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Calibration of Neutron Moisture Meter and Field Capacity Measurement in a Major Soil of Bangladesh

B. C. Basak
Bangladesh Institute of Nuclear Agriculture, P. O. Box, Mymensingh

A. A. Hassan
Bangladesh Institute of Nuclear Agriculture, P. O. Box , Mymensingh

Abstract/ Executive Summary:

A field experiment was conducted to calibrate neutron moisture meter and measure' field capacity in the Bangladesh Agricultural Research Institute Farm, Jarnalpur. Regression equation ? = -0.046 + 0.436CR developed from plotting volumetric moisture content against count ratio represents almost the same from the manufacturer's one ? = - 0.044 + 0,433CR. Therefore, either equation can be used to calculate the volumetric moisture content of the profile. Field capacity values showed variation from 13.01 to 45 percent from 15 cm depth to 120 cm depth, the minimum being in the surface soil. Soils at. 75, 90, 105 and 120 cm depths showed almost similar F. C. values ot 42.15%, 44.00%, 44 .50% and 45.00% respectively . Hours of variation to reach field capacity at different depths implied the presence of relatively impervious or clay layer at 60 cm depth, which helps in holding water in the upper layers to meet up the crop water demand through capillary-fringe action and complementary to reduce the frequency of irrigation.

Keywords: Calibration, Neutron moisture meter, Field capacity

Location: Bangladesh Agricultural Research Institute Farm, Jarnalpur

Start Date: 00-01-1984

End Date: 00-12-1984

Program Area: Crop-Soil-Water Management

Commodity: Water management

Objectives:

1. To find out the moisture versus time curve for obtaining field capacity values of soils at different depth with a neutron moisture meter. These field capacity values can be used to calculate the amount of irrigation water to be applied to a field crop at any particular time.

Methodology:

Calibration of Neutron Moisture Meter: For calibration of neutron probe ten aluminum access tubes were installed in the study area at 10 randomly selected locations. Neutron readings were taken at all the 10 locations and soils were collected for deter- mining volumetric soil moisture percentage following procedure given by IAEA. The soils from various depths were analysed for their particle size distribution. Field capacity Measurement: For determining field capacity, an area of 2.44m x 2.44m was taken and diked all around. Three aluminum access tubes were installed in the area using a hand driven 5.08 em diameter auger. All precautions were taken so that there was no gap between the out side wall of the tube and the access hole. About 80 em of water was applied in the diked area to bring the soil to saturation upto a depth of 1. 52 m and it was then covered with a polythene sheet to prevent upward flux of water and also to save the area from rainfall, dew fall etc. The neutron counts were taken every twelve hours upto 5 days at an interval of 15 cm upto 120 cm depth. Zero time was taken at the point when applied water infiltrated completely through the soil surface. Moisture content was calculated from the regression equation

Source of Information: Bangladesh J. Nuclear Agric. 1 (1) : 50 - 54; 1985

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Hours of variation to reach field capacity at different depths implied the presence of relatively impervious or clay layer at 60 cm depth, which helps in holding water in the upper layers to meet up the crop water demand through capillary-fringe action and complementary to reduce the frequency of irrigation.

Knowledge Management: Journal