Justus von Liebig was a 19th century German scientist (1803-1873) who is regarded as one of founders of organic chemistry. He is also commonly considered as the “father of agricultural chemistry and the fertilizer industry.”
Liebig developed several important analytical methods used in a broad range of applications as well as many other important contributions and developments. Liebig was one of the great chemistry teachers of the 19th century that served as a foundation for the robust German chemical industry of the 20thand 21st centuries.
In 1840 Justus von Liebig presented a concept that is known as the “Law of the Minimum”, which was built upon a theory that had first been developed by Carl Sprengel, a German botanist (1787-1859). The Law of the Minimum basically states that a plant’s rate and extent of growth and overall health is dependent on the amount of the scarcest of the essential nutrients that are available to the plant (Figure 1; Liebig, 1840 and van der Ploeg et al., 1999).
The Law of the Minimum has been further applied into a general model of all organisms and biological functions, including the limiting effects of other environmental factors i.e., sunlight and water in terrestrial ecosystems, as well as excesses of nutrients and other environmental factors (Bruuselma and Nigon, 2023; Davidson, 2016; and Mosaic, 2023).
An important way to consider the Law of the Minimum is that the growth of plants, or crops, is not dependent on the total amount of nutrients available, but rather by the scarcest nutrient or resource (i.e., water). This is particularly important in relation to nutrients such as nitrogen, which is the nutrient required in largest amounts by plants, and it is the most common limiting plant nutrient. In desert agriculture, water is commonly the first most common limiting factor in plant growth and development, closely followed by bio-available nitrogen.
The Law of the Minimum is important to understand in managing fertilizer and other agronomic inputs to a crop. This has been demonstrated when fertilizer prices are high, particularly for nitrogen and phosphate fertilizers, and growers may be inclined to reduce or eliminate fertilizer applications.
Liebig’s Law of the Minimum is most applicable for nutrients and plant growth factors that are mobile in the soil. This is particularly relevant for nitrogen, which is available to plants in the nitrate form (NO3--N), which is mobile in the soil. Thus, (NO3--N) moves with soil-water.
Accordingly, the Liebig Law of the Minimum also pertains to water in a soil-plant system. Other growth factors or nutrients will not compensate for a deficiency in a given nutrient or plant growth factor. Plant-available nitrate-nitrogen (NO3--N) or water are good examples, there are no substitutes.
The Liebig Law of the Minimum is an important concept in soil fertility and plant nutrition and overall agronomic crop management in an irrigated production system.
Figure 1. Graphic illustration of the Law of the Minimum with shortest stave in
the barrel representing the most limiting nutrient in the soil-plant system.
References:
Bruulsema, T, and Nigon, L.L. Crops & Soils Magazine, November–December 2023 American Society of Agronomy. pp. 54-59.
Davidson, D. 2016. Nutrient Management Magazine.https://www.no-tillfarmer.com/articles/5648-no-till-notes-how-to-plan-your-summer-fertility-program?v=preview
Liebig, J. 1840. Die organische Chemie in ihrer Anwendung auf Agri- Sprengel, C. 1831. Chemie fu¨ r Landwirthe, Forstma¨nner und Cameralisten (Chemistry for agronomists, foresters, and agricultural econo-cultur und Physiologie (Organic chemistry in its applications to agri-culture and physiology). Friedrich Vieweg und Sohn Publ. Co., mists). Volume 1. Vandenhoeck und Ruprecht Publ. Co., Go¨ ttingen, Germany. Braunschweig, Germany.
Mosaic. 2023. How Law of the Minimum Impacts Crops' Nutrient Use. In: No-Till Farmer. https://www.notillfarmer.com/articles/12637-how-law-of-the-minimum-impacts-crops-nutrient-use
Vander Ploeg, A.R; Böhm, W.; and M. B. Kirkham. 1999. On the Origin of the Theory of Mineral Nutrition of Plants and the Law of the Minimum. Soil Sci. Soc. Am. J. 63:1055–1062.
Interested in staying up to date on the latest robotic ag technologies? FIRA USA and a number of other entities are organizing a 3-day forum focused on autonomous farming and agricultural robotics solutions. The event will be held October 22-24 in Woodland/Sacramento, CA. The program includes top-level keynote speakers, breakout sessions, a trade show and field demos. Over 35 robots will be demoed and/or on display including 8 machines designed for weeding vegetable crops. Some of the latest technologies for in-row weeding will be featured including lasers (2 companies) and high precision spot spraying (3 companies). If you are interested in ag tech, FIRA 2024 promises to be a quality event and one well worth attending. For more information, visit https://fira-usa.com/.
Fig. 1. Robotic technologies on display and being demoed in the field at
FIRA USA 2024. The event will be held October 22-24 in Woodland/Sacramento,
CA. (Photo credits: FIRA USA).
One commonly used product has been Roundup, and the label recommendations are the following: “This product provides weed control when applied prior to harvest of feed barley and wheat. For feed barley, apply after the hard-dough stage and when the grain contains 20 percent moisture or less. For wheat, apply after the hard-dough stage of grain at 30 percent or less grain moisture” 3.
There are concerns of the presence of glyphosate in shipments from US and Canada which they attribute to “the practice of pre-harvest spraying”. Therefore, some growers are looking for alternatives to this herbicide2.
Sharpen (saflufenacil) is a quick acting burndown product for broadleaf weed control in field crops and it has been labeled and approved in the US for this purpose.
Consulting with a BASF representative we learned that Sharpen is labeled in Arizona (not CA) for this use. The recommended rate is 1-2 fl oz., adding Ammonium Sulfate adjuvant and Methylated Seed Oil. Also, apply at the hard dough stage with no more than 30% moisture, with 10 GPA by ground or 5 GPA by air.
Knezevic (2009) stated “MSO was the adjuvant that provided the greatest enhancement of saflufenacil across all species tested. COC was the second-best adjuvant and provided control similar to MSO on many weed species. NIS provided the least enhancement of saflufenacil4.
An Agronomy Update from Kansas State University recommended to “Consult grain buyer to see if they will accept Sharpen treated wheat because of export restrictions”5.
References:
1. http://canola.okstate.edu/cropproduction/herbicides/labels/Roundup%20PowerMax%20Label.pdf
2. https://sustainablepulse.com/2019/08/29/unique-hair-testing-project-reveals-high-levels-of-glyphosate-and-ampa-in-members-of-the-japanese-parliament/
3. https://www.farmprogress.com/weeds/controlling-broadleaf-weeds-in-winter-wheat-is-essential
4. Knezevic, S. Z., Datta, A., Scott, J., & Charvat, L. D. (2009). Adjuvants influenced saflufenacil efficacy on fall-emerging weeds. Weed Technology, 23(3), 340-345.
5. https://cropwatch.unl.edu/2019/ksu-pre-harvest-weed-control-wheat-sharpen-update
The push-pull strategy, a stimulo-deterrent diversionary strategy, combines behavior-modifying stimuli that manipulate the distribution and abundance of insect pests and/or natural enemies. When your main crop is intercropped with plant species that can mask the host (main crop) appearance or emit undesirable volatiles (smells) that divert the pests away from the main crop (push), on the other hand, other plants in your intercropping system can be extremely attractive using stimuli that are highly apparent and attractive to the pest, hence trapping the pest (pull) (Fig. 1). Insects use visual, chemical, or tactile cues. Thus, by intercropping the main crop with plants that emit more attractive smells, are more visually appealing, or release undesirable smells, one can cause the pest to be trapped and repelled from the main crops, resulting in effective control of the pests.
Figure 1. Pictorial representation of push-pull strategy.
In Brazil, the push-pull strategy has been found effective in managing major kale pests. They found that using mustard as a preferred host pulled the pests away from the kale crops, while marigold plants increased the beneficial arthropod population which provided additional control of the pests (da Silva et al. 2022; https://www.sciencedirect.com/science/article/pii/S1049964421003029). My
lab plans to evaluate the efficacy of similar systems for insect pest management in organic vegetable crops in Arizona.
In Salinas, California, intercropping lettuce with sweet alysum has favored some measurable aphid control. Sweet alyssum attracts and feeds hoverflies, which then lay eggs in lettuce, producing hoverfly larvae that consume aphids. In this video, Dr. Brennan describes in detail how this system works. This research was conducted about a decade ago, but I believe this could be an important tactic to consider for aphid control in lettuce. We also plan to evaluate this system for aphid management in lettuce in Arizona lettuce growing regions.
Figure 2. Graphical representation of Lettuce-Alyssum intercropping system for aphids control. (Image source: Brannan 2013).
