VERTICAL DISTRIBUTION OF DTPA-EXTRACTABLE MICRONUTRIENTS IN SOILS OF CUMBUM VALLEY, TAMIL NADU

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1 Agric. Sci. Digest., 30 (2) : 79-84, 2010 AGRICULTURAL RESEARCH COMMUNICATION CENTRE / indianjournals.com VERTICAL DISTRIBUTION OF DTPA-EXTRACTABLE MICRONUTRIENTS IN SOILS OF CUMBUM VALLEY, TAMIL NADU T. Alagu Nagendran* and A. Angayarkanni Department of Soil Science, Faculty of Agriculture, Annamalai University, Annamalainagar , India ABSTRACT Fifty six soil samples from sixteen pedons in two transects representing various physiographic positions along a double toposequence of Cumbum valley of Tamil Nadu were studied for vertical distribution of DTPA extractable iron, manganese, zinc and copper and their relationship with some soil properties. Soil reaction (ph), free calcium carbonate, organic carbon and particle size fractions had strong influence on the distribution pattern of these micronutrients in the profile. The content of micronutrients increased with the increase in organic carbon and decreased with increase in ph and free CaCO 3. In general, all these micronutrients decreased with increase in depth but they had no definite correlation with topography. As per the critical limit suggested for Tamil Nadu soils, Iron and Manganese were found to be sufficient in most soils except calcareous and recent alluvial soils. Zinc and copper were deficient uniformly in all soils. Site- specific residual copper accumulation was also found. Key words: DTPA extractable cations, Toposequence, Red and alluvial soils, Critical limit INTRODUCTION Now- a- days, the productivity decline is becoming a common phenomenon that can be widely attributed to the soil micronutrients deficiency due to intensive agriculture and indiscriminate and imbalanced fertilizer use by the farmers. In order to advocate more scientific and site-specific nutrient management strategies to farmers, an understanding of the vertical distribution of micronutrient cations in the soils is essential. Studies were conducted by many re-searchers (Singh et al., 1999; Sharma and Gupta, 2001) to understand the content and distribution pattern of the micronutrient cations in different soils under different agro-climatic conditions and their relationship with soil physical and chemical properties. However, the available information in this regard for soils of Cumbum valley of Tamil Nadu is scanty and therefore, an attempt has been made to assess the available micronutrient status in these soils along a toposequence and to study their relationship with some important soil properties. * angai66@yahoo.co.in MATERIAL AND METHODS The study area occupies the South western portion of the VIII agro ecological region mainly located in the Eastern Ghats(Tamil Nadu uplands) and lies between " and " N latitude and " to " E longitude with an elevation ranging from 301 to 546 m above MSL. The geology of the area mainly includes two prime rock types of Charnockites and Khondalites of Archaean age. The study area is characterized by an undulating plain and the slope ranges from 1 to 3 per cent in the lower physiographic positions and 3 to 8 per cent in the higher physiographic positions. The climate is semi-arid (dry half) with an an-nual rainfall of around 740 mm. The moisture regime in the study area is ustic and soil temperature regime is iso-hyperthermic. The crops grown in the study area are rice, sorghum, maize, cotton, legumes, vegetables, coconut and grapes. As the study area of Cumbum valley resembles a boat, and lies between the Western Ghats and Varushanadu (Megamalai) hill ranges, two distinct transects (T1 and T2) were chosen with

2 80 AGRICULTURAL SCIENCE DIGEST both of their left ends starting from the foothills of Western Ghats and their right ends starting from the foothills of Varushanadu (Megamalai) hills meeting in the alluvial fan position. Four pedons in each of left (LP) and right (RP) hands of transect representing the major physiographic units viz., foot hill, middle terrace, lower terrace and alluvial fan were dug up and studied. Horizon wise soil samples were col-lected from the studied pedons and analyzed for ph, OC, free CaCO 3 and par-ticle-size distribution following standard procedures. The available micronutrient cat-ions were extracted with DTPA-TEA extractant (ph 7.3) and determined with an Atomic Absorption Spectrophotometer- ECIL4129 (Lindsay and Norvell, 1978). Simple correlations were done statistically between DTPAextractable micronutrient cations and selected soil properties. RESULTS AND DISCUSSION In general, the soils were slightly acidic to neutral except T1LP 2 and T2LP2 soils which showed slight to moderate alkalinity and observed ph ranging from 6.32 to Organic carbon content was low (0.15 to 0.69 %) and de-creased with depth in pedons of all soils except in T1LP4, T1RP4, T2LP4 and T2RP4 soils having an irregular trend. The soils were mostly non-calcareous except T1LP1 and T2LP2 soils in which moderate to strong calcareousness was found and free CaCO 3 content varied from 0.03 to 3.18 per cent in these soils (Table 1). The surface texture of the soils ranged from sandy loam to clay loam and the sub-surface texture of the soils from loamy sand to clay with clay content ranging from 12.4 to 48.2 per cent. The clay plus silt content ranged from 19.8 to 69.1 per cent. The clay and clay plus silt content increased with depth in pedons showing the migration of finer particles in the pedons of all soils except in T1LP4, T1RP4, T2LP4 and T2RP4 soils having an irregular trend revealing their recentness and stratified nature. The availability of all four micronutrients decreased with depth in pedons uniformly except in T1LP4, T1RP4, T2LP4 and T2RP4 soils having an irregular trend. The distribution pattern of these micronutrient cations in the pedons clearly indicated their close association with the organic carbon content (Table 1). The distribution pattern showed an opposite trend to that of clay, clay plus silt, ph and free CaCO 3 content. The relatively high availability of these cations in surface horizons might also be due to regular addition of organic manure, plant residues and chemical fertilizers (Satyavathi and Suryanarayan Reddy, 2004). The DTPA extractable Fe content in the pedons of these soils varied between 1.0 and 16.8 mg kg -1. Considering the critical limit of 3.7 mg kg -1 for Fe in non-calcareous and 6.3 mg kg -1 for calcareous soils (Muhr et al., 1965), all the soils were sufficient in available Fe content except T1LP2, T2LP2, T1LP4, T1RP4, T2LP4 and T2RP4 soils which were deficient. The deficient status of Fe in these soils might be mainly due to the relatively higher ph and free CaCO 3 (Yelvikar et al., 1996) in the former two soils and relatively coarse textured nature of solum and free internal drainage leading to excessive leaching of these cations in case of latter four alluvial soils (Alagunagendran,1997). The available Fe content was significantly and negatively correlated with ph (r = -0.53**) and free CaCO 3 (r = -0.32*).The organic carbon had no significant influence over available Fe content. The DTPA extractable Mn content in the soils of the study area ranged between 0.88 and 13.2 mg kg -1 in different horizons. As per the criti-cal limit of 2.0 mg kg -1 suggested (Muhr et al., 1965), the available Mn status was uniformly above the critical level in all the soils except T1LP2, T2LP2, T1LP4, T1RP4, T2LP4 and T2RP4 soils which were deficient. The vertical distribution of available Mn in the pedons of all soils closely resembles that of available Fe profile which might be due to due to similar reasons discussed under Fe. Similar interpretations were made earlier by Mehra and Baser (1989). The available Mn content was significantly and negatively correlated with ph (r = -0.58**) and free CaCO 3 (r = -0.35*). The DTPA extractable Zn content in the pedons of these soils varied between 0.13 and 0.90 mg kg -1. Considering the critical limit of 1.2 mg kg -1 for Zn (Muhr et al., 1965), all the soils were uniformly deficient in subsoil layers also. The decreasing Zn content with increase in depth in pedons might be due to the quick fixation of Zn in organo-clay complex in the surface horizons and the slow vertical mobility of this cation down the profile. Similar interpretations were made by Katyal and Sharma

3 Vol. 30, No. 2, Table 1 : Some physical and chemical properties and DTPA extractable micronutrient cations in Cumbum valley soils Profile Location Horizon Depth TextureParticle distribution % ph(1:2) CaCO 3 O.C DTPA extractable cations (mg kg -1 ) size soil: (%) (%) (m) (USDA) Clay Silt Sand water Fe Mn Zn Cu Transect-I. LP1 : Loamy, mixed, iso-hyperthermic Typic Haplustepts (Foot hill) 9 o 51 41"N Lat. Ap sl o 17 16"E Long. Bw scl m above MSL Transect-I. LP2 : Fine, mixed, calcareous, iso-hyperthermic Typic Haplustalfs (Middle terrace) 9 o 54 31"N Lat. Ap scl o 19 59"E Long. Btk cl m above MSL Btk sc Btk sc Transect-I. LP3 : Fine, mixed, iso-hyperthermic Typic Rhodustalfs (Lower terrace) 9 o 57 04"N Lat. Ap scl o 25 23"E Long. Btc cl m above MSL Btc (g)c Transect-I. LP4 : Coarse loamy, mixed, iso-hyperthermic Typic Ustifluvents (Alluvial fan) 9 o 57 47"N Lat. Ap cl o 26 50"E Long. C sl m above MSL C scl C ls Transect-I. RP1 : Fine, mixed, iso-hyperthermic Typic Rhodustalfs (Foot hill) 9 o 46 00"N Lat. Ap scl o 23 51"E Long. Bt sc m above MSL Bt cl Bt cl Contd...

4 82 AGRICULTURAL SCIENCE DIGEST Transect I. RP2 : Fine loamy, mixed, iso-hyperthermic, Typic Haplustalfs (Middle terrace) 9 o 52 00"N Lat. Ap sl o 25 33"E Long. Bt scl m above MSL Bt cl Bt cl Transect I. RP3 : Fine, mixed, iso-hyper thermic, Typic Rhodustalfs (Lower terrace) 9 o 56 00"N Lat. Ap scl o 26 10"E Long. Btc cl m above MSL Btc (g)c Transect I. RP4 : Coarse loamy, mixed, iso-hyperthermic, Typic Ustifluvents (Alluvial fan) 9 o 56 45"N Lat. Ap cl o 26 48"E Long. C sl m above MSL C scl C ls Transect II. LP1 : Fine loamy, mixed, iso-hyperthermic Typic Haplustalfs ( Foot hill) 9 o 44 43"N Lat. Ap sl o 14 31"E Long. Btk scl m above MSL Btk cl Btk sc Transect II. LP2: Fine, mixed, calcareous, iso-hyperthermic Typic Haplustalfs (Middle terrace) 9 o 46 56"N Lat. Ap scl o 19 13"E Long. Btk cl m above MSL Btk sc Btk c Transect-II. LP3 : Fine, mixed, iso-hyperthermic Typic Rhodustalfs (Lower terrace) 9 o 48 04"N Lat. Ap scl o 19 46"E Long. Btc cl m above MSL Btc (g) sc Contd...

5 Vol. 30, No. 2, Transect-II. LP4 : Coarse loamy, mixed, iso-hyperthermic Typic Ustifluvents (Alluvial fan) 9 o 51 06"N Lat. Ap scl o 21 48"E Long. C sl m above MSL C cl C sl Transect-II. RP1 : Coarse loamy, mixed, iso-hyperthermic Typic Haplustepts (Foot hill) 9 o 43 46"N Lat. Ap sl o 20 06"E Long. Bw scl m above MSL Transect-II. RP2: Fine, mixed, iso-hyperthermic Typic Rhodustalfs (Middle terrace) 9 o 46 27"N Lat. Ap scl o 20 20"E Long. Bt cl m above MSL Bt cl Bt sc Transect-II. RP3 : Fine, mixed, iso-hyperthermic Typic Rhodustalfs (Lower terrace) 9 o 49 56"N Lat. Ap scl o 22 36"E Long. Btc cl m above MSL Btc (g) sc Transect II. RP4 : Fine loamy, mixed, iso-hyperthermic Typic Ustifluvents (Alluvial fan) 9 o 50 28"N Lat. Ap scl o 22 52"E Long. C sl m above MSL C cl C sl

6 84 AGRICULTURAL SCIENCE DIGEST (1991). In all the soils, the available Zn content had a significant and positive correlation with organic carbon(r = 0.70**) and a significant negative correlation with ph (r = -0.41**) and free CaCO 3 (r = -0.38**). The DTPA extractable Cu content in the pedons ranged from 0.14 to 1.32 mg kg -1 and decreased with depth in all pedons. Considering 1.2 mg kg -1 as critical limit for Cu (Muhr et al., 1965), the soils were rated deficient in avail-able Cu except in T2RP1 soil having adequate Cu content(1.32 mg kg -1 ) in the surface horizon. The intensive grapes cultivation being practiced in these soils with indiscriminate use of Cu containing fungicides coupled with heavy manure application might have led to the residual accumulation of this cation in soil. Soil reaction (ph) and free CaCO 3 content showed a significant negative correlation (r = **and -0.33* respectively) with Cu but soil organic carbon (r = 0.44**) had a significant and positive cor-relation. These results are in agreement with the observations of Dhane and Shukla (1995) and Chattopadhyay et al. (1996). CONCLUSIONS The study revealed that the DTPA available micronutrient cations viz., Fe, Mn, Zn and Cu in general decrease with depth in pedons of all soils. They had no specific relationship with topography and their distribution is mainly influenced by soil texture, ph and free CaCO 3 content. Iron and Manganese content was sufficient in all soils except in calcareous and young alluvial soils. Zinc and copper content was mostly deficient in all soils necessitating the site-specific application of micronutrients for sustainable yields. The content of micronutrients increased with increase in organic carbon and decreased with increase in ph and free CaCO 3 content. Hence, micronutrient management is very essential in calcareous and alkaline soils of Cumbum valley. REFERENCES Alagunagendran, T. (1997). M.Sc Ag. Thesis Tamil Nadu Agricultural University, Coimbatore.India Chattopadhyay,T., et al. (1996). J.Indian Soc. Soil Sci., 44: Dhane, S.S. and Shukla, L.M. (1995). J.Indian Soc. Soil Sci., 43: Katyal, J.C. and Sharma, B.D. (1991). Geoderma. 49: Lindsay,W.L. and Norvell, W.A. (1978). Soil Sci. Soc. Amer. J., 42: Mehra, R.K. and Baser, B.L. (1989). Ann Arid Zone. 28 : Muhr, G.R. et al., (1965). Soil Testing in India. United States Agency for International Development mission to India, New Delhi Satyavathi, P.L.A. and Reddy, M. (2004). Agropedology. 14(1): Sharma, Y.M. and Gupta, G.P. (2001). Ann. Agric.Res. 22: Singh, A.K., Khan, S.K. and Nongkynrih, P. (1999). J.Indian So-c. Soil Sci., 47(2): Yelvikar, N.S., (1996). J.Indian Soc. Soil Sci., 44: