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Allelopathic Effect of Rice Straw in Soil on Nutrient and Chlorophyll Contents of Transplanted Aman Rice

Dr. Md. Asaduzzaman
Scientific Officer
Olericulture Division, Horticulture Research Center Bangladesh Agricultural Research Institute Joydebpur, Gazipur-1701, BANGLADESH.

Dr. Md. Habibur Rahman Pramanik
Professor
Department of Crop Botany Bangladesh Agricultural University Mymensingh-2202, Bangladesh

Abstract/ Executive Summary:

An experiment was conducted at the field laboratory of Department of Crop Botany, Bangladesh Agricultural University, Mymensingh, during 5 August 2004 to 3 December 2004 to study the allelopathic effects of added rice straws in soil on the nutrient status and chlorophyll content in T. aman rice. Rice straw was incorporated into soil at the rate of 0 (control), 5, 10, 20, and 40 t ha^–1 immediately before transplanting. Soil and plant samples were collected from the straw treated plots and analyzed for nutrient contents. Results revealed that the amounts of the nutrients (N, P and K) in soil as well as plant declined for excess addition of rice straw (20 or 40 t ha^-1) while others nutrient (S, Ca, and Na) contents slightly increased for the same. Chlorophyll contents at vegetative stage in rice plants declined for the higher amount of straw addition. The bioassay of alcoholic extract of the soils treated with rice straw (20 or 40 t ha^-1) showed strongest inhibition in radicle and plumule length of lettuce seedling. It appears that excess amount of rice straw addition in soil affects nutrient uptake and chlorophyll contents in rice plants possibly for sufficient release of toxic chemicals from the added rice straw.

Keywords: Rice straw, Nutrient content, Chlorophyll content, Transplanted aman rice.

Location: Experimental Field Lab, Department of Crop Botany, BAU, Mymensingh

Start Date: 05-08-2004

End Date: 03-12-2004

Program Area: Crop-Soil-Water Management

Commodity: Rice

Objectives:

The study was carried to find out the effect of rice straw added into soil on the nutrient uptake and chlorophyll contents in rice plants and to observe the phytotoxic effects, if any, of the of extracts from the straw treated soils.

Methodology:

Cultivation procedures: Threshed and semi-decomposed (kept in an open field for two months) Aus rice straws (BRRI dhan26) were chopped into small pieces (about 10 cm) and incorporated manually into the puddled land at the rate of 0 (control), 5, 10, 20, and 40 t ha^-1before transplantation. The experiment was laid out in Randomized Complete Block Design (RCBD) with four replications. Thirty day old rice seedlings (BRRI dhan30) were transplanted in the straw treated plots each of 10 m² size. Intercultural operations such as weeding, fertilizer application and pest control were furnished as and when necessary.

Estimation of Chlorophyll: Total chlorophyll content in the leaves of rice plants were estimated following the procedure of Coombs et al., (1985).

Determination of mineral nutrients in soil and plant samples: Soil samples were collected treatment wise from top 15 cm depth for analyses of different nutrients. Total nitrogen content of soil was determined by Semi-micro Kjeldahl method (Micro Kjeldahl method following concentrated sulphuric acid digestion and distillation with 40% sodium hydroxide) developed by Black (1965). Available phosphorus present in soil was determined by Olsen's method colorimetrically. Available sulphur was determined turbidimetrically by calcium chloride extraction method (Page, et. al. 1982) by spectrophotometer (Systronics UV-VIS, USA) at 420 nm wave length. Soil extracts were prepared by 50 ml 1 M ammonium acetate for K, Ca, and Na determination by flame photometer (JENWAY PFP7). Plant samples collected from the experimental plots were analysed for N, P, K, S, and Na contents. Digestion of plant samples were made with Sulphuric-Perchloric acid in 2:1 ratio for N determination. Nitrogen in the digest was estimated by distillation with 40% NaOH followed by titration of the distillate trapped in H₃BO₃ with 0.01N H₂SO₄ (Page et al., 1982). Digestion of plant samples with Nitric-Perchloric acid in 2:1 ratio for P, K, S, and Na determination. Each value of nutrient content of soil and plant samples was made by averaging three reading.

Bioassay: Soil (500 g) from each straw treated plot was collected at 30 day after transplanting and suspended in 500 ml 40% Ethanol. The suspension was filtered (Whatmann no.1) and the filtrate was evaporated to dryness using the Labconco freeze dryer (Model-77550). The dried residues were dissolved in 60 ml distilled water and treated as stock solution. Five milliliters from the stock solution was used to moisten the tissue paper (germination medium) taken in petridishes as per treatments. Thirty lettuce seeds (Lactuca sativa var. Green wave) were placed in each treated petridish with six replications and were kept in dark at room temperature (24-25^oC). After four days, the inhibition potentials of the soil extracts were evaluated by the level of reduction in radicle and plumule lengths against distilled water (control) or extracts from controlled plots.

Source of Information: Bangladesh J. Environ. Sci. Vol. 11, No. 2, 359-363, 2005

Article Link (Online Journal):

Funding Source:

1.	Budget: 10,000

Total Budget (Tk.) : 10,000

Achievement/Findings:

Amounts of the nutrients (N, P and K) in soil as well as plant declined for excess addition of rice straw (20 or 40 t ha^-1) while others nutrient (S, Ca, and Na) contents slightly increased for the same. Chlorophyll contents at vegetative stage in rice plants declined for the higher amount of straw addition. The bioassay of alcoholic extract of the soils treated with rice straw (20 or 40 t ha^-1) showed strongest inhibition in radicle and plumule length of lettuce seedling. Excess amount of rice straw addition in soil affects nutrient uptake and chlorophyll contents in rice plants possibly for sufficient release of toxic chemicals from the added rice straw. Extract from the soil alone did not show phytotoxicity in lettuce while those from the straw-treated soils showed phytotoxicity. This indicates that excess addition of rice straw (S₂₀ and S₄₀) caused sufficient release of phytotoxic chemicals which had affected the growth of rice plants which is the result of remarkable decrease in the nutrient status in soil and plants and also in chlorophyll content in rice plant. So, identification of chemicals in straw-treated soil extracts and assessment of their toxicity level should be studied for a final conclusion.

Knowledge Management: Journal