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Study of Evapotranspiration and Water Use Pattern by Soybean

M.M. Hossain
Regional Agricultural Research Station, BARl, Jamalpur, Bangladesh

M.H. Rashid
Irrigation and Water Management Division, BARl, Gazipur, Bangladesh

Abstract/ Executive Summary:

The study was conducted with four levels of irrigation in lysimeters with soybean, variety sohag (PB-1), in order to find out the actual evapotranspiration (ET) requirement of the crop. The total seasonal (133 days from sowing) ET was 587 mm for a grain yield of 3.58 t/ha and dry matter production (shoot only) of 6.28 t/ha, for the treatment with one irrigation at budding stage. Least water use and highest water use efficiency (60.98 kg/ha-cm) was found for this treatment. Higher evapotranspiration (ET) was observed during the period from 14^th to 17^th week after sowing with peak (8.83 mm/day) during the 15^th week. Average crop coefficients (k.) values for the whole season were 1.02 and 1.19 and for peak period ET were 1.7 and 1.45 as referred to potential evapotranspiration and pan evaporation, respectively. Actual evapotranspiration may therefore, be better predicted by pan evaporation than potential evapotranspiraion calculated by Hargreave's equation.

Keywords: Evapotranspiration, Water, Soybean

Location: Regional Agricultural Research Station, Jamalpur.

Start Date: 00-00-1996

End Date: 00-00-1997

Program Area: Crop-Soil-Water Management

Commodity: Soybean

Objectives:

determine actual evapotranspiration (ET_c) requirement of soybean for differennt soil moisture regimes
determine optimum evapotranspiration requirement of the crop judged by yield
correlate the actual evapotranspiration of soybean with pan evaporation and potential evapotranspiration
study the water use pattern by soybean e) observe the effect of different levels of irrigation on soybean.

Methodology:

The experiment was conducted at the Regional Agricultural Research Station, Jamalpur during the winter season of 1996-97 with soybean (variety-Sohag, PB-1). Water applied in each irrigation was the amount required to bring the soil moisture level of the lysimeter tanks to field capacity. The following treatments were set in lysimetrs. T₁= Irrigation at every 14 days interval (I14 DI), T₂= Irrigation at budding stage (IBS), T₃ = Irrigation at vegetative and pod-filling stages (IVS+PFS), T₄= Irrigation at pod filling stage (IPFS). At each irrigation measured amount of water was applied to have some drainage beneath the lysimeter tanks to ensure attaining field capacity of the whole soil profile. As usual in most of the precision lysimeters, replication was not possible since only 4 lysimeter tanks were available. Each tank had 1 meter square surface area and 90 cm effective soil depth. Physical properties of the lysimeter soils were as presented. Moisture contents of lysimeter soils were as presented. Seeds were sown on December 11, 1996 at 33 cm line spacing, at the rate of 60 kg/ha. Fertilizers were applied at the rates of 65, 135, 115, and 14 kg urea, TSP, MP, gypsum, and zinc sulphate per hectare; respectively. The whole of urea TSP, MP and zinc sulphate were applied during the final land preparation. Around lysimeter tanks, wide fetches with the same crop were grown to maintain the same environment lysimeter tanks had similar soybean to a distance of 12 m on the south, 14 m on the north, 4 m on the west and 15 m on the east. Beyond these boundaries, there were other crops like mustard, sesame, vegetables, wheat etc. The crop was harvested on April 23, 1997 (133 days after sowing). The crop was threshed by hand and dried well under sun for 3 to 4 days. where I, R, D and S represent irrigation, rainfall, drainage and soil moisture use, respectively; all are in units of depth. Soil moisture use for each period was determined using gravimetic method by subtracting the soil moisture content at the end of the period from that of the start of the period. A U.S. class A evaporation pan was used for measuring pan evaporation (Ep). A maximum-minimum thermometer was kept in an well ventilated box 1.4 m above ground level for recording daily maximum and minimum temperature. The rainfall was recorded by a simple rain gauge. The met station where all these were recorded was approximately 0.4 km apart from the lysimeter.

Source of Information: Bangladesh Journal of Agriculture, Vol: 24 (2), PP: 53-60, 1999, ISSN: 0253-5408

Article Link (Online Journal):

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

One irrigation at budding stage would be enough for maximum yield of soybean with minimum water use and highest water use efficiency. Actual evapotranspiration may be better predicted by pan evaporation than potential evapotranspiraion calculated by Hargreaves' equation.

Knowledge Management: Journal