Effect of N fertilizer source and timing on yield and N use efficiency of rainfed maize (Zea mays L.) in Kashmir–Pakistan

Efficient N fertilization is considered one of the most important management strategies for sustaining or increasing crop yield and quality, and improving nitrogen use efficiency (NUE). A 2-yr (2008–2009) field experiment with rainfed maize (Zea mays L.) was conducted in the hilly region of Rawalakot Azad Jammu and Kashmir (AJK), Pakistan to evaluate the effect of time and source of N fertilizer application on the growth, yield, N-uptake and NUE of maize. The experiment consisted of a factorial arrangement of 2 years, two methods/timings and four N sources including a control, arranged in a completely randomized block design replicated three times. Treatments included two application timings i.e. single application of N at planting and a split application i.e. 1/2 at sowing + 1/2 at V6 stage, and three N fertilizer sources i.e. urea, calcium ammonium nitrate (CAN), and ammonium sulfate (AS), and a control. Results indicated that response of growth characteristics to N sources was in the order CAN > AS > urea. Similarly, straw and grain yields were highest in CAN followed by AS while urea exhibited the lowest. The relative increase in grain yield by CAN and AS was 11 and 10% in 2008 and 8 and 5% in 2009 over urea N. Split application of N increased grain yield between 4 to 9% in 2008 and 3% in 2009 over single N application. The amount of N taken up by plants depended upon the source of N fertilizer and was in the order urea > CAN > AS. The NUE ranged between 31 to 61% in 2008 and 40 to 67% in 2009 and urea exhibited the highest NUE. Split application of N increased NUE by 23 and 21% over single N application. Results of this study indicated that yield and N balance of maize was significantly affected by N sources and application timing. However, response of both traits to N sources was distinctive. Further studies (long term basis) are suggested to explore the effects of N sources on maize productivity particularly yield and N balance relationship.

► N management is an important strategy to increase NUE and crop productivity.
► Selection of an appropriate N fertilizer source may increase NUE and crop yield.
► Among N sources tested, CAN found superior to urea and AS for maize yield
► The relative increase in grain yields by CAN and AS was 5–11% over the urea N.
► Splitting of N increased maize grain yield by 3–9% and NUE by 21–23%.