Influence of unpadded transplanting on rice ( Oryza sativa L.) retained reside of previous mustard

On-farm research was conducted at Gouripur sub-district under Mymensingh district of Bangladesh during boro (mid November-June) season in 2013-14 and 2014-15 to evaluate the performance of unpadded rice cultivation with crop residue retention. The rice var. BRRI dhan28 was transplanted by two tillage practices viz., puddled conventional tillage (CT) and non-puddled strip tillage (ST) and two levels of mustard residues, i.e., no residue (R 0 ) and 50% residue (R 50 ). The experiment had designed in a randomized complete block design with four replications. There were no significant yield differences between tillage practices and residue levels in 2013-14. But in the following year, ST yielded higher grains (5.72 t ha -1 ), which was about 9.36 % higher compared to CT. The higher grain yield in ST, leading to 22.23% higher BCR compared to CT. Retention of 50% residue increased by 3.15 % yield compared to no-residue, which contributed to 10.58 % higher benefit-cost ratio (BCR). The ST combine with 50 % residue retention yielded the highest grain yield (5.81 t ha -1 ) which credited to obtain the highest BCR (1.06).


Introduction
Most of the farmers in the Asian continent cultivate rice (Oryza sativa L.) seedlings by transplanting in puddled soil for comfortable crop establishment. Lands had prepared by single or two passes in dry condition followed by exposure to the sun for a couple of days.
Then after inundation, the final field is prepared by ploughing, cross ploughing and laddering in standing water. However, this traditional puddling method is labour, fuel, time and capital consuming (Islam et al., 2014). Nowadays most of the tillage operations for puddling soil in Bangladesh are done by power tiller and is detrimental to physical soil conditions through destroying soil aggregates, breaking capillary pores, and dispersing the soils (Miah et al., 2002). Cloddy soil structure with less soil moisture and inadequate seedsoil contact resulted from the puddling makes land preparation difficult for the following crops (Islam et al. 2012). Not only that, puddled rice transplanting consumes about 20-40 % of the total water required for raising a crop, and it also promotes the formation of hardpan (Singh et al., 2014). It also reduces soil organic carbon at a double rate, thus decreases soil fertility has losses of irrigation water and damages the ecological environment (Sayre and Hoobs, 2004). Adoption of minimum tillage unpadded transplanting might be an excellent alternative to puddled transplanting to overcome these destructive issues, as it is using widely for many crops around the world (Singh et al., 2014). This technology has potentials to allow saving in labour, energy, water and time during rice establishment as well as improves soil fertility (Islam et al., 2012). Concerning the soil health, another agronomic option is the retaining the residues of previously cultivated crops are a significant factor for crop production through their effects on soil physical, chemical and biological functions as well as water and soil quality and increase crop yield (Kumar and Goh, 2000). Residue practice maintains soil micro-organisms and microbial activity which can also lead to weed suppression by the biological agents leading to increase crop yield (Shrivastav et al., 2015).
Considerable research work had done on puddle transplanting, but there is limited information on unpadded rice transplanting with crop residue retention under Bangladesh condition. Therefore, the present study had conducted to examine the performance of rice to the unpadded transplanting system with the retention of crop residues.

Materials and Methods
The experiment had conducted at farmer's field of Durbachara, Gouripur, Mymensingh, Bangladesh (the latitude of 24.75 0 N and the longitude of 90.50 0 E) ( Fig. 1) during boro (Mid November-June) season in 2013-14 and 2014-15. This experimental area belongs to the Old Brahmaputra Floodplain, which is characterized by dark grey non-calcareous alluvium soils and these soils are mostly sandy loam under Sonatala series (Brammer, 1996).
Soil characteristics had presented in Table 1. Climatic (rainfall and thermal condition) data were collected from the nearest weather station and illustrated in Fig. 2. The treatments were: (i) puddled condition conventional tillage (CT) and (ii) unpadded condition strip tillage (ST) and two levels of crop residue viz., no residue (R0) and 50% residue (R50). The treatments had laid out in randomized complete block design with four replications using unit plots of 9 m × 5 m. In tillage practice, CT consisted of two passes primary tillage by two-wheeler tractor (2 WT) and exposed to the sun for two days followed by inundating whole plot and puddling by 2WT with two passes to complete land preparation. The ST had done by a versatile multi-crop planter in a single pass operation before flooding the field.
Three days before ST, pre-plant glyphosate herbicide had applied @ 75 ml 10 L -1 water.
After ST, the land had inundated with 3-5 cm standing water one day before transplanting operation for making the soil soft enough to transplant seedlings (Islam et al., 2014). Thirtyfive days old seedlings of rice var. BRRI dhan28 had transplanted. Fertilizers have applied according to the recommendation of BRRI (2014). A spacing of 25 cm × 15 cm was maintained for both CT and ST with 2 or 3 seedlings hill -1 . The crops were harvested at maturity from 3 m × 3 m each, and then data had recorded. Grain yield had adjusted to 14% moisture content. Data were subjected to ANOVA using STAR software and means were separated by Duncan's Multiple Range Test (Gomez and Gomez, 1984).

Effect of tillage practice on yield contributing characters, yield and the benefit-cost ratio (BCR) of rice
In 2013-14, although none of the parameters except the BCR, varied significantly due to tillage practices but in 2014-15 yield contributing characters were significantly affected except the plant height, panicle length, and the weight of thousand-grains ( Table 2). The highest and lowest numbers of effective and non-effective tillers m -2 , respectively as well as the highest and lowest numbers of grains and sterile spikelets panicle -1 , respectively, were recorded from the ST which attributed to higher yield (9.36 % higher in 2014-15) in ST than CT. The higher yield in ST might have credited the higher BCR (22.23 % higher) compared to CT during this time (Table 2).

Effect of residue levels on yield contributing characters, yield and the benefit-cost ratio (BCR) of rice
During the first year of experimentation, there was no significant effect of residues on the yield and yield attributes of rice. But in the second year, retention of 50% residue improved the numbers of effective tiller m -2 and the numbers of grain panicle -1 while declined the numbers of non-effective tiller m -2 and the numbers of sterile spikelets panicle -1 , compared to no-residue (Table 3). Retention of 50% residue yielded around 3.15 % higher rice which attributed to earning 10.58 % higher BCR in 2014-15 (Table 3).

Combination effect of tillage practice and residue levels on yield characters, yield and the benefit-cost ratio (BCR) of rice
Combination of tillage practice and residue level exerted significant effect only on BCR while the rest of the parameters did not vary significantly during 2013-14. Whereas in 2014-15, a combination of treatments had a significant impact on all the parameters except plant height, panicle length, number of sterile spikelets panicle -1 and weight of thousand grain (Table 4).
Strip tillage retained 50% residue produced the highest BCR which might have credited from the highest grain yield. The highest grain yield might have attributed from the highest number of effective tillers m -2 and grains panicle -1 , and the lowest numbers of non-effective tillers m -2 .
CT or ST with residue yielded the higher values of these parameters compared to no-residues.
CT without residue produced the lowest grain yield, consequently the lowest BCR. Also, about 5.19 % higher yield had found in 2014-15 than 2013-14.

Effect on the yield of rice
The higher yield in ST might have attributed from the changes in soil properties viz. the higher porosity and better soil moisture conservation in ST favoured the more robust root growth and nutrient uptake resulted in increasing grain yield. These results agree Huang et al. (2012) stating that minimum tillage (MT) unpadded condition provides more favourable soil physical environment for better crop growth than CT. Pittelkow et al. (2015) about Qi et al. (2011) also reported that higher and more stable crop yields in MT than CT. In CT, heavy grinding of the surface soil by 2 WT forms hardpan by exerting massive pressure. Hence, leading to loss of structure and fusing the cultivated layer resulting in the disruption of the soil pores.
On the other hand, crop yield increase in MT might have occurred from the improved soil structure and stability. They were moreover facilitating better water holding capacity and drainage that reduces the extremes of waterlogging and drought (Holland, 2004), ultimately improving soil fertility by sequestering organic carbon in farmland soils (Zheng et al., 2014).
This finding supports the research result of Liu et al. (2010) who found 20% higher maize yield in MT than CT due to increase of soil organic carbon, soil total nitrogen and soil total phosphorus by 25, 18 and 7%, respectively. These results have implications for understanding how conservation tillage practices increase crop yield by improving soil quality and sustainability in unpadded strip tillage practices as also clinched by Hossain et al. (2016) and Mvumi et al. (2017). Some research findings also concluded no yield differences between ST and CT. Haque et al. (2016) found the similar grain yield of rice in unpadded ST transplanting and CT, which confirms the earlier findings of Hossain et al. (2015) who also found no yield penalty of wheat and rice between ST and CT. In another study, Sharma et al. (2011) also reported similar rice yield in unpadded transplanting to the CT. Wiatrak et al. (2005) found identical cotton yield in ST and CT while Al-Kaisi and Licht (2004)  In this study, retention of 50 % of crop residues increased the grain yield of rice by about 3.15% over no-residue. Research finding of Shrivastav et al. (2015) confirm this stating residue converts to mineralized nutrients which causes sufficient crop growth and facilitates higher yield over no-residue. Kaschuk et al. (2010) in support Qin et al. (2010) concluded straw residue retention directly increases the input of organic matter and nutrients into the soil, in turn improving soil nutrient availability for crop growth and better yield over no-residue. The earlier study of Thomas et al. (2007) and Govaerts et al. (2007) also found the benefits of residue retention on crop yield. Improved soil fertility and water availability might occur from the supplies of organic matter from straw residue for heterotrophic N fixing micro-organisms, which could be utilized by the crops, consequently results in the higher yield. Straw residues for controlling weeds in different crops have suggested by Devasinghe et al. (2011), andHossain et al. (2016) concluded residues prevent weed growth and thus retards crop weed completions. Hence, the crop is grown stronger and favoured to higher yield.
In this study, 5.19 % higher yield in the 2014-15 year than 2013-14 might be due to the variation of monthly average temperature, rainfall, relative humidity and sunshine hours of the experimental site during 2013-2015 (Fig. 2). Such interpretations of all climatic parameters during various phonological stages of rice viz., germination to transplanting, tillering, and anthesis to physiological maturity exerted definite stresses on the growth and development of rice. Such pressures might have influenced to vary the yield in two consecutive years by controlling the variation of yield attributes such as the number of effective and non-tillers m -2 and grains and sterile spikelets panicle -1 (Safdar et al., 2013).

Effect on the benefit-cost ratio (BCR) of rice
Partial economic analysis disclosed that among the treatments ST with 50% residue earned the On the other hand, ST reduced fuel and labour requirements during land preparation. About 10.58 % higher profit in 50% residue might have occurred solely from 3.15% higher grain yield than no-residue. Therefore, the study claimed that rice cultivation through practising unpadded strip tillage with the retention of 50% crop residue could achieve a higher profit compared to existing conventional tillage of rice cultivation in Bangladesh.

Conclusion
Based on the result of this study, we can conclude that unpadded rice transplanting with the retention of crop residues may be an excellent alternative to existing conventional tillage operation and farmers are likely to be benefited through adopting this practice.