Nutrient Mobility Concept
In two recent articles published in this newsletter on 27 November 2024, Volume 15, No. 24 and 25, I presented the Bray Nutrient Mobility Concept (Bray, 1954) in relation to mobile and immobile nutrients (Silvertooth,2024a and Silvertooth, 2024b). This article provides a summary of the nutrient mobility concept and the implications of mobile and immobile nutrient behavior in soil-plant systems and plant nutrition management.
In 1954, Dr. Roger H. Bray at the University of Illinois proposed a nutrient mobility concept that has proven to be very important inthe management of nutrients for optimum efficiency (agronomically, economically, and environmentally). Bray essentially simplified all soil nutrient chemistry to the fact that some plant nutrients are mobile in the soil, and some are not (Bray, 1954; Raun, 2017; Warren et al., 2017, Havlin et al. 2014; Troeh and Thompson, 2005).
Mobile Nutrients and the Root System Sorption Zone
Mobile plant nutrients in the soil move with the soil water. Thus, plants can extract mobile nutrients from a large volume of soil beyond the direct root system. Accordingly, plants take up mobile nutrients from a “root system sorption zone” (Figure 1). This gives plants the capacity to utilize most of the mobile nutrients in the root system sorption zone as those nutrients will move to the plant roots with soil water as it is taken up by the plant (Silvertooth, 2024a).
We consider the mobile plant nutrients to be nitrogen (N), sulfur (S), boron (B), and chlorine (Cl). These mobile plant nutrients are taken up by the plant in the following form: nitrate-nitrogen (NO3--N), sulfate-sulfur (SO42- - S), boric acid (H3BO3) and borate ions (BO33- - B), and chlorine is taken up as the chloride ion (Cl-).
Figure 1. The root system sorption zone and an illustration of the large volume of soil
from which plants extract mobile nutrients.
Root system sorption zones of adjacent plants commonly overlap, and plants compete for water and mobile nutrients (Figure 2) in the soil and for light at the canopy surface. This is one of the reasons plant populations are important for optimum yield.
Figure 2. Competition among plants brought about by increasing yield goal.
Immobile Nutrients
Plant nutrients that are immobile in the soil include phosphorus(P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), zinc (Zn), manganese (Mn), copper (Cu), and molybdenum (Mo). Immobile nutrients do not move as freely in the soil solution as the mobile nutrients do. These nutrients interact more directly with soil colloids and root surfaces.
Immobile nutrients are absorbed by the plant from the soil and soil solution that is directly next to the root surface. Plant roots must grow through the soil volume to come into direct contact with the immobile nutrients.
Figure 3 describes this soil volume and plant root interface as the root surface sorption zone.
Figure 3. The root surface sorption zone and an illustration of the small volume of
soil from which plants extract immobile nutrients.
Since only a thin layer of soil surrounding and in direct contact with the plant roots are involved in supplying immobile nutrients to the plant, there is little or no competition among plants for immobile nutrients. Competition among plants only occurs at points where roots from adjacent plants come in direct contact with one another (Figure 4).
Figure 4. Limited competition among plants for immobile nutrients.
Plant Nutrient Management Implications
The nutrient mobility concept and these basic illustrations can help us understand the basis for some common observations and resultant crop management practices.
Fertilizers with immobile plant nutrients are more effective when they are incorporated into soil and particularly in soil zones where there is a high probability of plant roots encountering the immobile nutrients.
Banded applications of immobile nutrients are generally more effective than the same rates broadcast and incorporated into the soil. In contrast, mobile nutrients like nitrogen (N) can be broadcast and moved into the root system sorption zone by water.
Soil concentrations of immobile nutrients do not usually change rapidly but they can be slowly mined out of the soil by a series of crops without proper fertilization. On the other hand, continued or over-applications of immobile nutrient fertilizers, such as phosphorus (P), will cause a buildup of that nutrient in the soil since only a small fraction (commonly 15-20% for most crops) of the nutrient or fertilizer comes into direct contact with the plant roots.
Appropriate soil tests that are properly correlated and calibrated with crop-specific response categories are important in evaluating immobile plant nutrient status.
References:
Bray, R.H.1954. A Nutrient Mobility Concept of soil-plant relationships. Soil Sci. 78(1), p. 9-22.
Havlin, J.L., Beaton, J.D., Tisdale, S.L. and Nelson, W.L. 2014. Soil Fertility and Fertilizers; An Introduction to Nutrient Management. 6thEdition, Prentice Hall, Upper Saddle River, NJ.
Silvertooth,J.C. 2024a. Soil Health - Bray’sNutrient Mobility Concept and Mobile Plant Nutrients University of ArizonaVegetable IPM Newsletter, Volume 15, No. 24.
Silvertooth, J.C. 2024b. Soil Health - Bray’s Nutrient Mobility Concept and Immobile Plant Nutrients University of Arizona Vegetable IPM Newsletter, Volume 15, No. 25,
Raun, W.R. 2017. In: Warren et al. 2017. Oklahoma Soil Fertility Handbook, Id:E-1039
Troeh, F.R. and Thompson, L.M. (2005) Soils and Soil Fertility. Sixth Edition, Blackwell, Ames, Iowa, 489.
Warren, J., H. Zhang, B. Arnall, J. Bushong, B. Raun, C. Penn, and J. Abit. 2017. Oklahoma Soil Fertility Handbook. Id: E-1039
Weil, R.R. and Brady, N.C. (2017) The Nature and Properties of Soils. 15th Edition, Pearson, New York.
The Desert Difference: A Showcase of Ag Tech Opportunities for Growing in the Desert begins TODAY Wednesday, November 13th with a Field Demo Day at the Yuma Agricultural Center. The educational workshop will feature 13 of the latest automated and robotic technologies for pest control and improved vegetable production being demonstrated in the field. Registration begins at 7:00 am and the program starts at 7:30 am (agenda below).
The Field Demo Day is part of at wo-day event. The second day will be a standard conference with keynote speakers, breakout sessions and trade booths. The event will be held Thursday, November 14th at the Yuma Civic Center. Details of the event and Conference Day (Day 2) activities can be found here.
Looking forward to seeing everyone at both events!
Fig. 1. Field Demo Day agenda (Day 1) for The Desert Difference: A Showcase of Ag
Tech Opportunities for Growing in the Desert event. More information about the event
and Conference Day activities (Day 2) can be found here.
Question to IPM team:
I applied Raptor and Pursuit to an alfalfa field. Can you provide some information on the carryover and phytotoxicity to onions?
IPM Team: We haven’t done plant back evaluations with these products. The soil persistence that is mentioned in the AZ PCA study guide is 2-4 months for the Raptor and 3-12 months for Pursuit. The label specifies longer replanting intervals for various crops and suggests that “before planting any crop not listed elsewhere in Rotational Crop Restrictions, a successful field bioassay must be completed. The field bioassay consists of a test strip of the intended rotational crop planted across the previously treated field and grown to maturity”.
An interesting journal article “Injury to Vegetable Crops from Herbicides Applied in Previous Years”, mentions In 1995, residual imazethapyr delayed tomato maturity but did not reduce tomato yield. Other vegetable crops were not injured by herbicide residues. Then in 1997 “imazethapyr carryover injured cabbage, onion, and tomato plants and reduced tomato yield most injury occurred at 2X and 4X rates1.
The “Carrington Research Center in NDSU did an herbicide carryover study included here which presents the “response of onions to herbicides applied to soybean the previous year2” including Raptor and Pursuit. Also, in this study (table below) onion injury was significant in the 2X and 4X rates.
Another “Evaluation of Pre and Post Emergence Herbicides on Yield Contributing and Quality Characters in Onion” found that “Imazethapyr @ 100 g a.i / ha as post emergence application (20 DAT) coupled with preemergence herbicides produced the lower (yield) values than weedy check as Imazethapyr found to be toxic to the Onion3”.
The field study “Efficacy of imidazolinone herbicides applied to imidazolinone resistant maize and their carryover effect on rotational crops” showed sensitivity of rotational crops, from high to low, was the following: Beta vulgaris>Capsicum annum>Lycopersicum esculentum>Cucumis melo>Hordeum vulgare>Medicago sativa>Lolium multiflorum>Avena sativa>Pisum sativum>Allium cepa (onion)>Zea mays.
The label’s recommendation of doing a bioassay is very useful. Many factors can affect herbicide carryover and every case is different. Low soil moisture might not permit appropriate soil conditions for an efficient microbiological and chemical degradation of imidazolinone herbicides3. Other elements to consider are the soil texture, pH, soil temperature, microbial activity, photodegradation, previous crop, water applied after application of the herbicide, soil tillage intensity. The combinations of these elements could contribute to dissipation of these products. Also, having this information would help us determine the best IPM strategy.
References:
I am delighted to embark on my first produce season here in Yuma, AZ. I am looking forward to becoming acquainted with the growing region this fall as we begin identifying tools that can enhance our pest management strategies, specifically focusing on organic solutions for managing insect pests in the Desert Southwest. It is also important for me to gain a deeper understanding of the challenges and issues you are facing in the field. We are eager to evaluate both current and new biopesticides in our upcoming trials and look forward to engaging with potential collaborators.
Here is a list of our fall 2024 trials:
1- Evaluation of selected bioinsecticides against Lepidopteran pests in Brassicas
2- Evaluation of selected bioinsecticides against whiteflies in Brassicas
3- Alternative bioinsecticides for thrips management in lettuce
4- Assessing the effectiveness of beneficial insects (T. brassicae, T. pretiosum, and green lacewings) release for diamondback moth control in Brassicas
I hope everyone’s season gets off to a fantastic start. Please contact me or Macey if you have specific pest issues, biopesticides, or other organic IPM practices you would like us to evaluate. Your expertise is truly invaluable to us!
Contact Information:
• Wilfrid Calvin
Assistant Professor & Extension Specialist
Cell: (979) 709-9762
Office: (928) 782-5861
e-mail: wilfridcalvin@arizona.edu
• Macey Keith
Assistant in Extension
Cell: (928) 580-5785
e-mail: maceyw@catmail.arizona.edu
