Resource conservation technology for sustainable productivity of intensive rice-based cropping pattern in Bangladesh

Exhaustive conventional tillage and removing residues of previous crops in the rice-based cropping system are labor intensive, costly, soil destructive and nonecofriendly. In recent years, increased concerns for healthier food production and environmental quality, and increased emphasis on sustaining the productive capacity of soils, have raised concern in the maintenance and improvement of soil organic matter through appropriate land use and management practices. Strip tillage with the application of herbicides and crop residue mulching are being developed to overcome this challenge. A two-year experiment of the summer rice-mustard-winter rice (R-M-R) system was conducted at the farmers’ fi eld in the northern Bangladesh during 2014-2016. Summer rice (BRRI hybrid dhan6), mustard (BARI Mustard 14) and winter rice (BRRI dhan28) were grown under, T1: Conventional tillage (CT) + three hand weeding (Control) and T2: Pre-plant herbicide (PRE) + strip tillage (ST) + pre-emergence herbicide (PE) + post-emergence herbicide (PO) with two levels of crop residue mulching, M0: no-mulch and M50: 50% standing mulch. The CT consisted of two primary tillage operations by a two-wheel tractor, and ST had done by a Versatile Multi-crop Planter in a single-pass process. The PRE (glyphosate) and PE (pendimethalin) in all crops and the PO (ethoxysulfuron-ethyl in rice and isoproturon in mustard) were applied at recommended dose and time. The combination of applied PRE, ST, followed by PE and PO herbicide and the retention of 50% mulch fetched the highest yield and economic returns of individual crop and the productivity of the summer rice-mustardwinter rice system. Research Article Resource conservation technology for sustainable productivity of intensive ricebased cropping pattern in Bangladesh Mobarak Hossain1*, Mahfuza Begum2, Moshiur Rahman2, Abul Hashem3 and Richard Bell4 1Rice Breeding Platform, International Rice Research Institute, Dhaka-1213, Bangladesh 2Department of Agronomy, Bangladesh Agricultural University, Mymensingh 2202,


Introduction
Planting of crops in exhaustive tilled soil after removing the residues of previous crops is the most common traditional cropping practice in Bangladesh. Generally, rice grown in the soil is usually puddled, followed by manual transplanting. Nonrice crops (mustard, wheat etc.) are grown in heavily pulverized soils. These traditional practices pose concerns regarding the sustainability of crop production. Intensive tillage degrades soil structure, depletes Soil Organic Matter (SOM), and increases labor and fuel requirements and overall production costs [1].
It also lags the establishment of succeeding crops, leading to reduced yield. Further, there is a growing concern regarding labor scarcity for agriculture due to less profi t and migration from rural to urban areas within and outside the countries [2]. Thus, there is an urgent need for labor and other inputeffi cient alternate systems that produce more at fewer costs.
Without a new and more sustainable increase to productivity, Citation: Hossain  herbicide, less availability of appropriate herbicide molecules with the higher prices, and environmental pollution-related issues urge the need to adopt integrated weed management strategies to increase the sustainability of ST. Agronomic options like crop residues and crop intensifi cation had reported earlier to manage weeds in ST practice [11].
There are many pieces of evidence that crop residue retention and crop intensifi cation promote nutrient cycling, increase nutrients availability to crops, and increases SOM content, additionally suppress weeds and increases soil water content, and reduce irrigation water requirements by suppressing soil evaporation [12]. Residue retention could also play an important role in R-M-R systems, where the residues of both crops are generally removed from the fi elds. High yielding R-M-R systems are more extractive of nutrients, particularly N, P, or K than rice-rice systems. Further, the inclusion of mustard in the system and its' residue retention can improve the nitrogen economy of the following crop.

Experimental site and season with the edaphic, and climatic condition
A two-year crop sequence (summer rice-mustard-winter rice) experiment was conducted at the farmers' fi eld located at

Experimental materials, treatments, and design
A summer season (June-September) rice (Oryza sativa L.) -rabi (October-December) season mustard (Brassica napus L.) -winter season (January-May) rice (Ory za sativa L.) cropping agricultural supply will hardly keep pace with the rapidly rising demand caused by increasing population and changing consumer preferences with income growth. Potential strategies to tackle these challenges could be the Resource Conserving Technology (RCT).
The RCT primarily focus on soil resource savings through minimal tillage, ensuring soil nutrients and moisture conservation through crop residues and adoption of spatial and temporal crop sequencing [3]. Reduced tillage with residue retention can improve soil physical, chemical, and biological properties, facilitate timely planting, and decrease production costs related to labor, fuel, and machinery. The use reduced tillage can also reduce drudgery and sustain profi t [4]. However, a meta-analysis of a large set of global data demonstrated RCT may potentially tackle labor and energy shortage in agriculture of Bangladesh.
The summer rice-mustard-winter rice rotation is the principal cropping system in Bangladesh. In this system, summer rice is grown during the warm rainy season (June- Subsequently, pre-emergence herbicide followed by a postemergence also needs to apply because of remaining viable weed seeds on the surface still after pre-plant herbicide application [7]. Now-a-days farmers are switching to herbicidal weed control as it is a quick, effective, and low-cost weed control method to address the crisis of labor availability with high wages during peak demand periods [8]. Previous studies confi rmed the application of pre-plant, pre-emergence and post-emergence herbicides ensured continuous and effective control of weeds and provided the better yield over manual weeding [9]. But, the repeated use of herbicide with the same mode of action may lead to developing quick herbicide resistance in weeds, making weed control more diffi cult [10].

Plan ting operations
In each 9 m × 5 m plot, CT was done using a two-wheel tractor (2 WT) by four plowings and cross plowing followed by sun-drying for two days, fi nally fl ooding and leveling.  Table 1. Among the all herbicides, only ethoxysulfuron-ethyl was applied in standing water condition in the fi eld while rest others were applied in fi eld capacity condition.
In the no-residue treatment, planting was done without retaining residues of previous crop. In 50% residue practice rice and mustard was harvested keeping 50% plant standing in the respective plots. Summer rice (cv. BRRI hybrid dhan6), mustard (cv. BARI Sharisha 14) and winter rice (cv. BRRI dhan28) were grown in this study. In rice (after harvest mustard and rice, respectively), the fi nal fi eld was prepared by additional fl ooding and laddering in CT. After ST, the land was inundated with 3-5 cm water one day before transplanting to allow the strips to be soft enough to transplant rice seedlings. Then seedlings were transplanted (single seedling of summer hybrid rice and 2/3 seedling of winter rice hill -1 ) in the raised furrows.
Seeds of mustard (after summer rice harvest) was sown in lines on the same date using VMP in ST and manually in CT. In this study, 10 kg and 20 kg seeds of summer hybrid rice and winter rice, respectively, was used. 25-and 35-days aged seedling of summer and winter rice seedlings were transplanted at 25 cm × 15 cm distance. Seven kg seeds of mustard were sown continuously seeding at 20 cm apart lines.

Cultural operations
The recommended dose of Nitrogen (N), Phosphorus (P), Potassium (K) and Sulfur (S) was applied to the respective crop.
The N in the form of urea was applied @ 80 and 20 ha -1 in rice and mustard, respectively. A basal dose of phos phorus (22 and 22 kg ha -1 ) from triple super phosphate, potassium (35 and 15  kg ha -1 ) from muriate of potash and sulfur (12 and 10 kg ha -1 ) from gypsum was applied to rice and mustard, respectively.
The entire amount of P, K, and S was broadcasted before seeding/transplanting and mulching in all crops. In rice, N was applied in three equal installments at 15, 30 and 45 DAT. While in mustard the full amount of N was applied before seeding.
In summer rice, no additional irrigation was required due to suffi cient rainfall. In winter rice, three irrigations were

Results and Discussion
Effect of treatments on the yield of summer and winter rice, and mustard In this section, we have presented the mean data of the two-year study. Data revealed that tillage systems, weed control practice and residue mulching exerted signifi cant (P<0.05) effect the numbe r of pr oductive tillers m -2 and grains panicle -1 and grain yield were infl uenced signifi cantly (P<0.05) of both summer and winter rice, whereas the number of hill m -2 , sterile spikelets panicle -1 and 1000-grains weight were statistically non-signifi cant (Tables 2,3). The highest number of productive tillers m -2 and grains panicle -1 was recorded in PRE + ST + PE + PO plus 50% residue, followed by the same treatment without residue. While the lowest value was recorded in CT + 3 HW without residue, followed by CT + 3 HW with 50% residue. Differences in the number of productive tillers m -2 and grains panicle -1 had attributed the yield of rice on these treatments, respectively. About 14% higher yield in PRE + ST + PE + PO than CT + 3 HW and 6% higher yield in 50% residue than no-residue was found.
In mustard, the number of siliqua plant -1 and seed yield were infl uenced signifi cantly (P<0.05), whereas the number of plants m -2 , seeds siliqua -1 , 1000-seeds weight was statistically non-signifi cant by the combined effect of tillage, weed control and residue levels (   Differences in the yield among the treatments might be attributed to the variation in yield contributing characters of crops like the number of productive tillers m -2 , and grains panicle -1 both summer and winter rice while the number of siliqua plant -1 in mustard. The higher yield in ST of present study agrees the research fi ndings of previous study found the higher crop yield in ST than CT due the benefi cial effect of ST on grain yield could be attributed to that change in soil properties. Higher total soil porosity, better soil moisture conservation and better soil physical environment favored the root growth and nutrient uptake resulted in increase in grain yield [13]. It was also reported that the higher and more stable crop yields in ST than CT occurred from the formation of surface crust by heavy pulverization of the surface soil [14], leading to loss of structure and homogenization of the cultivated layer, which resulting in discontinuity of the conducting pores and compaction of the soil below the cultivated layer due to the pressure from the tractor wheels in CT.
In addition to that, crop yield increase in ST may also reported through improving soil fertility by conserving soil and water and sequestering organic carbon in farmland soils that reduces the extremes of water logging and drought [15,16]. In another study, yield increase in ST also might be associated with the improvement of soil structure and stability thereby facilitating better drainage and water holding capacity. The higher infi ltration rates and propitious moisture dynamics supported up to 30% yield increase in maize [7,18] due to increase of soil organic carbon, soil total nitrogen and soil total phosphorus by 25, 18 and 7%, respectively in the ST than CT. These fi ndings have implications for understanding how conservation tillage practices increase crop yield by improving soil quality and sustainability in ST of conservation agriculture practices.
The physical shock or disturbance in normal growth of crop plants occurred during hand weeding CT plots which may retards the development of crops for short times and ultimately yield might be affected [19]. By contrast, herbicides did not exert any shock to crop plant. Herbicides applied at fi eld rates, also have hormetic effect [20,21] infl uencing the growth and development of crops which may have attributed to obtains better crop yields in this study. Glyphosate can increase plant growth, induce shikimic acid accumulation, increase photosynthesis and stomatal opening which leads to increase seed production with shortening the plant life cycle [22]. On the other hand, glyphosate was reported to inhibit rust diseases in crop thus improving grain yield [23]. The results of glyphosate, together with the pendimethalin can induce 25% higher stimulation in total biomass growth in crop plant [24] while pendimethalin and ethoxysulfuron-ethyl [25] is reported to contribute total biomass in rice leaded to produce higher number of tillers m -2 area and higher yield. The above discussed reasons might lead to obtain higher seed yield of mustard by pendimethalin and isoproturon, in ST than CT in the present study.
In this study, retention of 50% crop residue increased grain yield of summer and winter rice and mustard by about 3-4% over no-residue. This might be due to the benefi cial effect of crop residues on the soil fertility, which is associated with the betterment of crop yield. Because crop residues are an important source of SOM that can be returned to soil for nutrient recycling, and to improve soil physical, chemical and biological properties. Retention of plant residues has been found to have many long-term benefi ts around the world. These crop stubble constitutes a mulch cover that protects the soil against run-off and erosion and increases the percentage of SOM and nutrients in the surface soil layer [26]. The capacity of the soil surface to intercept rainfall is improved because of changes in soil roughness, soil surface porosity, and hydraulic conductivity of the topsoil. Mulching also reduces temperature extremes and direct evaporation [15]. Thus, crop residues regulate the nutrient cycles within the soil. Moreover, the effects of residue return to soil and associated tillage on soil physical, chemical and biological properties occur concurrently and hence are diffi cult to separate from each other. Another study has shown that 80% of changes in soil C levels under cropping were attributable to tillage (conservation vs. conventional) and 20% to residue management (stubble retained vs. burnt) [27].
The cumulative effect of conservation tillage and crop residue mulching might have enhanced the better yield in 50% residue retention practice than no-residue in this study. Hence, the above discussed points confi rm the result of present study that one pre-plant herbicide before ST, followed by one preand a post-emergence herbicide with 50% crop residues, is an excellent alternative to obtain the higher crop yield CT with manual hand weeding without retaining residue.

Effect of treatments on the benefi t-cost ratio (BCR) of summer and winter rice, and mustard
In all the three cops, the maximum average BCR had transcribed from the PRE + ST + PE + PO plus 50% residue followed by the same treatment without residue. While the lowest BCR was recorded from the CT + 3 HW without residue, followed by the same treatment with 50% residue (Figure 2).
The treatment PRE + ST + PE + PO achieved about 39, 21 and 30% higher BCR than CT + 3 HW in summer and winter rice and mustard, respectively. On the other hand, 50% mulching increased the BCR by about 7% than no-mulching in all the crops. The highest BCR in PRE + ST + PE + PO was attributed to the highest yield and lowest production cost in this treatment. The lowest production cost was calculated due to considerable savings in the cost of tillage costs, weeding and labor requirements in all the crops (Table 5).  (25, 29 and 22%) in summer rice, mustard, and winter rice, respectively (Table 5).
This estimation is in line with previous study estimating 70% [28] and 49% [29] [30]. Previous research also reported higher weeding costs in manual weeding are economically non-profi table over herbicidal weed control and the application of appropriate herbicide can replace hand weeding successfully [31].
About 7% higher profi t in 50% residue might be occurred solely from about 5-9% higher grain yield than no-residue in all crops of summer rice-mustard-winter rice system. Therefore, the study claimed that, crop cultivation using strip tillage, applied a pre-plant, pre-emergence, and postemergence herbicide in sequence; with the retention of 50% crop residue could achieve the higher profi t compared to the existing conventional practice of crop cultivation.

Total pattern productivity of summer rice -mustard-rice pattern
The tillage options, weed control practices and residue mulching had infl uenced the productivity in terms of rice equivalent yield (REY) of the pattern (Table 6). Results revealed that PRE + ST + PE + PO and 50% residue increased productivity by 21 and 4% than CT + 3 HW and no-residue, respectively. It was found that the incorporation of mustard had increased the productivity of the R-M-R system by 41% than the R -R system.
The total pattern productivity of the summer rice-mustardwinter rice pattern was about 41% higher than the s ummer rice-fallow-winter rice pattern. The incorporation of mustard with an average yield of 1. 57 t ha -1 might have benefi ted such benefi t in the summer rice-fallow-winter rice pattern. This