Dry spells in rainfed agriculture lead to a significant reduction in crop yield or to total loss. Supplemental irrigation (SI) with brackish water can reduce the negative impacts of dry spells on net CO₂ assimilation in rainfed farming in semi-arid tropical regions and maintain crop productivity. Thus, the objective of this study was to evaluate the net carbon assimilation rates, indexes for water use efficiency, and indicators of salt and water stress in maize plants under different water scenarios, with and without supplemental irrigation with brackish water. The experiment followed a randomized block design in a split-plot design with four replications. The main plots simulated four water scenarios found in the Brazilian semi-arid region (Rainy, Normal, Drought, and Severe Drought), while the subplots were with or without supplemental irrigation using brackish water with an electrical conductivity of 4.5 dS m⁻¹. The dry spells reduced the photosynthetic capacity of maize, especially under the Drought (70% reduction) and Severe Drought scenarios (79% reduction), due to stomatal and nonstomatal effects. Supplemental irrigation with brackish water reduced plant water stress, averted the excessive accumulation of salts in the soil and sodium in the leaves, and improved CO₂ assimilation rates. The supplemental irrigation with brackish water also promoted an increase in the physical water productivity, reaching values 1.34, 1.91, and 3.03 times higher than treatment without SI for Normal, Drought, and Severe Drought scenarios, respectively. Thus, the use of brackish water represents an important strategy that can be employed in biosaline agriculture for tropical semi-arid regions, which are increasingly impacted by water shortage. Future studies are required to evaluate this strategy in other important crop systems under nonsimulated conditions, as well as the long-term effects of salts on different soil types in this region.

The salinity of irrigation water and soil create considerable challenges in agriculture, as they harm the physiological processes and growth of plants. The exogenous application of antioxidant compounds, such as salicylic acid, can reduce the damage caused by salt stress. Thus, this study aimed to evaluate the attenuation of salt stress induced by salicylic acid in Ocimum basilicum “Cinnamon”. The experiment was performed in randomized blocks with five irrigation water salinity levels (0.5, 1.3, 3.25, 5.2 and 6.0 dS m-1) and five salicylic acid concentrations (0, 0.29, 1.0, 1.71 and 2.0 mM), with five repetitions and two plants per plot. Growth, gas exchange, and chlorophyll indices and fluorescence were evaluated 30 days after the salt treatment was applied. An increase in the salinity of irrigation water decreased the plant height, stem diameter, number of leaves, stomatal conductance, instantaneous water use efficiency, and initial fluorescence of basil “Cinnamon”. Salicylic acid was revealed to attenuate the harmful effects of irrigation water salinity on gas exchange, total chlorophyll, and initial and maximum fluorescence of basil plants.

Mechanisms of tolerance to water deficit and physiological responses to rehydration in cowpea

Several technologies have been implemented to improve plant performance in irrigated crops, and one of them is the use of nanobiostimulants. Therefore, the aim of the present study was to explore the effects of applying different concentrations of a carbon-based biostimulant on the morphophysiology of cowpea plants subjected to varying electrical conductivities of irrigation water. The experiment was performed in a completely randomized design, in a 2 × 6 factorial scheme, with two electrical conductivities of irrigation water (ECw: 0.35 and 4.0 dS m^-1) and six concentrations of nanobiostimulant applied through the leaves (0, 80, 160, 240, 320, and 400 mg L^-1), with four replications. Growth and gas exchange variables were evaluated 31 days after sowing (V9 stage). Concentrations between 240 and 320 mg L^-1 of carbon-based nanobiostimulant promoted greater increases in growth and physiological variables, but they caused decreases in non-photochemical quenching. Water electrical conductivity of 4.0 dS m^-1 reduced the number of leaves (17.1%), stem diameter (10.0%), SPAD index (10.3%), net photosynthesis (10.9%), stomatal conductance (46.4%), transpiration (34.5%), instantaneous carboxylation efficiency (22.4%), and photochemical quenching (4.5%); in contrast, it increased the ratio between internal and ambient CO₂ concentration (18.0%), leaf temperature (2.9%), water use efficiency (32.5%), and non-photochemical quenching (12.4%). Concentrations of 240 to 320 mg L^-1 of the nanobiostimulant enhance the development and gas exchange of cowpea plants under non-stress conditions, whereas the concentration of 240 mg L^-1 promotes the maximum increase in plant height under salinity.

This study aimed to evaluate the effect of different doses (0, 10, 20, 30, 40, and 50 t ha-1) of green coconut fiber in growth substrate on the early development and physiology of two soybean cultivars (Pampeana 40RR and Pampeana 60RR). The experiment was carried out in a greenhouse using a completely randomized experimental design in a 2x6 factorial arrangement (two genotypes and six doses) with five replicates. Each replicate was made up of one plant, totaling 60 experimental units. Biometric variables (height, number of leaves, stem diameter, leaf area, and dry matter) and physiological variables (photosynthesis, stomatal conductance, transpiration, internal carbon, water use efficiency, and photosynthetic pigments) were evaluated. After obtaining the data 30 d after sowing, the means were subjected to an analysis of variance and, when significant for the F test, they were subjected to regression analysis and comparison of means by the Tukey's test. Through the regression analysis, the ideal minimum dose for each variable could be calculated. We observed an increase in plant height, stem diameter, number of leaves, leaf area, leaf dry mass, stem dry mass, and root dry mass of around 51.10%, 31.60%, 52.83 %, 61.78%, 79.65%, 81.52%, and 6.06%, respectively, when we compared the values of the minimum doses with the maximum points found in each variable. Regarding the gas exchange, cultivar 60 RR was superior to cultivar 40 RR. In conclusion, the green coconut fiber compound had a positive influence on the growth and physiology of the cultivars, with the best response being obtained at the dose of 30 t ha-1.

Soil salinization negatively affects the growth and yield of economically valuable crops such as soybeans. New technologies are being developed to minimize the damage caused by saline stress and improve crop performance. Therefore, the use of biostimulants in agriculture may offer an alternative method to mitigate the deleterious effects of salinity. Extracts of the seaweed, Ascophyllum nodosum and humic substances (fulvic acids) are commonly used. Therefore, this study aimed to evaluate the action of a biostimulant composed of A. nodosum seaweed extract and fulvic acid applied at different phenological stages on the biometric, biochemical, and physiological parameters of soybeans (Glycine max) subjected to irrigation with saline water. The experimental design used was completely randomized in a 3 × 2 + 2 factorial scheme, referring to three applications of the biostimulant at different soybean phenological stages: V3, V3R1, and V3R1R4, two levels of electrical conductivity of irrigation water (ECw): 0.5 (S0) and 5.0 dS m-1 (S1), two additional controls, one with a positive control (PC) and the other with a negative control (NC). The experiment had five replicates with one plant per plot. The results of this study suggest that the application of the biostimulant can mitigate the harmful effects of salt stress in soybeans. The results obtained with V3R1 application in the parameters stem diameter, leaf area, shoot dry mass, electrolyte leakage, and chlorophyll b represent greater efficiency in mitigating the harmful effects of salinity in soybean cultivation.