Several studies have been conducted evaluating the management of fertilizers as strategies to mitigate the deleterious effects of salt stress, so the objective of this work was to evaluate the quality of ‘Crioula’ guava seedlings under irrigation with water of different salinity levels and fertilized with combinations of nitrogen and potassium. The experiment was performed in a protected (screened) environment using a randomized block design and analyzed in a 5 × 4 factorial scheme, with four replicates, with the plot formed by two plants. The treatments were formed from the combination of the factor electrical conductivity of irrigation water (ECw 0.3, 1.1, 1.9, 2.7 and 3.5 dS m^-1), with the factor combinations (C) of nitrogen (N) and potassium (K₂O) doses, being C1 = 70% N + 50% K₂O, C2 = 100% N + 75% K₂O, C3= 130% N + 100% K₂O and C4= 160% N + 125% K₂O. The recommended dose of 100% N and K, respectively, was 541.1 mg N dm^-3 soil and 798.6 mg K dm^-3 soil. The combinations of N and K fertilization corresponding to 70% N + 50% K₂O and 100% N + 75% K₂O of the recommended doses promoted greater growth of ‘Crioula’ guava seedlings. Water with ECw of 2.1 dS m^-1 promotes the formation of quality ‘Crioula’ guava seedlings.

Custard apple (Annona squamosa L.) is a sensitive fruit crop to salinity. One of the alternatives to minimize the deleterious effects of salt stress is adopting mineral fertilization management practices, promoting increased crop tolerance to salts. Therefore, the objective of the present study was to evaluate NPK doses to mitigate salt stress in custard apple seedlings irrigated with saline wastewater. The experiment was performed in a greenhouse, adopting a randomized block design in a 3 × 5 factorial scheme, corresponding to three irrigation waters (local-supply water of 0.53 dS m^-1 electrical conductivity (control); desalination reject of 3.5 dS m^-1; fish farming effluent of 3.5 dS m^-1) and five proportions of the NPK recommendation (25, 50, 75, 100, and 125% of the fertilization recommendation), with four replicates. The growth, biomass accumulation, and nutrients were evaluated. Irrigation with desalination reject, and fish farming effluent restricted the growth of custard apple seedlings, regardless of the NPK dose used. The ionic homeostasis of seedlings irrigated with desalination reject and fish farming effluent is optimized by fertilization with 50% of the NPK recommendation corresponding to 50, 150, and 75 mg of N, P₂O₅, and K₂O dm^-3, respectively. For the production of seedlings irrigated with local-supply water, the dose of 75% NPK, corresponding to 75, 225, and 112.5 mg of N, P₂O₅, and K₂O dm^-3, respectively, is recommended.

Salt stress is a major constraint on cowpea cultivation in semi-arid regions, primarily due to excess salts in irrigation water and soils. We aimed to investigate the effects of foliar magnesium (Mg) application on the production, phenology, and seed vigor of the cowpea landraces “Pingo de Ouro” and “Costela de Vaca” under salt stress conditions. Two experiments were conducted. The first was carried out in a greenhouse using a randomized block design with five replicates, in a 2 × 3 × 4 factorial scheme: two cowpea landraces (“Pingo de Ouro” and “Costela de Vaca”), three irrigation water salinity levels (0.54, 3.50, and 5.00 dS m⁻¹), and four foliar doses of a product (0.0, 1.0, 2.0 and 3.0 mL L⁻¹) containing 8% magnesium. Morphological traits and seed production were evaluated. The second experiment was conducted in a laboratory using a completely randomized design, also in a 2 × 3 × 4 factorial, with four replicates of 25 seeds each. In the first experiment, the 1 mL L⁻¹ dose provided the best results for pod length in the variety “Pingo de Ouro” under an electrical conductivity salinity of 5.00 dS m⁻¹. In the variety “Costela de Vaca”, this same dose increased the number of seeds per pod and the 100-seed weight under the same salinity level. In the second experiment, seedlings of “Pingo de Ouro” grown from seeds produced by plants treated with 2 and 3 mL L⁻¹ doses showed greater shoot length, root length, stem diameter, and shoot fresh mass, particularly under 0.54 dS m⁻¹ salinity. Therefore, “Pingo de Ouro” exhibited superior seedling growth at doses of 2 and 3 mL L⁻¹, particularly under conditions of low salinity. These findings support the use of foliar magnesium fertilization as an effective agronomic strategy to enhance seed production and quality in cowpea landraces under salt stress conditions.

Soursop (Annona muricata L.) is a tropical fruit grown in the semi-arid region of Brazil, where problems of quantitative and qualitative scarcity of water for irrigation are frequent. Using alternative water sources, such as fish farming effluents, can increase water availability; however, it presents risks due to its high salinity levels. We aimed to evaluate the effect of irrigation with saline fish farming effluent and NPK doses on soursop seedlings’ ecophysiology. We conducted a greenhouse experiment using a randomized complete block design with a 2 × 5 factorial scheme. The factors consisted of two irrigation water sources (local supply water with 0.5 dS m⁻¹ and fish farming effluent with 3.5 dS m⁻¹) and five doses of NPK (25%, 50%, 75%, 100%, and 125% of the fertilizer recommendation of 100:300:150 mg dm⁻³ of N:P₂O₅:K₂O for soil). The soursop seedlings showed the best growth results for plant height, stem diameter, and shoot dry mass when irrigated with low-salinity water at 95% of the recommended NPK dose. However, under saline stress, the soursop seedlings showed optimal growth when fertilized with 69% of NPK dose. We recommend the following NPK fertilization for soursop seedlings: 95:285:143 mg dm⁻³ of N:P₂O₅:K₂O for those irrigated with low-salinity water and 69:207:104 mg dm⁻³ for those irrigated with fish farm effluent. Irrigating with fish farm effluent can be a practical option for soursop seedlings as it can help save fertilizers and promote environmental sustainability.

Excess salts in water used for irrigation in the semi-arid region cause losses in growth and yield of cucurbits, such as watermelon. However, the choice of salinity-tolerant varieties can reduce the impact of stress on crop yield. Thus, the objective of this study was to evaluate the tolerance of watermelon varieties to irrigation water salinity during initial development. The experiment was conducted in a protected environment located at the Federal Rural University of the Semi-arid Region, Mossoró, RN, Brazil, in a randomized block experimental design in a 7 x 3 factorial scheme with four replicates, consisting of seven cultivars (Rochedo F1, Crimson Select, Charleston Gray, Fairfax, Crimson Sweet, Sugar Baby, Preciosa) and three irrigation water salinity levels (0.5, 4.5, and 9.0 dS m^-1). Increasing irrigation water salinity reduced emergence, growth, and dry mass accumulation in seedlings. There was a tendency for photosynthetic pigments of watermelon seedlings to increase with increasing salts in the irrigation water, indicating that the time of exposure to salt stress was not sufficient to significantly reduce the levels of chlorophyll a, chlorophyll b and total chlorophyll. The Rochedo F1, Crimson Select and Fairfax varieties showed greater tolerance to salinity, while Sugar Baby and Preciosa were classified as moderately sensitive to electrical conductivity levels of 4.5 and 9.0 dS m^-1 in the irrigation water.

Evaluating the availability of potassium (K) in soils of the semi-arid region of Brazil is complex, as it varies greatly between soils, especially soils with larger amounts of 2:1 minerals. The aim of this study was to evaluate the efficiency of ammonium acetate, ammonium chloride, Mehlich-1 and mixed ion-exchange resin as extractants in quantifying the K content available to maize plants in soils of the semi-arid region of Brazil. The treatments were distributed in randomised blocks, and included six types of soil (a Red Yellow Argisol, a Fluvic Neosol, two Haplic Cambisols, a Rendzic Chernosol and a Haplic Vertisol) and five levels of K, with three replications. Each plot consisted of a plastic pot containing 3.0 dm3 soil, where two maize plants were grown for 35 days. There was a good correlation between the extractants under evaluation and the amount of K accumulated by the plants. The ion-exchange resin presented a lower K extraction capacity in the more-clayey soils with a higher CEC and greater quantity of 2:1 minerals, and is not recommended for soils with these characteristics. The extraction capacity of Mehlich-1 may be reduced in alkaline soils with high levels of CaCO3 equivalent, and should not be used in these soils. Ammonium acetate extracted the greatest amounts of K from the soils and showed no limitations in any of the soils under evaluation, making it the most recommended for assessing potassium availability in semi-arid soils. A disponibilidade de potássio (K) em solos do semiárido brasileiro varia bastante entre solos e sua avaliação é complexa, sobretudo nos solos com maior quantidade de minerais do tipo 2:1. Neste trabalho objetivou-se avaliar a eficiência dos extratores acetato de amônio, cloreto de amônio, Mehlich-1 e resina de troca iônica mista para quantificação do K disponível para plantas de milho em solos do semiárido brasileiro. Os tratamentos foram distribuídos em blocos casualizados, com seis solos (um Argissolo Vermelho Amarelo, um Neossolo Flúvico, dois Cambissolos Háplicos, um Chernossolo Rêndzico e um Vertissolo Háplico) e cinco doses de K, com três repetições. Cada parcela consistiu em um vaso plástico contendo 3,0 dm3 de solo, onde foram cultivadas duas plantas de milho durante 35 dias. Para cada extrator, o K disponível foi correlacionado com o K acumulado na parte aérea das plantas. Todos os extratores avaliados mostraram boa correlação com o K acumulado pela planta. A resina de troca iônica apresentou menor capacidade de extração de K nos solos mais argilosos, com maior CTC e maior quantidade de minerais 2:1, não sendo recomendada para solos com essas características. O extrator Mehlich-1 sofreu desgaste na sua capacidade de extração em solos alcalinos com teores elevados de CaCO3 equivalente não devendo ser utilizado para esse tipo de solo. O extrator acetato de amônio extraiu as maiores quantidades de K dos solos e não apresentou limitações em nenhum solo, sendo o mais recomendado para a avaliação da disponibilidade de potássio em solos do semiárido.