Root systems 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, and root systems have unique characteristics among plants species.
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.
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.
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. 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 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 generally long-lived. In contrast, fibrous roots tend to be smaller, short-lived, with less branching. As roots age, they become more important 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) and organic matter.
We do not see the plant root system on a regular basis 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. So, it is good to review and understand root structure and function as we work to manage crop plants for optimum growth and development.
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
More information:
Over the last couple of years, we have been investigating the use of band-steam to control weeds and soilborne pathogens. The technique has been discussed in previous mechanization UA Veg IPM articles (link). Briefly, the concept behind band-steam is to disinfest narrow bands of soil centered on the seedline using high temperature steam prior to planting. After the soil cools (<1 day), the crop is planted into the disinfested band (Fig. 1). Weed emergence and disease inoculum is reduced in the seedline. Weeds outside the seedline can be easily removed through cultivation.
Trials results have been impressive, particularly for in-row weed control (Fig. 2). We’ll be demonstrating our 2ndgeneration prototype band-steam applicator and sharing study results at the 2023 Southwest Ag Summit Field Demo, February 22nd (Fig. 3) We’ll also discuss and like to get your input on a new project – development and evaluation of a commercial scale band-steam applicator. The goal of the project is to build a self-propelled steam applicator and evaluate the viability of band steaming at the commercial field scale level. We’re in the preliminary design process now; a concept sketch is shown in Fig. 4. We’d love to get your input/feedback at this stage of the process. Please feel free to reach out to me anytime.
Fig. 1. Treatment sequence: 1) steam is injected into soil where seedline will be
located, then 2) later the crop is planted in the steamed seedline.
Fig. 2. Weed control in lettuce seedlines of beds treated with band-steam (right)
and untreated (left).
Fig. 3. 2nd generation band steam applicator to be demoed at the 2023 Southwest
Ag Summit Field Demo held February 22rd, 2023 in Yuma, AZ
(https://yumafreshveg.com/southwest-ag-summit/).
Fig. 4. Concept drawing of a proposed commercial style steam applicator. The
unit has a propane fueled engine and steam generator. The steam injection occurs
at the back of the machine. Water is carried in tanks below the engine, and rubber
tracks are proposed to disperse the weight and avoid soil compaction.
We published this booklet last July. Please let us know what you think by responding our five questions in the link provided below. The first 25 respondents WILL RECEIVE a copy of the guide. Additionally…first five to take the survey and ID the weeds in the cover of the booklet will also get a Navy Blue UA Vegetable IPM HAT.
There are abundant resources for weed identification of mature plants. These include very complete guides such as “Weeds of California and Other Western States” by Joseph DiTomaso published by University of California. “An Illustrated Guide to Arizona Weeds” by Kittie F. Parker with excellent drawings by Lucretia Breazeale Hamilton. There are also several phone apps for weed identification. However, the cotyledons of weeds frequently have a different shape than the true leaves, which makes identification of seedlings difficult for some species. The purpose of this pocket booklet is to provide a quick reference with good images that can be carried in your truck to help you identify the most common broadleaved weeds in Southwestern and Central Arizona.
The method for identification presented is not by using a dichotomous key or answering complicated questions about the species. The idea is to leaf through the booklet and find images that match plants you see in the field. If there are unusual characteristics, we note them in our comments for each weed. Here is a link to the guide in PDF format: HERE
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.
