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Duckweed and Duckweed-urea Complemented Treatments Affecting Accumulation of Mineral Nitrogen in Soil Under Water-logged Condition

S. G. Hussain
Bangladesh Agricultural Research Council, Farmgate, Dhaka-1215

Z. Ahmad
Department of Soil Science, Dhaka University, Bangladesh

Abstract/ Executive Summary:

In a water-logged incubation experiment the accumulation of mineral-N in soil as affected by application of various proportions of duckweed (Lemna minor) and urea were studied. It was found that accumulation of mineral-N increased significantly at the end of fourth week of incubation in treatments where only duckweed was applied. This trend continued up to 24th weeks. Accumulation of mineral-N increased sharply up to second week of incubation and then gradually decreased in the treatments complemented with duckweed-urea and urea alone.

Keywords: Mineral nitrogen, Soil, Water-logged, Duckweed-urea

Location: Department of Soil, Water and Environment, University of Dhaka, Bangladesh.

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Soil fertility

Objectives:

To determine the variations in the amount of mineral nitrogen in soil with time as affected by the rate of application of duckweed with and without fertilizer nitrogen (urea) under water-logged condition.

Methodology:

An incubation experiment was set up to study the pattern of mineral-N release in soil under water-logged condition from duckweed applied at different doses alone or in combinations with urea. This study was conducted with a· silty loam soil , (pH 5.2, organic carbon 0.84%, CEC 9.16 meq/ 100 g soil, total nitrogen 0.1 I %) collected from the surface layer (0-15 cm) of a low land rice field, Duckweed was collected from Ramna Park pond, containing 4.2 of nitrogen and 29.64% organic carbon (oven dry basis). One hundred and sixty eight test tubes of 50 ml capacity were filled with soil corresponding to 20 g oven dry soil. In each of the test tubes triple super phosphate @ 80 kg P₂0₅/ha and muriate of potash @ 40 kg K 20/ha were applied. To maintain anaerobic environment, water was added at a level of 2.5 em from the soil surface in the test tubes. The amount of water added in each test tube was determined by weighing and was accounted for extraction. All the test tubes were covered with polyethylene film and were incubated at 30 ± 2⁰C temperature for 1 , 2, 4, 8, 12 and 24 weeks. Water was added at intervals to compensate the loss during incubation. Three replications of the experiment were used. Standard analytical methods were followed for determining soil properties as described. Nitrogen and organic carbon contents in duckweed were estimated by following micro-Kjeldahl method and wet oxidation method, respectively. After a stipulated time interval of incubation, the entire soil sample from each test tube was extracted with 200 ml neutral N KCI in a shaking bottle separately and was shaken for one hour in a reciprocating shaker. The suspension was then filtered. A portion of the filtrate was used for the determination of mineral nitrogen release during various time Intervals of incubation and was determined by micro-Kjeldahl method using Devarda's alloy as proposed.

Source of Information: The Bangladesh Journal of Scientific Research, Vol. – 7, No. – 1, June – 1989.

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Incorporation of duckweed nitrogen from 60 kg N/ ha up to 210 kg N/ ha showed a steady and gradual increase in the amount of mineral nitrogen. On the other hand, complementary application of 80 kg N/ha from duckweed and urea, and 80 kg N/ ha from urea alone increased the amount of mineral nitrogen very rapidly. Jn the later treatments maximum amount of mine ral nitrogen was recorded at the end of second week of incubation and was followed by a sharp decline in mineral nitrogen content. The amount of mineral nitrogen in the U60D0 treatment reached its maximum (100.90 ppm N) at the end of second week a nd declined sharply there after. This might be attributed to the cause pointed out by Islam and Parsons (1979). They concluded that under anaerobic condition regardless of rate of hydrolysis of urea, de nitrification quickly removed the mineralized nitrogen that had formed. At the end of 24th weeks in incubation the amount of accumulated mineral nitrogen in treatments- U0D60, U0D60, U0D05 and U0D210 exceeded the amount that was present in the control (52.65 ppm N) by 37.40, 41.50, 43.60 and 53.10 ppm, respectively.

Knowledge Management: Journal