Root Architecture and Early Growth of Soybean as Influenced by Nitrogen Fertilizer Placement

Brazil stands out as one of the world’s largest producers and exporters of grains, particularly soybeans. This crop exhibits high nitrogen demand, an essential nutrient for its development. However, soybean possesses the ability to meet part of its nitrogen requirements through Biological Nitrogen Fixation (BNF), carried out by bacteria of the genus Bradyrhizobium, thereby reducing dependence on nitrogen fertilizers and generating economic and environmental benefits. Despite the efficiency of BNF, supplementary nitrogen application may influence the crop’s early growth, especially under adverse environmental conditions. The form and placement of nitrogen fertilizer application can significantly impact plant development. To investigate these effects, an experiment was conducted in a randomized complete block design (RCBD), with four treatments and four replications. Treatments consisted of: T1 – no nitrogen fertilizer application (control); T2 – 50 kg/ha of nitrogen incorporated into the soil; T3 – 50 kg/ha of nitrogen applied directly into the seed furrow prior to seed placement; and T4 – 50 kg/ha of nitrogen applied superficially after sowing, without incorporation. Evaluated variables included: root length (RL), shoot height (SH), number of leaves (NL), and dry matter production of roots and shoots. Results indicated that furrow-applied fertilizer favored root deepening and increased leaf number, while surface application stimulated greater shoot dry matter production. Soil-incorporated fertilization promoted greater lateral root formation, whereas the absence of fertilizer resulted in the highest total root biomass. These effects were strongly influenced by water availability, with fertilizer proximity to roots being a determining factor under low-water conditions. The objective of this study was to evaluate the early development of soybean as influenced by different placement methods of nitrogen fertilizer application.