Bangladesh Agron. J. 2019, 22 (1): 105-113 FUNCTIONAL RELATIONSHIP BETWEEN GRAIN YIELD AND SPIKES PER SQUARE METER OF WHEAT AS INFLUENCED BY SEED RATE UNDER LATE SOWN CONDITION M.A.K. Mian*, A.A. Begum and R.R. Saha Agronomy Division, BARI, Gazipur 1701 Corresponding E-mail: mianmd.abulkhayer@yahoo.com (Received: 29 August 2019, Accepted: 16 October 2019) Keywords: Functional model, grain yield, spikes/m2, wheat, late sown Abstract An experiment was conducted at Agronomy Research Field of Bangladesh Agricultural Research Institute, Gazipur for five consecutive years (2014- 2015 to 2018-2019) to establish a functional relationship between grain yield and spikes/m2 of wheat at late sown condition. Variation of spikes/m2 was created by five seed rates (90, 120, 150, 180 and 210 kg/ha). Pooled average value of spikes / m2 was observed the highest (479-506) in 180-210 kg seed /ha. From the structural treatment, the highest grain yield (pooled average of 3876-4153 kg/ha ranged 3295- 5028 kg/ha) of wheat was produced in the seed rate of 150-180 kg/ha. The estimated optimum seed rate was found 162.29 kg/ha with the estimated grain yield 3989 kg/ha of wheat at late sown condition through the developed function model of Y=485.91+43.17X-0.133X2 (R2=0.87). Again, the estimate optimum spikes/m2 was noticed 423 when the estimated grain yield of wheat was 4135 kg/ha at late sown condition through the developed functional model of Y=-2837+32.98X- 0.039X2 (R2=0.83). The grain yield would be increased about 13% as compared to recommended seed rate (120 kg/ha) of wheat. Spikes / m2 had significant positive correlation with seed rate (r=0.79 at p=0.05) of wheat. Relationship between observed grain yield and predicted grain yield (when relationship between spikes/m2 and grain yield) showed a good consistency (Y=1.0006X, R2=0.94 and r = 0.97 at p<0.01). From the results of the study it is concluded that 162 kg/ha of seed rate and 423 spikes / m2 would be optimum for maximum yield) 4135 gk/ah) of wheat at late sown condition. Introduction Wheat is an important cereal food grain after rice in Bangladesh. Wheat cultivation increased (4.29 times) after independence of Bangladesh (1971) due to development of high yielding varieties along with improved production technology (BARI, 2011; BARI, 2017; AIS, 2018). In Bangladesh, area coverage of wheat is 428800 hectares with an annual production of 1423600 tons (AIS, 2018). Optimum sowing time of wheat is 15 November to 30 November in Bangladesh (BARI, 2017). The majority farmers usually grow wheat in the same land after harvesting of T. aman rice and thus, sowing of wheat is often delayed (BARC, 2013). Sowing of wheat in Bangladesh may extend upto 20 December depending on the weather, topography and harvesting of the preceding rice crop (BARC, 2013). Grain yield of wheat is reduced @ 82-87 kg/ha/day (32-36%) after 30 November sowing (Begum and Mian, 2019). Spikes/m2 is a major yield component which has a significant effect on the grain yield of wheat (Kadumet al., 2019). The increase of spikes/m2 increased the grain yield of 112 Mian et al. wheat (Mian, 2008; Shankarraoet al., 2010). Spikes/m2 is mainly influenced by seed rate and yield is the function of spikes/m2 of wheat (Bolton, 2018; Sokoto et al., 2012). More number of tillers as well as more number of spikes/m2 is generally noticed in higher seed rate (BARI, 2018; Nimat et al., 2013). Proper growth environment also enhances tillering as well as spikes/m2 of wheat (Mian, 2008; Njuguna et al., 2010). Again, the excess seed rate would create more competition among the tillers producing lower effective spikes/m2 and grain yield of wheat (Seleiman et al., 2016). On the other hand, lower seed rate produces higher number of tillers per plant up to a level if proper growth environment is provided. Delayed sowing due to late harvesting of T. amanrice and excess soil moisture in southern part of the country reduce grain yield of wheat (BARC, 2013). At late sown condition, crop growth is retarded with reduced tillering of wheat producing lower grain yield. Moreover, only main tiller (stem) produces effective spikes but lateral or tender tiller fail to produce effective tiller or spike at late sown condition. In modeling concept scientists are trying to establish relationship between yield and spikes/m2 of wheat for estimating the optimum spikes/m2 for maximum yield (Mian et al., 2012; Moucheshi et al., 2013; Bolton, 2018). Therefore, the experiment was undertaken to establish a functional relationship between grain yield and spikes/m2 of wheat and to estimate the optimum spikes / m2 for maximum grain yield at late sown condition. Materials and Methods An experiment was conducted at Agronomy Research Field of Bangladesh Agricultural Research Institute, Gazipur to establish a functional relationship between grain yield and spikes / m2 of wheat at late sown condition. The experiment was conducted for five consecutive years of 2014-2015 to 2018- 2019. Variation of spikes /m2 was created by five seed rates (90, 120, 150, 180 and 210 kg/ha). The wheat var. BARI Gom-30 was sown on 15-20 December (late sown condition) in 2014 - 2019. But the optimum sowing time of wheat is 15-30 November in Bangladesh (BARI, 2017). The experiment was laid out in a RCB design with four replications. Unit plot size was 8 m× 5 m. The crop was fertilized with 100-36-25-20-1.8-1.0 kg/ha of N-P-K-S-Zn-B (BARI, 2011). All the nutrients including two third of N were applied as basal. Rest one third of N was top dressed at CRI stage. Three irrigations were applied at 20 days after emergence (DAE), 60 DAE and 80 DAE. Crop field was weeded at 25 DAE by spading. The crop was harvested on 27-31 March in 2014-- 2019. Data on crop yield and yield components of wheat were recorded. There was no blast infection in the experimental field. Attempt was made to establish functional relationship between grain yield and spikes /m2 of wheat using the quadratic equation like Y= a + bx - cx2. Optimum seed rate and spikes / m2could be estimated with the following formula from the developed functional model (Mian et al., 2012). Optimum seed rate and spikes / m2=-b/2c (where b and c are the coefficients). The experiment was repeated for the consecutive five years to get sufficient data for establishing the functional relationship. Five years’ data on spikes/m2 and grain yield of wheat from 2014-2015 to 2018-2019 were used to develop functional relationship. Some important yield components of wheat were recorded and presented on the basis of year wise and combined analysis (only combined effect). The data was subjected to statistical analysis (year wise and combined) and mean values were compared by LSD (0.05). Results and Discussion Functional Relationship of Wheat 113 Yield component and yield Spikes/m2 was significantly influenced by seed rate (Table 1). The maximum number of spikes/m2 was produced of 210 kg seed /ha (533) followed 180 kg seed / ha (505) while the lowest in 90 kg seed /ha (395) in 2014-2015. Similar trend of spikes / m2 (the highest value ranged 444-573and the lowest value ranged 348-457) was noticed in the subsequent growing season of 2015- 2016 to 2018-2019. The highest pooled value of spikes/m2 was observed in 210 kg seed /ha (506) followed by 180 kg seed /ha (479) while the lowest in 90 kg seed /ha (398) (Table 1). The results expressed that increasing seed rate increased spikes/m2gradually. Similarly, higher spikes/m2 in higher seed rate (160 kg/ha as compared to 120 kg/ha) was also reported by BARI (2018). Seed rate had significant effect on grains / spike (Table 2). The highest grains/ spike was obtained in 90 kg seed /ha (42) followed by 120 kg seed /ha (41) but the lowest in 210 kg seed /ha (34) in 2014-2015 (Table 2). Similar trend of grains / spike (the highest value ranged 38-52 and the lowest value ranged 26-39) was noticed in the following growing seasons of 2015-2016 to 2018-2019. The highest pooled value of grains/ spike was noticed in 90 kg seed /ha (43) followed by 120 kg seed /ha (40). On the other hand, the lowest value was found in 210 kg seed /ha (32) (Table 2). The results reveal that grains/spike was reduced gradually with the increase of seed rate. Higher seed rate possibly exerted inter tiller competition resulting less number of grains/pike. Less number of grains/spike in higher seed rate was also reported by Seleiman et al. (2016) and BARI (2018). The weight of 1000-grain was found the highest in 90 kg seed /ha (45 g) followed by 120 kg seed /ha (44 g) while the lowest in 210 kg seed /ha (39 g) in 2014-2015 (Table 3). Similar trend of 1000-grain weight (the highest value ranged 42-58 g and the lowest value ranged 32-45 g) was observed in the growing season of 2015-2016 to 2018-2019. Pooled value of 1000-grain weight was recorded the highest in 90 kg seed /ha (48 g) followed by 120 kg seed /ha (46 g) giving the lowest in 210 kg seed /ha (38 g) (Table 3). Higher seed rate possibly exerted inter tiller competition reducing individual grain size and weight as well as lower 1000-grain weight. Reduced 1000-grain weight of wheat at higher seed rate (160 kg/ha) was also reported by Seleiman et al. (2016) and BARI (2018). The grain yield of wheat was significantly influenced by seed rate (Table 4). The highest grain yield (3803-3858 kg/ha) was produced in 150-180 kg seed /ha but the lowest (3652 kg/ha) in 90 kg seed /ha in 2014-2015. On the other hand, the highest grain yield (5028 kg/ha) was observed in 180 kg seed /ha followed by the 210 kg seed /ha (4839 kg/ha) while the lowest (3652 kg/ha) in 90 kg seed /ha in 2015-2016 (Table 4). Similar trend of grain yield (the highest grain yield ranged 3738-4376 kg/ha and the lowest value ranged 2436-3225 kg/ha) was noticed in the subsequent growing season of 2016-2017 to 2018-2019. Pooled grain yield was obtained the highest in 180 kg seed /ha (4153 kg/ha) followed by 150 kg seed /ha (3876 kg/ha) producing the lowest in 90 kg seed /ha (3418 kg/ha) (Table 4). Grain yield was mainly contributed by spikes/m2. Similar results have also been described by other investigators (Nemat et al., 2013; Sherwan et al., 2015). Grain yield increased about 6-14% in 150-180 kg seed /ha as compared to recommended seed rate (120 kg/ha). The results expressed that higher seed rate up to 180 kg/ha increased grain yield, afterwards the grain yield declined as the increase of seed rate (210 kg/ha). Higher seed rate (210 kg/ha) might have exerted more inter tiller competition resulting poorer yield component and grain yield of wheat. Moreover, higher seed rate leads the crop to lodging producing lower grain yield. Higher seed rates (200 kg/ha) resulted in higher lodging of wheat was also reported by (Laghari et al., 2011). The results are in agreement with the observation of Seleiman et al. (2016). 112 Mian et al. Table 1. Spikes/m2 (no.) of wheat as influenced by seed rate under late sown condition Seed rate (kg/ha) 2014- 2015 2015- 2016 2016- 2017 2017- 2018 2018- 2019 Pooled 90 395 348 457 383 408 398 120 447 362 480 412 428 426 150 483 389 493 443 468 455 180 505 426 523 464 478 479 210 533 444 573 493 485 506 LSD (0.05) 41 30 34 24 32 33 CV (%) 5.66 4.87 4.33 4.69 4.91 4.89 Table 2. Grains/spike (no.) of wheat as influenced by seed rate under late sown condition Seed rate (kg/ha) 2014-2015 2015-2016 2016-2017 2017-2018 2018-2019 Pooled 90 42 52 40 41 38 43 120 41 48 39 37 36 40 150 38 45 38 34 35 38 180 37 44 35 30 31 35 210 34 39 33 28 26 32 LSD(0.05) 2.69 2.45 2.07 3.37 2.96 2.48 CV (%) 4.55 3.49 3.22 4.11 5.79 4.29 Table 3. Weight of 1000-grain (g) of wheat as influenced by seed rate under late sown condition Seed rate (kg/ha) 2014-2015 2015-2016 2016-2017 2017-2018 2018-2019 Pooled 90 45 58 43 42 50 48 120 44 57 41 41 49 46 150 43 48 36 38 47 42 180 40 46 34 35 46 40 210 39 43 32 32 45 38 L SD (0.05) 2.89 4.03 3.65 2.05 2.11 2.89 CV (%) 4.46 5.92 4.86 2.54 2.87 4.37 Table 4. Seed yield (kg/ha) of wheat as influenced by seed rate under late sown condition Seed rate (kg/ha) 2014-2015 2015-2016 2016-2017 2017-2018 2018-2019 Pooled 90 3652 4520 3225 3187 2436 3418 120 3781 4592 3743 3405 2804 3651 150 3858 4633 4061 3532 3295 3876 180 3803 5028 4376 3738 3822 4153 210 3586 4839 4065 3584 2464 3708 LSD (0.05) 287 378 373 318 313 328 CV (%) 4.98 5.21 6.22 5.93 5.59 5.66 Functional relationship Functional Relationship of Wheat 113 Functional relationship between seed rate and spikes/m2 indicates that the effect of seed rate on spikes/m2 of wheat can be explained 72% by functional model of Y=2.8613X (R2=0.72) (Table 5 and Fig.1). The coefficient value of 2.8613 indicates that the number of spikes/m2 would be increased @ 2.8613 with the increase of 1 kg/ha of seed rate. Spikes/m2 showed significant positive correlation with the seed rate (r=0.79 at p=0.05). Functional relationship between seed rate and grain yield of wheat shows that the effect of seed rate on grain yield can be explained 87% by functional model of Y=485.91+43.17X-0.133X2 (R2=0.87) (Table 5 and Fig.2). Number of spikes/m2 had a great impact on the grain yield of wheat as described by Moucheshi et al. (2013). The optimum seed rate was estimated at 162.29 kg/ha by the functional model of Y=485.91+43.17X-0.133X2 (R2=0.87). Then the grain yield would be 3989 kg/ha at the estimated seed rate of 162.29 kg/ha. Again, functional relationship between spikes/m2 and grain yield of wheat indicates that the effect of spikes/m2 on grain yield can be explained 83% by functional model of Y=-2837+32.98X- 0.039X2 (R2=0.83) (Table 5 and Fig. 3). The estimated optimum spikes/m2 was found 423 by the functional model of Y=-2837+32.98X-0.039X2(R2=0.83). Table 5. Relationship between different parameters of wheat as influenced by seed rate Fig. no. Variable Functional relationship R2 1. Seed rate and spikes/m2 Y =2.8613X R² = 0.72 2. Seed rate and grain yield Y =485.91+43.17X- 0.133X2 R² = 0.87 3. Spike/m2 and grain yield Y= -2837+ 32.98 X- 0.039X2 R² = 0.83 4. Observed and predicted grain yield Y= 1.0006X R² = 0.94 - Seed rate and spikes/m2 correlation coefficient r=0.79 at p=0.05 - Observed grain yield and predicted grain yield correlation coefficient r=0.97 at p<0.01 Then the grain yield would be 4135 kg/ha at the estimated spikes/m2 of 423 giving 13% higher grain yield as compared to recommended seed rate (120 kg/ha) of wheat. Kadum et al. (2019) reported that 481-492 spikes/m2 gave the highest grain yield (6.46-6.62 t/ha) of wheat. Sokoto et al. (2012) also found that spikes/m2 had significant positive correlation with grain yield of wheat. Relationship between observed grain yield and predicted grain yield (when relationship between spikes/m2 and grain yield by the functional model of Y=- 2837+32.98X-0.039X2, R2=0.83) showed a good consistency (Y=1.0006X, R2=0.94 and r=0.97 at p<0.01) (Table 5 and Fig. 4). 112 Mian et al. Fig. 1. Functional relationship between seed rate and spikes/m2 of wheat Fig. 2. Functional relationship between seed rate and grain yield of wheat Y =2.8613X R² = 0.72 0 100 200 300 400 500 600 60 90 120 150 180 210 240 S p ik es /m 2 Seed rate (kg/ha) Y =485.91+43.17X-0.133X2 R² = 0.87 0 1000 2000 3000 4000 5000 6000 60 90 120 150 180 210 240 G ra in y ie ld ( k g /h a) Seed rate (kg/ha) Functional Relationship of Wheat 113 Fig. 3. Functional relationship between spike/m2 and grain yield of wheat Fig. 4. Relationship between observed and predicted grain yield of wheat (Functional model of spike/m2 and grain yield of wheat; Y= -2837+ 32.98X-0.039X2, R² = 0.83) Conclusion Y= -2837+ 32.98 X-0.039X2 R² = 0.83 0 1000 2000 3000 4000 5000 6000 200 300 400 500 600 G ra in y ie ld ( k g /h a) Spikes/m2 Y= 1.0006X R² = 0.94 r=0.97 0 1000 2000 3000 4000 5000 6000 0 1000 2000 3000 4000 5000 6000 P re d ic te d g ra in y ie ld ( k g /h a ) Observed grain yield (kg/ha) 112 Mian et al. From the structural treatment, the highest grain yield (pooled of 3876-4153 kg/ha ranged 3295-5028 kg/ha) of wheat was produced with 150-180 kg seed / ha. The estimated optimum seed rate was 162.29 kg/ha when the estimated grain yield was 3989 kg/ha of wheat at late sown condition through the developed function. Furthermore, the estimated optimum spikes / m2was 423 with the estimated grain yield of 4135 kg/ha of wheat at late sown condition through the developed function. 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