Crop Establishment Methods and Weed Management Practices on Productivity and Economics of Transplanted Rice

Field experiments were conducted in clay loam soil of wetland farm, Tamil Nadu Agricultural University, Coimbatore during rabi, 2011-12 and 2012-13 to evaluate different crop establishment methods and weed management practices in lowland transplanted rice. The experiment was laid out in strip plot design with three replications. The treatments consisted of three crop establishment methods in horizontal strips and six weed management practices in vertical strips. The results of the study indicated that mechanical transplanting at 30 x 20 cm with conoweeding four times at 10 days interval starting from 10 DAT resulted in higher grain yield, higher net returns and B:C ratio. This practice was comparable with mechanical transplanting at 30 x 20 cm with preemergence application of pretilachlor @ 0.75kg a.i. ha -1 + early post emergence application of bispyribac sodium @ 20g a.i. ha -1 coupled with conoweeding at 40 DAT.

The area under rice crop is decreasing year by year due to various factors such as increased cost of inputs, labour shortage and less profitability. Transplanting of rice seedlings in the traditional way is labourious, time consuming and causes drudgery. Non-availability of labourers for transplanting at appropriate time leads to late planting, which results in poor yields. In rice, planting methods have an impact on the growth and yield, besides cost of cultivation and labour requirement. Rice transplanting is done manually and requires about 306 man-h ha"1, which is roughly 42 per cent of the total labour requirement of rice production. At transplanting time, acute labour shortage results in increased wages and delay in the operation. Manual transplanting will not be uniform and results in inadequate population. These problems necessitated the introduction of mechanized rice transplanting, to achieve timely planting and better crop stands (Hemmat and Taki, 2003). In addition, weeds are the bounding factors in agricultural production, and compete with crop plants due to their rapid growth. Weeds decrease about 25 per cent of potential yield and pose serious threat to crop production (Jacob and Syriac, 2005). Besides, weeds compete for water, light and space creating disturbance in cultivation and maintenance with an ultimate result of yield withdrawal, reduction in quality and quantity of produce. Herbicides seems to be promising and viable options because of their immediate performance in decreasing weeds competition, easy usage, low cost and require less workforce. Agronomical manipulations such as crop establishment methods with appropriate weed management practices may offer an effective option for better control of weeds in rice, thereby enhancing rice yield. In cognizance of the above, the present study was undertaken.

Materials and Methods
Field experiments were conducted during rabi 2011-12 and 2012-13 at Tamilnadu Agricultural university, Coimbatore to elucidate the effect of crop establishment methods and weed management practices on the productivity and economics of rice cultivation. The experiment was replicated thrice in strip plot design with three crop establishment techniques viz., conventional planting (C1), System of Rice Intensification (SRI) -marker planting (C2), System of Rice Intensification (SRI) -machine planting (C3) in horizontal strips; and six weed management practices in vertical strips viz., conoweeding 4 times at 10, 20, 30 and 40 DAT (W1), pre emergence (PE) Pretilachlor 50 % EC @ 0.75kg a.i. ha-1 + conoweeding at 20 and 40 DAT (W2), PE Pretilachlor 50 % EC @ 0.75kg a.i. ha-1 + early post emergence (EPOE) Bispyribac sodium 10 % SC @ 20g a.i. ha-1 (W3), PE Pretilachlor 50 % EC @ 0.75kg a.i. ha-1 + EPOE Bispyribac sodium 10 % SC @ 20g a.i. ha-1 + conoweeding at 40 DAT (W4), EPOE Laundax power @ 10 kg ha-1 + conoweeding at 30 and 40 DAT (W5) and un-weeded control (W6). The variety CO (R) 49 was used in both the seasons of the study. The experimental soil was clay loam in texture with low available nitrogen, medium level phosphorus and high potassium. *Corresponding author email : chandrusan2007@gmail.com SRI machine planting and marker planting involved 12 days old single seedlings hill-1 at 30 x 20 cm and 25 x 25cm spacing, respectively in comparison to conventional transplanting (CT) of 21 days old 2-3 seedlings hill-1 at 20 cm x 10 cm spacing. The seed requirement in SRI marker and machine planting was 8 and 10 kg ha-1, respectively and 40 kg ha-1for conventional planting. Raised bed nursery for SRI planting (Baskar, 2009), tray type nursery for SRI mechanical transplanting (Bell et al., 2003) and conventional nursery for conventional transplanting (CPG, 2005) were prepared. Other cultural practices and plant protection measures were followed as per recommendations of CPG, 2005. The herbicide was dissolved in 500 litres of water and sprayed with knapsack sprayer using deflector nozzle at 3 days after sowing. The pre emergence herbicide was sprayed 3 days after transplanting. The post emergence herbicide was sprayed 15 days after transplanting. Data on total 33 weed dry weight was recorded 60 days after transplanting using 0.25 m2 quadrate at four places at random and analysed after subjecting the original data to square root ( X + 2) transformation.

Results and Discussion
Weed flora Important weed species observed in the experimental field were Echinochloa colonum, Cyperus difformis, Eclipta alba, Marselia quadrifoliata and Ammania baccifera.

Total weed dry weight
Crop establishment methods exerted significant influence on the total weed dry weight recorded on 60 DAT. In SRI machine transplanting total weed dry weight was significantly lower, which was on par with SRI marker planting. Conventional transplanting recorded higher weed dry weight (Table 1). This

Table 1. Effect of establishment methods and weed management practices on total weed dry weight and grain yield in rice
Total dry weight (kg ha-1) Grain yield (kg ha-1)  Balasubramanian et al. (2003), who reported that occurrence of more number of weed species, higher density unit area-1 favoured better growing conditions turning the competition in favour of weeds, thus resulted in increased weed dry weight.
Among the vertical strips, considerable reduction in total weed dry weight was recorded with conoweeding four times at 10 days interval, which was on par with PE Pretilachlor followed by EPOE Bispyribac sodium. This might be attributed to the minimum number of total weeds with less biomass during the cropping period (Table 1). Conoweeding four times at 10 days interval recorded lesser weed dry weight due to the incorporation of weeds into soil due to frequent cono weeding. This finding is in line with the findings of Anitha and Chellappan (2011).
Crop establishment methods and weed management practices had significant interaction at all the stages of crop. SRI machine transplanting with conoweeding four times at 10 days interval significantly lowered the weed dry weight followed by PE Pretilachlor and EPOE Bispyribac sodium. This is in conformity with the findings of Uprety (2010), who revealed that machine planting with frequent conoweeding had encouraged frequent loosening of soil stimulating aerobic conditions with concomitant reduction in the density of weeds, dry matter. Also incorporation of weeds manure to served as the crop.

Grain yield
Crop establishment methods and weed management practices had significant influence on grain yield during both the years of experimentation (Table 1). The SRI machine transplanting (C3) produced distinctly higher grain yield than conventional transplanting (CT). However, it was comparable with SRI marker planting (C2) . This might be due to less crop weed competition, larger root system and crop canopy and higher microbial population, which might have facilitated the enhanced nutrient uptake, photosynthetic activity and remobilization of photosynthates to grain resulting in higher yield attributes and yield. This is in accordance with the findings of Hugar et al. (2009), who stated that SRI gave higher grain yield due to large root volume, strong tillers with improved yield attributes. Chandrapala et al. (2010) also reported increased grain yield with SRI, which was attributed to lesser competition, enhanced solar radiation interception, nutrients uptake and higher yield attributes.
Conoweeding four times at 10 days interval starting from 10 DAT (W1) recorded higher grain yield, which was on par with Pretilachlor followed by Bispyribac sodium + conoweeding on 40 DAT (W4) than unweeded control (W6). This finding is in accordance with the results of Thiyagarajan et al. (2002), who found that use of conoweeder resulted in increased yield of rice.
Crop establishment methods and weed management practices had significant interaction with each other at all the crop growth stages. The SRI machine transplanting with conoweeding four times at 10 days interval starting from 10 DAT (C3W1) registered higher grain yield than other combinations. This might be due to larger canopy with greater root development and activity, less intra plant competition, improved remobilization of assimilates to grain.
These results are in accordance with the findings of Mohaptra et al. (2012), who reported that machine planting with mechanical weeding had encouraged profuse tillering and influenced yield attributes such as number of panicle m-2 and number grains panicle-1. The least grain yield was recorded under conventional planting with unweeded check (C1W6).

Straw yield
Significant difference with respect to straw yield due to crop establishment methods and weed management practices was evident during both the years ( Table 2). The SRI machine transplanting (C3) resulted in significantly higher straw yield. However, comparable straw yield was observed with SRI marker planting (C2) with that of SRI machine transplanting (C3 )This was mainly due to more number of tillers and increased the dry matter production. This result is in corroboration with the findings of Revathi (2009), who also reported that higher straw yield in SRI due to higher tillers and DMP.
Conoweeding four times at 10 days interval starting from 10 DAT (W1 ) recorded higher straw yield over all other weed management practices during both the years. However, comparable straw yield was noticed with combined application of Pretilachlor (0.75kg a.i. ha-1 pre-emergence) + Bispyribac sodium (20g a.i. ha-1 early postemergence) + conoweeding at 40 DAT (W4) during both the years. Invariably, lesser straw yield was registered with unweeded control (W6) over all other weed management practices during both the years. Ramamoorthy (2004) and  reported that four times conoweeding had removed most of the weeds and incorporated them in to soil, responsible for loosening of top soil. This operation had further stimulated aerobic soil condition and provided weed free environment, which enhanced growth components resulting in increased straw yield.
Crop establishment methods and weed management practices had significant interaction with each other at all the stages of crop growth. SRI machine transplanting with conoweeding four times at 10 days interval starting from 10 DAT (C3W1) registered higher grain yield than other combinations. This might be due to larger canopy with greater root development and activity, less intra plant competition, improved remobilization of assimilates to grain. This is corroborated with the findings of Mohapatra et al.,(2012). The least grain yield was recorded under conventional planting with unweeded check (C1W6).

Economics
Crop establishment methods and weed management practices showed variations on cost of cultivation, income obtained and benefit: cost ratio ( Table 3). The SRI machine transplanting along with conoweeding four times at 10 days interval starting from 10 DAT (C3W1) incurred lesser cost of cultivation and registered higher net return due to lesser labour requirement for transplanting and weeding. This was followed by SRI machine transplanting along with Pretilachlor (0.75 kg a.i. ha-1 pre-emergence) + Bispyribac sodium (20 g a.i. ha-1 early postemergence) + conoweeding at 40 DAT (C3W4) and SRI machine transplanting along with Laundax power @ 10 kg a.i. ha-1 + cono weeding at 30 and 40 DAT (C3 W5). The B:C ratio was higher with SRI machine transplanting along with conoweeding four times at 10 days interval starting from 10 DAT (C3W1) during both the years because of lesser cost involved in transplanting and weeding. Similar results were reported by Mohanty and Barik (2010), who stated that benefit cost ratio of rice transplanter was higher when compared to conventional transplanting. Further Sajitha Rani and Jayakiran (2010) stated that the net return in SRI machine planting was higher with increased B: C ratio due to higher grain yield when compared to line transplanting. This was mainly because of low cost incurred in transplanting and less seed requirement reduced cost of nursery preparation and less labour cost for weed control.

Conclusion
From the present study, it could be concluded that SRI machine transplanting with conoweeding four times at 10 days interval starting from 10 DAT (C3W1) of rice will be a promising practice to increase the rice productivity and profitability. Under labour scarcity situation, machine planting with the application of Pretilachlor (0.75 kg a.i. ha-1 pre-emergence) + Bispyribac sodium (20 g a.i. ha-1 early post-emergence) + conoweeding at 40 DAT will be the best alternative option.