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Transformation of Inorganic Phosphorus in Flooded Soils Under Rice Cropping

A. ISLAM
Department of Soil Science, University of Dacca, East Pakistan

Abstract/ Executive Summary:

The concentrations of water soluble and ammonium acetate extractable phosphorus in all the soils under investigation first increased and then decreased with time of submergence under rice cropping. The increase in soluble phosphorus in the three acid soils of Luisiana, Casiguran and Guadalupe was related to decrease in the concentration of iron, calcium and reductant soluble phosphates, while in slightly acidic Maahas clay, the increase was associated with decrease in iron and aluminium phosphates. But in the calcareous soil, the increase was due to decrease in the concentration of aluminium and reductant soluble phosphates. The decrease was due to the re-formation of insoluble aluminium, iron- and calcium phosphates in Luisiana and Guadalupe clays, to the formation of aluminium and calcium phosphates in Maahas and to the formation of calcium phosphate only in Casiguran fine sand. The application of phosphorus at the rate of 100 pounds per acre produced better tillering, more panicles and higher straw and grain productions in Luisiana, Casiguran and Guadalupe only where the level of soluble phosphate was very low in pots where no phosphorus was applied. This study, thus, indicated the necessity of phosphorus fertilization in low land rice for soils which are low in phosphorus and high in active iron and aluminium.

Keywords: Transformation, Inorganic phoshorus, Flooded soils, Rice cropping

Location: Department of Soil Science, University of Dacca

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Fertilizer

Objectives:

To determine the transformation of inorganic phoshorus in flooded soils under rice cropping

Methodology:

Greenhouse experiment: An experiment was set in the soil chemistry glasshouse of the International Rice Research Institute with five rice growing soils of Philippine differing in pH, texture and chemical properties. 7 pounds of Krilium-treated and air-dried soil were taken in each pot. The experiment was arranged in a completely randomized design with three replications and two rates of phosphorus fertilization. The treatment one received no fertilizer while treatment two was fertilized with superphosphate at the rate of 100 pounds per acre of phosphorus. All the pots received 100 pounds of nitrogen and potassium each per acre. The fertilizers were thoroughly mixed with the soil and then submerged to a depth of 3 inches on 11 th March. A day later, 2 fifteen days' old rice (Atlai variety) seedlings were transplanted in each pot. Two more dressings of nitrogen at the rate of 100 pounds per acre were applied during the growing period of rice. Sampling was done at two-weeks interval. Soil solution was drawn out from the bottom of the pots in strict absence of air in 125 ml Erlenmeyer flasks which had previously been filled with nitrogen. Soils samples were obtained by pushing a glass tube of 15 mm diameter down to the bottom of the pots, stoppering and withdrawing in a circular motion. The ends of the tube of phosphorus was done within 6 hours of sampling. Plants were harvested on May 28. The panicles were removed, dried in oven at 75⁰C and dry weights of straw and grain were measured separately. Tiller numbers were also counted. Soil Analysis: Soil samples representing each type were dried, ground and screened through a 2 mm mesh sieve and analyzed for pH, organic matter, active Fe and Mn, exchangeable AI, Ca, Mg and K. The pH was determined at a 1:1 soil to water ratio with Beckman pH meter. Organic matter contents were estimated by Walkley and Black's method. Active Fe and Mn were measured by following the method of Asami and Kurnada, Chenery's modified aluminon method was used to determine exchangeable AI. Exchangeable Ca and Mg were determined by EDT A titrimetric method while exchangeable K was recorded by Beckman flame photometer. Phosphorus in the soil solution and Morgan's ammonium acetate extract was estimated colorimetrically using modified benzeneisobutanol method of Martin and Doty. Finally discrete inorganic phosphorus compounds were determined by the chang and Jacksons procedure as modified by Glenn et. al.

Source of Information: Plant and Soil 33: 533-544, 1970

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

This study, indicated the necessity of phosphorus fertilization in low land rice for soils which are low in phosphorus and high in active iron and aluminium.

Knowledge Management: Journal