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Effect of Mechanical Impedance on Root and Shoot Growth of Rice at Time Intervals

A. H. M. Z. ALI
Department of Soil, Water and Environment, University of Dhaka, Dhaka-1000, Bangladesh

Abstract/ Executive Summary:

In a phytotron chamber the effect of mechanical impedance on root and shoot growth of BR?29 variety of rice at different time intervals reaveled that length of the seminal axis and length of the longest leaf extended linearly in both unimpeded and impeded treatments. Diameter of roots increased in impeded treatment. The number of first order laterals also increased linearly with time in both unimpeded and impeded treatments. Although there were always significantly more laterals on the unimpeded root axes, lateral spacing does not show any tendency to change with time. Root growth rate was nearly half in impeded than in unimpeded treatment. The pattern of root length in unimpeded (UI) did not differ from that of the pattern in impeded (I) treatment as the ratios (I/UI) were more or less constant with time. The time of leaf appearance was delayed by one ? two days and leaf growth period was shortened by one day in impeded than in unimpeded treatment. Leaf growth rates did not differ significantly between day and night time although night time growth rates were always slightly less than day time. Introduction

Keywords: Mechanical impedance, Pattern of root growth, Time interval, Shoot growth, Rice

Location: Department of Plant & Soil Science, University of Aberdeen, Aberdeen

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Rice

Objectives:

1. To see the effect of mechanical impedance on root and shoot growth of rice at different time intervals.

Methodology:

Two different lengths of perspex cylinders were used: 300 and 200 mm. Their internal diameter was 49 mm. Metal mesh of 60 mm diameter was fitted to the base of each cylinder using adhesive tape. A small circle of general purpose J?cloth was fitted inside the metal mesh to prevent soil or sand from escaping through mesh. There were (a) two levels of mechanical impedances (MI), unimpeded soil and impeded sand; (b) one cultivar (CV), BR?29; (c) one temperature regime, 27°C; (d) seven growing periods (GP), 36 hours, 3, 5, 7, 9, 11 and 15 days. The cylinders were arranged in a completely randomised design inside the phytotron. Cylinders were re?randomised after every three days and the top of all of the cylinders were kept at roughly the same level. The growth cylinders were packed with soil or sand uniformly mixed with nutrient solution following the packing styles developed for an unimpeded treatment with a penetration resistance (PR) of 0.05 MPa (using soil) and an impeded treatment with a PR of 3.2 MPa (using sand). Penetration resistances were measured by needle penetrometer. Seeds of BR?29 variety of rice were germinated on wet filter paper. Preliminary germination trials were carried out to determine germination rates under these conditions. Thus the times when the seeds were placed on wet filter paper were chosen to ensure that each seed was at the same stage of germination when transferred to the packed growth cylinders. Germinated seeds with a 4 mm long radicle were transplanted into the cylinders at a depth of 10 mm below the soil surface using green light between 10:00 ? 11:00 hours. The lights in the phytotron were switched on at 11:00 hours and switched off at 23:00 hours. The cylinders were weighed after packing and reweighed after 5 days interval and water was then added at 5 cm depth to restore the original weight of these cylinders using a hypodermic needle inserted at different points into the top of the cylinder. The aim was to rewet the zone of maximum depletion. Soil temperature was recorded at 1 hour intervals throughout the experiment using thermistors connected to a data logger. Thermistors were placed at the centre of the cylinders at the depth of sowing by bending their wires at a 90°, 25 mm from the end. The wire was secured in place with adhesive tape at the level of the thermistor and at the top of the cylinder. The remainder of the cylinder was packed according to the required treatment. Cylinders were placed in a high light phytotron with irradiance ranging between 320 and 430 μmol/s/m² at plant height. Relative humidity was set to 70 ? 80%, and temperature at 27°C. Air temperature inside the phytotron was also recorded with thermistors connected to the data logger. At the time of harvesting, the growth cylinders were collected from the high light phytotron and submerged in a container full of water for one hour after removing the base of cylinders. When the soil became loose it fell freely down the cylinder as it was removed from the cylinder. The plants were then collected from the container placed in a Petri dish, and washed thoroughly with distilled water to remove soil or sand attached to the roots. The plants were temporarily kept in these Petri dishes full of water during measurement of root and shoot parameters. The length of the seminal axis and root diameter 10 mm above the root tip were measured using digital vernier callipers (± 0.01. The number of first order laterals were counted under a large?field illuminated bench magnifier keeping the root system in a Petri dish. The distance between the first and the last lateral (L₁) was measured using a digital vernier callipers. Average lateral spacing (Ls) was calculated as given in the following equation(8): Ls = L1/n⁻¹ (where n is the total number of laterals). The length of the leaf was measured to ± 0.01 mm using digital vernier callipers. Length of leaves were measured at 12 hour intervals ( at 11:00 and 23:00 hrs) for the 15 days growing period, but for the other growing periods only the longest leaf was measured at harvest time. The first day of appearance for leaf 1, 2, 3, 4, 5 and 6 was recorded by observing the plants at six hours interval for the 15 days growth period plants. Statistical analysis was done using Minitab Statistical Software, release 10 Xtra. Significant differences between pairs of means were tested using the value of least significant difference (LSD).

Source of Information: Dhaka Univ. J. Biol. Sci. 19(2): 119‐128, 2010 (July)

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Knowledge Management: Journal