Salinity may strongly influence the interaction between plant roots and surrounding soil, but this has been poorly studied for sodium sulfate (Na₂SO₄). The aim of this study was to investigate the effect of sodium chloride (NaCl) and Na₂SO₄ salinities on the soil chemical properties as well as rice physiological- and yield-related parameters of two contrasted cultivars (V14 (salt-sensitive) and Pokkali (salt-resistant)). Pot experiments were conducted using soil and electrolyte solutions, namely NaCl and Na₂SO₄, inducing two electrical conductivity levels (EC: 5 or 10 dS m⁻¹) of the soil solutions. The control treatment was water with salt-free tap water. Our results showed that soil pH increased under Na₂SO₄ salinity, while soil EC increased as the level of saline stress increased. Salinity induced an increase in Na⁺ concentrations on solid soil complex and in soil solution. NaCl reduced the stomatal density in salt-sensitive cultivar. The total protein contents in rice grain were higher in V14 than in Pokkali cultivar. Saline stress significantly affected all yield-related parameters and NaCl was more toxic than Na₂SO₄ for most of the studied parameters. Pokkali exhibited a higher tolerance to saline stress than V14, whatever the considered type of salt. It is concluded that different types of salts differently influence soil properties and plant responses and that those differences partly depend on the salt-resistance level of the considered cultivar.

To elucidate the comparative effect of chloride and sulfate salinities on photosynthesis and yield components in rice, plants of Oryza sativa (cv. I Kong Pao (salt-sensitive)) were exposed in nutrient solutions to 20 mM Na₂SO₄ or 40 mM NaCl (electrical conductivity of c.a. 4.30 dS m⁻¹ for both solutions) from seedlings to maturity stage. Both types of salt induced a strong decrease in net photosynthesis (A_N) at the seedling and tillering stages, while the intercellular CO₂ concentrations (Ci) remained unaffected. Instantaneous transpiration (E) and stomatal conductance (g_s) decreased at the tillering and seedling stages, respectively, only in plants exposed to NaCl. Chloride salinity also strongly decreased photosynthetic pigments, while no impact was detected in response to Na₂SO₄. All yield-related parameters were affected by salinities, but NaCl was significantly more deleterious than Na₂SO₄ for the mean number of tillers produced per plant, spikelets sterility and non-viable pollen percentage. In contrast, both types of salinity similarly impacted the percentage of fertile tillers and 1000-grain weight. At the grain level, more than 90% of toxic ions (Na⁺, excess of Cl⁻ and S⁶⁺) accumulated in the hulls, thus preserving the internal part of the caryopses from toxic ion injuries.

In field conditions, soil salinity may be due to an excess of different soluble salts. In order to compare the impact of chloride and sulfate salinities on rice, two contrasted cultivars (IKP: salt-sensitive and Pokkali: salt-resistant) were exposed to iso-strength Na⁺ nutrient solutions (NaCl 50 mM or Na₂SO₄ 25 mM; EC: 5.31 dS m⁻¹) for 2 weeks under controlled environmental conditions. It was found that NaCl was more toxic than Na₂SO₄, especially for the salt-sensitive IKP. Sodium and proline accumulation were higher while shoot osmotic potential was lower in NaCl-treated plants than in those exposed to Na₂SO₄. Chloride-treated plants exhibited a higher shoot malondialdehyde concentration, suggesting a higher level of lipid peroxidation while Na₂SO₄-treated plants presented a slightly higher total antioxidant activity. Pokkali was more tolerant than IKP to both types of toxicities although it accumulated similar concentration of toxic ions. Pokkali was able to reduce the root osmotic potential and to quickly recycle oxidized glutathione to reduced glutathione, which may help the plant to more efficiently control its oxidative status in stress conditions. It is concluded that different salts may have distinct impacts on the plant physiology and that differences may vary according to the considered cultivar.

In Burundi, landslides are frequent on the western slope of the Congo-Nile ridge. Unfortunately, they are poorly studied and understood despite their deadly consequences. Previous reports have suggested that slope steepness, lithology and clay soils expose this slope to landslides, while heavy and intense rainfall is a trigger. However, the role of soil in the vulnerability of this specific slope to landslides is unknown. Here we investigate on soil characteristics involved in land sliding in this area.We selected and sampled black and red soils in two Muhunguzi landslides. We determined the soil plasticity from Atterberg limits as well as the particle size distribution. In addition, we measured the soil weathering stage, and further identified the clay minerals from measuring the cation exchange capacity of the clay fraction and analyzing clay samples with X-ray diffraction (XRD).Both the black and red soils are moderately weathered since TRB values in the B horizons range between 330 and 425 cmol(+) kg-1. The soils are loamy clayey to clayey (% clay: 33-55%), and contain high charge clay minerals. They do not differ in their Atterberg limits, which classify the soils as medium plasticity soils in the Casagrande plasticity diagram. Our data further show that both soils have a medium swelling potential. XRD show that the clay fraction consists of kaolinite and smectite and/or vermiculite. The latter 2:1 clay minerals are expandable and swelling clays, respectively. They give these two soils their plasticity and swelling properties. These two properties play an important role in the mechanical behavior of water-saturated soils. Indeed, swelling reduces soil cohesion while the plasticity index and the liquidity limit vary inversely with the internal angle of friction of the soil; cohesion and internal angle of friction being the fundamental parameters of the soil shear resistance. In addition, the soil mantle covers a hard schistose rock whose declivity is parallel to the soil surface slope. Thus, after intense rainfall during the wet season, the water-saturated soil reaches a level of liquidity sufficient to favor a landslide, all the more easily if the slope of the hard rock is inclined in the direction of the gravity flow.gru