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Determination of Crop Co-efficient Values of Soybean (glycine Max [l.] Merrill) by Lysimeter Study

A. J. Mila
Irrigation and Water Management Division, Bangladesh Agricultural Research Institute (BARI), Gazipur-1701, Bangladesh

A. R. Akanda
Irrigation and Water Management Division, Bangladesh Agricultural Research Institute (BARI), Gazipur-1701, Bangladesh

K. K. Sarkar
Irrigation and Water Management Division, Bangladesh Agricultural Research Institute (BARI), Gazipur-1701, Bangladesh

Abstract/ Executive Summary:

Local level calibration of crop coefficient (K_c) values is critical for regional level planning and allocation of water resources for irrigation. In this regard, an experiment was conducted at the Irrigation and Water Management Division of Bangladesh Agricultural Research Institute (BARI), Gazipur, in order to estimate crop coefficient values of soybean under the local climatic condition. An improved crop variety- BARI Soybean-6 was used in this experiment. The crop was grown under four irrigation treatments, allowing irrigation at an interval of 10, 15, 20 and 25 days. The treatments were so designed that drainage was allowed between the consecutive irrigation. Irrigation at 15 days interval produced the highest seed yield of 1.26 t/ha and was considered to be suitable for estimating seasonal crop evapotranspiration (ET_c) and K_c values. The seasonal highest cumulative ET_c was 308.43 mm under this treatment. The K_c values of soybean at initial, development, mid-season and late season stages were found as 0.67, 1.46, 1.59 and 0.62, respectively.

Keywords: Crop coefficient values, Evapotranspiration, Crop evapotranspiration, Soybean, Lysimeter

Location: Bangladesh Agricultural Research Institute, Gazipur,

Start Date: 00-11-2015

End Date: 00-03-2016

Program Area: Crop-Soil-Water Management

Commodity: Soybean, Irrigation scheduling

Objectives:

This study was undertaken with the objective of determining the crop coefficient values of soybean at its different growth stages

Methodology:

An experiment on soybean cultivation was conducted in a micro-lysimeter installed at the research farm of Bangladesh Agricultural Research Institute, Gazipur, during the rabi season (November to March) of 2015–2016. The climate was warm and dry with average temperature of 22.5°C. The maximum and minimum relative humidity, and maximum and average wind speed were 93%, 34%, 10.64 m/s and 1.60m/s, respectively. The highest rainfall of 25 mm occurred on 8 March 2016, and the highest solar radiation was 22.8 MJ/m²/day. The soil of the experimental field was silty clay loam, with field capacity and bulk density of 29.5% and 1.50 g/cm³, respectively. A hybrid variety of soybean (BARI Soybean-6) was selected for the lysimeter experiment. Seeds were sown in a 1 m × 1m micro-lysimeter platform at a spacing of 0.30 m × 0.10 m on 19 November 2015. The seeds were treated using Bavistin @ 2 g/kg of seed. The same crop was grown surrounding the lysimeter tanks with a view to create a similar cropping environment as in the lysimeter. Recommended fertilizer doses (FRG, 2012) were applied and necessary intercultural operations were done as and when required. In order to reduce fruit fly infestation, Sumethion 57 EC @ 2 ml/L of water was sprayed at 35, 47 and 17 days after sowing. The drainage type micro–lysimeter contains four tanks each of area 1 square meter. The crop was grown in the lysimeter in a controlled environment since the lysimeter was hydrologically separated from the surrounding soil (Michael, 2014). When crops are grown under such conditions, there is no need for further replication as argued by Khan et al. (1993). The similar system was used by other researchers for estimating crop coefficient values of hybrid maize and sunflower. Our experiment comprised four treatments as: T₁ = Irrigation at 10 days interval allowing drainage until receive the next irrigation; T₂ = Irrigation at 15 days interval allowing drainage until receive the next irrigation; T₃ = Irrigation at 20 days interval allowing drainage until receive the next irrigation; T₄ = Irrigation at 25 days interval allowing drainage until receive the next irrigation. Measured quantity of water was applied as irrigation to the crops grown in the lysimeter tanks by ensuring provision of adequate drainage. In addition, the soybean plots adjacent to the tanks were also irrigated. Drainage water from the lysimeter tanks was collected and measured using graduated cylinders. The crop evapotranspiration, ET_c, was calculated from the irrigation and drainage quantities by using water balance principle. Prior to irrigation, soil moisture was measured in order to determine soil-water depletion during a particular time period. The crop evapotranspiration was calculated by using water balance equation given by: ET_c = W_a – (D_w ± ΔS_s) ..... (1); where, ET_c is crop evapotranspiration during a specified time period (mm), W_a is applied water plus rainfall during the time period (mm), D_w is drainage water during the time period (mm) and ΔS_s is stored soil moisture during the time period (mm). There are several methods for determining reference evapotranspiration, ET_o. Among them, Penman-Monteith method has been recommended for empirical determination of ET_o using climatic data viz., temperature, humidity, sunshine duration and wind speed (Allen et al., 1998; Michael, 2014). According to Smith et al. (1992), FAO Penman-Monteith method gives more consistent ET_o estimates and has been shown to perform better than other methods. In this study, reference evapotranspiration, ET_o, was estimated by using CROPWAT software that uses Penman-Monteith model to calculate ET_o. This model requires only insertion of location (latitude, longitude and elevation), and climate data (maximum and minimum air temperature, humidity, sunshine hour and wind speed). The crop coefficient, K_c, was estimated by using the following formula: ET_c = K_c × ET_o .......(2). At 111 days after sowing, the data on plant height and number of branches per plant were recorded from 10 plant samples in each lysimeter. Pods were collected three times during the crop maturity stage as flowering and pod formation occurred simultaneously. Data for leaf area index (LAI) was collected during the crop period starting from vegetative stage. The yield and yield contributing data were collected during and after harvesting of the crop.

Source of Information: The Agriculturists 14(2): 14-23 (2016)

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Achievement/Findings:

An experiment was carried out at the research field of Irrigation and Water Management Division, Bangladesh Agricultural Research Institute, Gazipur to know the crop evapotranspiration and crop coefficient values of soybean. Results showed that irrigation at 15 days interval including drainage within two consecutive irrigation gave the highest yield of soybean in this semi-arid region. Seasonal crop evapotranspiration of soybean was 308.43 mm when irrigation was provided at 15 days interval. The crop coefficient values of BARI Soybean-6 were 0.67, 1.46, 1.59 and 0.62 at the initial, development, mid-season and late season stages, respectively. The estimated values of crop coefficient for soybean vary considerably over the growth stages from those recommended by FAO except for the late season stage. Nevertheless, the locally calibrated values of the crop co-efficient can be used for more reliable planning and distribution of regional water resources for irrigation.

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