Nutrient dynamics and transformation in aerobic and flooded systems of rice in lateritic soils of kerala
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Date
2015
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Department of soil science and agricultural chemistry, College of Horticulture, Vellanikkara
Abstract
Field experiments on aerobic and flooded systems of rice were conducted in second crop season with the objectives to study the nutrient dynamics and transformations in these systems in second crop season with rice (variety Jyothi), in farmer’s field, at Nellikkattiri, Thirumittakode panchayat, Palakkad district. The treatments with two doses of fertilizers (as per Package of Practices Recommendations, KAU and based on soil test) and three doses of lime (as per POP, as per ΔpH and as per SMP buffer method) were imposed in plots of 20m2 area in Randomized Block Design with four replications. Under flooded condition, two field experiments were conducted to standardize the method of sampling and analysis for soil test based application of lime and fertilizers. One was based on sampling and soil testing on wet basis keeping the anaerobic environment unchanged, while the other was based on routine sampling and analysis after air drying. Better correlations with respect to available nutrients and plant nutrient content were obtained for wet analysis based recommendation and hence the data from this experiment were considered for comparison of the nutrient dynamics with that of the experiment on aerobic rice. In situ measurement of pH, electrical conductivity and redox potential was done under both systems of rice cultivation. Redox potential was measured from three different depths under flooded system (15, 30 and 45 cm) and from two different depths under aerobic system (30 and 45 cm). The soil and plant samples were collected at three stages viz. at active tillering, panicle initiation and at harvest of the crop. The soil samples collected were analysed for pH, EC, OC available nutrients (P, K, Ca, Mg, S, Fe, Cu, Mn Zn and B), and were also assayed to estimate fractions of soil phosphorus, iron, zinc and boron. The plant samples were analysed for N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu and B. At harvest straw and grain samples were analysed separately. The increase in pH in both systems was in proportion to the quantity of lime applied. Higher rate of increase in pH was observed under aerobic system. Increase in EC was in proportion to the quantity of lime and fertilizers added, and it was more in aerobic system due to less dilution. The redox potential became negative due to reduced environment in flooded system within two weeks of transplanting while it was consistently positive under aerobic system. The organic carbon content was higher under aerobic environment at active tillering and panicle initiation due to quicker decomposition of applied organic matter especially in presence of lime while it was lower under flooded condition initially due to slower rate of decomposition. Available P was highest under flooded system due to release of bound P from Fe and Mn by reduction of these elements to their respective soluble forms. Under aerobic condition, the available P recorded at active tillering and panicle initiation was lower than that of the initial value, due to its precipitation as tri calcium phosphate [Ca3 (PO4)2]. The available K status was higher under aerobic condition throughout the crop growth because of reduced rate of leaching under this environment. The rate of increase in available K was concurrent to the quantity of fertilizer added under both systems of rice cultivation. Highest K content in plant was recorded under aerobic rice system. The highest available Ca was recorded at active tillering and panicle initiation in flooded system of rice cultivation, because of the solubilization of applied lime. At harvest, the available Ca became precipitated as tri calcium phosphate which decreased the availability of both Ca and P under flooded condition. The transformation of tri calcium phosphate to mono calcium phosphate occurred only under aerobic condition during later stages. The highest Mg in plant was recorded in treatment where fertilizer application was done based on soil test under both systems of rice cultivation. The available sulphur status was higher under flooded condition during all the stages of sampling because of the increased solubility of applied factomphos and MgSO4. The status of available Fe was higher under flooded environment because of the reduction of Fe3+ to soluble Fe2+, while the available Fe status was found to decrease under aerobic condition due to oxidation of Fe2+ to insoluble Fe3+. The available Mn status under flooded environment decreased when compared to that of aerobic condition because of enhanced absorption by rice. The lower status of available Zn under aerobic condition resulted from more absorption of Zn by the crop, because of decreased competition from cations such as Fe3+ and Mn4+ under aerobic condition. The available boron status and boron content in plant was high under flooded condition because of the enhanced solubility of applied borax. Ultimately, aerobic rice recorded significantly higher grain and straw yield (6.23 t ha-1 and 6.35 t ha-1 respectively) than that under flooded system (5.12 t ha-1 and 5.52 t ha-1 respectively). The treatment with fertilizer application based on soil test and with lime as per SMP buffer method under aerobic situation recorded significantly higher grain yield of 6.8 t ha-1 because of balanced nutrition in this treatment combination. Higher root CEC, root mass, shoot mass root volume and root length were recorded under aerobic system. The decline in productive tillers during active growth phase was observed under flooded environment. Well developed aerenchymatic tissue in the roots was observed only under flooded environment. The water requirement was reduced by 57 % in aerobic rice, than that in flooded rice.
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PhD
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