Effect of planting date and nitrogen and zinc fertilizers on phenological traits, and grain yield and quality of bread wheat in Ahvaz climatic conditions

There is a considerable gap between the grain yield of bread wheat and its production potential in Khuzestan province, but it seems that the yield of wheat can be increased with proper direction of environmental effects through suitable agronomical management. In this regard, planting date and nutrient application are very important. However, the application of little or much nitrogen reduces the grain yield under high temperature conditions, and in addition, using too much nitrogen can cause environmental pollution. Therefore, it is necessary to accurately determine the optimal level of nitrogen for different planting dates. The objective of the current experiment was to study the effect of planting date and application of nitrogen and zinc fertilizers on growth and yield of wheat.

To investigate the effect of planting dates and the application of nitrogen and zinc fertilizers on growth and yield of wheat (cv. Chamran), an experiment was conducted in experimental field of Khuzestan Agricultural University, Khuzestan province, Iran, during 2018-19 growing season. The experiment was carried out as split-split plots in randomized complete plot design with four replications. Planting date at three levels (Nov. 22, Dec. 11, and Dec. 31) were considered as main plots, nitrogen at four levels (0, 75, 150, and 225 kg.ha-1) as sub-plots, and zinc at three levels (0, 10, and 20 kg.ha-1) as sub-sub-plots. The evaluated traits were including grain weight, number of grains per unit area, number of days from planting to pollination, number of days from pollination to maturity, grain yield, grain protein percentage, grain zinc content, grain protein accumulation rate, grain filling rate and grain filling period.

The results of analysis of variance showed that three-way interaction of planting date × nitrogen × zinc was significant on all studied traits at 1% probability level, except for number of grains per unit area which was only affected by nitrogen levels. The highest wheat grain yield (7486 kg.ha-1) was belonged to the first planting date (Nov 22) along with the second level of nitrogen (75 kg.ha-1) and zinc (10 kg.ha-1). The delay in planting led to a decrease in grain yield, so that planting on Dec. 11 and Dec. 31 caused a decrease of about 23 and 40 percent in wheat grain yield, respectively. The application of chemical fertilizers at delayed planting date led to a certain extent to compensate for the decrease in grain yield, so that the application of 75, 150 and 225 kg.ha-1 of nitrogen on the planting date of Dec. 11 increased grain yield of wheat by 44%, 52% and 55%, respectively. With the delay of planting from Nov. 22 to Dec. 31, grain filling rate and grain protein percentage increased by 19% and 25%, respectively, but the grain filling period (28%), grain weight (20%), protein accumulation rate (27%), protein yield (50%) and grain zinc content (3%) decreased. The highest grain filling rate (1.37 mg.day-1) and the highest grain protein content (12.7%) of wheat were obtained on the planting date of Dec. 31 along with 150 kg.ha-1 N and 10 kg.ha-1 Zn. Also, the highest grain filling period (46.1 days) was observed on the first planting date (Nov. 22), but there was no significant difference among different levels of nitrogen and zinc in this regard.

In total, the results of the current experiments showed that to avoid exposure of wheat to high temperatures during the grain filling period in the studied region, it is better to do planting on earlier date (Nov. 22). In delayed planting dates, using 150 kg.ha-1 N and 10 kg.ha-1 Zn can relatively compensate for the negative effects of high temperature after anthesis. The delay in planting, increased the grain protein content due to the acceleration of the grain filling period, however, it decreased total protein yield, which shows that the protein yield (kg.ha-1) is more dependent on the grain yield.