ABSTRACT Compaction modifies the structural arrangement and essential functions of soil pores. In this context, the objective of this study was to evaluate the impact of different compaction levels in an Argissolo Amarelo (Ultisol) on the physical-hydraulic attributes that indicate the functionality of soil pores. The experiment was conducted using 0.05 x 0.05 m soil cylinders with 4 compaction levels (CL): 61, 71, 82 and 92%, and at each CL, the pore-size distribution, intrinsic soil air permeability (Kair), pore continuity index N, soil water characteristic curve and cumulative pore-size frequency were quantified under a completely randomized design. The increase in CL did not impact the amount of micropores, but reduced the amount of macropores to values lower than the minimum required from the CL of 82%. The increase in CL caused reductions in N index, Kair and aeration porosity, but with different amplitude depending on the CL and the water tension in the soil. CL above 61% reduced the water content at the tension range between 0 and 6 kPa and, as a consequence, increased the percentage of aeration pores, besides promoting greater water retention within the range between 10 and 1500 kPa. The evaluation of the physical-hydraulic attributes of the Argissolo Amarelo (Ultisol) revealed that the increase in the compaction level altered soil structure, reduced and formed pores that were poorly continuous and less permeable to air flow and, despite the higher water retention at the higher tensions, promoted lower available moisture content.

ABSTRACT Environmental degradation impacts negatively the diversity and quantity of invertebrates living in the soil, mainly in semiarid regions. Generally, a high diversity of invertebrates indicates good biofunctionality and sustainable use of the soil. We evaluated the effects of 14 years of grazing deferment and the presence of the native trees Mimosa tenuiflora and Cnidoscolus quercifolius on the soil mesofauna of a degraded Caatinga area, according to the χ 2 test, applied to assess the abundance of these microorganisms. The grazing deferment alone more than tripled the soil mesofauna. The abundance of the mesofauna under M. tenuiflora canopies increased by a factor of 3.17 and 3.41 in grazed and ungrazed areas, respectively, and under C. quercifolius canopies increased by a factor of 22.6 in the ungrazed area. The effect of M. tenuiflora in the grazed area was similar to 14 years of grazing deferment. The quantity of mesofauna under C. quercifolius canopies after 14 years of grazing deferment was 6.6-fold higher than that under M. tenuiflora canopies, under similar conditions. The grazing deferment and trees, especially C. quercifolius, increased the soil mesofauna; however, full recovery of such organisms in degraded Caatinga areas may need more than 14 years. Considering the current scenario of increasing environmental degradation, our findings regarding the relationships between soil mesofauna, grazing deferment and native trees are important to devise strategies and procedures for the recovery of degraded areas in the Caatinga biome.

ABSTRACT The objective of this study was to evaluate, through multivariate data analysis, the effect of exogenous application of hydrogen peroxide on the photosynthetic pigments, gas exchange and growth of soursop seedlings under salt stress. The study was conducted in a greenhouse, at Federal University of Campina Grande - Paraíba. The assay was carried out from May to October 2018. The treatments were distributed in a randomized block design, in a 5 × 5 factorial arrangement, corresponding to five levels of irrigation water electrical conductivity - ECw (0.6-control, 1.2, 1.8, 2.4, and 3.0 dS m-1) and five concentrations of hydrogen peroxide - H2O2 (0, 10, 20, 30, and 40 μM), with two plants per plot and four replicates. Irrigation water salinity from 1.2 dS m-1 negatively affected the biosynthesis of photosynthetic pigments, gas exchange and growth of soursop. Application of hydrogen peroxide at the concentration of 20 μM resulted in attenuation of salt stress effects on the biosynthesis of photosynthetic pigments, gas exchange and growth of soursop. Hydrogen peroxide concentrations above 30 μM intensified the deleterious effect of irrigation water salinity on the photosynthetic pigments, gas exchange and growth of soursop.

ABSTRACT As a fresh food, sweet potatoes are highlighted for their taste and appearance. In the industry, they are valued for their starch and sugar content. In both scenarios, much attention has been given to the composition of bioactive compounds. The application of abiotic stresses seems to induce an overproduction of these compounds in some vegetables. The objective was to examine the influence of harvest time on the synthesis and accumulation of bioactive compounds in varieties of minimally processed sweet potatoes with different flesh colors. Sweet potato cultivars (Beterraba, Jerimum, Mãe de Família Roxa, and BRS Cuia) were harvested at 120, 150, and 180 days after planting, then subjected to minimal processing and stored at 5 ºC for 10 days. The most recommended time for harvesting sweet potatoes in semi-arid conditions for minimal processing by the industry is between 150 and 180 days. This is the period when the sweet potatoes exhibit the best quality for fresh consumption, as detected in ‘Mãe de Família Roxa’ and ‘Jerimum’. ‘BRS Cuia’ harvested at 120 days showed the highest phenolic compound levels, the highest polyphenol oxidase and peroxidase enzyme activities, and the most intense browning symptoms. In addition to its starch content, it can be used as a raw material for the extraction of phenolic compounds of interest. ‘Beterraba’ showed low sugar values, rendering them unfavorable for fresh consumption or minimal processing. However, this cultivar also exhibited a high content of carotenoids, making them bio-factories for the food and pharmaceutical industries.

ABSTRACT Quantifying soil gas emissions is costly, since it requires specific methodologies and equipment. The objective of this study was to evaluate modeling by nonlinear regression and artificial neural networks (ANN) to estimate CO2 emissions caused by soil managements. CO2 emissions were evaluated in two different soil management systems: no-tillage and minimum tillage. Readings of CO2 flow were carried out by an automated closed system chamber; soil temperature, water content, density, and total organic carbon were also determined. The regression model and the ANN models were adjusted based on the correlation of the variables measured in the areas where the soil was managed with no-tillage and minimum tillage with data of CO2 emission. Artificial neural networks are more accurate to determine correlations between CO2 emissions and soil temperature, water content, density, and organic carbon content than linear regression.

ABSTRACT The use of intercropping system allows crops to better utilize inputs supplied and the productive capacity of the area, which can be advantageous to the farmer. Thus, the aim of this study was to evaluate the production performance of eggplant and industrial tomato intercropped as a function of the date of eggplant transplantation compared with tomato transplantation, in two seasons. Ten dates of eggplant transplantation were evaluated (-30, -25, -20, -15, -10, -5, 0, + 5, +10 and +15 days compared with tomato transplantation), with the first season from February to September 2009 and the second from August 2009 to February 2010. The number of commercial fruits per plant, commercial yield per plant and commercial yield of eggplant and tomato were influenced by the date of transplanting of eggplant. Highest eggplant yields were obtained in the second season, due to the more favorable weather conditions for the development of this crop. Late eggplant transplants resulted in yield losses due to tomato interference. For tomatoes, the later the eggplant was transplanted, the higher the yield. Therefore, it is concluded that the species have a high degree of interference with each other and the variation in the time of eggplant transplantation influenced the production characters of both crops. In terms of production, the intercropping of these species may not be economically viable for the farmer due to negative influences on the growth, development and production of these crops.

ABSTRACT The action of photosystem I (PSI) inhibiting herbicides depends on light to cause oxidative stress in plants. However, their translocation is inhibited due to their rapid action in the presence of light. The aim was to evaluate the efficacy of the herbicide diquat for control of corn plants subjected to different periods of absence of light after application. Two experiments (field and greenhouse) were conducted, applying the herbicide diquat (200 g a.i. ha−1) to maize plants at stage V4. The plants were subjected to different periods of absence of light after diquat application: 0; 1; 2; 3; 4; 5 and 6 hours. A treatment without herbicide application was used as a control. The control (%) and biomass of corn plants were evaluated in both experiments, and photosynthetic activity and hydrogen peroxide (H2O2) accumulation in leaves were evaluated in the greenhouse experiment. The results showed that diquat needs at least 5 hours of absence of light after application to fully control corn plants. The plants recovered when using shorter periods (4 hours or less) of darkness, and injuries were restricted to points where the herbicide had contact with the plant. The ability of plants to recover was related to the higher photosynthetic activity and oxidative stress induction due to early light exposure. Thus, the lower production of H2O2 in plants kept in the dark for longer periods after herbicide application allows the translocation of the herbicide to meristems, which prevents regrowth of corn plants.

ABSTRACT Plant breeding programs have been investing in the development of high commercial standard onions; thus, they depend on the genetic resources available for obtaining commercial hybrids. The objective of this study was to evaluate genetic parameters and diversity, and phenotypic and genotypic correlations of characters related to onion production. The experiment was conducted in Uberlândia, Minas Gerais, Brazil. Fifty-three onion strains were evaluated, and a randomized block design was used. The number of plant and bulb characteristics evaluated was 13. The statistical analyses were performed using Genes and R software. A genetic variability among the genotypes was found for most of the characters at 1% level of significance in the F test. The heritability of most characters presented moderate to high values (≥ 70%) and high CVg/CVe ratio (≥ 1). The UPGMA method separated the genotypes into 20 groups, while the Tocher method separated them into 19 groups. The groups that stood out were V, XIV, XV, XV, XVI, XVII, XVIII, XIX, and XX. The results of t-test showed six significant phenotypic correlations with low to moderate degree of association, and the genotypic correlations, in most cases, were higher than the phenotypic ones and showed the same sign. From the genetic parameters studied, the possibility of gains in the selection is high. The separation of groups of divergent genitors was possible due to the wide genetic variability for the studied characters. Moreover, the phenotypic and genotypic correlations showed that indirect selection is not feasible.

ABSTRACT Erythrina velutina Willd. (Fabaceae) is drought tolerant and has the potential for reforestation in the semi-arid region. The response of its seeds to the environmental conditions of each production area influences their size, weight, physiological potential, and health. Thus, this study aimed to assess how the environmental conditions of the different regions of Paraíba influence the biometric characteristics of E. velutina seeds. Seeds from 19 mother plants collected in Juru, Sumé, Araçagi, Guarabira, São João do Cariri, Esperança, Queimadas, Cuité, Boa Vista, and Areia, in the state of Paraíba, Brazil, were used in this study. Water content, thousand-seed weight, and biometric characteristics (length, width, and thickness) were determined in the seeds from each location. The water content ranged from 3.11 to 6.84%, while the thousand-seed weight was higher in mother plants grown in Sumé and Cuité. Seed length ranged from 9.00 to 16.84 mm, being higher in mother plants grown in Juru. Seed thickness and width ranged from 5 to 12.99 mm and were larger in mother plants from Cuité. Temperature, humidity, solar radiation, wind, and precipitation caused variations in the length, width, and thickness of E. velutina seeds, with higher means observed in mother plants grown in Cuité.

ABSTRACT The objective of this study was to evaluate the effect of different irrigation depths applied by drip system and nitrogen fertilization levels that promote higher yield and water use efficiency in onion (Allium cepa L.). The treatments consisted of five irrigation depths (50; 75; 100; 125; 150% of crop evapotranspiration), applied by drip system, combined with five nitrogen fertilization rates (0, 40, 80, 120 and 160 kg ha−1), in a 5 x 5 factorial scheme, in a randomized block experimental design, with four replicates. Irrigation depths estimated at 120.2% and 77.81% of crop evapotranspiration promoted higher yield and water use efficiency for total yield of onion bulbs, respectively. Nitrogen dose of 160 kg ha−1 promoted maximum total yield and water use efficiency.