7 minute read
Mind Your P's & K's
BY STEPHEN BROOKES, NPK TECHNOLOGY
The Cold Fire: Phosphorus
The cold fire glows in the dark as it reacts with oxygen in the air to produce a greenwhite light known as chemiluminescence. This is the reaction that Hennig Brand saw in 1669 after discovering phosphorous, which was given its name from the Greek derivative meaning ‘bringer of light’. Others nicknamed it the ‘devils element’ because of how easily it burst into flames, and for its placement as the 13 th element in the periodic table.
The Potash: Potassium
The cold fire was the name used to describe phosphorous in the 1600’s, but it is the hot fire that is used to describe potash, from which potassium gets its name. Interestingly enough, the symbol for potassium is ‘K’ from the Latin, Kalium. Potash came from the Dutch word ‘potaschen’ in 1477 when people used to soak plant ashes in water and then evaporate the solution in big pots, leaving a white residue behind called potash.
With peak production of phosphorous being hit as early as 2030 and our dependency on phosphate rock (non-renewable), the global reserves could be gone within the next 50-100 years. The impact of this on the worldwide food industry will be enormous.
Modern industry and agricultural techniques mean we have much more refined phosphorous and potassium available as fertilizer compared to the 1600s, however, with peak production of phosphorous being hit as early as 2030 and our dependency on phosphate rock (non-renewable), the global reserves could be gone within the next 50-100 years. The impact of this on the worldwide food industry will be enormous, and we need to start thinking about how we can correct this. ³
The Use of P and K
Fruiting plants require a change of diet from the vegetative growth phase, but it is a common misconception that they need less nitrogen. Actually, we need equal amounts of nitrogen throughout growth and bloom ⁴. What the plant really needs during high energy times such as flowering, is more phosphorous (P) and potassium (K). This is because the energy currency of a plant is a molecule called Adenosine Triphosphate (ATP), of which the central atom is P. More phosphorous means a bigger pool of ATP for energy ⁵
Adenosine Triphosphate (ATP):
Potassium (K) is vital for protein synthesis and photosynthesis, amongst other processes. In flowering, the energy requirements of the plant increases, requiring higher rates of photosynthesis. It will also need more nutrients, more water, and more potassium. Believe it or not, potassium has no direct effect on flowering; indirectly, a deficiency can severely hinder yields, and the reason we need more K is for water movement within the plant 6,7,8 .
When one plant cell requires water, it cannot steal some from another. Water also cannot enter a cell without reason. Plants actually force water to flow by moving charged nutrient particles called ions. We call these pathways ‘ion pumps’, and potassium ion pumps will move K+ into a cell to make it salty. The result is a cell with a more significant negative osmotic gradient than an adjoining cell, which moves water between the two cells until the osmotic gradients are the same. More K+ pumped adds up to more water moved between cells. This simple feature of potassium is crucial to the function of stomata, which are the gateways to water loss and CO 2 absorption.
There are several other processes that P and K are needed for during flowering, but photosynthesis, water movement, and stomatal regulation, along with the increased requirement of ATP, are the main reasons we like to increase our ratio during flower.
Uptake of P and K
Here’s where it can get a little tricky. For the majority of growers, all we need to know is that P and K are absorbed by the roots quite well and can also be foliar fed with good results. If you’re looking to increase the availability of phosphorus to the plant, using an excellent microbial inoculant can work wonders. However, we need to understand that the movement of phosphorus from the soil into the root, and eventually into a cell, is through a process called active uptake, which is a selective process. This means ions of P are not absorbed because of their ratios in the soil but rather due to plant demand. Therefore, plants do not consume more phosphorus simply because you add more of it. Instead, they will increase their access to P by increasing the volume of roots close to the soil, creating a more extensive root system.
It is critical to understand that irrigating with too much P can be a waste of money (i.e. washed away nutrients) and can damage the plant (i.e. nutrient burn). However, not enough P can mean the plant spends more energy on root growth and searching for P than shoot and fruit development 12 . The trick is to know your plants, know your environment, and dose P and K as necessary for optimal plant health. Using microbials can help alleviate this potential guessing game and give optimal results. For me, the growing game is a sweet science to achieve consistent, reliable, and highend results, and that’s really all a good grower needs to know. Well, almost everything; symplastic uptake is the primary means of potassium and phosphorus supply to plants... that’s everything!
Geek Science of P&K
As roots mature, the Casparian strip starts to develop, and this is a band within the root cell (endodermal cell) which acts as a barrier to movement of water and ions. When this develops further, the Casparian strip ensures that water and ionic movement into the plant takes place through the plasma membrane, which ultimately brings nutrient uptake under the metabolic control of the plant 13 . The plant is ultimately in control of the uptake of phosphorous and potassium, which is why it’s vital to watch and understand the plant to see when it requires various elements or changes to be made in its environment.
The Casparian Strip
Final Message
Find the right PK for you: research PK ratios and the benefits of different ones, understand that adding more of a PK additive will not mean increased uptake and that ultimately, you, the grower, have the control of whether your plants yield to their genetic capability. Become a plant whisperer!
Lastly, understand that our resources are finite and we need to take an interest in different aspects of growing if we are to continue the global trend of survival.
BIO
Stephen Brookes is a science fanatic, hydroponics obsessed bookworm. His experience comes from running two grow shops, an additives company, and NPK Media. Along with obtaining a bachelor degree of Science in Outdoor Education and Geography and an MSc in Nutrition and Scientific Investigation, he is now working on a PhD, researching the effects of different ratios in cannabinoids on the human body. Motto: The more you learn, the less you know!
References
(1) Etymonline.com. (201 8). potash | Origin and meaning of potash by Online Etymology Dictionary. [online] Available at: https://www.etymonline.com/word/potash [Accessed 30 Oct. 2018].
(2) Davy, H. (1808). The Bakerian Lecture: On Some New Phenomena of Chemical Changes Produced by Electricity, Particularly the Decomposition of the Fixed Alkalies, and the Exhibition of the New Substances Which Constitute Their Bases; And on the General Nature of Alkaline Bodies. Philosophical Transactions of the Royal Society of London, 98(0), pp.1-44.
(3) Cordell, D., Drangert, J. and White, S. (2009). The story of phosphorus: Global food security and food for thought. Global Environmental Change, 19(2), pp.292-305.
(4) Hartz, T., LeStrange, M. and May, D. (1993). Nitrogen Requirements of Drip-irrigated Peppers. [online] Hortsci.ashspublications.org. Available at: http://hortsci.ashspublications.org/content/28/11/1097. short[Accessed 31 Oct. 2018].
(5) Mller, S., Hagemann, O. and Ansorge, H. (1986). The effect of various phosphorus fertilizers on yields, phosphorus uptake by plants and conversion of phosphorus fertilizers in long-term experiments on different soils. Fertilizer Research, 10(3), pp.231-236.
(6) Rao, N. (1986). Potassium requirements for growth and its related processes determined by plant analysis in wheat. Plant and Soil, 96(1), pp.125-131.
(7) Hartz, T., Miyao, G., Mullen, R., Cahn, M., Valencia, J. and Brittan, K. (2018). Potassium Requirements for Maximum Yield and Fruit Quality of Processing Tomato. [online] Journal.ashspublications.org. Available at: http://journal.ashspublications.org/content/124/2/199. short [Accessed 31 Oct. 2018].
(8) Pinkerton, A. and Randall, P. (1993). A comparison of the potassium requirements during early growth of Lotus pedunculatus, Medicago murex, M. polymorpha, M. truncatula, Ornithopus compressus, Trifolium balansae, T. resupinatum, Pennisetum clandestinum, and Phalaris aquatica.
(9) Wang M, Zheng Q, Shen Q, Guo S. The Critical Role of Potassium in Plant Stress Response. International Journal of Molecular Sciences. 2013; 14(4):7370-7390.
(10) Hirsch, R. (1998). A Role for the AKT1 Potassium Channel in Plant Nutrition. Science, 280(5365), pp.918-921.
(11) Lauchli, A. and Pfluger, R. (2018). Potassium transport through plant cell membranes and metabolic role of potassium in plants.. [online] Available at: https://www.cabdirect.org/cabdirect/abstract/19796731472 [Accessed 31 Oct. 2018].
(12) Greenway Biotech, Inc. (2018). What’s the function of Phosphorus (P) in plants?. [online] Available at: https://www.greenwaybiotech.com/blogs/news/whats-the-function-of-phosphorus-p-inplants[Accessed 1st Nov. 2018].
(13) School of Land, Crop and Food Science, (2018). [online] Available at: https://grdc.com.au/resources-and-publications/grdc-update-papers/tab-content/grdc-update-papers/2009/02/the-science-of-phosphorus-nutrition-forms-in-the-soil-plant-uptake-andplant-response [Accessed 5 Nov. 2018].
