Stem reserve accumulation and mobilization in wheat (Triticum aestivum L.) as affected by sowing date and N-P-K levels under Mediterranean conditions

Some parts of the dry matter accumulated in the wheat stem during the vegetative period are translocated to grain during the grain-filling period. This study assesses the changes in dry matter accumulation in wheat, and the translocation of different internodes of the main stem as affected by some cultural practices. Field experiments, including 3 sowing dates (early, conventional, and late), and 4 N - P - K levels, F-1 - (0 - 0 - 0), F-2 - (110 - 90 - 80), F-3 - (70 - 50 - 40) and F-4 - (150 - 130 - 120), were conducted at the Agricultural Faculty of Shahid Chamran University during 2008 and 2009. The main stem internodes length, weight, dry matter accumulation, and mobilization were measured. Our results showed that the behaviors of the 4 N - P - K levels were similar as they ranged in the same order for pre-anthesis and post-anthesis dry matter accumulation; also, differences in fertilizer application induced similar changes in dry matter accumulation and remobilization. Dry matter translocation was an average of 2% higher for all fertilized treatments, when compared to the control, which has shown the low influence of fertilization on this efficiency in our study. The effect of sowing dates in pre-anthesis dry matter contribution to reproductive organs was much more than the influence associated with the N - P - K levels. However, we recorded differences in dry matter, mobilization efficiency, and mobilization dry matter among sowing dates. The early sowing dates show the best value for mobilized dry matter and dry matter in all stem internodes. Nevertheless, mobilization efficiency had lowest value at this time. The highest mobilization efficiency in all stem internodes was associated with lowest N - P - K level application; also, mobilized dry matter decreased with increasing fertilizer application with all sowing dates and stem internodes, except with early sowing dates for peduncle internodes. With a delay in sowing date, and/or increase in N - P - K levels, the amount of dry matter remobilization decreased, mainly due to a decrease in stem weight. However, the sowing dates had greater influence on dry matter accumulation and remobilization than the fertilizer application.