RESPONSE OF CLIMATE RESILIENT WHEAT VARIETIES UNDER VARYING SOWING DATES IRRIGATION AND NITROGEN APPLICATION

Abstract

Field experiments were conducted where four at Sher-e-Bangla Agricultural University, Dhaka and the rest one at at Shahpur, Charghat, Rajshahi to identify climate change resilient heat tolerant varieties, suitable sowing dates, irrigation regimes and application of supplemental N of wheat during two rabi seasons. The first experiment conducted in 2014-15 rabi season consisted of two varieties (V = BARI Gom 21,V 2 =BARI Gom 23) four sowing dates (S 1 = 10 November, S = 20 November, S 3 = 30 November, S = 10 December). The second experiment implemented in 2014-15 rabi season with variety BARI Gom 26 comprised three irrigation levels (I 1 = field capacity, I 4 2 = of the field capacity and I of the field capacity), four sowing dates (S 1 =10 November, S 2 3 = =20 November, S =30 November and S =10 December) and two top dressing of nitrogen at the reproductive stage (N 4 1 = no nitrogen application, N =20% N of the basal as top dressing). Third experiment carried out in 2014-15 rabi season with BARI Gom 25 focused on four sowing dates (S 1 =10 November, S 2 2 = 20 November, S = 30 November and S 4 =10 December), three irrigation levels (I =Irrigation at heading stage, I 2 =Irrigation after 10 days of I 1, I 3 1 =Irrigation after 10 days of I ) and two supplemental N application at the post heading stage (N 0 2 = no supplemental N application and N =application of 20% supplemental N). The fourth and fifth experiments were implemented during rabi 2016-17 season at SAU and Rajshahi, respectively to examine phenology, chlorophyll, canopy temperature, growth and yield as influenced by sowing dates (S 1 1 = November 20, S 2 = November 30, S 3 3 = Dec 10, S = Dec 20, S 5 = Dec 30) and varieties (V 1 = BARI Gom 25,V 2 = BARI Gom 26, V = BARI Gom 27, V 4 = BARI Gom 28, V 5 = BARI Gom 29, V = BARI Gom 30). In experiment 1 significantly, the highest seed yields (4.23 - 4.27 t ha 6 -1 ) were obtained with variety BARI Gom 23 when sown on November 10 and November 20. In experiment 2 significantly the highest grain yields (3.2 to 4.3 t ha -1 ) were obtained with November 10 and November 30 sowing treatments. Irrigation keeping the soil at field capacity level showed significantly highest grain yield (3.95 t ha -1 ). In this experiment the combination treatment I 1 S 2 N 2 had the highest grain yield (4.81 t ha ) which was significantly different than other combination treatments. This was attributed to the significantly higher number of grain spike -1 (50.83) and 1000 seed weight (50.57 g) of the treatment I 1 S 2 N 2 compared to the lowest grain spike -1 3 -1 2 4 (46.83), 1000 seed weight 3 1 (48.90 g) when irrigated at 25% water of the field capacity . In experiment 3 November20 sowing gave the highest grain yield. Irrigation application at 10 days after heading produced the highest grain yield (3.9 t ha vii

-1 ) which was at par with irrigation at heading. The higher grain yield was attributed to the higher values of grains spike -1 (43.63) and 1000 seed weight (53.90 g). The combined effect of sowing date and irrigation showed that November 20 sowing with giving irrigation either at heading or 10 days after heading had significantly the highest grain yield (4.81 t ha ). An extra irrigation 10 days after heading and supplying supplemental 20% N at post heading stage in experiment 3 had seed yields (4.6-4.81 t ha ) which was significantly higher than the lowest grain yield of November 10 sowing (3.3 t ha ) under the above conditions. The November 20 sowing with extra N application had higher grain yield (4.47 t ha -1 ). Again the combination treatments I had significantly higher seed yields (4.480 and 4.600 tha -1 respectively) than other combined treatments. In Rajshahi (in experiment 4), the sowing date treatment November 30 and December 10 gave significantly higher grain yields (at or over 3.52 t/ha). While in experiment five the varieties BARI Gom 28 and BARI Gom 30 at SAU had significantly higher but identical seed yields (3.72 to 3.81 t ha -1 ). The correlation analysis using the data of yield and yield attributes of the experiment 2 and 3 at SAU, showed that higher correlations of grain yield were found with the number of spikelet spike -1 (r=0.820 - 0.814), 1000 seed weight (0.806-0.819), biological yield (r=0.802-0.912) and harvest index (r=0.802-0.912). The linear as well as polynomial regression showed that the higher temperature at the vegetative stage had positive impact on grain weight/plant and grain yield ha -1 1 (slope+6 to 2086, R =0.120 to 0.957), while at the anthesis to maturity, values of most grain yield and yield attributes decreased due the increase in ambient temperatures. The grain yield was higher at minimum and average temperature not above 15.5 and 22.5°C, respectively (R 2 =0.922-0.992). The polygonal regression also revealed that for obtaining the maximum yield/ha, the maximum temperature should not be above 25.5°C before anthesis while the maximum, minimum and average temperature after anthesis should not be beyond 29.5, 15.5 and 22.5°C, respectively.