Plant Cuttings

Schematic showing operation of self-irrigating, self-fertilising hydrogel [SISRH] in agriculture: SISRH becomes hydrated during night and dehydrated during day releasing water and slowly releasing fertilizer for plant growth (graphic borrowed from article by Jungjoon Park et al., 2024).

It’s that season when Mr P Cuttings’ botanical knowledge is shown to be sorely deficient when it comes to gardening. This year in particular he has ‘watering woes’ with his tomatoes. Specifically, the issues of tomato skins being tough and cracking, and blossom end rot. Apparently, cracks and thick skins are related to an inconsistent watering regime (Megan Hughes, Melissa Womack, Heather Rhoades). Although blossom end rot is a calcium nutrient problem (Cody), it also has a watering dimension (Melissa Womack). Hey-Ho(e), gardening is a lifelong study, and here’s hoping that I get irrigation in check next year. But, my own gardening travails leads me neatly to the topic of this week’s post, water (and nutrients) and soil.

Fact: Plants require water. In fact, water is one of the most fundamental environmental factors that plant require to just survive, let alone thrive*. Plants also need a supply of inorganic nutrients from the environment. For most plants their major source of water – and the majority of their nutrients – is the soil (Andrew McElrone et al., 2013) in which they’re rooted. But, globally, sufficiency of supplies of water are under threat (Claire Klobucista & Kali Robinson), and agricultural uses of water must compete with other demands (Martina Flörke et al., 2018) upon that precious and becoming-scarcer resource. Interest in developing more efficient ways to harvest and manage this resource is understandably high on the agenda of sustainability and future water-sufficiency.

Not surprisingly, therefore, investigators investigating methods to ensure plants get sufficient water and nutrients tend to focus on the soil. That is certainly where the attention of Jungjoon Park et al. (2024) was directed**. Their report showcases how “A newly engineered type of soil can capture water out of thin air to keep plants hydrated and manage controlled release of fertilizer for a constant supply of nutrients”, which sounds quite remarkable.

Park et al. (2024)’s contribution is the development of SISRH, a self- irrigation and slow-release fertilizer hydrogel*** that “enhances plant growth through controlled yet self-sustained water and nutrient delivery”. This is achieved by the hydrogel absorbing water vapour (from the atmosphere) at night and releasing it as liquid water to the soil during the day. In other words, freely-available water from the air is ‘harvested’ during the relative coolness of the night, and released by the higher temperature of the daylight hours. Furthermore, the hydrogel incorporates calcium chloride (CaCl₂). This hygroscopic compound not only enhances the ability of the hydrogel to absorb water vapour, but also acts as a source of calcium, an element essential for proper plant growth and development (Kathrin Thor, 2019). As a result, “Overall, SISRH reduces total water consumption and releases nutrients in a controlled manner. The improved water efficiency can thus potentially lead to enhanced harvest quality and increased production yields” (Park et al., 2024).

In support of that statement, growth experiments were undertaken with radish. Unfortunately, no scientific name was given [neither in the paper nor the accompanying supporting information here], so Mr P Cuttings assumes that ‘radish’ refers to Raphanus sativus (Yukio Kaneko & Yasuo Matsuzawa, 1993; Abinaya Manivannan et al., 2019). In growth experiments – which compared plants grown in ‘soil mixed with 0.1 g of SISRH (SISRH-soil)’ with those in ‘soil without SISRH (sandy-soil)’. Differences were found. For example, “In conditions of 90% RH [relative humidity], plants in SISRH-soil exhibit longer stems and both more numerous and larger buds compared to those in sandy-soil,”, and “Under conditions of 90% RH with 6 mL irrigation at 3-day intervals, the average stem length in sandy-soil is 8.6 cm, whereas it reached 11.9 cm in SISRH-soil, representing an increase to 138% of the original length in sandy-soil” (Park et al., 2024).

Whilst such results are encouraging, they must be regarded as preliminary indications only of the potential of this interesting and intriguing irrigation-intervention. It’s not clear from Park et al’‘s experimental set-up whether harvestable radishes were grown: Can SISRH sustain crops to harvest, i.e. through a complete life-cycle for seed crops? If harvestable crop is produced, is it an increase over non-SISRH yields – quantitatively, or in terms of quality? Can nutrients other than calcium be integrated into the hydrogel? Although of some importance, as a crop (Takeshi Nishio, 2017), radish is dwarfed in comparison with much-more commercially, agriculturally, and global food-supply relevant and important crops such as wheat and maize (Olaf Erenstein et al., 2022): Can SISRH assist in their production?

Clearly, questions are raised, and more work is needed, on a field-scale, with a greater range of crops, in a wider variety of environmental conditions – and soil types – to see how effective the SISRH methodology is in delivering the goals of “enhanced harvest quality and increased production yields” (Park et al., 2024). But, as a ‘proof-of-concept’, this is very promising work.

* It’s not just plants for which water is essential, animals also have an absolute requirement for this compound. In that regard, previous work from this lab [Materials Science and Engineering Program and Walker Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas, USA developed a “Low-cost gel film [that] can pluck drinking water from desert air” (Youhong Guo et al., 2022).

** For more SciComm articles on this item, see here, here, here, Emma Bryce, Gianluca Riccio, Rodielon Putol, and Joshua Shavit. And for an audio presentation about the work, see ‘Golahura’ here.

*** For more on hydrogels, see Ros Azlinawati Ramli (2019), and Xingyi Zhou et al. (2020).

REFERENCES

Olaf Erenstein et al., 2022. Global maize production, consumption and trade: trends and R&D implications. Food Sec. 14: 1295–1319; https://doi.org/10.1007/s12571-022-01288-7.

Martina Flörke et al., 2018. Water competition between cities and agriculture driven by climate change and urban growth. Nat Sustain 1: 51–58; https://doi.org/10.1038/s41893-017-0006-8.

Youhong Guo et al.,2022. Scalable super hygroscopic polymer films for sustainable moisture harvesting in arid environments. Nat Commun 13, 2761; https://doi.org/10.1038/s41467-022-30505-2.

Yukio Kaneko & Yasuo Matsuzawa, 1993. 35 – Radish: Raphanus sativus L., Pages 487-510. In: G Kalloo & BO Bergh (Editors), Genetic Improvement of Vegetable Crops, Pergamon; https://doi.org/10.1016/B978-0-08-040826-2.50039-4.

Abinaya Manivannan et al., 2019. Deciphering the Nutraceutical Potential of Raphanus sativus—A Comprehensive Overview. Nutrients 11(2): 402; doi: 10.3390/nu11020402.

Andrew McElrone et al., 2013. Water Uptake and Transport in Vascular Plants. Nature Education Knowledge 4(5): 6.

Takeshi Nishio, 2017. Economic and Academic Importance of Radish, Pages 1-10. In: Takeshi Nishio & Hiroyasu Kitashiba (eds) The Radish Genome. Compendium of Plant Genomes. Springer, Cham. https://doi.org/10.1007/978-3-319-59253-4_1.

Jungjoon Park et al., 2024. Self-Irrigation and Slow-Release Fertilizer Hydrogels for Sustainable Agriculture. ACS Materials Letters, 3471; doi: 10.1021/acsmaterialslett.4c01120.

Ros Azlinawati Ramli, 2019. Slow release fertilizer hydrogels: a review. Polym. Chem. 10: 6073-6090; https://doi.org/10.1039/C9PY01036J.

Kathrin Thor, 2019. Calcium—Nutrient and Messenger. Front. Plant Sci. 10: 440; https://doi.org/10.3389/fpls.2019.00440.

Xingyi Zhou et al., 2020. Super Moisture Absorbent Gels for Sustainable Agriculture via Atmospheric Water Irrigation, ACS Materials Letters; doi: 10.1021/acsmaterialslett.0c00439.