The large variation in the response of sunflower to nitrogen fertilization indicates the need for studies to better adjust the optimum levels of this nutrient for production conditions. Our objectives were to analyze the agronomic yield of sunflower cultivars as a function of nitrogen fertilization; indicate the cultivar with high nitrogen use efficiency; and measure the adequate N dose for sunflower through nutritional efficiency. The completely randomized block design with split plots was used to conduct the experiments. The treatments included five nitrogen rates being allocated in the plots and the four sunflower cultivars. To estimate the nutrient use efficiency in the sunflower, we measured agronomic efficiency (AE), physiological efficiency (PE), agrophysiological efficiency (APE), apparent recovery efficiency (ARE), and utilization efficiency (UE). The results indicate that all cultivars had a reduction in AE due to the increase in N doses in the first crop. For PE, the highest values were observed for Altis 99 during the 2016 harvest. In that same harvest, Altis 99 had the highest APE. The dose of 30 kg ha⁻¹ provided greater ARE for all cultivars in both crops, with greater emphasis on BRS 122 and Altis 99. The cultivation of cultivars Altis 99 and Multissol at a dose of 30 kg ha⁻¹ in is recommended semiarid regions.

Sunflower is an oleaginous plant of great importance worldwide that stands out in the production of edible oil and human food. The identification of differences between cultivars regarding the use of phosphorus and the production of achenes at different levels of phosphate fertilization is a viable strategy to allow its cultivation in soils with different concentrations of phosphorus, without compromising yield and reducing environmental damage associated with excessive applications of phosphate fertilizers. Thus, the objective of this study was to evaluate different levels of phosphorus fertilization and sunflower cultivars regarding the efficiency of phosphorus use in two agricultural crops. The experimental design was in randomized blocks with four replications in split-plots, where four doses of phosphorus (50, 100, 150, and 200 kg ha⁻¹ of P₂O₅) were allocated in the plots, and in the subplots three sunflower cultivars (Aguará 06, Altis 99, and BRS 122). The phosphorus use efficiency of sunflower cultivars was estimated through agronomic efficiency, vegetative efficiency, agrophysiological efficiency, apparent recovery efficiency, and utilization efficiency. The dose of 50 kg ha⁻¹ of P₂O₅ provided the best phosphorus efficiency indices for the different sunflower cultivars in the two studied crops. Cultivar Aguará 06 was more efficient in conditions with P₂O₅ supply below 150 kg ha⁻¹, regardless of the crop. Sunflower cultivars had the best efficiency indices of phosphorus applied in the 2016 harvest.

In Brazil, the atrazine has been applied frequently to join with glyphosate to control resistant biotypes and weed tolerant species to glyphosate. However, there are no studies about atrazine's behavior in soil when applied in admixture with glyphosate. Knowledge of atrazine's sorption and desorption mixed with glyphosate is necessary because the lower sorption and higher desorption may increase the leaching and runoff of pesticides, reaching groundwaters and rivers. Thereby, the objective of this study was to evaluate the adsorption mechanisms of atrazine when isolated and mixed with glyphosate formulations in a Red-Yellow Latosol. The maximum adsorbed amount of atrazine in equilibrium (q_e) was not altered due to glyphosate formulations. The time to reach equilibrium was shortest when atrazine was mixed with the Roundup Ready^® (te = 4.3 hours) due to the higher adsorption velocity (k₂ = 2.3 mg min^-1) in the soil. The highest sorption of atrazine occurred when mixed with the Roundup WG^®, with the Freundlich sorption coefficient (Kf) equal to 2.51 and 2.43 for both formulation concentrations. However, other glyphosate formulations did not affect the sorption of atrazine. The desorption of atrazine was high for all treatments, with values close to 80% of the initial adsorbed amount, without differences among isolated and mixed treatments. The change in the velocity and capacity of sorption for the atrazine mixed with some glyphosate formulations indicates that further studies should be conducted to identify the mechanisms involved in this process.

The objective of this study was to model the spatio-temporal distribution of Digitaria insularis (D. insularis) and analyze the risk of selection of glyphosate-resistant biotypes in eucalyptus cultivation in Brazil. Global data on the distribution of the specie were collected and associated with their ideal growth characteristics. The models were generated using Climex software, providing a predictive modeling technique. Biological data, species distribution, and climatic parameters were used to predict and map potential areas for the species of interest through the combination of growth and stress indices, giving rise to the Ecoclimatic Index (EI). The spatial distribution of D. insularis is predominantly in South and Central America and southern North America. The model had a good fit with the collected data and predicted higher EI values for tropical and subtropical regions, as was the case in Brazil. Species growth can occur throughout the year, with lower rates in winter, mainly in the country’s southern regions. Brazil has high climatic suitability for the occurrence of Digitaria insularis. Due to the climate suitability evidenced by the models and the expressive use of the same active ingredient, there is a risk of selecting glyphosate-resistant Digitaria insularis biotypes in eucalyptus cultivation areas.