Root systems provide the foundation for plant development. At the time of seeding and plant establishment, it is important to monitor and evaluate the newly developing root systems; subsequent plant growth depends on them.
Roots are responsible for all water and nutrient uptake by the plant, and they provide the physical anchoring and support of the plant structure. Each plant and crop species has its own “personality” and growth habits, including root systems. Accordingly, root systems have unique characteristics among plants species.
Young plant roots, particularly at the time of germination and stand establishment, are generally the most sensitive plant part to soil and water salinity. In fact, seedling plant sensitivity to salinity can often be measured by approximately ½ of the tabulated salinity tolerance guidelines.
In general plant root systems constitute 30-50% of the total plant dry matter. When post-harvest plant residues are incorporated into the soil, the root systems provide a significant contribution to that plant material and final carbon (C) contributions to the soil, which is an important factor contributing to soil health.
The first thing a seed develops in the germination process is a primary root that grows downward into the soil. We often refer to this as the “stinger” root that extends from a germinating seed. New cells are formed at the tip of the primary root as it extends downward into the soil forming a “thimble-shaped” cluster of cells called a root cap (Figure 1).
The root cap serves as a type of shield that helps the root penetrate the soil matrix and protect the developing root tissue. As the root grows downward into the soil the root cap cells are sloughed off creating a slimy surface that helps lubricate the root as it extends deeper into the soil.
The growing point (apical meristem) for the developing root is just behind the root cap and this is the zone of new cell formation that facilitates root growth and replaces the cells that are sloughed off as the root grows through the soil. The new cells elongate and serve to extend the roots into the soil (Figure 1).
The most active parts of the plant root system for mineral nutrient and water uptake are in the tiny root hairs that are formed in zone behind the apical meristem. Root hairs are only formed in the relatively new and freshly developed root tissue. The root hairs are extremely small, tender, and physiologically active. Healthy fresh young roots and root hairs should be clean and white.
Root hairs are often referred to as “feeder roots” due to their high-level of activity in securing water and nutrients from the soil for the growing plant. In the process of transplanting, it is important to protect the feeder roots as much as possible and promote their health to ensure rapid adaptation to the new soil environment.
Young plants have the capacity to develop basic aboveground tissue to perform sufficient photosynthesis for establishment and growth due to the plant’s ability to take up mineral nutrients and water from the soil from the root system. Sometimes it can appear that plants are not growing rapidly while the young crop is investing energy and resources into root system development, which is the foundation for the subsequent plant growth and development.
The depth of the roots will vary according to the soil physical conditions and effective soil depth, soil fertility and salinity management, plant-available water, and of course the natural rooting characteristics of the plant.
In general, there are two basic types of plant root systems. Broadleaf plants (dicotyledonous) and coniferous plants (gymnosperms) commonly have a taproot system the extends downward through the soil developing root branches from the primary root stem (Figure 2).
Grass plants and their relatives (monocotyledonous plants) produce fibrous root systems that branch extensively and radiate out into the soil from the plant base (Figure 2).
In general, taproots tend to be deeper with extensive branching from the primary root, develop woody tissue on older roots, and are generally long-lived. In contrast, fibrous roots tend to be smaller, short-lived, with less branching.
As roots age, they become more fully developed in conducting nutrients and water to the growing points of the plant, both above and belowground. In all cases, the young and freshly developed root hairs (feeder roots) are the primary zone of water and mineral nutrient uptake.
As root systems age, the older roots will die, and new root tissue is formed. As dead roots are sloughed off, the discarded tissue is attacked by naturally occurring, beneficial soil organisms (bacteria, fungi, protozoa, and worms) the release mineral nutrients and produce soil organic matter. Turnover of root tissue is an extremely important aspect of plant contributions to soil carbon (C), organic matter, and general soil health.
We do not see the plant root systems and we cannot watch root hair development. But it is good to be conscious of root system development since all mineral nutrient, water uptake, and structural support is provided through the roots.
It is necessary to sacrifice a few plants occasionally and evaluate root system health and development. Accordingly, it is good to review and understand normal root structure and function as we work to manage crop plants for optimum growth, development, and yield.
Figure 1. Basic root tip anatomy.
Figure 2. Examples of taproot and fibrous root systems.
Frost and freeze damage affect countless fruit and vegetable growers leading to yield losses and occasionally the loss of the entire crop. Frost damage occurs when the temperature briefly dips below freezing (32°F).With a frost, the water within plant tissue may or may not actually freeze, depending on other conditions. A frost becomes a freeze event when ice forms within and between the cell walls of plant tissue. When this occurs, water expands and can burst cell walls. Symptoms of frost damage on vegetables include brown or blackening of plant tissues, dropping of leaves and flowers, translucent limp leaves, and cracking of the fruit. Symptoms are usually vegetable specific and vary depending on the hardiness of the crop and lowest temperature reached. A lot of times frost injury is followed by secondary infection by bacteria or opportunist fungi confusing with plant disease.
Most susceptible to frost and freezing injury: Asparagus, snap beans, Cucumbers, eggplant, lemons, lettuce, limes, okra, peppers, sweet potato
Moderately susceptible to frost and freezing injury: Broccoli, Carrots, Cauliflower, Celery, Grapefruit, Grapes, Oranges, Parsley, Radish, Spinach, Squash
Least susceptible to frost and freezing injury: Brussels sprouts, Cabbage, Dates, Kale, Kohlrabi, Parsnips, Turnips, Beets
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At the UC Cooperative Extension 2024 Automated Technology Field Day in Salinas, CA a couple of weeks ago, 12 of the latest automated and robotic technologies were demonstrated in the field. Most were designed for weed control or thinning vegetable crops. Several of the technologies shown are relatively “new” for the 2024 season. These included laser weeders that also are capable of thinning lettuce (Fig. 1 & 2), a smart cultivator/side-dresser that cultivates between individual crop plants and simultaneously applies fertilizer at a variable rate depending on plant size (Fig. 3), a spot sprayer that utilizes superheated vegetable oil to kill weeds (Fig. 4), and a self-propelled machine that disinfests soil prior to planting using steam. Although the test runs were short, I was impressed with the possibilities for these machines. Company representatives said they will be in Arizona this upcoming season and are interested in meeting with growers. Company contact information can be found at their respective websites, or feel free to contact me if you would like additional information.
Fig. 1. Carbon Robotics’1 (Seattle, WA) LaserWeederTM. The unit utilizes a vision
system to detect crop plants and weeds. A laser is used to kill unwanted plants.
The machine can be used for weeding or thinning lettuce crops (bottom).
Fig. 2. L&A1 (Chico, WA) autonomous laser weeding/thinning robot. The unit is
equipped with a vision system to detect crop plants and weeds, and a laser to kill
unwanted plants. The machine can be used for crop thinning or weeding (weeded
carrot crop, bottom).
Fig. 3. Stout Industrial Technology’s1 (Salinas, CA) smart cultivator/side
dresser. The unit is equipped with a vision system for detecting crop plants, and
blades that move in and out of the crop row to remove in-row weeds. Liquid
fertilizer (shown colored with blue dye) is applied at a variable rate depending on
plant size.
Fig. 4. Tensorfield Agriculture1 (Union City, CA) precision spot spray weeding
machine. The unit has an 80” wide spray boom equipped with 232 individually
controllable spray nozzles to spot spray weeds with superheated vegetable oil
(bottom left, bottom right). A vision system is used to detect weeds and spot
spray resolution is ¼”.
Fig. 5. UA/UC Davis self-propelled band-steam applicator. Device injects steam
into the soil to kill weed seed and soilborne pathogens prior to planting.
[1] Reference to a product or company is for specific information only and does not endorse or recommend that product or company to the exclusion of others that may be suitable.
We did some trials at the University of Arizona Yuma Agricultural Center in broccoli to evaluate and compare Napropamide (Devrinol) liquid formulation 2XT versus the Dry formulation DF-XT.
This product inhibits the production of fatty acids in plants, which is crucial for plant development. It affects primarily the meristematic cells which are in growing points of the stems and roots. We saw activity especially on seedling development that we show in some pictures at the end of the article.
Some growers expressed their concern on the safety of different levels of incorporation with sprinkler irrigation. Therefore, we established a test in which we applied the product as a broadcast application after planting. Then we used different levels of incorporation in some sections using 12, 24 and 36 hours of sprinkler irrigation. No difference was observed with the incorporation level in our trial. We observed temporary phytotoxicity from 4-10%. The data was obtained from visual evaluations. Also, a 0.5 to 1” height reduction was exhibited when compared to untreated plots.
It is common that growers and PCAs make management decisions on herbicide applications in different crops knowing that some injury is expected. Such is the case for alfalfa, wheat, spinach, lettuce and in this case broccoli. Frequently slight stunting it is not noticed because commercial fields don’t have untreated areas for comparison.
We talked to PCA’s and growers at the SW Ag Summit and asked for their experience with napropamide this past season. Some noticed the broccoli exhibited similar levels of phyto, which they considered economically tolerable.
We noticed that good soil prep was important for before the application of the product and avoiding direct contact of the seed with the product for best results.
On weed control we noticed good activity on nettleleaf goosefoot and lambsquarter.
At the 45day we collected data counting SMALL and LARGE weeds and at the 60 day evaluation we noticed most of the SMALL goosefoot and lambsquarter in the high rate of napropamide plots stayed small (pic. below).
Results of pheromone and sticky trap catches can be viewed here.
Corn earworm: CEW moth counts remain at low levels in all areas, well below average for this time of year.
Beet armyworm: Trap increased areawide; above average compared to previous years.
Cabbage looper: Cabbage looper counts decreased in all areas; below average for this time of season.
Diamondback moth: DBM moth counts decreased in most areas. About average for this time of the year.
Whitefly: Adult movement beginning at low levels, average for early spring.
Thrips: Thrips adult counts reached their peak for the season. Above average compared with previous years.
Aphids: Aphid movement decreased in all areas; below average for late-March.
Leafminers: Adults remain low in most locations, below average for March.
