Study on Residue Management Options in Combine Harvested Rice Field in Relation to Yield and Economic Benefits of Succeeding Rice Crop

Every year, around 140 mt of paddy straw was burned in India, which causes sever air pollution (Prasanthkumar and Vallal kannan, 2018). Rice straw contains 0.5 to 0.8 per cent N, 0.16 to 0.27 per cent P, 1.4 to 2.0 per cent K, 0.05 to 0.10 per cent S and 4 to 7 per cent silica (Si) in its dry matter (Dobermann and Fairhurst, 2002). Though the nutrient availability of rice straw is well known at the same time rice straw have lower decomposition rate due to its higher C:N ratio (33) compared to cow dung and Dhaincha (Chowdhury et al., 2002). Under such condition, if planting is taken up immediately after incorporating the straw of preceding crop, the establishment of the succeeding rice crop may be hampered (Udayasoorian et al., 1997). To overcome these problems, combine harvester paddy straw is incorporated along with additional N source, Bio mineralizer, cow dung slurry and its combinations to know the effect on succeeding rice crop yield and economic benefits. Keeping the above factors in mind, the present study was undertaken with the objectives viz., to study the effect of paddy straw incorporation on yield and yield attributes of rice crop and find out the economics for various residue management options.

The field experiment was conducted at Agricultural College and Research Institute, Killikulam during Pishanam season of October 2014 - February 2015, to study the yield and economic benefits of rice crop under different rice residue management options. The farm is geographically situated in the southern part of Tamil Nadu at 8°46¢ N latitude and   77°42¢ E longitude at an altitude of 40 m above mean sea level. The soil of the experimental field is sandy clay loam in texture, neutral in reaction and low in available N and medium in available P and K contents (Table 1). The experiment was laid out in Randomized Block Design with nine treatments [T₁ - Incorporation of rice straw; T₂ - T₁ + 25 kg additional N ha^-1 as basal; T₃ - T₁ + Bio-mineralizer (2 kg t^-1 rice residue); T₄ - T₁ + Cow dung slurry (5%); T₅ - T₁ + 25kg additional N ha^-1 as basal + Bio-mineralizer (2 kg t^-1 rice residue); T₆ - T₁+ 25 kg additional N ha^-1 as basal + Cow dung slurry (5%); T₇ - T₁ + Bio-mineralizer (2 kg t^-1 rice residue) + Cow dung slurry (5%); T₈ - T₁ + 25 kg additional N ha^-1 as basal + Bio-mineralizer (2 kg t^-1 rice residue) + Cow dung slurry (5%); T₉ - Control (no residue)] and replicated thrice. Eight different rice straw residue management techniques were randomly allotted in the experiment along with one control plot for comparison. Rice variety ADT (R) 45 with the duration of 110 days was used as a test variety. After combine harvesting, the rice straw retained on the field was collected and quantified at 5 t ha^-1. The rice straw was uniformly distributed to all the plots [The gross plot size and net plot size is 45 m² (7.5 m × 6.0 m) and 38.5 m² (7.0 m × 5.5 m) respectively] except control. TNAU Bio mineralizer was made into slurry by mixing with water (for 2 kg of material 40 liters of water) and sprinkled on the straw of respective experimental plots at 2 kg t^-1 of rice residue on the next day of combine harvest of preceding rice crop i.e. 15 days ahead of transplanting. Cow dung slurry (5%) was prepared and sprinkled over the paddy straw in the corresponding treatment plots on the next day of combine harvest of preceding rice crop. After 15 days, every plot was individually puddled and levelled properly and rice transplanted with recommended dose of fertilizers. Apart from the treatment, all the cultural practices for lowland rice strictly followed as per TNAU crop production guide. The observations on yield attributes and yield were measured at the time of harvest. The harvest index was worked out using the formula (HI = Economic yield / Biological yield) suggested by Donald (1962). The cost of cultivation, gross return, net return and benefit cost ratio were computed for each treatment, considering the prevailing market rate for inputs, produce and wages paid to labourers at central farm, Agricultural College and Research Institute, Killikulam (Table 2).    





The computed data were subjected to statistical analysis as per the procedure given by Gomez and Gomez (1984).

Effect of residue management on yield attributes
 
The various residue management practices significantly influenced the productive tillers, number of grains per panicle, panicle length, number of filled grains per panicle and spikelet filled percentage of rice crop (Table 3). Incorporation of straw alone without additives (T1) registered reduced number of productive tillers (335), number of grains per panicle (129), panicle length (19.4 cm), number of filled grains per panicle (108) and spikelet filled percentage (72) of rice crop. This was due to the temporary immobilization of N (Nicolardot et al., 2001), it leads to poor growth and development and subsequently decreased number of productive tillers per m², total number of grains, filled grains and spikelet filled percentage, it might cause overall reduction in biological yield.


       
When additives are used with straw incorporation, yieldattributes were improved significantly. In overall, combinationof all additives further increased the number of productive tillers (409), number of grains per panicle (162), panicle length (23.8 cm), number of filled grains per panicle (132) and spikelet filled percentage (87) in T₈. It was due to the favourable soil environment caused by enhanced nutrient availability by microbial inoculants, which degrade the straw and release the nutrient gradually (Sangakara et al., 2014). Application of 25 kg additional N at basal balanced the N, which was immobilized by straw incorporation due to wide C:N ratio (Huang et al., 2008 and Mary et al., 1996). The C:N ratio was reduced by additives with straw and increased the nutrient availability and also increased photosynthetic accumulation and translocation of photosynthates and it might have caused increased crop growth and thus influenced the yield attributes (Balasubramanian, 1980). These results are in line with findings of Patnaik et  al. (1989) and Sharma and Bali (1998). Test (1000 grains) weight was not much influenced by residue management practices as the variation was non-significant between treatments.

Effect of residue management on yield
 
Grain and straw yield was significantly influenced by different residue management practices (Table 4). Among the different treatments, rice straw incorporated without additives (T₁) registered the lowest grain and straw yield of 5250 kg ha^-1 and 6020 kg ha^-1 respectively than other treatments. Direct incorporation of straw into soil is known to reduce the availability of nutrients to the growing plants by formation of organic complexes (Martin et al., 1978).



Incorporation of rice straw with different additives significantly increased the grain and straw yield than incorporation of straw alone (T₁). Among these, T₂ recorded higher grain and straw yield of 6615 kg ha^-1 and 7850 kg ha^-1. This was on par with T₄ and T₃, which recorded the grain yield of 6230 and 6015 kg ha^-1 respectively and straw yield of 7130 kg ha^-1 and 6870 kg ha^-1 respectively. Among the combined application of additives, T₆ recorded the higher grain and straw yield of 7160 kg ha^-1 and 8170 kg ha^-1. This was on par with the T₅ registered 6960 kg ha^-1 of grain yield and 7960 kg ha^-1 of straw yield. In overall, combined application of all additives significantly enhanced the grain and straw yield than all other treatments. The T₈ significantly registered the highest grain yield of 7395 kg ha^-1 and straw yield of 8440 kg ha^-1. The increase in yield with this treatment was 11.8 per cent over T₂ and 40.9 per cent over straw incorporation without additives. This was due to the integrated effect of bio-mineralizer and cow dung slurry on rapid straw decomposition (Joshi et al., 2013; TNAU portal, 2015; Fitriatin et al., 2014). At the same time, 25 kg additional N substitute the N needs of crop as it was immobilized by wide C:N ratio at initial stage of incorporation (Singh et al., 2005; Singh et al., 2009; Dhar et al., 2014). Also, combination of all additives with straw incorporation improves the soil physical, chemical and biological properties (Arshadullah et al., 2012), it leads to better availability of nutrients to crop plant and subsequently more number of productive tillers, number of filled grains per panicle results in highest grain yield, straw yield and harvest index. Similar findings also reported by Singh et al., (2002) in lentil crop. These results are in line with the findings of Jayadeva et al. (2010) and Polthanee et al. (2011). The control (T₉ - no residue) significantly registered lesser grain yield of 5370 kg ha^-1 and straw yield of 6140 kg ha^-1. The value of harvest index did not vary much due to the influence of residue management practices.
 
Effect of residue management on economics
 
The maximum gross return of `1,13,646 ha<sup>-1</sup> and `1,10,670 ha^-1  were obtained in T₈ and T₆. The lowest gross return of  81900 ha^-1 was obtained in T₁. Among various residue management practices, T₈ recorded the highest net return of  69,079 ha^-1. Next to this T₆, registered the net return of   66,603 ha^-1 and were on a par with each other. The higher yield realized under the above treatments would be the reason for more economic return as against the cost of cultivation with higher net gain and B:C ratio. These results are conformity with the findings of Vijayakumar (1997), Hemalatha (2001) and Sridhar (2003).

From the experiment result and discussion, it could be enlightened that application of 25 kg additional N ha^-1 as basal, bio-mineralizer (2 kg t^-1 of rice residue) and cow dung slurry (5%) could be considered as a better option for achieving higher productivity and profitability in combine harvested rice field.