Broadcast nitrogen application can negatively affect maize leaf area index and grain yield components under weed competition

Nitrogen (N) application and weed control play critical roles in the development of crops. In maize (Zea mays L.) cultivation, surface broadcast N application aiming at higher productivities is a common practice. However, N addition under weed competition could promote weeds rather than maize. To investigate this, a field study was developed over a Brazilian eutric nitisol for summer maize. We manipulated the presence (+) or absence (−) of surface broadcast N fertilization (N_S) at the recommended dose (90 ​kg ​ha⁻¹ N) and weed control (W_C), obtaining the treatments N_S+W_C+, N_S+W_C−, N_S−W_C+, N_S−W_C−. We aimed to determine 1) whether maize could profit from N application even under weed competition, and 2) how treatments would affect maize's leaf area index and all grain yield components (cobs area⁻¹, rows cob⁻¹, grains row⁻¹ and individual grain weight). We hypothesized that broadcast N application could jeopardize maize productivity by favoring weed development. Under no weed control, N application increased weed biomass by ∼58%, which resulted in reductions of 57% in leaf area index, 6.9% in rows per cob, 48% in grains per row, and 18.7% in grain weight. Ultimately, the grain yield (8216 ​kg ​ha⁻¹) of the best performing treatment (N_S+W_C+) was 66% higher than that with the worst performance (N_S+W_C−), of 2797.3 ​kg ​ha⁻¹. We conclude that in fertilized areas, weed control should be a priority, since the N applied under weed competition could be detrimental to maize's leaf area index, and affect most yield components and overall productivity.