Yield Gap of Stress Tolerant Rice Varieties Binadhan-10 & Binadhan-11 in Some Selected Areas of Bangladesh

Binadhan-10 & Binadhan-11 are climate smart stress tolerant high yielding rice varieties (yield > 4 t∙ha −1 ) have saline tolerant EC up to 12 ds/m and submergence tolerant up to 20 - 25 days capacity. The present study was an attempt to analyze the yield gap of stress tolerant varieties Binadhan-10 & Binadhan-11 in some selected areas of Bangladesh. The objectives of the study were: 1) to estimate the yield gap of Binadhan-10 &-11 growers among the study areas; 2) to identify the factors affecting the yield of these variety; and 3) to suggest some policy guidelines to minimize the yield gap. The study was conducted in eight Binadhan-10 & Binadhan-11 growing areas in Bangladesh. In this study, four districts namely Satkhira, Khulna, Barishal, and Cox’s Bazar were used for Binadhan-10 and Mymensingh, Jamalpur, Sherpur and Sunamgonj were taken for Binadhan-11. It is based on primary level data from eight sub-districts among the study areas. A total of 240 farmers were randomly selected (30 from each location) to collect the data with a pre-designed questionnaire. Farmer were grouped according to saline affected and not-affected for saline tolerant variety Binadhan-10 and not affected, affected (1 - 10 days) and highly affected (10 - 20 days) for submergence tolerant rice variety Binadhan-11 to identify existing yield gap. Tabu-lar as well as Zandstra method were applied for analysis the data. The study also found factors affecting the gap and some policy guidelines to minimize the gap.


Introduction
Global environment is changing due to change in temperature in alarming rate. Rice is the crop of the Asia-Pacific Region, but production of rice is hampering due to change in climate. In other hand yield gap causes lowering in production. The projected demand of rice by the year 2025 is mind boggling [1], as in major Asian countries rice consumption will increase faster than the population growth. Demand for rice is expected to grow faster than the production in most countries [2] so much so that by 2025 we will need 800 million tonnes of it annually. The population of Bangladesh will reach near about 215 million in 2050. So food grain must be increased for upcoming future generation. At that time requirement of rice will be 44.6 million metric tonnes. In summary, in Asia, the rice consumption by the year 2025, over the base year 1995, will increase by more than 51 percent ( Table 1) Figure 3 shows the global map of current percentage rates of changes in different field crops yield such as: 1) maize, 2) rice, 3) wheat, and 4) soybean. In this figure, the red areas in the map showed where yields are decreasing whereas the fluorescent green areas show where rates of yield increase if continued it would twice over production by 2050.
In Bangladesh, various high yielding stress tolerant rice varieties have been developed by different institute & organization. Binahan-10 & Binadhan-11 are the two stress tolerant varieties develop by BINA. Binadhan-10 is a salt tolerant variety for boro season which can tolerate up to 12 dS/m of salinity, released in 2012. The variety is capable to produce higher seed yield (5 -6 t/ha under salt stress). Binadhan-10 is early maturing (127 -132 days) than other salt tolerant varieties. In non-saline condition, potential yield is 8.5 t/ha (average 7.5 t/ha). Grain is medium long, slender and bright colour. The variety is suitable for both aman and boro seasons. Binadhan-11 has been released as a submergence tolerant early maturing rice variety for aman season. This variety possesses green and erect flag leaves. Duration of this variety is 130 -135 days (under 20 -25 days submerged condition) and 115 -120 days for non-submerged condition. In submerged condition, potential yield is 4.5 t/ha (average 4.2 t/ha). This variety is capable to produce 5.0 -5.4 t/ha in non-submerged condition. Despite the technologies developed by different National Agricultural Research System (NARS) institutes and extension agencies to disseminate the technologies, yield gaps exist in different crops of Bangladesh, such as rice, wheat, potato, oilseeds, pulses, etc. that may range from 19% to about 64% of the potential yield [5]- [11]. The existence of yield gaps was also observed in rice, mustard, and cotton in India  [12]. According to a study conducted by BRRI, the yield gap in rice was about 1.74 t•ha −1 and at least Tk. 1260 billion could be earned from the additional production annually by minimizing the yield gap [13]. It is, therefore, essential to minimize the yield gaps and increase the productivity of the crops to feed the growing population of the country.

Sample Size and Location
The study was conducted in eight Binadhan-10 & Binadhan-11 growing areas in Bangladesh. In this study four districts namely Satkhira, Khulna, Barishal, and Cox's Bazar were used for Binadhan-10 and Mymensingh, Jamalpur, Sherpur and Sunamgonj were taken for Binadhan-11. It is based on primary level data from eight sub-districts among the study areas ( Figure 4) and there were 240 (30 from each location) randomly selected farmers to conduct the study.

Analytical Technique
In the study, the concept of yield gap as suggested by Zandstra et al. (1981) [14] was used. Total yield gap can be decomposed into two parts i.e. Yield   and potential farm yield obtained at demonstration plots, while Yield Gap II, reflecting the effects of biophysical and socio-economic constraints, was the difference between yield obtained at the nearest demonstration plot and actual yield obtained on farmers' fields. The yield gaps were estimated as follows: where, Y R is the research station yield, Y D is the demonstration plot yield, and Y F is the actual farm yield.

Results and Discussion
The results presented in Table 2 showed that the highest yield was obtained in  Cox's Bazar (4.16 t•ha −1 ) district. The average yield of Binadhan-10 was 4.96 t•ha −1 .
In Figure 5, the green, red & blue area of diagram indicating actual farm yield, demonstration yield and research station yield, respectively and in Figure  6 the green, red & blue area of diagram indicating total yield gap, yield gap II and yield gap I, respectively in different districts of Bindhan-10 in Bangladesh.
As seen from Figure 6, the estimated yield gap I was 0.69 t•ha −1 (10.33%.) and yield gap II was 0.99 t•ha −1 (16.58%.). The lowest gap was 1.02 t•ha −1 (16.83%) found in Khulna district and it was the highest 2.34 t•ha −1 (39.53%) in case of Cox's Bazar district. Considering all, the average yield gap was 1.67 t•ha −1 (26.92%) and much scope for yield enhancement in the variety.
In Figure 7, the green, red & blue area of diagram indicating actual farm yield, demonstration yield and research station yield, respectively and in Figure  8 the green, red & blue area of diagram indicating total yield gap, yield gap II and yield gap I, respectively in different districts of Binadhan-11 in Bangladesh.
As seen from Figure 8 the estimated yield gap I was 0.69 t•ha −1 (12.57%) and yield gap II was 0.83 t•ha −1 (17.18%). The lowest gap was 1.42 t•ha −1 (27.74%) observed in Sherpur district and it was the highest 1.73 t•ha −1 (33.64%) in case of Mymensingh district. Considering all, the average yield gap was 1.52 t•ha −1 (29.76%) and much scope for yield enhancement in the variety.
Major factors that were responsible for the yield gap of Binadhan-10 were described in Table 4. It was found from the Table 4, most of the farmers did not consider the recommended doses of seed rate, fertilizer and seedling age. The average seed rate was 40. 60 Kg•ha −1 , Urea 162.07 Kg•ha −1 , TSP 99.62 Kg•ha −1 , MoP 62.07 Kg•ha −1 and seedling age 29.45 days respectively, indicates that they are either below or above the recommendation. Agricultural Sciences         It can be seen that soil fertility was important factor for both of the variety.
The overall soil fertility was the highest in case of medium flood affected farmer as well as their yield was also the highest 4.1 t•ha −1 .
Correlation between different factors in rice cultivation and yield in the study areas Correlation co-efficient were computed to ascertain the relationships between different factors in rice cultivation and yield in these varieties. The findings presented in Table 8 show that all the inputs in case of Binadhan-10 cultivation had significant positive relationships with the yield. This meant that yield of rice increased with the increase level of inputs.
The results showed that all the inputs in Binadhan-11 cultivation had significant positive relationships with the yield (Table 9). This meant that yield of rice increased with the increase level of inputs.