Feb 7, 2024Keep an Eye Out for Corn Earworm in Spring Head LettuceTo contact John Palumbo go to: jpalumbo@ag.Arizona.edu
Soil health involves the fundamentals associated with soil, crops, and overall agricultural management practices that serve to enhance good soil system function. The concept of soil health basically addresses how well a soil is functioning. A simple analogy is with human health and as we see with a healthy person there is good overall system function and there are many interactive components in soil systems, like the human health system.
Soil health has been defined by the U.S. Department of Agriculture Natural Resource Conservation Service as “The continued capacity of a soil to function as a vital living ecosystem that sustains plants, animals, and humans” (USDA-NRCS, 2022).
The principles of soil health include soil quality parameters that serve to maximize biodiversity, soil cover, encouraging strong plant root system development, reduced tillage and practices that minimize soil disturbance, and will develop good soil conditions that are conducive to better infiltration and soil water holding capacity, sequester carbon (C), improve nutrient cycling, enhance ecosystem services, and many other benefits that are associated with healthy soils. Thus, soil health represents an extremely broad set of concepts and functions, and it is a good way to present the holistic aspects of soil systems.
As an agronomist and soil scientist working professionally for over 45 years, I find it interesting that what is now commonly referred to as “soil health” might be a new term but it is not a recent discovery. What is often referred to as soil health has often been described for many years as “soil quality” (NRCS, 2015).
Soil quality is the ability of a soil to perform the basic functions necessary for its intended use. These soil system functions typically include:
● sustaining biological diversity, activity, and productivity
● regulation of water and solute flow
● filtering, buffering, degrading organic and inorganic materials
● storing and cycling nutrients and carbon
● providing physical stability and support
Soils have been recognized as living entities for many decades and we commonly address soil function in terms of the three categories of physical, chemical, and biological properties. However, these categories overlap in function and are not always clearly defined as an independent soil property in a soil system since each can affect multiple soil functions.
Thus, soil health serves to integrate the dynamic functions of a soil system among the physical, chemical, and biological properties associated within a given soil system (Figure 1).
Figure 1. Soil health and the integration of fundamental soil
properties. Source: University of Tennessee Cooperative Extension.
One of the principal aspects of soil health is the emphasis on the relationship between soils and soil systems to human health via the function of soils as a fundamental component of terrestrial ecosystems, Figure 2.
Figure 2. The broad and integrated aspects of soil health and relationship to human health. Source: van Es and Frost, 2016.
In agricultural systems these relationships are commonly recognized but this new emphasis is good in my view because of the capacity to bring the importance of soil systems into a better realm of understanding and appreciation by the public and non-agriculturalists who have never really thought about this before. It is also important for us to recognize that whatever we do to impact a soil system in one aspect, it will have impacts on other aspects as well.
The study of soil fertility in the context of soil-plant relationships has often served to integrate the physical, chemical, and biological properties in relation to plant or crop growth. The concepts of soil health commonly place an emphasis on soil carbon (C) content, particularly in relation to stable organic carbon (SOC). This is related to the common reference to soil organic matter (SOM) content in soil health discussions.
It is important to distinguish the difference between organic materials and organic matter in soils. Organic materials include crop residues and SOM is the stable, residual forms of C compounds left in soils following microbial decomposition. For example, after the harvesting of a crop the crop residues are organic materials and they do not equate to SOM. The SOM is the final result of the crop residue breakdown and it is usually a very small fraction of the total organic material that was originally deposited.
Soil organic C represents the net balance of inputs and outputs of C to the soil over time. Inputs of C into a soil system consist largely of root exudates, residues of leaves, stems, and roots, and it also includes the deposition of materials transported by wind and water. In agricultural systems these inputs can include organic amendments such as manure, compost, biosolids, biochar, etc. to supply nutrients or organic matter.
Inputs of C into the soil system are counterbalanced by the C outputs which are dominated by the mineralization of SOC to carbon dioxide by microbes. In an agricultural soil system, microbial degradation and the transformation of plant inputs creates a complex of microbially derived organic compounds in the soil (Grandy and Neff, 2008). Outputs also include any harvested crops, residue burning and erosion.
Typically, soil health measurements focus on the soil surface properties, usually the upper foot (30 cm) of the soil surface. Thus, the transport of C deeper into the soil profile by water or tillage pedoturbation would result in a decrease in the measured SOC in the surface.
In a desert agricultural setting, it is important to review the basics of C cycling in soil systems as shown in Figure 3.
Figure 3. Soil carbon cycle. Source: Lavallee and Cotrufo, Colorado State University, 2020.
Desert crop production systems can produce large amounts of organic material, plant structures and residues. However, much of the C captured in plant residues and incorporated into the soil is soon lost to the atmosphere due to the high amounts of solar energy inputs, an abundance of soil microbes, with sufficient soil moisture and aeration as a function of good soil drainage, and a good nutrient supply (particularly nitrogen).
These are all functions of healthy soils, which are common in desert agricultural settings. The result is a relatively low level of stable organic matter (SOM), usually less than 2% on a soil mass basis and most often ~ 1% or less in desert agricultural soils. Even if difficult, trying to enhance SOM accumulation in desert soils is a worthy goal.
It is important to understand the basic concepts and complexities associated with soil health and to consider agronomic aspects (soil and crop factors) of soil and crop system management that serve to enhance healthy soils for both short and long-term productivity and sustainability.
Lavallee, J. and F. Cotrufo, 2020. Soil carbon is a valuable resource, but all soil carbon is not created equal. The Conversation and Colorado State University, 2020.
Grandy, A.S., Neff, J.C., 2008. Molecular C dynamics downstream: the biochemical
decomposition sequence and its impact on soil organic matter structure and
function. The Science of the Total Environment 404, 297–307.
USDA-Natural Resource Conservation Service (NRCS). 2015. Soil Quality Indicators Physical, Chemical, and Biological Indicators for Soil Quality Assessment and Management.
USDA-NRCS. 2022. https://www.nrcs.usda.gov/wps/portal/nrcs/main/soils/health/
van Es, H. and P. Frost. 2016. Gaining Ground on Soil Health. Tata Cornell Institute.
Botrytis rot is not considered a major problem in lettuce but it can cause significant damage/loss when the field conditions are favorable for the pathogen. Cool wet conditions are favorable for the pathogen. Symptoms include water-soaked, brownish-gray to brownish-orange, soft wet rot that occurs on the oldest leaves in contact with the soil. Old leaves are more susceptible than young leaves and the fungus can move into the healthy parts. Fuzzy gray growth can be observed in the disease area which is characteristic of the pathogen. In worse cases, the entire plant can collapse. Romaine cultivars, transplanted lettuce that are big and have leaves touching the soil are more susceptible.
The pathogen: Botrytis cinerea
Botrytis cinerea affects most vegetable and fruit crops, as well as a large number of shrubs, trees, flowers, and weeds. Outdoors Botrytis overwinters in the soil as mycelium on plant debris, and as black, hard, flat or irregular sclerotia in the soil and plant debris, or mixed with seed. The fungus is spread by anything that moves soil or plant debris, or transports sclerotia. The fungus requires free moisture (wet surfaces) for germination, and cool 60 to 77 F, damp weather with little wind for optimal infection, growth, sporulation, and spore release. Botrytis is also active at low temperatures, and can cause problems on vegetables stored for weeks or months at temperatures ranging from 32 to 50. Infection rarely occurs at temperatures above 77 F. Once infection occurs, the fungus grows over a range of 32 to 96 F.
Masses of microscopic conidia (asexual spores) are produced on the surface of colonized tissues in tiny grape-like clusters (see picture). They are carried by humid air currents, splashing water, tools, and clothing, to healthy plants where they initiate new infections. Conidia usually do not penetrate living tissue directly, but rather infect through wounds, or by first colonizing dead tissues (old flower petals, dying foliage, etc.) then growing into the living parts of the plant.
1. Buy high-quality seed of recommended varieties. Treat the seed before planting.
2. Practice clean cultivation. Plant in a light, well-drained, well-prepared, fertile seedbed at the time recommended for your area. If feasible, sterilize the seedbed soil before planting, preferably with heat. Steam all soil used for plantbeds at 180 F (81 C) for 30 minutes or 160 F (71 C) for one hour.
3. Avoid heavy soils, heavy seeding, overcrowding, poor air circulation, planting too deep, over-fertilizing (especially with nitrogen), and wet mulches.
4. Focus on healthy plant vigor. Do not over fertilize.
5. Use drop or furrow irrigation instead of sprinklers. If sprinklers have to be used, irrigate morning or early afternoon giving enough time for foliage to dry.
6. Apply recommended fungicides when conditions favor disease development. Make sure to rotate fungicide to avoid development of resistance.
Interested in the latest developments in automated weeding machines? There are a couple of opportunities at the upcoming 2023 Southwest Ag Summit to stay up to date. The first is the “Innovations in Weed Control Technologies” breakout session where university experts and cutting-edge innovators will provide updates on the latest advances in high precision smart spot sprayers, autonomous ag robots and towed automated weeders (agenda below). The session will be held Thursday, February 23rd from 9:30-11:30 am at Arizona Western College (AWC) in Yuma, AZ. The other is the Southwest Ag Summit Field Demo on February 22nd, where several of these technologies and other state-of-the-art automated weeders will be demonstrated operating in the field. The Field Demos will also be held at AWC and begin at 10:30 am.
For more information about the Southwest Ag Summit, visit https://yumafreshveg.com/southwest-ag-summit/. Please note that at the time of this writing, the website has some incorrect dates and programming information. It will be updated soon, so please check back for accurate information. The flyer below has the correct dates (Fig. 2).
Fig. 1. Agenda for the “Innovations in Weed Control Technologies” educational
session at the 2023 Southwest Ag Summit. Session will be held Thursday,
February 23th at Arizona Western College, Yuma, AZ.
Fig. 2. 2023 Southwest Ag Summit flyer. Event will be held at Arizona
Western College in Yuma, AZ.
Occasionally in organic agriculture, mechanical practices, prevention, and management of natural cycles for weed control could fail. With the limited number of herbicides available in organic production systems any information and data collected can be useful. We established a trial in a celery field with a high infestation of Annual Bluegrass (Poa annua). Our goal was to obtain data from an evaluation of Supress herbicide EC.
This organic herbicide contains Caprylic acid (47%), Capric acid (32%) it’s a post-emergent, non- selective, broad spectrum, non-volatile, and non-systemic. The idea was to test the efficacy is in controlling annual bluegrass and celery’s tolerance to it.
Plots consisted of one 80” bed 30ft long replicated four times with 6 seed lines, and the test was established in a randomized complete block design with four replications. A CO2 backpack with a 4 flat fan nozzle boom spaced at 20” was used delivering 20 gallons/acre. The application was done December 28, 2022 with grass at ~10 leaves.
Figure 1. View of the plots at 5 and 9 days after caprylic acid application.
Figure 2. Difference in celery size nine days after application
The low rate of Supress (9%) did not control the grass causing only minor temporary symptoms. At the 5-day evaluation it appeared like the grass and cilantro wouldn’t survive the 2x rate. In the 9-day evaluation the grass and cilantro were recovering.
In this test annual bluegrass at 10-12 leaves was not fully controlled with 9% and 18% solution of Suppress. Although reduced in size the crop and the grass both recovered from this non-selective herbicide. Could this product be used in this crop to control a more susceptible weed at a lower rate? Let us know what you think and if we can be of help putting some test plots.