Nitrogen fertilizer sources for rainfed wheat (Triticum aestivum L.) production planted in permanent beds

Aim of study: The objective was to test the wheat response to five nitrogen (N) sources and one control plot (0N) without fertilization. Area of study: This study was conducted at CEVAMEX for 12 crop seasons under the planting system of permanent beds with crop residue retention. CEVAMEX is located in the eastern region of the trans-Mexican volcanic belt. Material and methods: The fertilizer sources used were calcium nitrate (10 kg N/ha), ammonium sulfate (40 kg N/ha), urea + zeolite (30 kg N/ha), foliar urea (3 kg N/ha), and granular urea (40 kg N/ha). The treatments were allocated in a randomized complete block design with three replicates. Main results: The average grain yield was 2.7 Mg/ha; the yield difference between the fertilized treatments and the control plot (0N) was negligible. The slope regressions for the yield-year relationship of each treatment were not significantly different. The range of grain N uptake in the control plot (0N) was 37-88 kg/ha. This parameter, plus the N rate, explained 45-86% of yield variability. The soil N-NH4 concentration was associated with N uptake. Soil N-H4 concentration was generally greater than the N-NO3. According to the yield response index (RI) [ratio of fertilized treatment/control plot (0N)], which was generally < 1.1, the soil supplied the N amount required to produce acceptable yields. Therefore, the yield was independent of the RI, meaning that the N fertilizer did not affect the yield. However, the RI of granular and foliar urea was associated with the rainfall distribution during the grain filling stage. Research highlights: Further studies should aim to test improved liquid and granular N formulations, which may enhance the RI.