LATE SOWING AND IRRIGATION CUTBACK EFFECTS ON YIELD AND ECONOMIC PERFORMANCES OF DRY DIRECT SEEDED BORO RICE

Dry direct seeding (DDS) is a water saving rice cultivation technology. The sowing of dry direct seeded rice in boro season is generally delayed when grown under the T. aman rice – Rabi crops – DDS boro rice pattern. An experiment was conducted at the Agronomy Field of Bangladesh Agricultural University, Mymensingh to study the effect of sowing date and irrigation schedule on growth and yield of DDS boro rice. The experiment used two sets of treatments (a) two sowing dates viz. 22 February and 13 March; and (b) six irrigation regimes viz. no irrigation, one irrigation at 25% Field Capacity (FC), two irrigations at 25% FC and 1 week after (WA) 25% FC, three irrigations at 25% FC, 1WA 25% FC and 2 WA 25% FC, four irrigations at 25% FC, 1 WA 25% FC, 2 WA 25% FC and 3 WA 25% FC and one irrigation at 3 weeks after 25% FC and the treatments were arranged in a split-plot design with three replications allocating sowing dates into the main plot and irrigation schedule into the subplots. BRRI dhan58 was used as test crop. The result showed that grain yield of the crop did not differ significantly for sowing on 13 March and 22 February. The study revealed that BRRI dhan58 sown on 13 March with four irrigations applied at 25% FC, 1 WA 25% FC, 2 WA 25% FC and 3 WA 25% FC produced the highest economic return and hence it is concluded that the sowing date of boro rice could be delayed up to 13 March with four irrigations.


INTRODUCTION
In Bangladesh, transplanting seedlings onto puddle land is the most common way of establishing rice.Puddle transplanted rice (PTR) technique demands more labor and irrigation water.Under this conventional method, rice production in the boro (winter) season is threatened by shortage of labor, rising wage rates and water scarcity.As rainfall is so limited throughout the boro season, irrigation is the must for rice farming (Acharjee et al., 2017).Additionally, the need for power and diesel is being increased by irrigation for boro rice (Sattar et al., 2009).The main obstacles to the viability of traditional puddle transplanted boro rice farming are thus the lack of water and labor.The profit margins of PTR in boro season have been slashed because of high water inputs and labor costs (Pandy and Velasco, 1999).Boro rice under puddled transplanted irrigated system uses 3000-5000 liters of water for every kilogram of rice produced.Dry direct seeded rice (DDSR) technology has just recently emerged as a competitive substitute for the puddle transplanting approach (Rahman, 2019).Rice grown in the DDS technique produces higher or similar yields than rice grown in the PTR system while consuming 50-60% less irrigation water (Rahman and Masood, 2014).No standing water is kept in a dry direct seeded system from sowing to panicle initiation but standing water (3-5cm) is maintained from panicle initiation (PI) to blooming or milking stage.Thus, water conservation in the DDS system is primarily achieved by avoiding puddling and preserving aerobic soil conditions from sowing to PI stage.In this arrangement, water loss due to seepage, percolation and evaporation is minimal.As a result, dry direct seeding requires less water and uses water more efficiently than transplanted rice (Liu et al., 2015).In addition to being an excellent water-saving technology, the DDS for boro season also lowers production costs, saves money on power and diesel, and reduces soil and environmental pollution.This approach eliminates the need for seedbed preparation, seedling care in the seedbed, seedling pulling, transportation, and transplanting procedures.Additionally, direct seeded rice may reach maturity 7 to 10 days earlier than transplanted rice (Rahman et al., 2009).By requiring less irrigation, the dry direct sowing method would minimize greenhouse gas emissions and arsenic poisoning of the soil and rice.According to reports, crops that have been poisoned with irrigated water absorb significant concentrations of arsenic through their roots, straw, and grain, which then enters the food chain.A million kilograms of arsenic are thought to be added to Bangladesh's fertile soil each year via shallow aquifer irrigation, primarily in paddy fields (FAO, 2017).
Among the numerous cropping patterns in Bangladesh, T. aman rice -Fallow -Boro rice is the most dominant one.In this pattern, land remains fallow in between aman rice and boro rice.Farmers can easily cultivate rabi crops during this period and thereby cropping intensity can be increased.Therefore, T. aman -Rabi crops -Boro rice pattern can be easily adopted for increased cropping intensity, diversity and farm income.Cultivation of boro rice after a rabi crop could lead to late planting of boro rice especially when rabi crops are expected to have a long duration.In general, boro rice is transplanted during mid-December to mid-January and directly sown during mid-January to mid-February (Uddin, 2019).Under the context of water scarcity, PTR system of boro cultivation can be easily replaced by DDS system as it has many other advantages.DDS system generally requires 4-6 irrigations during the vegetative phase of rice.However, it is imperative to know the response of DDS rice to irrigation regime during vegetative phase to optimize irrigation requirement.To maximize output while utilizing the least amount of water, the current study was conducted with the goal of examining the impact of late sowing and irrigation regime on growth and yield of dry direct seeded boro rice.

Description of the study site
The experiment was conducted at the Agronomy Field of Bangladesh Agricultural University, Mymensingh during February-July 2021 to study the effect of sowing date and irrigation regimes on yield performance of late sown dry direct seeded boro rice variety BRRI dhan58.The experimental field was located at an elevation of 18m above the sea level.The experimental field belongs to non-calcareous dark grey floodplain soil under the Sonatala series of the Old Brahmaputra Floodplain Agroecological Zone (AEZ-9).The experimental field was a medium high land with moderate drainage condition.The soil was silty loam in texture having pH 6.50, 1.29% organic matter, 1.0% total N, 16.72 ppm available P, 0.12 ppm exchangeable K and 14.2 ppm available Sulphur.The bulk density, particle density and porosity of the soil were 2.60 g/cc, 1.35 g/cc and 46.67%, respectively.The climate of the locality is sub-tropical in nature and is characterized by high temperature and heavy rainfall during Kharif season (April-September) and scanty rainfall associated with moderately low temperature during rabi season (October-March).The daily average air temperature, total rainfall, sunshine hours and evaporation during the experimental period have been presented in Fig. 1.

Experimental treatment, design and layout
Two sets of treatments included in this experiment are (a) date of sowing viz.22 February (D 1 ) and 13 March 2021 (D 2 ) and (b) six irrigation regimes viz.no irrigation (I 0 ), one irrigation at 25% field capacity (25%FC; I 1 ), two irrigations at 25% FC and at 1 week after 25% FC (I 2 ), three irrigations at 25% FC, at 1 and at 2 weeks after 25% FC (I 3 ), four irrigations at 25% FC, 1, 2 and 3 weeks after 25% FC (I 4 ), and one irrigation at 3 weeks after 25% FC (I 5 ).The experiment was laid out in a spilt-plot design with three replications.Sowing dates were allocated into the main plot and irrigation regime into the sub plots.Thus, there were 36 plots in the experiment and the unit plot size was 10 m 2 (4 m ×2.5 m).

Julian Calendar Days
Evaporation Sunshine hours 1 .The field was fertilized at the rate of 325, 100, 130, 115 and 4 kg ha -1 of urea, triple super phosphate, muriate of potash, gypsum and Zinc sulphate (monohydrate) respectively as per recommendation of FRG ( 2012).The whole amount of triple super phosphate, muriate of potash, gypsum and zinc sulphate were applied as basal dose at the time of final land preparation.Urea was top dressed in three equal splits at 15, 30 and 45 days after sowing (DAS).A pre-emergence herbicide Panida 33 EC (Pendimethalin) was applied at 3 DAS @ 50 ml 10 L -1 and weeding was done thrice at 30, 45 and 60 DAS.Insecticide carbofuran @ 33 kg ha -1 was applied twice to control the rice stem borer.Polythene lining was done around the bunds in each plot to protect water inflow and outflow.

Sampling, harvesting and processing
The crop was harvested at maturity when 90% of the grains became golden yellow in color.Five hills (excluding border hills) were randomly selected from each unit plot and uprooted before harvesting for data recording on yield parameters.For recording data on grain and straw yield the crop was harvested from central 3.0 m -2 area (2.0 m × 1.5 m).The harvested crops of individual plot were bundled, properly tagged and then brought to threshing floor.The grains and straws were dried in the sun and finally the grain yield was adjusted at 14% moisture basis and converted to t ha -1 .

Data recording
Field capacity and soil moisture content: The field capacity is the amount of water retained in the soil after all the excess water at saturation has been drained out (Rai et al., 2017).It was measured by taking soil samples from the field after 2 days of saturation and the soil sample was oven dried at 105 o C for 48 hours.The moisture content of soil (P w ) was calculated by oven-dry weight basis by using the following formula.
Where, W1 = weight of wet soil sample W2 = weight of dry soil sample The soil moisture content at field capacity was 35.3%.The Management Allowable Depletion (MAD) of soil moisture at which irrigation to be applied was scheduled to be at 25% of field capacity and that condition of field reached at 26.1% soil moisture content.The soil moisture content of the rice field was monitored at 7 days interval by collecting soil samples from three selected spots of the field.The soil moisture content at different day after sowing was noted and presented in Fig. 2.

Economic Analysis
Costs for all heads of expenditure were recorded for studying the economic performance of the DDS boro rice under different sowing dates and irrigation regimes.The non-material input costs, material input costs, overhead costs and fixed costs were recorded to estimate the total costs of production (TCP) per hectare.Gross return (GR), gross margin (GM) and benefit cost ratios (BCR) were also calculated.Gross margin (GM) was obtained by deducting total variable cost (TVC) from gross return (GR) (Barnard and Nix, 1999).Benefit Cost Ratio (BCR) was calculated using the following formula: Benefit Cost Ratio (

Statistical Analysis
The collected data were compiled and tabulated in proper form and were subjected to statistical analysis.Data were analyzed using the analysis of variance (ANOVA) technique with the help of computer package program STATISTIX-10 and mean differences were adjudged by LSD Test.

Effect of sowing date
Sowing date had no significant effect on plant height, number of total, effective and non-effective tillers hill -1 , numbers of sterile spikelets panicle -1 , 1000-grain weight, grain yield and straw yield but had significant effect on panicle length and number of grain panicle -1 (Table 1 and 2).The crop sown on 13 March produced higher number of grains panicle -1 (88.46) than 22 February sown crop (78.18).On the other hand, 22 February sown crop gave longer panicles (22.09 cm) than 13 March sown crop (20.78 cm).It was noted that the number of grains panicle was higher for 13 March sowing but number of effective tiller was higher in 22 February sown crop (Table 1  and 2).Thus, it may be revealed that the yield did not differ due to the differential effects of the yield contributing characters in response to sowing dates.

Effect of irrigation regime
Irrigation regime had significant effect on number of total tillers hill -1 , number of effective tillers hill -1 , number of grains panicle -1 , 1000-grain weight, grain yield and straw yield but not on plant height, number of non-effective tillers hill -1 , panicle length and sterile spikelet panicle -1 (Table 3 and 4).The highest number of total tiller hill -1 (23.32) was found with I 3 (three irrigations at 25%FC, 1 weeks after 25%FC and 2 weeks after 25%FC) while the lowest one was found with I 0 (No irrigation).The second highest number of total tiller hill -1 was found with I 5 (22.0) and it was statistically at par with I 2 (21.23).The number of effective tiller hill -1 was the highest with I 3 (18.59),that was statistically similar with I 1 , I 2 and I 5 and the lowest value was found with I 0 (15.87).The highest number of grains panicle -1 was found with I 4 (92.62) and the lowest value was found with I 0 (72.05).The second highest value was found with I 3 which was statistically at par with I 2 (85.32) and I 1 (83.53).The highest 1000-grain weight (19.89 g) was found with I 4 (four irrigations at 25% FC, 1, 2, 3 and 4 weeks after 25%FC), which was statistically similar with I 3 (19.61g).The lowest grain weight was found with I 0 (18.63 g).The highest grain yield (6.0 t ha -1 ) was found with I 4 which was statically similar with I 3 (5.44 t ha -1 ).The lowest grain yield was noted in I 0 (3.71 t ha -1 ).The similar trend was noted for straw yield (Table 4).The highest value was noted in I 4 (6.32 t ha -1 ) which was similar with I 3 (6.09t ha -1 ).In a column, figures with same letter or without letter do not differ significantly whereas figures with dissimilar letter differ significantly as per LSD test; NS = Not significant; ** = Significant at 1% level of probability; *** = Significant at 0.1% level of probability; I 0 =No irrigation; I 1 =One irrigation at 25% Field Capacity (FC); I 2 = Two irrigations at 25% FC and 1 week after (WA) 25%FC; I 3 = Three irrigations at 25% FC, 1 WA 25% FC and 2 WA 25% FC; I 4 =Four irrigations at 25% FC, 1 WA 25% FC, 2 WA 25% FC and 3WA25% FC; I 5 =One irrigation at 3 weeks after 25% FC The lowest straw yield was observed in I 0 (5.72 t ha -1 ) which was at par with I 1 , I 2 and I 5 .The result indicated that the water stress may adversely affect yield and related attributes.The present study showed that four irrigations resulted highest grain yield of 6.0 t ha -1 while no irrigation gave the lowest grain yield of 3.71 t ha -1 .
In case when only one irrigation applied at 25% FC, the yield was reduced by 1.09 t ha -1 but when only one irrigation was applied at 3 weeks after 25% FC reduced yield by 1.53 t ha -1 .The yield reduction for two and three irrigation plots were 0.94 and 0.56 t ha -1 , respectively.The result also revealed that the lowest grain yield was produced with no irrigation (I 0 ) plot, which was similar with the plots one irrigation only at the late vegetative stage (I 5 ).All other irrigation treatments gave significant higher yield than these I 0 and I 5 treatments.In a column, figures with same letter or without letter do not differ significantly whereas figures with dissimilar letter differ significantly as per LSD test; NS = Not significant; ** = Significant at 1% level of probability; *** = Significant at 0.1% level of probability; I 0 = No irrigation; I 1 = One irrigation at 25% Field Capacity (FC); I 2 = Two irrigations at 25% FC and 1 week after (WA) 25%FC; I 3 = Three irrigations at 25% FC, 1 WA 25% FC and 2 WA 25% FC; I 4 = Four irrigations at 25% FC, 1 WA 25% FC, 2 WA 25% FC and 3WA25% FC; I 5 = One irrigation at 3 weeks after 25% FC Thus the result clearly showed that water stress during early vegetative phase is less detrimental than that imposed at late vegetative stage.The yield reductions in case of no irrigation, one irrigation, two irrigation and three irrigation plots were mainly attributed to the reduction in number of grain panicle and grain weight.Thus, it is better to use three or four irrigations during vegetative phase and it could be started at the point when soil moisture is depleted at 25% of the field capacity.

Interaction effect of sowing date and irrigation regime
The result showed that there was no significant interaction effect of sowing date and irrigation regime on plant height, number of effective tiller hill -1 , number of noneffective tiller hill -1 , panicle length, number of grains panicle -1 , number of sterile spikelet panicle -1 , grain yield, straw yield, but had significant effect on number of total tiller hill -1 and 1000-grain weight (Table 5 and 6).The crop sown on 22 February with four irrigations (D 1 × I 4 ) gave the highest number of total tiller hill -1 which was statistically similar with those of D 1 × I 1 , D 1 × I 2 , D 1 × I 3 , D 2 × I 3 and D 2 × I 4 (Table 5).It was noted that the plots having no irrigation (I 0 ) produced the lowest grain yield which was similar to that of I 5 (one irrigation given at 3 weeks after 25% FC).In case of 1000-grain weight, the highest weight was achieved ( Here, Total cost of production (TCP) includes total variable cost (TVC) and fixed cost (FC) per hectare.Total variable cost includes: Land preparation = 8000 tk, Fertilizer application = 1600 tk, Seed sowing = (25*400=10000 tk), Cost per irrigation = 1500 tk, Weeding and herbicide = 4000 tk, Harvesting = 12000 tk, Post-harvest operation = 8000 tk, Seed cost = 3000 tk, Fertilizer cost = 17425 tk, Pesticide = 2000 tk, Gross return (GR) includes return from grain and straw (Grain @30000 tk t-1 and Straw @5000 tk t -1), Fixed cost (FC) includes: Interest on operation cost = 5% of TVC and Rental value of land = 25000 tk ha -1 .GM = Gross margin and BCR = Benefit cost ratio.D 1 = 10 February D 2 = 01 March; I 0 = No irrigation; I 1 = One irrigation at 25% Field Capacity (FC); I 2 = Two irrigations at 25% FC and 1 week after (WA) 25%FC; I 3 = Three irrigations at 25% FC, 1 WA 25% FC and 2 WA 25% FC; I 4 =Four irrigations at 25% FC, 1 WA 25% FC, 2 WA 25% FC and 3WA25% FC; I =One irrigation at 3 weeks after 25% FC.

Figure 1 .
Figure 1.Daily average (a) temperature and rainfall and (b) sunshine hours and evaporation of the experimental site during 01 January to 30 June 2021

Figure 2 .
Figure 2. Soil moisture content at different weeks after sowing of dry direct seeded rice in 2021

Table 1 .
Effect of sowing date on plant height, tiller production and panicle length of dry direct seeded boro rice var.BRRI dhan58

Table 2 .
Effect of sowing date on yield contributing characters and yield of dry direct seeded boro rice var.BRRI dhan58

Table 3 .
Effect of irrigation schedule on plant height, tiller production and panicle length of dry direct seeded boro rice var.BRRI dhan58

Table 4 .
Effect of irrigation schedule on yield contributing characters and yield of dry direct seeded boro rice var.BRRI dhan58

Table 5 .
Effect of interaction between sowing date and irrigation schedule on plant height, tiller production and panicle length

Table 6
a similar way due to irrigation in both the sowing dates, indicating that water availability is the key factor in harnessing higher yield of boro rice under dry direct seeded system.Therefore, delayed sowing would not affect grain yield of rice in DDS system if water supply is adequate.

Table 6 .
Effect of interaction between sowing date and irrigation schedule on yield contributing characters and yield of dry direct seeded boro rice var.BRRI dhan58