Comparative effectiveness of urea and calcium ammonium nitrate for wheat fertilization in south-western Buenos Aires (Argentina)

The objective of this paper was to report on the relative effectiveness of urea (U - 46% N) and calcium ammonium nitrate (CAN - 27% N) for wheat fertilization in southwestern Buenos Aires Province (Argentina). Five experiments were carried out between 1996 and 1998. Treatments were N rates (0 to 45/60kg ha(-1)) and sources (U and CAN), applied broadcast at tillering. Crop variables studied were: crop yield (CY), protein grain concentration (CPG) and N yield (NY). Effect of sources was analyzed by comparison of crop variables for individual treatments and by the calculation of two parameters i) efficiency ratio (ER) and ii) substitution value (SV). CAN treatments gave higher values of CY and NY in 4 of the 5 experiments and of CPG in 50% of the cases. However, none of these were significant. Both ER and SV varied with experiments. ER was around 1.35, 1.25 and 0.98 for CY, NY and CPG. This means on average CY response was 35% higher for plots fertilized with CAN, with very little reduction of CPG. SV was around 1.5 for CY, i.e. U attained the same CY as CAN if U rates were increased by 50%. An advantage of using SV for CY is that direct comparisons with price ratios can be made for a simple economic analysis. CAN superiority was related not only to a greater N apparent recovery but also to increased physiological efficiency. This could be explained through the different availability in time of the two sources.