Reports & publications

The interest in ‘saline agriculture’- as a possible solution for farmers in salt-affected areas around the world- is reflected in the increasing amount of studies/reports being published on this subject.

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Many scientific tests and studies were conducted before it could safely be concluded that not only do salt tolerant crops exist, but they can also be successfully grown on salt-affected soil.

A list of reports and publications on the subject can be found below, all of which will be updated on a regular basis. 

An improved methodology to evaluate crop salt tolerance from field trials

G.van Straten, A.C.de Vos, J.Rozema, Bruning, P.M.van Bodegome (2018)

Read: https://www.sciencedirect.com/science/article/pii/S0378377418310370

The salt tolerance of crops is commonly expressed in descriptive parameters such as threshold or 50%-yield soil salinity and shape parameters describing the yield curve. Estimation by visual or simplified ordinary least squares (OLS) regression methods has multiple issues: parameter bias due to uncertainty in soil salinity, lack of independent estimates of the reference yield, questionable robustness of the threshold parameter and missing information about uncertainty and correlation of the parameter estimates. Here, we present a comprehensive OLS method together with an analysis of its statistical properties to alleviate and overcome such issues, on the basis of a numerical experiment that mimics observed yield responses to saline groundwater across a range of salinities in the experimental test facility Salt Farm Texel.The results indicate under which experimental conditions bias is not a major problem. The method allows estimation of the zero-observed-effect yield from the data, which is relevant to agricultural practice. Estimates for zero-observed-effect yield and threshold ECe are negatively correlated, underlining the difficulty of obtaining reliable threshold values. The estimated confidence regions are reliable and robust against soil salinity uncertainty, but large observation error jeopardizes the confidence intervals, especially for the slope parameter. Data uncertainty alone can be responsible for substantial differences from experiment to experiment, providing a partial explanation for the wide variety in reported parameters in the literature, and stressing the need for long-term repetitions. Given the lack of robustness of the threshold parameter, we propose to adopt the 90%-yield EC (ECe90) as tolerance parameter. Its confidence bounds can be obtained from a simple reformulation of the original models. We also present uncertainty ellipses as a suitable tool to unite multiple-year estimates. The method is offered as a solid and generic basis for reliable assessment of the cultivation potential of varieties and crops on salt-affected soils.Read more

Report Crop Salt Tolerance-Salt Farm Texel

De Vos A, Bruning B, van Straten G, Oosterbaan R, Rozema J, van Bodegom P (2016)

Download: Report_Crop_Salt_Tolerance-Salt_Farm_Texel.pdf

Since 2006 different field trials regarding crop salt tolerance have been performed on the island of Texel, the Netherlands. Details of this work can be found in De Vos (2011), among others. Although the trials focused on obtaining practical results for breeders and farmers, the set up of the various trials was scientifically solid, demonstrated by the publication of Bruning et al., in 2015.
In 2016 the Dutch Ministry of Economic Affairs and Wageningen Environmental Research (Alterra) commissioned Salt Farm Texel to publish the data on crop salt tolerance that had been collected between 2012 and 2015 at the open-air laboratory of Salt Farm Texel (The Netherlands), which has resulted in this report.
At the research facility of Salt Farm Texel, controlled field trials can be conducted at seven different salinity levels. In the period 2012-2015 trials have been conducted with potato, carrot, barley, lettuce, cabbage and onion. This report describes the results of these trials. To be able to compare these results with the standard crop salt tolerance data currently in use in the international literature, salt tolerance is expressed in terms of a yield reduction curve at various salinity levels.
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Growth and nitrogen fixation of legumes at increased salinity under field conditions: implications for the use of green manures in saline environments

Bruning B, van Logtestijn R, Broekman R, de Vos A, González A, Rozema J (2015)

Read: https://academic.oup.com/aobpla/article/doi/10.1093/aobpla/plv010/199788

The use of legumes as green manure can potentially increase crop productivity in saline environments and thus contribute to the sustainability of agricultural systems. Here, we present results from a field experiment conducted in the Netherlands that addressed the efficiency of nitrogen (N) fixation by a legume at varying salinities.
We grew Melilotus officinalis in an agricultural field using drip irrigation with water salinity varying in electrical conductivity between 1.7 and 20 dS m−1. In the experiment, nearly 100 % of total plant N in M. officinaliswas derived from symbiotic fixation at all but the highest salinity level (20 dS m−1). Our results indicated that this species derived substantial amounts of N via symbiotic fixation, the N becoming available in the soil (and thus available to crops) when cultivated legumes senesce and decompose.
Based on the growth performance of M. officinalis and its ability to fix N at moderate soil salinity in our field experiments, we identified this species as a promising source for green manure in saline agriculture in temperate regions.
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Comparing salt tolerance of beet cultivars and their halophytic ancestor: consequences of domestication and breeding programmes

Rozema J, Cornelisse D, Zhang Y, Li H, Bruning B, Katschnig D, Broekman Rob, Ji B, van Bodegom P (2015)

Read: https://academic.oup.com/aobpla/article/doi/10.1093/aobpla/plu083/198191

Salt tolerance of higher plants is determined by a complex set of traits, the timing and rate of evolution of which are largely unknown. We compared the salt tolerance of cultivars of sugar beet and their ancestor, sea beet, in hydroponic studies and evaluated whether traditional domestication and more recent breeding have changed salt tolerance of the cultivars relative to their ancestor.
Our comparison of salt tolerance of crop cultivars is based on values of the relative growth rate (RGR) of the entire plant at various salinity levels. We found considerable salt tolerance of the sea beet and slightly, but significantly, reduced salt tolerance of the sugar beet cultivars. This indicates that traditional domestication by selection for morphological traits such as leaf size, beet shape and size, enhanced productivity, sugar content and palatability slightly affected salt tolerance of sugar beet cultivars.
Salt tolerance among four sugar beet cultivars, three of which have been claimed to be salt tolerant, did not differ. We analysed the components of RGR to understand the mechanism of salt tolerance at the whole-plant level. The growth rate reduction at higher salinity was linked with reduced leaf area at the whole-plant level (leaf area ratio) and at the individual leaf level (specific leaf area). The leaf weight fraction was not affected by increased salinity. On the other hand, succulence and leaf thickness and the net assimilation per unit of leaf area (unit leaf rate) increased in response to salt treatment, thus partially counteracting reduced capture of light by lower leaf area.
This compensatory mechanism may form part of the salt tolerance mechanism of sea beet and the four studied sugar beet cultivars. Together, our results indicate that domestication of the halophytic ancestor sea beet slightly reduced salt tolerance and that breeding for improved salt tolerance of sugar beet cultivars has not been effective.
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Field tests of dielectric sensors in a facility for studying salt tolerance of crops

van Straten G, de Vos A, Vlaming R, Oosterbaan R (2014)

Read: http://114.255.9.31/iaej/EN/Y2016/V25/I2/102

Seven salinity levels ranging from 1.7 to 35 dS/m are applied to groups of eight fields each in a field facility for testing the salt tolerance of crops. Each of the 56 test fields is equipped with one or two dielectric sensors for soil volumetric water content (VWC) and bulk electric conductivity (ECb). Several models for calibrating the sensors in the laboratory were tested and parameterized.
Overall, the root mean square error was in the range of 0.57-0.59 dS/m in terms of soil bulk EC. The models differed in their robustness against inversion to obtain pore water EC from measured bulk EC. The laboratory calibration formula overestimates the pore water EC at low EC (5 dS/m), and underestimates it at high EC (25 dS/m). In practice, calculated sensor pore water EC?s in fields with the same salinity treatment differ among each other, showing the limitations of laboratory calibrations.
However, in fields where pore water samples are available, a direct proportionality between pore water EC and sensor bulk EC suffices without correction for VWC in this well irrigated case. Moreover there is a good correlation between the low frequent EC time series of suction cup samples and the high frequent sensor readings. When used with care, sensors can give valuable information about the dynamics of soil conditions during crop salinity tolerance tests.
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Developing and testing new halophyte crops: A case study of salt tolerance of two species of the Brassicaceae, Diplotaxis tenuifolia and Cochlearia officinalis

de Vos A, Broekman R, de Almeida Guerra C, van Rijsselberghe M, Rozema J (2013)

Read: http://www.sciencedirect.com/science/article/pii/S0098847212001633

Diplotaxis tenuifolia (L.) and Cochlearia officinalis (L.) were presumed to be salt tolerant with potential as vegetable halophyte crops. The response to increasing salinity was analysed by means of the relative growth rate (RGR) and its components and mineral composition. No growth reductions occurred up to 100 mM NaCl for D. tenuifolia, whereas C. officinalis showed a 37% decrease in total dry weight at this concentration of NaCl, corresponding to a 9% decrease in RGR.
The RGR at higher salinity levels (≥200 mM NaCl) showed reductions around 20% for both species, largely due to changes of leaf morphology (decrease in specific leaf area, increase in leaf succulence) rather than toxic leaf Na+ concentrations. In comparison to seven other species of the Brassicaceae, including salt sensitive and highly salt tolerant species, both D. tenuifolia and C. officinalis showed an intermediate response to increasing salinity.
Both species were able to survive the highest salinity treatment (300 mM NaCl for D. tenuifolia and 400 mM NaCl for C. officinalis) and can be classified as salt tolerant with potential as vegetable crops for saline agriculture. Since D. tenuifolia is already in use as an agricultural crop, little constraints are foreseen for its introduction as a saline crop. Before C. officinalis can be used as a saline crop, agricultural practices and marketing still have to be addressed. A hands-on tool is provided for this process, which combines science, agronomy, the social system, and the business sector.
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New handbook for standardized measurement of plant functional traits worldwide

N. Pérez-Harguindeguy et al. (2013)

Read: http://www.publish.csiro.au/bt/pdf/BT12225

Plant functional traits are the features (morphological, physiological, phenological) that represent ecological strategies and determine how plants respond to environmental factors, affect other trophic levels and influence ecosystem properties. Variation in plant functional traits, and trait syndromes, has proven useful for tackling many important ecological questions at a range of scales, giving rise to a demand for standardised ways to measure ecologically meaningful plant traits.
This line of research has been among the most fruitful avenues for understanding ecological and evolutionary patterns and processes. It also has the potential both to build a predictive set of local, regional and global relationships between plants and environment and to quantify a wide range of natural and human-driven processes, including changes in biodiversity, the impacts of species invasions, alterations in biogeochemical processes and vegetation–atmosphere interactions.
The importance of these topics dictates the urgent need for more and better data, and increases the value of standardised protocols for quantifying trait variation of different species, in particular for traits with power to predict plant- and ecosystem level processes, and for traits that can be measured relatively easily. Updated and expanded from the widely used previous version, this handbook retains the focus on clearly presented, widely applicable, step-by-step recipes, with a minimum of text on theory, and not only includes updated methods for the traits previously covered, but also introduces many new protocols for further traits.
This new handbook has a better balance between whole-plant traits, leaf traits, root and stem traits and regenerative traits, and puts particular emphasis on traits important for predicting species’ effects on key ecosystem properties.We hope this new handbook becomes a standard companion in local and global efforts to learn about the responses and impacts of different plant species with respect to environmental changes in the present, past and future.
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Symbiotic nitrogen fixation in legumes: perspectives for saline agriculture

Bruning B, Rozema J (2013)

Read: https://www.sciencedirect.com/science/article/pii/S0098847212001748

Saline agriculture provides a solution for at least two environmental and social problems. It allows us to return to agricultural production areas that have been lost as a consequence of salinization and it can save valuable fresh water by using brackish or salt water to irrigate arable lands. Sea water contains micronutrients that can provide the additional benefit of a reduced need of fertilization in saline agriculture. However, nitrogen is only present in very low quantities in seawater.
A salt tolerant nitrogen-fixing legume used as a vegetable crop, fodder or green manure could increase the availability of soil nitrogen as well as the sustainability of saline agriculture while minimizing the application of inorganic fertilizer. Besides the use of salt-tolerant legumes as green manure, such species could also be useful in salinized areas as fodder and/or human food. In this review, we assess the feasibility of the use of legumes in saline agriculture. Most legumes are sensitive to salinity, as is the process of nitrogen fixation by microorganisms in the nodules of the legumes. First, we identify different steps in nodulation and their respective sensitivity to salinity.
We will then look at the sensitivity of the process of nitrogen fixation in various crop and non-crop legumes, differing in their tolerance to salinity. We will also look into the differential response of nitrogen fixation and biomass production to salinity. Finally, a list of salt tolerant legumes is presented (derived from the HALOPH database). We then evaluate the applicability and perspective of salt tolerant legumes in saline agriculture considering the diversity in growth forms, ecotypes and economic uses.
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Salt tolerance of halophytes, research questions reviewed in the perspective of saline agriculture

Rozema J, Schat H (2013)

Read: https://research.vu.nl/en/publications/salt-tolerance-of-halophytes-research-questions-reviewed-in-the-p

Halophytes of the lower coastal salt marsh show increased salt tolerance, and under high salinity they grow faster than upper marsh species. We could not show reduced growth rate of halophytes compared with glycophytes when grown under non-saline conditions. This indicates limited energy costs associated with high-salt tolerance in plants of genera such as Salicornia, providing a good perspective of saline agriculture cultivating Salicornia as a vegetable crop.
We show that halophytes do not occur on non-saline or inland sites because of a reduced growth rate at low soil salinity, but probably due to other ecological traits of glycophytic upper marsh species. These traits provide competitive advantage over lower salt marsh halophytes, such as earlier germination and increased growing season length.Read more

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