Physico-chimie de sols rizicultivés affectés par la salinité dans la basse vallée de la Rusizi au Burundi

Although salinization of Mugerero paddy soils is the main constraint to rice production, this process has not yet been investigated thoroughly. This work has been done to fill this gap. Physico-chemical analysis of soils of this area show that their exchange complex is mostly occupied by nearly equal percentages of Ca and Mg, while exchangeable sodium percentage vary up to 60% in some cases. Soil solution is characterized by large amount of sulfate or bicarbonate and sodium while chloride anion is poorly represented, and an alkaline pH. The Na - (Ca + Mg) exchange is well described either by a single Vanselow selectivity coefficient equal to 0.5 or by a single Gaines-Thomas selectivity coefficient equal to 0.3, while the Ca - Mg exchange is described by a single selectivity coefficient equal to 1.5. Moreover, analysis of correlations between yield components of rice and geochemical variables reveals positive effects of Ca and K ions on rice yield and negative effects of pH, salinity and / or soluble Na, SO4 or HCO3. The exploration of the cation contents of the soluble and exchangeable phases in five soil to water ratios shows that their variations as a function of water content are in conformity to the law of ion exchange and that the composition of solution and exchange phases for any moisture content can be estimated accurately from measurements carried out at 1/2 soil to water ratio using regression equations. Furthermore, incubation of the soil does not induce any important release of Fe and Mn in soil solution probably due to high values of pH. Moreover, potassium buffering capacity of these soils can be well predicted from clay content or sand content. Finally, soils of interest exhibit problems of salinity, sodicity and alkalinity that deserve to be keenly investigated for a best management in order to increase agricultural production.La salinisation des sols du périmètre rizicole de Mugerero, bien qu’elle soit la principale contrainte à la production rizicole, n’a pas encore fait l’objet de recherche approfondie. Ce travail a été effectué pour combler cette lacune. Les analyses physico-chimiques de ces sols montrent que le complexe d’échange est saturé par des taux de Ca et de Mg quasi-équivalents et des taux de Na variables jusqu’à 60%. La salinité est de type sulfaté ou bicarbonaté avec dominance du Na et faible part du Cl. La sélectivité du complexe d’échange pour le Na par rapport aux divalents (Ca+Mg) est bien décrite par une valeur unique du coefficient de sélectivité de Vanselow égale à 0,5 ou par une valeur unique du coefficient de sélectivité de Gaines et Thomas égale à 0,3. Quant à la sélectivité de l’échangeur pour le Ca par rapport au Mg, elle est bien décrite par une valeur unique du coefficient de sélectivité égale à 1,5. L’analyse des corrélations entre les composantes du rendement du riz et les variables pédochimiques révèle des effets positifs du Ca et du K sur le rendement rizicole et des effets négatifs du pH, de la salinité et/ou des ions solubles Na, SO4 ou HCO3. L’analyse des teneurs en cations solubles et échangeables à cinq rapports sol/eau montre que leurs variations en fonction de la dilution sont conformes à la loi des échanges ioniques et que les mesures faites à la dilution 1/2 peuvent servir au calcul des valeurs correspondantes à n’importe quelle dilution. Par ailleurs, l’engorgement des sols en anaérobiose n’est pas suivi de libération des cations Fe et Mn en raison des pH élevés. En outre, le pouvoir tampon vis-à-vis du K peut être bien prédit à partir du taux d’argile ou de sable. En définitive, les sols de Mugerero connaissent des problèmes de salinité, de sodicité et d’alcalinité qui méritent d’être profondément étudiés en vue d’une bonne production agricole.(AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 201

NaCl and Na2SO4 Salinities Have Different Impact on Photosynthesis and Yield-Related Parameters in Rice (Oryza sativa L.)

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 (AN) at the seedling and tillering stages, while the intercellular CO2 concentrations (Ci) remained unaffected. Instantaneous transpiration (E) and stomatal conductance (gs) 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 injurie

Differential effects of sulfate and chloride salinities on rice (Oryza sativa L.) gene expression patterns: a comparative transcriptomic and physiological approach

Salinity is a challenge to rice production but most studies are dealing with NaCl and rarely consider Na2SO4 despite its importance in numerous areas of the world. To elucidate genome-level responses to chloride or sulfate salinity stress, seedlings from rice cv. IKP have been exposed for 48 h to two types of Na+-isostrenght nutrient solution (NaCl 200 mM (EC18.84 dS m-1; Ψs = -0.983 MPa); and Na2SO4 100 mM (EC18.05 dS m-1; Ψs = -0.838 MPa)). A combined transcriptomic (microarray analysis) and physiological study was performed. NaCl was more toxic than Na2SO4 to rice seedlings. Contrasting genes were expressed under sulfate and chloride salinity, the difference being the most remarkable in root. Most of the genes involved in response to salt stress were up-regulated in Na2SO4-treated plants while more genes were down-regulated in NaCl-treated plants. Proline accumulated to a higher extent in NaCl-treated plants in relation to up-regulation of genes coding for Δ1-pyrroline-5-carboxylate synthetase and Ornithine-δ-aminotransferase which induced a higher activity of these enzymes in plants exposed to NaCl compared to Na2SO4. In contrast, sucrose accumulated in Na2SO4-treated plants while reducing sugars accumulated in NaCl-exposed ones. These differences could be explained by activities of sucrose-phosphate-synthase, sucrose synthase and acidic invertase but not by upregulation of the corresponding genes. Regulations of the expression of genes coding for signal sensing, perception and transduction and for transcription factors were completely different in response to NaCl and Na2SO4 suggesting that the nature of the counter anion is of primary importance in stress perception and plant response

Yield Responses of Maize (Zea mays L.) and Successive Potato (Solanum tuberosum L.) Crops to Maize Stover co-composted with Calliandra Calothyrsus Meisn Green Manure

The present investigation aimed at evaluating the effect of Calliandra calothyrsus Meisn green manure on the quality improvement of maize (Zea mays L.) stover compost. To that end, two field experiments were installed with maize (Zea mays L.) and a successive potato (Solanum tuberosum L.) crop, which was specifically set up to investigate the potential residual effects of tested organo-mineral fertilizers. The potato (Solanum tuberosum L.) crop did not receive any fertilizer, either organic or mineral. The experimental design was a randomized complete block with three replicates. The basic experimental plot was 1.6 m wide and 3 m long (4.8 m²). Treatments under evaluation were: T1=Control, T2=Maize stover co-composted with mineral fertilizer, T3=Maize stover co-compost with Calliandra calothyrsus Meisn green manure; T4=Farm manure+45-60-30; and T5=Maize stover co-composted with Calliandra calothyrsus Meisn green manure+45-60-30. Evaluated parameters were grain yields, root biomass, above-ground biomass, Harvest Index, and Root/Shoot ratio for maize (Zea mays L.). Potato yields were categorized into small size (< 35 mm), medium size (35-65 mm) and big size tubers (> 65 mm). Significant effects (p < 0.001) of tested fertilizer treatments were observed for maize grain yields (GY), above-ground biomass (AGB), and root biomass (RB). No effect (p > 0.05) of fertilizer treatments could be noticed on the harvest index (HI=0.31-0.38) or R/S ratio (0.079-0.088). For the successive potato crop, a significant effect (p < 0.001) of tested treatments was only observed for the seed-oriented medium size tubers (MST) potato yield. Overall, the most relevant observation of the maize experiment is that treatments T4 and T5 gave higher and equivalent grain and biomass yields. From there, we derive that maize stover co-composted with Calliandra calothyrsus Meisn green manure could be a sound substitute to farm manure. Additionally, the potato experiment highlighted the residual effects of the T3 treatment, statistically equivalent to that of T2. Consequently, we advise that the effects of compost-based organo-mineral fertilizers on crop yields should be evaluated beyond a single seasonal crop, in order to fully catch their residual fertilizer potentials. &nbsp

Comparative effects of chloride and sulfate salinities on two contrasting rice cultivars (Oryza sativa L.) at the seedling stage

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

NaCl- and Na2SO4-Induced Salinity Differentially Affect Clay Soil Chemical Properties and Yield Components of Two Rice Cultivars (Oryza sativa L.) in Burundi

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 m1) 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

Direct and residual fertilizer values of maize (Zea mays L.) stover co-composted with Tithonia diversifolia (Hemsl.) A. Gray green manure

The present investigation highlights and compares the direct and residual fertilizer values of maize (Zea mays L.) stover composted with Calliandra calothyrsus Meisn and Tithonia diversifolia (Hemsl.) A. Gray-green manure on maize (Zea mays L.) and successive potato (Solanum tuberosum L.).  Two field studies were installed with maize and successive potato crops in a completely randomized block design (CRBD) with three replicates. Statistical analyses were performed using R commander, version 4.0.2. Grain yields, root biomass, above ground biomass and calculated parameters (Root/Shoot ratio, Harvest Index and GinningRate) were evaluated for maize. Total potato yields were evaluated and categorized into small size tubers (SST < 35 mm) medium size tubers (MST: 35-65 mm) and big size tubers (BST > 65 mm). Treatments under evaluation were: T1=Control, T2=Farm (cow) manure alone, T3=Maize stover co-composted with Calliandra calothyrsus Meisn green manure; T4= Maize stover co-composted with Tithonia diversifolia (Hemsl.) A. Gray green manure; T5= Farm (cow) manure+45-60-30; T6= Maize stover co-composted with Calliandra calothyrsus Meisn green manure+45-60-30; T7=Maize stover co-composted with Tithonia diversifolia (Hemsl.) A. Gray green manure+45-60-30; and T8=Farm (cow) manure+FOMI Imbura+FOMI Totahaza. Obtained results indicated highest maize yields with FOMI organo-mineral fertilizers (2.7 T/ha) seconded by the recommended fertilizer practice T5 (2 T/ha). In the same line, highest R/S value (=0.38) was registered with the same FOMI treatment (T8), while the highest HI value (0.21) was observed with the maize stover co-composted with Tithonia diversifolia (Hemsl.) A. Gray (T4). Highest potato total yields were observed with the maize stover compost enriched with Tithonia diversifolia (Hemsl.) A. Gray and supplemented with mineral fertilizer (7.61 T/ha), followed by the same compost without mineral fertilizer addition (6.35 T/ha). We conclude our study with the following statements: i) the highest direct fertilizer value was observed with the FOMI treatment; ii) the residual fertilizer effects were more expressed with the maize stover co-composted with Tithonia diversifolia A. Gray green manure with or without mineral additive, followed by farm manure and maize stover enriched with Calliandra calothyrsus Meisn green manure. Consequently, we restate that the effects of compost-based organo-mineral fertilizers on crop yields should be definitely evaluated on a multiseasonal basis so as to fully capture their residual fertilizer potentials