Semiarid soils may be poor in organic carbon, a necessary source of energy for soil microorganisms that affect plant growth. Although the addition of organic carbon may improve soil chemical characteristics, the concentration of humic compounds in the organic component may vary and affect soil chemical composition. We evaluated the effect of two sources of humic compounds on a dystrophic yellow Oxisol cultivated with passion fruit (Passiflora edulis Sims f. edulis) and irrigated with saline water during a severe drought in the Brazilian semiarid region. Soil fertility was evaluated during two seasons. A bovine biofertilizer and an organic commercial amendment (Humistar) were used as sources of humic compounds. Salinity resulted in reduced soil fertility, mainly during the lower rainfall period. The combination of humic substances and salinity increased soil salinity. Humistar, more concentrated in humic acid than fulvic acid, increased both acidity and salinity of the Oxisol under study during the lower rainfall period. Our results contradict the general idea that organic matter can mitigate the harmful effects of salts in semiarid soils because the addition of organic sources to the soil, mainly during a severe drought period, may reduce soil fertility. Although this response may depend on the concentration of humic acids in the amendment, our results suggest that the correction of soil chemistry with the application of either amendment to Oxisols under semiarid conditions, mainly during severe drought, is not economically feasible. Core Ideas Saline irrigation reduces the fertility of Oxisols, mainly in low‐rainfall periods. The combination of humic substances and salinity increased salinity of Oxisols. During low‐rainfall periods, humic substances reduced Oxisol fertility.

Saline-sodic soils are a major impediment for agricultural production in semi-arid regions. Salinity and sodicity drastically reduce agricultural crop yields, damage farm equipment, jeopardize food security, and render soils unusable for agriculture. However, many farmers in developing semi-arid regions cannot afford expensive amendments to reclaim saline-sodic soils. Furthermore, existing research does not cover soil types (e.g., Luvisols and Lixisols) that are found in many semi-arid regions of South America. Therefore, we used percolation columns to evaluate the effect of inexpensive chemical and organic amendments (gypsum and cow manure) on the reclamation of saline-sodic soils in the northeast of Brazil. Soil samples from two layers (0–20 cm and 20–40 cm in depth) were collected and placed in percolation columns. Then, we applied gypsum into the columns, with and without cow manure. The experiment followed a complete randomized design with three replications. The chemical amendment treatments included a control and four combinations of gypsum and cow manure. Percolation columns were subjected to a constant flood layer of 55 mm. We evaluated the effectiveness of sodic soil reclamation treatments via changes in soil hydraulic conductivity, chemical composition (cations and anions), electrical conductivity of the saturated soil-paste extract, pH, and the exchangeable sodium percentage. These results suggest that the combined use of gypsum and cow manure is better to reduce soil sodicity, improve soil chemical properties, and increase water infiltration than gypsum alone. Cow manure at 40 ton ha−1 was better than at 80 ton ha−1 to reduce the sodium adsorption ratio.

The change in the use of the soil causes an imbalance in the ecosystems, altering the chemical and physical properties, which can make their natural recovery unviable. This study aimed to characterize chemically and physically an Entisol under the Caatinga area in a 30 years ecological succession stage in the Semiarid region of Paraiba. The experiment was carried out at the Experimental Station Professor Ignácio Salcêdo, belonging to the National Institute of Semiarid (INSA), located in the municipality of Campina Grande, in the state of Paraíba, soil samples were collected in the 0-10 cm layer, for the determination of pH levels (H2O), exchangeable acidity (Al3+) and potential acidity (H + Al), Ca2+, Mg2+, K+, P, Na+, CTC and SB, Total organic carbon (TOC) and organic matter (OM). In the physical analyses, texture, soil density, particle density, total porosity and aggregate stability were determined. The chemical characterization observed the presence of high levels of K+, Ca2+, Mg2+, CTC and SB, and low levels of Al3+ and Na+ with reduced OM and TOC contents in the 0-10 cm layer. As for physics, the textural classification was sandy loam soil, the soil density, soil porosity and aggregate stability showed values below the critical root growth index in sandy soils. The soil presented recovery characteristics of its chemical and physical quality. The description of the Entisol in the field in soil surveys contributes to a new database in order to predict a better way of use, and these results are references in studies of soil quality recovery in degraded areas in the Caatinga area.

Passiflora edulis f. flavicarpa (yellow passion fruit) is a high-value tropical crop explored for both fruit and nutraceutical markets. As the fruit production in the US rises, the crop must be investigated for the effects of salinity under semi-arid climates. We assessed the effects of irrigation-water salinity, leaf age, and drying method on leaf antioxidant capacity (LAC) and plant genetic responses. Plants were grown in outdoor lysimeter tanks for three years, with waters of electrical conductivities of 3.0, 6.0, and 12.0 dS m−1. Both Na and Cl significantly increased with salinity; leaf biomass at 3.0 and 6.0 dS m−1 were similar but reduced significantly at 12.0 dS m−1. Salinity had no effect on LAC, but new leaves had the highest LAC compared to older leaves. Low-temperature oven-dried (LTO) and freeze-dried (FD) leaves had the same LAC. The analyses of twelve transporter genes, six involved in Na+ transport and six in Cl− transport, showed higher expressions in roots than in leaves, indicating a critical role of roots in ion transport and the control of leaf salt concentration. Passion fruit’s moderate tolerance to salinity and its high leaf antioxidant capacity make it a potential new fruit crop for California, as well as a rich source of flavonoids for the nutraceutical market. Low-temperature oven drying is a potential alternative to lyophilization in preparation for Oxygen Radical Absorbance Capacity (ORAC) analysis of passion fruit leaves.

No abstract

The study evaluated the effect of the cultivation of five species of grasses of the genus Brachiaria (B. decumbens, B. ruziziensis, B. brizantha, B. humidicola and B. brizantha CV MG-5) in physical and chemical properties and in the formation and stabilization of aggregates of a Yellow Oxisol. The test with the grasses in the absence and presence of fertilization was conducted in the Chã de Jardim area, belonging to the Centro de Ciências Agrárias-UFPB, located in the county Areia-PB. The experimental design was in randomized blocks, with subdivided parcels, in factorial scheme 5 × 2 × 4, with four repetitions, being: five species of Grass (Braquiarias), two conditions of mineral fertilization with NPK (absence or presence) and four depths of soil samples collection (0-5, 5-10, 10-20, 20-30 cm), totaling 40 subplots of 5.0 × 5.0 m, with 3 repetitions, totaling 120 sampling points. The grasses favored the formation of aggregates and contributed to their stability. Brachiaria brizantha is the most suitable grass to raise the organic matter content of an Oxisol without mineral fertilization.