Increasing rainwater use efficiency, gross return, and grain protein of rain-fed maize under nitrate and urea nitrogen forms

The soil's capability to adjust and mitigate the effects of water shortage due to climate change is limited in some regions such those that suffer from the low rainfall rates. This experimental field study aimed to assess the effects of two inorganic nitrogen forms on maize performance (i.e., growth, yield, grain protein content, and gross returns) and rainwater use efficiency (RUE). Treatments comprised three replicates of synthetic nitrogen forms (i.e., urea and nitrate) that were located in the main plots with four levels that were assigned to the subplots (i.e., 0, 25, 50, and 100 kg N ha-1). Nitrate application resulted in a higher plant height (62 cm) at the vegetative phase with superior values (11.6%) recorded in grain protein than those obtained from other treatments. In addition, the highest grain yield was obtained in nitrate-treated plots in comparison to other N application forms. The leaf area index registered optimal values when 50 kg N ha-1 was applied. On the application of two nitrogen forms, nitrate resulted in a higher RUE (2.1-3.4 kg ha-1 mm-1) than that obtained from maize treated with urea (1.3-1.9 kg ha-1 mm-1). This translated to a 123-234% increase in RUE over the control (N0), which is the key smallholder farmers’ practice. It is recommended that producing maize using nitrate nitrogen at 50 kg N ha-1 as opposed to urea can increase yield stability, and rain use efficiency with higher gross returns in water-scarce agro-ecologies in SSA.