consumer Safety Officer: FDA-CFSAN Produce Safety Staff
FDA Perspectives on Soil Health
Dr. Michele Jay-Russell
Project Director: UC Davis Western Center for Food Safety
Organic Production Soil Health Considerations
Dr. Jeff Mitchell
Cropping Systems Specialist: UC Davis
Conservation Tillage in Vegetable Cropping Systems
Conservation Education Director, AZ Association of Conservation Districts (AACD)
Funding for Soil Health Programs
Module 3: Soil Pest Control
3:00pm - 6:00pm
Dr. John Palumbo
Extension Entomologist: University of Arizona
Soil Applied Insecticides
Extension Weed Scientist: University of Arizona
Persistence of Herbicides in the Soils of the Low Desert
Dr. Stephanie Slinski
Associate Director: Yuma Center for Excellence in Desert Agriculture
Soil Borne Pathogens
Dr. Channah Rock
Extension Water Quality Specialist: University of Arizona
Water Treatment Effects of Soil Borne Pathogens
Dr. Mark Siemens
Extension Ag Engineer: University of Arizona
Point Injection Systems – Fertilizer/Pesticide Application with Minimal Soil Disturbance
- Author: Kristian Salgado
For more information on the CDFA Healthy Soils Program: Click here
Kristian M. Salgado
Community Education Specialist 2 (CES2)
Climate Smart Agriculture
Under our feet, in the soil, is a wealth of microbial activity. Just like humans have different metabolisms and food choices, so do those microbes. In fact, microbes play an important role in making nutrients available to plants.
A recent review paper from Xinda Lu and his team looks at different roles that various soil microbes have in soil's nitrogen cycle. Lu is a researcher at Massachusetts Institute of Technology.
According to Lu, "Soil microbes catalyze most of the transformations of soil nitrogen into plant-usable forms. Diverse microbes use different processes - and sometimes work together. Knowing the various styles of soil microbes, and linking microbes to specific soil processes, can be important knowledge for farmers."
Modern nitrogen fertilizers are applied in the form of ammonium. Through a biological process called nitrification, soil microbes convert ammonium to nitrates that plants can absorb. In order to be efficient at this process, microbes need oxygen. Researchers are studying nitrification because it can be linked to greenhouse gases and loss of fertilizer.
Although microbiologists have been studying the nitrogen cycle for over a century, not all steps were well understood. New microorganisms have recently been identified. A type of prokaryote (single-celled organism) called archaea has also been playing a role in nitrification.
Archaea are not technically soil bacteria, due to their structure. These are newly a newly classified group that really do some amazing things. There are many more archaea that contribute to nitrification in some soils than there are bacteria responsible for the same activity. Including the role of archaea in nitrification has broadened the understanding of scientists and researchers.
Researchers reviewed various studies of soil nitrification. This included the abundance of microbes in soil in relation to various environmental factors. Soil pH, temperature and the ratio of soil carbon to soil nitrogen were all compared to the number of microbes in each soil sample. Soil depth and other factors also influence microbe abundance.
Previous studies have shown, for example, that nitrification archaea are more abundant than bacteria in warmer temperatures. Other microbes thrive in lower temperatures.
Soil pH also influences how active soil microbes are in the nitrification process. Soil bacteria Nitrospira were more dominant in acidic soils, including forests and farm fields.
Researchers have also studied how various microbes "talk" to each other. This keeps the nitrification process running smoothly. Various mechanisms have been proposed, including cell signaling. The presence of nitric oxide in soils may enhance interactions between microbes.
Soil scientists are sure they have not found all the microbes that contribute to the vast array of services soils provide. Just as astronomers discover new stars in the sky as tools advance, so will soil microbiologists find new soil microbes. Some may be involved in nitrification.
Collecting and cataloging the type, abundance and location of soil microbes will continue to advance the knowledge we have about the soil nitrogen cycle.
Crenarchaeota are involved with nitrification in the soil. Here's a cell of this group infected by virus STSV1 observed under microscopy.