Tanzania Journal of Agricultural Sciences 2014, Vol. 12(2): 55-65The wide gap between potential and actual yields of maize in Tanzania, due low productivity is the major constraint to improvement of food security and livelihood of farmers. The objective of this study was to evaluate the potential of the use of small amount of nitrogen fertilizer as a measure to reduce maize yield gap under rain fed conditions. Field experiments were conducted at Sokoine University of Agriculture, Morogoro during the dry and rainy seasons of 2012/2013 using Maize cultivar PIONEER PHB 3253. The nitrogen application rateswere 0 (control), 15 (low N dose) and 80 kg N ha-1 (recommended rate). Three water application regimes were tested. Irrigation water was applied from crop establishment up to; grain filling; 50% anthesis; and between 50% anthesis and grain filling. The treatments were applied in a completely randomized block design, in factorial layout forthe dry season experiment. Nitrogen treatments were repeated during the 2012/2013 rain season under rain-fed conditions. Both experiments were replicated three times. In a dry season experiment, the water application regimes significantly (P≤0.05) increase biomass at both 50% and harvest maturity stages. Total tissue N content decreased under nonstressedwater regime relative to water-stressed treatments. The interaction between irrigation andnitrogen interaction significantly (P≤0.05) affected grain yield. Application of recommended N rate did not result into yield increase when water was limiting. In the rainy season experiment, the recommended Nrate resulted in highest biomass at end of juvenile (1 t ha-1), 50% anthesis (7.7 t ha-1) and harvest maturity stages (13.1 t ha- 1). Total tissue N content and grain yield increased significantly with increase in N application rates during the rainy season. Under water stress conditions, low N dose produced an extra 1000 kg ha-1 grain yield over absolute control treatment. Under water stress conditions, recommended N rate a 54% reduction of yield gap was observed, which could not sufficiently reduce yield gap. However, under adequate soil moisture conditions, recommended N rate attained up to 26% yield gap, suggesting that it would be beneficial to apply nitrogen fertilizer when water is not limiting to close the yield gap. Small nitrogen doses can be an effective strategy towards narrowing yield gaps for resource poor farmers especially in drought prone areas. Further study should be done to extend the results beyond experimental site to test and validate the approach under farmers’ paradigms.