Department of Agronomy, Agricultural College and Research Institute, Madurai , India. Received : Accepted : ABSTRACT

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1 Indian J. Agric. Res., 4 (2) : 11-1, 211 AGRICULTURAL RESEARCH COMMUNICATION CENTRE ccjournals.com / indianjournals.com nals.com RHIZOSPHERE ENZYME ACTIVITIES AS INFLUENCED BY AGE OF SEEDLINGS, WEED MANAGEMENT PRACTICES AND HUMIC ACID APPLICATION UNDER SYSTEM OF RICE INTENSIFICATION TION M.P. Kavitha, V.. Ganesaraja, V.K..K. Paulpandi and R. Bala Subramanian Department of Agronomy, Agricultural College and Research Institute, Madurai 62 14, India. Received : Accepted : ABSTRACT Field experiments were conducted during two consecutive kharif seasons of the years 26 and 27, to study the rhizosphere activities under System of Rice Intensification. The results revealed that increased activities were noticed by transplanting 14 days old seedlings with pre emergence application of pretilachlor at the rate of.7 kg a.i. ha -1 + one mechanical weeding at 3 DAT T and combined application of humic acid as seedling dip (.3 per cent humic acid) + foliar spray (.1 per cent humic acid) twice at 3 and 4 DAT. Key words : Seedling age, Weed management, Humic acid, Enzyme activities. INTRODUCTION Rice is a staple food crop of India, providing 43 per cent of calorie requirement for more than 7 per cent of India s population. The area of rice grown in India (44 million ha) is the largest among all the rice growing countries with an annual production of around 89 million tonnes. The productivity of rice is low in India (3, kg ha -1 ) when compared to the world average of 4,4 kg ha -1 and leading rice growing countries like china (6,289 kg ha -1 ) (FAO, 26). The SRI has its own methodologies viz., transplanting of young seedlings usually 12 to 14 days old and not more than 1 days old, transplanting single seedling per hill at wider spacing in a square geometry which facilitates uniform spacing and use of mechanical weeder, permitting greater root growth, better tillering and provides other favourable conditions for better growth especially soil aeration. (Kumar and Shivay, 24).The biological transformation process in soil is carried out through a variety of biochemical reactions. These reactions are catalyzed by a group of s known as Soil Enzymes, and the soil activity is considered as an index of microbial activity in soil. Humic acid soils promote the enzymatic activities through linkage of soil humic materials either by ionic, hydrogen or covalent bonding (Tate, 199). Soil organic matter greatly affects the biology of the soil because it provides the food for the heterotrophic soil microorganisms. In system of rice intensification, mechanical weeding is done mainly for root pruning and soil aeration which may help in root proliferation. Since mechanical weeding is limited to some extent, humic acid is introduced to induce root and shoot activities and substitute the root pruning effect through mechanical weeding. Application of humic substances enhanced the soil microbial population. Deepa (21) found that application of humic acid as soil, root dipping and foliar spraying recorded increased activity of soil s viz., amylase, catalase and dehydrogenase. Transplanting of too young seedlings, root dipping of seedlings in humic per cent and root pruning by rotary weeder may definitely play a role in increasing the soil biological properties and soil activities.

2 12 INDIAN JOURNAL OF AGRICULTURAL RESEARCH MATERIALS AND METHODS A field experiment was carried out at Agricultural College and Research Institute, Madurai, during kharif seasons of 26 and 27. The experimental soil was sandy clay loam with ph of 7., which was medium in organic carbon (.3 %), low in available nitrogen (246.4 kg/ha), medium in phosphorus (19.4 kg/ha) and medium in potassium (2. kg/ha). The experiments were laid out in split plot design with three replications. The main plot consisted of age of seedlings and weed management practices. Three age of seedlings viz., 14 (A 1 ), 18 (A 2 ) and 22 (A 3 ) days old seedlings were evaluated with four levels of weed management practices viz., mechanical weeding three times at 1, 3 and 4 DAT (W 1 ), pre emergence application of kg a.i. ha -1 + one mechanical weeding at 3 DAT (W 2 ), pre emergence application of kg a.i. ha -1 + post emergence application of 2,4-D Na 1. kg a.i. ha -1 (W 3 ) and unweeded check (W 4 ). Three levels of humic acid application viz., seedling dip (.3 per cent humic acid) (T 1 ), foliar spray (.1 per cent humic acid) twice at 3 and 4 DAT (T 2 ) and seedling dip (.3 per cent humic acid) + foliar spray (.1 per cent humic acid) twice at 3 and 4 DAT (T 3 ) were assigned to sub plot. Outside the experimental area absolute control was maintained by transplanting conventional seedlings (2 days old seedlings) with integrated weed management practices and no humic acid application. Short duration rice cultivar ADT 4 was grown during kharif (June September) season of the years 26 and 27. Fourteen, eighteen and twenty two days old seedlings derived from modified dapog mat nursery were used for transplanting in main plots. Hand operated mechanical weeder (Rotary weeder) developed by Department of Agricultural Engineering, Tamil Nadu Table 1 : Effect of age of seedlings, weed management practices and humic acid application on biological properties of paddy rhizosphere soil at flowering stage. (Pooled data of two years). Enzyme activities Amylase(μg of Catalase(mg of KMnO 4 Dehydrogenase glucose released g h -1 ) oxidised g -1 2 min -1 ) (μg of TPF formed g h -1 ) Age of seedlings A 1 14 DAS A 2 18 DAS A 3 22 DAS CD (P=.) Weed management practices W 1 MW (thrice) W 2 Pre. + MW (once) W 3 Pre. + 2,4-D Na salt W 4 unweeded check CD (P=.) Humic acid application T 1 SD T 2 FS T 3 SD + FS CD (P=.) Absolute control

3 Agricultural University, Coimbatore, Tamil Nadu was used for mechanical weeding. Mechanical weeding was done as per treatment schedule. Application of herbicides viz., kg ha -1 as pre-emergence on third day after transplanting and 2, 4- D Na kg ha -1 as post emergence on 2 th day after transplanting were made. The roots of rice seedlings were dipped in.3 per cent humic acid solution for one hour and then transplanted. Nitrogen was applied as urea based on LCC schedule. The LCC values were recorded as per the standard procedure (IRRI, 1996) at weekly intervals starting from 14 DAT to flowering. Whenever LCC values were found to be below the fixed critical level (No. 4), 3 kg ha -1 was applied. The entire dose of phosphorus (38 kg ha -1 ) as single super phosphate (16 per cent P 2 O ) was applied as basal before transplanting. Recommended dose of potassium (38 kg ha -1 ) in the form of muriate of potash (6 per cent K 2 O) was Vol. 4, No. 2, applied in four splits viz., 2 per cent each at active tillering, panicle initiation, booting and flowering stages. Zinc 2 kg ha -1 was applied as basal to crop during both the seasons. The activities viz., amylase, catalase and dehydrogenase were analysed based on the standard procedures given by Kelley and Rodriguez (197), Johnson and Temple (1964) and Casida et al. (196) respectively. As the trend of data was similar in both years, pooled data are presented. RESULTS TS AND DISCUSSION Fourteen days old seedlings (A1) resulted in increased soil activities viz., amylase, catalase and dehydrogenase by 18 days old seedlings (A 2 ). This might be due to increased microbial population in the soil (Table 1) (Fig.1). The higher root volume and root biomass in 14 days old seedlings provided a better environment to the soil microorganisms. Increased aeration and Table 2 : Effect of age of seedlings, weed management practices and humic acid application on yield attributes and yield of rice (Pooled data of two years). Yield attributes and yield Panicle length Productive Total grains Grain yield Straw yield (cm) tillers m -2 panicle -1 (kg ha -1 ) (kg ha -1 ) Age of seedlings A 1 14 DAS A 2 18 DAS A 3 22 DAS CD (P=.) Weed management practices W 1 MW (thrice) W 2 Pre. + MW (once) W 3 Pre. + 2,4-D Na salt W 4 unweeded check CD (P=.) Humic acid application T 1 SD T 2 FS T 3 SD + FS CD (P=.) Absolute control

4 14 INDIAN JOURNAL OF AGRICULTURAL RESEARCH alternate wetting and drying increased the microbial number in the soil (Bloem et al., 1992). Increased activities inturn increased the yield attributes and yield.(table 2) During initial tillering stage, the mechanical weeding three times at 1, 3 and 4 DAT(W1) resulted in increased soil activities viz., amylase, catalase and dehydrogenase. But during later stages, soil activities were maximum with pre emergence application of kg a.i. ha -1 + one mechanical weeding at 3 DAT (W2) followed by mechanical weeding three times at 1, 3 and 4 DAT (Table 1) (Fig.1). and resulted in increased yield attributes and yield (Table 2). The mechanical weeding by rotary weeder facilitated soil aeration and increased the soil microbial population and there by soil activities. Generally application of herbicide disturbed and altered the biological equilibrium in soil. This was supported by Grossbard (198) who reported that the components present in the herbicide are unfavourable for the microbial growth and multiplication. Hence, at 2 DAT pre emergence application of kg a.i. ha -1 + one mechanical weeding at 3 DAT (W2) resulted in lower soil microbial population and soil activities. But at later stages, this treatment recorded higher number of microbial population and increased activity as one mechanical weeding done at 3 DAT, increased the soil aeration thereby increased microorganisms and activities. Minimum activity was observed with unweeded check (W 4 ) at all growth stages. In the present study, seedling dip (.3 per cent humic acid) + foliar spray (.1 per cent humic acid) twice at 3 and 4 DAT (T3) resulted in increased amylase activity. This result is in line with the findings of Deepa (21) who reported that the reducing sugar content increased with high levels of humic acid in paddy. The above said treatment Initial tillering stage Panicle initiation stage Flowering stage Harvest stage Amylase Catalase Dehydrogenase Bacteria Fungi Actinomycetes Fig. 1 : activities and microbial population.

5 Vol. 4, No. 2, resulted in increased dehydrogenase activity due to increase in concentration of organic carbon. The humic acid used in present investigation had a moderate organic carbon (26. per cent) which might have increased the dehydrogenase activity. The catalase activity was maximum with seedling dip (.3 per cent humic acid) + foliar spray (.1 per cent humic acid) twice at 3 and 4 DAT. The soil studies revealed that amylase, catalase and dehydrogenase activities were maximum due to the greater use efficiency of nitrogenous fertilizers with humus as reported by Anuratha (1994). Humic acid provides nutrition required for the microbes and hence they establish in the rhizosphere and increase in population favouring the growth and yield of paddy (Table 2) REFERENCES Anuratha, A. (1994) M.Sc.(Ag.) Thesis Tamil Nadu Agricultural University, Coimbatore, India. Bloem, C., D.E. et.al., (1992). Soil biol. Biochem., 24: Casida, L.E., et.al., (196). Soil.Sci., 98: Deepa, M. (21). M.Sc(Ag.) Thesis Tamil Nadu Agricultural University, Coimbatore, India. FAO. (26). Online databases. In: Grossbard. (198). Effects of glyphosate on the with reference to the decomposition of treated vegetation and interaction with some plant pathogens. (Audus J.J.(ed) Academic Press, London.p.181. Inst., P.O Box. 933, Manila 199, Philipines. IRRI. (1996). Use of Leaf Colour Chart (LCC) for N Management in Rice. Int. Rice Res. Inst., P.O Box. 933, Manila 199, Philippines. Johnson, J.L. and Temple. K.L. (1964). Soil Sci. Soc. Am. Proc., 28: Kelley, W.D. and Rodriguez. R. (197). Can. J. Microbiol., 21: 6-7 Kumar, D. and Shivay. V.S. (24). Indian Farming, 4 (8): Tate, RL. (199). In: Soil Microbilogy. John Wiley and Sons, Inc., New York. Pp.239.