The aim of this study was to evaluate the accumulation of salts in the soil from irrigation water and of N and K from fertilization. The experiment was conducted in PVC columns (20 cm in diameter and 100 cm in height), filled with non-saline soil, and cultivated with maize. A completely randomized block design in a 4 x 4 factorial was used, with four levels of salinity (0.5, 2.5, 5.0 and 7.5 dS m^-1), four N rates, and five replicates. Nitrogen was applied as urea and potassium nitrate at the following rates: N1: N recommendation for maize (2.6 g column^-1); N2: 0.3 times (0.78 g column^-1) the recommended N1 dose; N3 and N4 with N based on N1 and N2 doses, respectively, reduced proportionally based on the evapotranspiration reduction caused by salinity. After 74 days from sowing, root and soil samples were collected at different soil depths. The electrical conductivity of the saturated extract (ECe) and the concentration of ions (Ca²⁺, Na⁺, and Cl^-) increased as a function of salinity and soil depth. The opposite was observed for the root system. The increase in salinity also resulted in K⁺ and NO₃^- accumulation in the soil column, mainly in treatments with higher N rates (N1 and N3). At the end of the experiment, 88% of the NO₃^- applied at the highest salinity treatment (7.5 dS m^-1) and the highest N rate (N1) was below 20 cm soil depth, evidencing a N loss process caused by leaching.

Although leaching fraction (LF) is used to remove salts from the root zone under conditions of salinity, if miscalculated, it can decrease water use efficiency and lead to major losses of essential nutrients. This study evaluated the water use efficiency, leaf nutrient concentrations in maize plants, and nutrient losses as a function of two ways of determining the LF in maize crop grown in soil columns under salt stress. The experimental design used was completely randomized, with treatments arranged in split plots, with seven replicates. The plots were formed by two methods of determination of LF, and the subplots by four electrical conductivities of irrigation water - ECw (0.5, 2.0, 4.0, and 6.0 dS m-1). The leaching fractions were established according to 1) the formula proposed by Rhoades (RHO) and 2) by applying a LF of 0.15 calculated according to the soil water balance (SWB). The leaf concentrations of N, P, Ca, and Mg were higher in plants under SWB than under RHO method. The leaf concentrations of N, P, and K decreased with increased salinity, regardless of the LF. Adding a LF of 0.15 according to SWB resulted in decreased losses of nutrients and higher physical water productivity, as compared to the RHO. Thus, a more precise determination of the LF is needed to increase economic returns for maize cultivation in semi-arid regions when using brackish water for irrigation.

EFFECT OF LEACHING FRACTION DETERMINED BY TWO METHODS ON GROWTH AND YIELD OF MAIZE SUBMITTED TO SALT STRESS1 EMANUEL DIAS FREITAS2; CLAUDIVAN FEITOSA DE LACERDA3; JULIANA MATOS VIEIRA4; BRUNO GABRIEL MONTEIRO DA COSTA BEZERRA5 E AURELIANO DE ALBUQUERQUE RIBEIRO6 1Parte da tese de doutorado do primeiro autor. Projeto financiado pelo CNPq; 2 Departamento de Engenharia Agrícola, Universidade Federal do Ceará – UFC, CEP: 60451-970, Fortaleza, CE, e-mail:emanueldiasfreitas@gmail.com; 3 Departamento de Engenharia Agrícola, Universidade Federal do Ceará – UFC, CEP: 60451-970, Fortaleza, CE, e-mail:cfeitosa@ufc.br; 4 Departamento de Ciência do Solo, Universidade Federal do Ceará – UFC, CEP: 60451-970, Fortaleza, CE, e-mail:julianamatosvieira@gmail.com; 5 Departamento de Engenharia Agrícola, Universidade Federal do Ceará – UFC, CEP: 60451-970, Fortaleza, CE, e-mail:brunog768@gmail.com; 6 Departamento de Engenharia Agrícola, Universidade Federal do Ceará – UFC, CEP: 60451-970, Fortaleza, CE, e-mail:alburibeiro@gmail.com. 1 ABSTRACT The aim of this study was to evaluate the effects of the leaching fraction determined by two methods in maize cultivated in a soil column and submitted to irrigation with water of different salinities. The experiment was conducted in the meteorological station of the Federal University of Ceará, Fortaleza - CE, in a completely randomized design, composed by four levels of irrigation salinity water (0.5, 2.0, 4.0 and 6.0 dSm-1) and two methods of determination of the leaching fraction. Each treatment had seven replicates. The plots were constituted by maize cultivated in soil columns, measuring 20 cm in diameter and 100 cm in length. The leaching fractions (LF) were defined as follows: A. Application of the LF calculated according to the formula proposed by Rhoades (1974), Rhoades and Merrill (1976); B. Application of the LF of 15% calculated from the soil water balance of the experimental plots. The results showed that plants that were irrigated with ECw of 0.5 and 4 dS m-1, the LF of 5 and15%, respectively, were able to minimize the effects of salinity. For ECw of 6 dS m-1, the LF of 15 and 92% showed no improvement in maize growth and yield. Keywords: Zea mays L. soil columns, saline water. FREITAS, E. D.; LACERDA, C. F. DE; VIEIRA, J. M.; BEZERRA, B. G. M. DA C. E RIBEIRO, A. DE A. EFEITO DA FRAÇÃO DE LIXIVIAÇÃO DETERMINADO POR DOIS MÉTODOS NO CRESCIMENTO E PRODUÇÃO DO MILHO SUBMETIDO A ESTRESSE SALINO 2 RESUMO Objetivou-se com o trabalho avaliar os efeitos da fração de lixiviação determinado por dois métodos na cultura do milho cultivado em coluna de solo e submetido a irrigação com água de diferentes salinidades. O experimento foi instalado na estação meteorológica da Universidade Federal do Ceará, Fortaleza – CE, em delineamento inteiramente casualizado, composto por quatro salinidade de água de irrigação (0,5, 2,0, 4,0 e 6,0 dS m-1) e duas formas de determinação da...

Neem (Azadirachta indica A. Juss) extracts are widely used in agriculture as organic pesticides, but their effects on soil microbiota are uncertain. This study evaluated the impact of aqueous extracts of neem leaves and seeds on soil microbial activity, maize (Zea mays L.) development, and arbuscular mycorrhizal fungus (AMF) dynamics. The experiment used a 2 × 3 + 1 factorial design, with two extract sources (leaf and seed), three concentrations (5%, 10%, and 20%), and a control. The soil treated with 20% seed extract showed the highest microbial respiration (16,512 mg C-CO₂·kg⁻¹·day⁻¹) and total organic carbon (15.10 g·kg⁻¹) but the lowest microbial biomass (1330 mg·kg⁻¹) and microbial quotient (0.10%), indicating a stressed microbial environment. Paradoxically, maize plants under this same treatment exhibited a superior height, stem diameter, and biomass. Furthermore, the AMF spore density significantly increased in the seed extract treatments, suggesting a stress-induced reproductive response. These findings reveal that, although neem seed extract can negatively affect soil microbiota, it promotes maize growth, likely due to its organic and bioactive compounds. Thus, neem extract demonstrates potential as an organic input, but its application must be carefully managed due to potential ecological trade-offs.