Crop tolerance to seawater is the ability of an agricultural crop to withstand the high salinity induced by irrigation with seawater, or a mixture of fresh water and seawater. There are crops that can grow on seawater and demonstration farms have shown the feasibility.Monica Nicks, 2014. Consider The Salt-Tolerant Potato. In: Modern Farmer. On line: The government of the Netherlands reports a breakthrough in food security as specific varieties of potatoes, carrots, red onions, white cabbage and broccoli appear to thrive if they are irrigated with salt water.Government of The Netherlands, 2017. Dutch saline agricultural knowledge brings breakthrough in food security. News item | 23-02-2017 | 12:13. On line:
Salt Farm Texel
The Salt Farm Texel, a farm on the island of Texel, The Netherlands, is testing the salt tolerance of crops under controlled field conditions. There are 56 experimental plots of 160 m2 each that are treated in eight replicas with seven different salt concentrations. These concentrations are obtained with intensive daily drip irrigations of 10 or more mm (i.e. more than 10 liter per m2 per day) with water having a salt concentration expressed in electric conductivity (EC) of 2, 4, 8, 12, 16, 20 and 35 dS/m.Salt Farm Texel, 2017. Crop salt tolerance brochure. On line The range of EC values is obtained by mixing fresh water with the appropriate amount of seawater having a salinity corresponding to an EC value of about 50 dS/m. After planting, crops were allowed to germinate under fresh water conditions before the salt treatment started.
Soil salinity The soil salinity is expressed in the electric conductivity of the extract of a saturated soil paste (ECe in dS/m).L. A. Richards, Editor, 1954, Diagnosis and Improvement of saline and alkali soil, Agriculture Handbook No. 60, USDA.
Author Schleiff presented a classification of salt tolerance of crops based on ECe in dS/m Uwe Schleiff, Research for crop salt tolerance under brackish irrigation. On line: that may be summarized as follows:
Salt tolerance ECe (dS/m) ^) Tolerance classification < 2 very sensitive 2 – 4 sensitive 4 – 6 slightly sensitive 6 – 8 moderately tolerant 8 – 10 tolerant > 10 very tolerant ^) The crop performs well (no yield reduction) up to the soil salinity level listed in the table. Beyond that level, the yield goes down.
The main difference with the classification published by Richards in the USDA Agriculture Handbook No. 60, 1954 is that the classes are narrower with steps of 2 dS/m instead of 4.
Modeling
The Salt Farm Texel uses the Maas–Hoffman model for crop response to soil salinity.Maas EV, Hoffman GJ, 1977. Crop salt tolerance-current assessment. Journal of the Irrigation and Drainage Division, American Society of Civil Engineers 103: 115–134. The model uses a response function starting with a horizontal line connected further on to a downward sloping line. The connection point is also called threshold or tolerance. Up to the threshold the crop is not affected by soil salinity while beyond it the yield starts declining. The model is fitted to the data by piecewise linear regression.PennState Eberly College of Science. Piecewise Linear Regression Models. On line:
Results Crop Variety ^) Threshold *) (ECe in dS/m) Class Potato x) Mignonne #) 4.1 slightly sensitive Achilles 2.9 sensitive Foc 2.1 sensitive Met 1.9 very sensitive "927" 3.4 sensitiveCarrot Cas 4.5 slightly sensitive Ner 3.6 sensitive Nat < 1 very sensitive Ben < 1 very sensitive "101" 3.0 sensitive "102" 5.0 slightly sensitive Pri 2.1 sensitive Onion Alo 2.4 sensitive Red 5.9 slightly sensitive San 3.2 sensitive Hyb 3.4 sensitive Lettuce Batavia H < 1 very sensitive Batavia S 2.3 sensitive Butterhead L 1.8 very sensitiveCabbage White cabbage #) 4.6 slightly sensitive Broccoli 5.6 slightly sensitive Barley Que 2014 3.3 sensitive +) Que 2015 1.7 very sensitive +) ^) Many variety names are uncommon as they consist of 3 letters only *) It is not known what the results would have been if the planting was not done under fresh water conditions but in saline conditions. #) Graphs with scatter plots are shown in the report for these two varieties only. They show considerable variation both in Y (Yield) and X (ECe) direction. x) For potato only one comparable value is known in literature, namely for the very sensitive variety white rose having a threshold of 1.7 dS/m Bernstein, L., Ayers, A.D. & Wadleigh, C.H. 1951. The salt tolerance of white rose potatoes. Am. Soc. Hort. Sci., 57: 231–236. +) For barley, in contrast, the U.S. Salinity Laboratory mentions a threshold value of ECe = 8 dS/m, which makes it a tolerant crop U.S. Salinity Laboratory, United States Department of Agriculture, Agricultural Research Service, Salt Tolerance of Fiber, Grain and Special Crops. On line:
Summary
The highest tolerance is found for the onion variety "Red" which classifies as slightly sensitive. All crops classify in the range from very sensitive over sensitive to slightly sensitive. There is no crop classified as tolerant, not even moderately tolerant.
S-curve model
In the Texel report, also the Van Genuchten-Gupta model (giving an S-curve) was used to find the soil salinity at the 90% yield point. The rationale for this was not given.
Halophytes
Halophytes, or salt-loving plants, can be irrigated with pure seawater with the aim to grow fodder crops. A trial was made by Glenn et al. to use halophytes for feeding of sheep and it was concluded that the animals thrived well.Edward P. Glenn, J. Jed Brown and James W. O'Leary, 1998, Irrigating Crops with Seawater. In: Scientific American, August 1998. On line:
Setting the yield of an alfalfa (lucerne) fodder crop irrigated with fresh water (2 kg/m2) at 100%, the following results were obtained for the yield of halophytic crops irrigated with seawater:
Crop Relative yield (%) Atriplex lentiformis, quailbush 90 Pickleweed, turtleweed 89 Suaeda sp., sea blite 88 Dwarf glasswort, Salicornia bigelovii 87 Sesuvium portulacastrum, sea purslane 85 Distichlis palmeri, Palmers grass 65 Atriplex cinerea, coast salt bush 45
Barley After selecting the most salt tolerant cultivar, the University of California at Davis has grown barley irrigated with pure seawater and obtained half the normal yield per acre, i.e. half of the average yield per acre at national level.A. Rossiter, 1977. Scientists grow barley with seawater irrigation.. The Washington post. On line: The experiment was conducted at Bodega Bay, North of San Francisco, in a laboratory on the Pacific Ocean.
Rice Liu Shiping's team at Yangzhou University created rice varieties that can be grown in salt water, and achieve yields of 6.5 to 9.3 tons per hectare. As of 2021, seawater rice had been planted on in soils with up to 4 grams of salt per kilogram, with yields averaging 8.8 tons per hectare, according to Qingdao Saline-Alkali Tolerant Rice Research and Development Center.
Lettuce, chard and chicory In a recent trial comparing three seawater and freshwater blends (i.e. 5–10–15% of seawater), some scientists found that lettuce productivity was negatively affected by 10% and 15% blends of seawater, whereas chard and chicory's growth was not affected by any blend. Interestingly, water consumption dropped and WUE significantly increased in every tested crop accordingly with increased seawater concentrations. They concluded that certain amounts of seawater can be practically used in hydroponics, allowing freshwater savings and increasing concentrations of certain mineral nutrients.
See also
References