Germination and growth of spinach under potassium deficiency and irrigation with high-salinity water

Authors: UÇGUN, KADIR - Karamanoglu Mehmetbey University; Ferreira, Jorge; Liu, Xuan; FILHO, JAIME - University Of California; Suarez, Donald; LACERDA, CLAUDIVAN - Universidade Federal Do Ceara (UFC); Sandhu, Devinder

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2020
Publication Date: 12/9/2020
Citation: Uçgun, K., Ferreira, J.F.S., Liu, X., Filho, J.B., Suarez, D.L., Lacerda, C.F., Sandhu, D. 2020. Germination and growth of spinach under potassium deficiency and irrigation with high-salinity water. Plants. 9(12). Article 1739. https://doi.org/10.3390/plants9121739.
DOI: https://doi.org/10.3390/plants9121739

Interpretive Summary: Farmer interest in using treated wastewater (recycled water) as an affordable alternative to freshwater for crop irrigation in California and other semiarid regions is rapidly growing. However, recycled waters contain approximately three times more salts than freshwater leading to a yield reduction of salt-sensitive crops. Several studies have evaluated the application of fertilizers, additional to crop recommendation, to mitigate salinity-triggered mineral imbalance and reduced crop yield. However, studies evaluating the relationship between salinity and deficiency in fertilizers are rare. Increased salinity of soils and recycled irrigation water demand that farmers find crop cultivars that can tolerate moderate to high salinities. We evaluated the combination of five levels of water salinity (ranging from low to high) and four levels of K (ranging from deficient to enough) during both germination and vegetative growth of the spinach cultivars Raccoon and Gazelle. The results suggested that moderate salinity levels can benefit the growth of certain spinach cultivars when K is deficient. Spinach plants did not respond to K doses and plants grew well even with deficient K, indicating that spinach requires much less K for growth than previously recommended. Overall, these results are important because they indicate that spinach can be produced with recycled waters of moderate to high salinity without a considerable reduction of shoot yield and any effect in plant appearance. This research is important to spinach growers in areas where saline water is the only option for crop irrigation. California planted 50,800 acres of spinach in 2019 with a crop value of US$388.7 million, representing 75% of the total spinach yield in the US. Our finding that spinach did not respond to K fertilization may allow for a considerably lower potassium input leading not only to economic gains for farmers, but also to a smaller environmental footprint for the commercial production of spinach.

Technical Abstract: Information is scarce on the interaction of mineral deficiency and salinity. We evaluated two salt-tolerant spinach cultivars under potassium (K) doses (0.07, 0.15, 0.3, and 3.0 mmolc L-1) and saline irrigation (5, 30, 60, 120, and 160 mmolc L-1 NaCl) during germination and growth. There was no interaction between salinity and K. Salinity decreased germination percent (GP), not always significantly, and drastically reduced seedling biomass. ‘Raccoon’ significantly increased GP at 60 mmolc L-1 while ‘Gazelle’ maintained GP up to 60 or 120 mmolc L-1. After 50 days under saline irrigation, shoot biomass increased significantly at 30 and 60 mmolc L-1 at the lowest K dose but, in general, neither salinity nor K dose affected shoot biomass, suggesting that salinity supported plant growth at the most K-deficient dose. Salinity did not affect shoot N, P, or K but significantly reduced Ca, Mg, and S, although plants had no symptoms of salt toxicity or mineral deficiency. Although spinach seedlings are more sensitive to salt stress, plants adjusted to salinity with time. Potassium requirement for spinach growth was less than current crop recommendation, allowing its cultivation with waters of moderate to high salinity without considerable reduction in yield, appearance, or mineral composition.