Effect of Lime, Humic Acid and Moisture Regime on the Availability of Zinc in Alfisol

Research Article TheScientificWorldJOURNAL, (2007) 7, 1198–1206 ISSN 1537-744X; DOI 10.1100/tsw.2007.192 Effect of Lime, Humic Acid and Moisture Regime on the Availability of Zinc in Alfisol Sushanta Kumar Naik1* and Dilip Kumar Das2 1 National Research Centre for Orchids, Pakyong-737106, Sikkim, India; 2Department of Agricultural Chemistry and Soil Science, Faculty of Agriculture, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia-741252, West Bengal, India E-mail: Received March 6, 2007; Revised July 4, 2007; Accepted July 6, 2007; Published August 17, 2007 Lime and humic acid application can play an important role in the availability of zinc in paddy soils. We conducted laboratory incubation experiments on a rice growing soil (Alfisol) to determine the effect of lime, humic acid and different moisture regimes on the availability of Zn. Addition of half doses of liming material (powdered lime stone) recorded highest values of DTPA-Zn followed by no lime and 100% of lime requirement throughout the incubation period. With the progress of incubation, DTPA-Zn increased slightly during the first week and then decreased thereafter. The highest DTPAextractable Zn content of 2.85 mg/kg was found in the treatment Zn10 L1/2 at 7 days of incubation, showing 17.3 % increase in DTPA-Zn content over its corresponding treatment of Zn alone (Zn10L0). The DTPA-Zn concentration increased with the application of humic acid compared with no humic acid throughout 35 days of the incubation period and the peak value obtained was 3.12 mg/kg in the treatment Zn10 HA2 at 14 days after incubation, showing 50 % increase in Zn content over its corresponding treatment of Zn alone (Zn10HA0). The application of 0.2% humic acid compared with 0.1% resulted in greater increase in DTPA-Zn concentration in soil application. During the 35 days of incubation, highest values of DTPA-Zn were recorded in soil maintained at saturated compared to water logged conditions. However, under alternate wetting and drying condition the DTPA-Zn content gradually decreased up to 21 days and thereafter increased slowly. KEY WORDS: Alfisol, Humic acid, Lime, Moisture regime, Zinc availability INTRODUCTION Zinc (Zn) undergoes transformation in soils by various mechanisms i.e. sorption by clays, hydrous oxides, organic matter etc., which affect its availability of Zn in soils. Desorption of Zn into soil solution is controlled by the energy with which it is adsorbed onto the soil colloidal surfaces. This in turn depends on the soil characteristics particularly pH, cation exchange capacity (CEC), the nature and content of the clay, oxides of Fe, Al and Mn, and CaCO3[1]. The problem of Zn deficiency in flooded rice soils was believed to be associated with high pH or high amounts of CaCO3 and partly due to the intense reduction of soil causing increased concentration of ferrous iron (Fe2+) and manganous manganese (Mn2+) in soil[2]. *Corresponding author. ©2007 with author. Published by TheScientificWorld: www.thescientificworld.com 1198 Naik and Das: Zinc transformation in alfisol TheScientificWorldJOURNAL (2007) 7, 1198-1206 When soils are submerged the concentrations of most nutrient elements in the soils increases, but this is not true for Zn. In acid soils Zn availability decreases after flooding owing to an increase in pH and the precipitation of Zn(OH)2. However, if an alkali soil is submerged, the pH of the soil will decrease and as a result the solubility of Zn will increase. The availability of Zn has been found to be decreased with an increase in the amount of lime to the soil. Zn has also been found to be adsorbed less strongly on calcite (CaCO3) than magnesite and dolomite. Alfisol was characterized by grey to brown surface horizon, medium to high base supply, and subsurface horizons of clay accumulation, usually moist but may be dry during warm season. An Alfisol may also have fragipan, duripan, natric horizon, petrocalcic horizon, and plinthite. Some of the red and lateritic soils of India have been classified as Alfisol. Soil organic matter mainly consists of humic and fulvic acids are called humin materials[3,4]. It was reported that humic acid affects chemical properties of soils due to carboxyl (-COOH) and phenolic (OH) groups[5,6,7]. The release and uptake of the Zn2+, being the important micronutrient element in soil, is often regulated by the humic or fulvic substances present in the soil. Zn forms stable complexes with soil organic matter, where humic acid and fulvic acid fractions play an important role in the adsorption processes. Randhawa and Broadbent[8] found that three or more types of sites were involved in the retention of Zn by humic acids. The least stable fraction, which accounted for most of the adsorbed Zn, was believed to be associated with phenolic OH and COOH groups having pKa values between 2.8 and 4.4. The more stable fraction was assigned to strongly acidic COOH groups with lower pKa values (< 2.0). Although the strongly bound Zn represented less than 1% of the total retained, the sites responsible were believed to be of great importance because small quantities of Zn would be adsorbed preferentially in the most stable forms. Mandal et al.[9] observed that desorption of Zn in Alfisols was higher under alternate wetting and drying (67.1%) followed by flooded-dried (61.4%) and preflooding (47.3%) moisture regimes. The variation in Zn-desorption among soils and moisture treatments is the changes in soil pH, Fe-oxides, bonding energy constants, and free energies for Zn adsorption. Variation in the soil’s physico-chemical properties are largely controlled by different soil moisture regimes as soil moisture regimes control the restricted entry of atmospheric oxygen or escaping tendency of oxygen from soils to the atmosphere. Therefore, different soil moisture regimes bring about varying changes in soil physico-chemical and electrochemical properties such as pH, Eh, electrical conductivity, CaCO3 content, and amorphous and crystalline oxides of Fe and Mn, which are further accentuated by application of starch or manures[9]. Since problem of Zn deficiency persists in the soil under different moisture regime conditions and the requirement of Zn to the growing plant is essential for balanced nutrition. Therefore, an attempt has been made to study the effect of lime, humic acid, and moisture regime on the availability of Zn. EXPERIMENTAL METHODS The soil sample was collected from the farmer’s paddy field at Jhargram (Alfisol) in the West Midnapur district of West Bengal state, India during the year 2005. These were air dried, powdered and sieved through an 80 mesh sieve and analyzed for its different chemical properties following the standard methods of Jackson[10] and Black et al.[11]. The chemical properties of the experimental soil were: pH 5.6, EC 0.07 dS/m, CEC 16.21 cmol (p+)/kg, Organic carbon 2.9 g/kg, DTPA extractable Zn 1.58 mg/kg, with 60% sand, 17% silt, and 23% clay (l (...truncated)