ABSTRACT The production of seedlings of forest species for reforestation of biomes is a practice that restores the conditions of the environment, but water and substrates that favor the growth of seedlings are required. However, in the semi-arid region, water is a limiting factor, requiring the use of alternative sources such as treated domestic sewage. In this context, the objective was to evaluate the growth of Anadenanthera colubrina L. seedlings produced in substrates (soil + bovine manure and soil + coconut fiber) fertilized with treated domestic sewage effluent diluted in public-supply water in proportions (100, 75, 50 and 25% of domestic effluent) and using water from the supply network as a control. The treatments were arranged in a completely randomized design, in a split-plot with three replicates. The treated domestic effluent (TDE) used in the experiment came from the domestic sewage treatment plant of the decanter-digester type of the Projeto de Assentamento Milagre Apodi/RN. The study was conducted in a seedling production nursery at UFERSA, with growth and vigor evaluations at 30, 60, 90 and 120 days after transplanting. The production of seedlings fertigated with domestic effluent caused differences in all growth variables, with improvement in phytomass production. Seedlings fertigated with a dilution of 50% TDE and 50% water supply showed better results when produced with substrate composed of soil and coconut fiber. The seedlings showed good quality, and those cultivated with 50% and 75% of wastewater showed better quality after 120 days of cultivation.

ABSTRACT Underground dams have been widely deployed in the semi-arid region of Rio Grande do Norte, a state in the Brazilian Northeast, aiming to mitigate the effects caused by water scarcity. In this study, the geographic distribution of the electrical conductivity of water of underground dams was evaluated at the end of the dry season of 2018 and at the end of the rainy season of 2019. Maps were created in ArcGIS 10.4.1 software using the Inverse Distance Weighted interpolator. The results indicated high electrical conductivity variability in the evaluated underground dams. The highest values were obtained in the eastern portion of the Rio Grande do Norte state, except for two dams, located in the municipalities of Apodi and Severiano Melo. In most of the underground dams (64%), the water has an electrical conductivity with low soil salinization potential (EC < 0.7 dS m-1). It was observed that the salinity of the underground dams is influenced by several factors, such as climate, relief, land use and occupation due to rural agglomerations and animal husbandry in the dam hydrographic basin, and intensive nutritional management with fertilizers in the dam area.

ABSTRACT Soil management systems, including tillage and green manuring, are important for the control of nematodes and for the sustainable production. The objective was to select, through multivariate analysis, sustainable agroecosystems for yellow melon cultivated under irrigated conditions in the Brazilian semi-arid region. The long-term experiment is set up in Argissolo Vermelho- Amarelo (Ultisol) with six multifunctional agroecosystems, composed of the combination of three mixtures of cover crops (1 - 75% legumes + 25% grasses and oilseeds; 2 - 25% legumes + 75% grasses and oilseeds and 3 - spontaneous vegetation) and two types of soil management (no tillage-NT and tillage-T). The purpose was to evaluate the nutritional status of plants, soil fertility, nematode population in roots and soil, and the yield. Data were analyzed with multivariate techniques, allowing the grouping of the agroecosystems based on their similarities and complexity of functions. The incorporation of plant residues to the soil reduces nematode population, but their maintenance on the surface allows the improvement of fertility and yield, even under larger nematode populations. The agroecosystems that associate the nonincorporation of residues from cover crops with larger species diversity in composition constitute the most complex model, allowing different environmental functionalities. Thus, it is recommended not to incorporate the plant residues, planting the melon seedlings directly in the straw. However, considering that the results obtained with the non-incorporation of spontaneous vegetation were similar to those obtained with the incorporation of commercial cover crops, it is concluded that this practice is also viable and adapted to the semi-arid conditions.

ABSTRACT Fresh corn is a highly appreciated vegetable in Brazil; this crop has high added value and profitability when compared to dry corn. Despite the consumer market demand for quality, cultivars are not launched every crop season and there is a small number of cultivars available to growers. This denotes a need for breeding programs focused on generating information and genotypes that can occupy this market niche. The objective of this work was to evaluate the progress of five cycles of intrapopulation recurrent selection in half-sib progenies of fresh corn, in the southwest region of Goiás. A randomized block experimental design was used, with evaluation of 64 progenies of corn half-sib progenies and selection intensity of 30% per cycle, with three replications, in the 2011-2012, 2013-2014, 2015-2016, 2017-2018, and 2020-2021 summer crop seasons. The half-sib progenies of fresh corn exhibited genetic variability through intrapopulation recurrent selection in the different selection cycles, which is still promising for further selections after five cycles, with evaluation of 64 progenies per cycle. The base population from crossings between hybrids for tropical and temperate climates showed to be promising for increasing the genetic base of fresh corn populations, with satisfactory gains over the five cycles, presenting mean heritability between the cycles of approximately 78.9% for relative chlorophyll index, 62.2% for plant height, 75.1% for ear insertion height, 70% for ear diameter, 56.6% for ear length, 71.4% for unhusked ear yield, and 71% for marketable ear yield.

ABSTRACT The federal public agencies have prioritized the financing of underground dams as a strategy to decrease water scarcity in rural semiarid regions in Brazil. The objective of this work was to evaluated water quality in underground dams, for agricultural irrigation purposes, in Rio Grande do Norte, Brazil, at the end of the dry season in 2018 and at the end of the rainy season in 2019. The variables with the greatest impact on water quality were identified through multivariate analysis, using the software Statistica 7.0. The results showed that concentrations of variables correlated with salinity and ion toxicity in water of the dams decreased after the rainy season, whereas those correlated with clogging of localized irrigation systems increased. Salinity, sodicity, and/or toxicity in areas of underground dams were correlated with natural mineralization of geological components of soils; however, they also were affected by rainfall with marine hygroscopic nuclei, presence of rural clusters and corrals, and decomposition of organic matter in the damming area. The variables correlated with salinity presented higher effect on the hydrochemical variability of water within these dams in both sampling periods; electrical conductivity and chloride ions were the most significant variables.

ABSTRACT Current procedures for determining soil organic carbon (SOC) content are costly, time-consuming, and generate polluting chemical waste. Therefore, developing new protocols using aerial and orbital remote sensing and diffuse reflectance spectroscopy (DRS) for digitally mapping the stock of soil organic carbon (CS) is essential for promoting actions of research and monitoring SOC in Brazilian soils. Given this, three areas of commercial plots in the region of the Middle North of Mato Grosso were studied, where sampling was carried out for the determination of SOC in the layer from 0 to 30 cm, evaluated by the dry combustion method and estimated through DRS in the visible to near -infrared region - Vis-NIR-SWIR/350-2500 nm). To obtain the images by aerial remote sensing, the Carcará II® Unmanned Aerial Vehicle was used, with a MicaSense® multispectral camera (RGB + NIR + RedEdge) attached. The orbital sensors used were the Sentinel 2® and Planet® satellites. This study showed that soil carbon stock values could be predicted using different modeling approaches based on field and laboratory spectral measurements. Predictive models to estimate SOC can be established using remote and near sensing, thus allowing a better understanding of spatial patterns of SOC in crop fields.

ABSTRACT The objective of this study was to evaluate gas exchange, biomass, and quality of guava seedlings as a function of the cationic nature of the water used in irrigation and foliar application of salicylic acid. The experiment was carried out in a greenhouse in Pombal, PB, Brazil, using a randomized block design, in a 6 × 4 factorial scheme with six cationic compositions of irrigation water [S1 - Control (supply water); S2 - Na+; S3 - Ca2+; S4 - Na++Ca2+; S5 - Mg2+, and S6 - Na++Ca2++Mg2+], associated with four concentrations of salicylic acid (0, 1.3, 2.6, and 3.9 mM), with 3 replicates. Plants in control (S1) were irrigated with water of electrical conductivity (ECw) of 0.3 dS m-1, while in the other treatments were irrigated with different types of water and had an ECw of 4.3 dS m-1, consisting of different cations, in the form of chloride. In the seedling formation phase, guava plants were sensitive to calcic water, which resulted in a marked decrease in their growth. Stomatal conductance, transpiration, and biomass accumulation of guava seedlings were more affected by variation in electrical conductivity than by cationic nature of the water. Salicylic acid at concentrations of 2.9 and 1.9 mM increased stomatal conductance and stem dry biomass, respectively, of guava seedlings. Water with ECw of 4.3 dS m-1 allowed the formation of guava seedlings with acceptable quality for transplanting to the field, regardless of the cationic nature of the water.

ABSTRACT Growing forage cactus pear in semi-arid regions is an alternative when facing current climate changes, and improving its cropping systems is critical to increasing its yields. The objective was to evaluate morphometric characteristics and yield of ‘Gigante’ cactus pear under complementary irrigation with saline water and different planting densities. The research was carried out in the semiarid region of Bahia during the period from September 2017 to October 2019. A randomized block design was used with treatments arranged in split-split plots. Two irrigation intervals (7 and 14 days) were assigned to plots, four planting densities (20,000; 40,000; 60,000 and 80,000 plants per hectare) to subplots, and four irrigation levels (0, 11, 22 and 33% of ETo) to sub-subplots. High-salinity water (2.91 dS m-1), classified as C4S1, did not limit the growth and yield of ‘Gigante’ forage cactus pear for two crop cycles. Fresh matter and dry matter yields, fresh matter-based water use efficiency and dry matter-based water use efficiency were highest at planting densities of 61,465 and 67,786 plants ha-1, and 61,848 and 69,707 plants ha-1, respectively. The use of 33% ETo irrigation level increased morphometric characteristics, fresh matter yield in the first and second cycles, and dry matter yield in the first cycle. Applying increasing irrigation levels promotes reductions in fresh matterand dry matter-based water use efficiency.

ABSTRACT Sowing arrangements composed of double-row spacing in corn can favor the interception of solar radiation by the canopy and, consequently, the yield performance of the crop. However, it is possible that the microclimate provided by this spacing, especially at high plant densities, favors the occurrence of leaf diseases. Thus, the objective was to evaluate the effect of 0.45 m and double-row spacing arrangements on the severity of foliar diseases and yield performance of corn grown in the first and second-crop seasons. Two independent experiments were conducted (with and without the fungicide fluxapyroxad + pyraclostrobin) in the first and second-crop seasons in a randomized block design arranged in a split-plot scheme with four repetitions. The plots consisted of spacing (0.45 m) and double-row (0.30 × 0.60 m), and the subplots, four plant densities (59,200, 74,000, 81,400, and 96,200 plants ha-1). In the plant density factor, in the second-crop season, there is a decrease in the severity of white spot as plant density is increased. Also, for the plant density factor, in the first-crop season, there may be a significant yield increase as the plant density is increased.

ABSTRACT A great challenge of scientific research with carrot in semi-arid regions is obtaining the best productive characteristics and economic conditions by optimizing the green manure amounts using spontaneous species from the Caatinga biome, such as hairy woodrose (Merremia aegyptia L.) and roostertree (Calotropis procera Ait.). Therefore, this work aimed to agronomically and economically optimize the production of carrot roots in monocropping and of their components when fertilized with equitable biomass amounts of these spontaneous species in two cropping seasons in a semi-arid environment. The experimental design was a randomized complete block design, with five treatments and five replications. The treatments consisted of equitable amounts of hairy woodrose and roostertree biomass in amounts of 16, 29, 42, 55, and 68 t ha-1 on a dry basis. In each experiment, an additional carrot treatment without fertilizer (absolute control) was planted for comparison with the other treatments to determine maximum physical and economic efficiency. Carrot fertilization was performed with the incorporation of 48.87 t ha-1 of M. aegyptia and C. procera dry biomass into the soil to obtain the maximum optimized productive efficiency (commercial productivity). The maximum optimized agroeconomic efficiency (net income) of carrot cultivation was obtained when 49.64 t ha-1 of M. aegyptia and C. procera dry biomass was added to the soil. The use of biomass from these spontaneous species from the Caatinga biome as green manure is a viable technology for tuberose producers in monocropping in semiarid environments.