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Development of crop coefficient models of castor and maize crops
Europ. J. Agronomy 69 (2015) 59–62
Contents lists available at ScienceDirect
European Journal of Agronomy journal homepage: www.elsevier.com/locate/eja
Development of crop coefficient models of castor and maize crops K. Chandrasekhar Reddy ∗ Siddharth Institute of Engineering & Technology, Puttur, Andhra Pradesh, India
a r t i c l e
i n f o
Article history: Received 21 April 2015 Received in revised form 29 May 2015 Accepted 15 June 2015 Available online 24 June 2015 Keywords: Reference evapotranspiration Crop coefficients Polynomial equations, FAO-56 Penman-Monteith method
a b s t r a c t Castor and maize are the most commonly cultivated crops in the Rajendranagar region of Andhra Pradesh, India. The study aims to develop a crop coefficient (Kc ) models for these crops, using Lysimeter measured daily crop evapotranspiration (ETc ) data and daily reference evapotranspiration (ET0 ) computed using FAO-56 Penman-Monteith (PM) method. Kc values obtained using relationship Kc = ETc /ET0 , crop coefficient curves were derived as a function of days after sowing and polynomial model was fitted. The performances of the models were tested using performance indicators. The models performed well for both the crops. These models can, therefore, be used for estimating Kc values of castor and maize crops for any day after sowing in the study region. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Accurate estimation of the crop water requirement (crop evapotranspiration) is a vital part of agricultural planning. The water requirement varies widely from crop to crop and also during the growth period of the crop. Field measurement (with Lysimeter) of crop evapotranspiration (ETc ) is not so easy and it is often expensive and impractical. The most common and practical approach extensively used for estimating crop evapotranspiration (ETc ) is the crop coefficient (Kc ) approach (1977, Allen et al., 1998) which consists of multiplying reference evapotranspiration (ET0 ) with crop coefficients (Kc ) to find ETc (i.e., ETc = ET0 x Kc ). Reference evapotranspiration (ET0 ) is defined as the rate of evapotranspiration from a hypothetical reference green grass of actively growing, completely shading the ground, uniform height, and not short of water (Allen et al., 1998). Accurate field measurements of ET0 are also difficult and it is usually estimated using weather data. There are several empirical or semi-empirical equations are available to assess ET0 from meteorological data. Depends upon the data availability, climatic conditions of the area and degree of accuracy, we may choose the appropriative empirical equation to estimate ET0 . However, FAO-56 Penman-Monteith (PM) equation, which yields the results nearer to Lysimeter measured data, may be used as the standard method in all climatic conditions to estimate ET0. Experimentally determined ratios of ETc /ET0 called crop coefficients (Kc ) (Allen et al., 1998). The crop coefficients depend on the
∗ Corresponding author. Fax: +91 8577224888. E-mail address: [email protected] http://dx.doi.org/10.1016/j.eja.2015.06.003 1161-0301/© 2015 Elsevier B.V. All rights reserved.
type of crop and its varieties, crop height, leaf characteristics, soil properties, climate conditions, irrigation methods and so on. Different crops will have different crop coefficients (Kc ), even for the same crop Kc varies throughout the growth period due to changes in vegetation and ground cover. The growing period of the crop is generally divided into four phenological stages (initial, development, mid and late) for the purpose of stage-wise development of crop coefficients. The variations in Kc during the growing period are described in the form of a crop coefficient curve. Initially the concept of crop coefficients (Kc ) was introduced by Jensen Marvin (1968) and later many researchers (Doorenbos and Pruitt, 1977; Allen et al., 1998) are carried out investigations and recommended crop coefficient values for various crops grown under different climatic conditions. These values are normally used at places where local data are not available. However, there is a strong need for local calibration of crop coefficients because the climatic conditions in the field differ from the standard conditions. Shah and Edling (2000) evaluated PM, FAO-Penman and 1963 Penman combination models for their capabilities to predict rice ET using daily weather data. Crop coefficients of rice for the vegetative, flowering, and yield formation stages were found 1.39, 1.51, and 1.43, respectively. Tyagi et al., (2000) developed crop coefficients (Kc ) for wheat and sorghum from ETc measurements and weather data. It was pointed out that actual Kc values are significantly different from those suggested by the UN FAO indicating the need for generating these values at local/regional level. The relationships between standard UN FAO PM and other ET0 methods were also investigated. Kashyap and Panda (2001) made an attempt to develop regional relationships between the evapotranspiration measured by the Lysimeter and that estimated by the climatological
K.C. Reddy / Europ. J. Agronomy 69 (2015) 59–62
KC
60
2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0
Center: Rajendranagar Crop: Castor
1
11
21
31
41
51
61
71
81
101
91
111
121
131
2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0
Crop: Maize
1
11
21
31
41
51 Days
61
71
81
91
Fig. 1. Variation of daily Kc values.
7
Center: Rajendranagar Crop: Castor
6
ETc observed, mm/day
ETc observed, mm/day
7
5 4 3 2 1 0
Center: Rajendranagar Crop: Castor
6 5 4 3 2 1 0
0
1
2
3
4
5
6
7
0
ETc estim ated, m m /day
1
2
3
4
5
6
7
ETc estim ated, m m /day
8
8
Center: Rajendranagar Crop: Maize
7 6
ETc observed, mm/day
ETc observed, mm/day
KC
Days
5 4 3 2 1 0
Center: Rajendranagar Crop: Maize
7 6 5 4 3 2 1 0
0
1
2
3
4
5
6
7
8
0
1
2
3
4
5
6
7
ETc estim ated, m m /day
ETc estim ated, m m /day
Training period
Testing period
Fig. 2. Scatter plots of daily ETc observed with that estimated using polynomial Kc models and PM ET0 .
8
K.C. Reddy / Europ. J. Agronomy 69 (2015) 59–62
61
Table 1 Details of FAO-56 Penman-Monteith ET0 estimation method. Basic reference
Equation
ET0 =
Allen et al. (1998)
Input data
0.408(Rn −G)+
900 (e −e˛ ) Tmean +273 2 s
+(1+0.342 )
Primary
Secondary
Tmin , Tmax , RHmin , u2 , n
–
Table 2 Crop details and period of data collected. Crop
Crop varieties
Crop season
Crop period (days)
Period of data
Training period
Testing period
Castor (Ricinus communis) Maize (Zea mays)
ARUNA B21, CM202, CM119, CM104, GANGA5
Jun–Nov July–Oct
135 100
1978–1993
1978–1988
1989–1993
methods. The crop coefficients for potato crop were also estimated at different stages of growth and Kc value at the maturity stage was found to be considerably higher than the corresponding FAO recommended Kc value. This study deals with the derivation of crop coefficients and development of crop coefficient (Kc ) models of castor and maize crops in the Rajendranagar region of the study area.
Table 3 Polynomial regression Kc models. Crop
Regression equation
Castor
Kc = −9E-06 x3 + 0.001 x2 − 0.0212 x + 0.5032 (1 ≤ x ≤ 70) Kc = 1E-05 x3 − 0.0032 x2 + 0.3181 x − 9.0549 (x >70) Kc = −2E-05 x3 + 0.0017 x2 − 0.0229 x + 0.5192 (1 ≤ x ≤ 60) Kc = −4E-05 x3 + 0.0084 x2 − 0.5879 x + 14.9834 (x >60)
Maize
2.1. Crop coefficient models 2. Materials and methods Rajendranagar region, Rangareddy district, Andhra Pradesh, India, has been selected as the study area. The meteorological data in the study area for the period 1978–1993 was collected from IMD, Pune. Data from 1978 to 1988 is used for the purpose of training the Kc model and rest of data for testing the Kc model. Details of FAO56 Penman-Monteith method used for ET0 estimation and crops selected for the study are shown in Tables 1 and 2, respectively.
The crop coefficients for castor and maize crops were determined, as the ratio of Lysimeter measured ETc values to reference evapotranspiration (ET0 ) values computed using FAO-56 PenmanMonteith method, in the region of the study area. Lysimeter measured daily ETc data were used to derive daily crop coefficients for the crops. These Kc values were plotted with respect to days after sowing (x) and a dual polynomial function each for rising and falling trends of the curve was fitted to the data.
7 Center: Rajendranagar Crop: Castor
ETc (mm/day)
6 5 4 3 2 1
ETc observed
ETc estimated
0 1
11
21
31
41
51
61
71
81
91
101
111
121
131
Days
8 Center: Rajendranagar Crop: Maize
7 ETc (mm/day)
6 5 4 3 2 1
ET observed
ETc estimated
0 1
11
21
31
41
51
61
71
81
91
Days Fig. 3. Comparison of observed daily ETc values with those estimated using polynomialKc models and PM ET0 during testing period.
62
K.C. Reddy / Europ. J. Agronomy 69 (2015) 59–62
Table 4 Performance indicators of ETc models. Crop
Castor Maize
Slope of the scatter plot
Intercept of the scatter plot
R2
Training period
Testing period
Training period
Testing period
Training period
Testing period
Training period
Testing period
Training period
Testing period
0.8887 1.0233
1.0554 0.9273
0.1177 0.0456
0.0307 0.1587
0.8392 0.9090
0.8972 0.8623
0.48 0.46
0.47 0.58
83.92 90.90
89.72 86.23
RMSE (mm)
EC (%)
2.2. Performance evaluation criteria
4. Conclusion
The performance evaluation indices used in the present study, namely, Coefficient of Determination (R2 ), root mean square error (RMSE) and efficiency coefficient (EC).
The crop coefficient (Kc ) values were calculated for castor and maize crops in the Rajendranagar region and a third order polynomial Kc models were fitted. The performances of the models were tested using performance indicators. The models performed well for both the crops. It has been observed that crop evapotranspiration (ETc ) values computed based on these polynomial Kc models are comparable with those of Lysimeter measured ETc. These models can, therefore, be used for estimating Kc values of castor and maize crops for any day after sowing in the study region. These models are also suggested for other areas having similar climatic conditions and same crop varieties.
3. Results and discussion The daily crop coefficients for the crops in the region selected for the present study plotted against time i.e., days after sowing (x) are as shown in Fig. 1. It may be observed from these plots that Kc values showed an increasing trend with the advancement in crop growth up to physiological development and after that started declining. A dual polynomial function each for rising and falling trends of the curve was fitted to the data. A third order polynomial equation was fitted to both rising and falling trends as presented in Table 3. The ETc values for the crops calculated as the product of Kc estimated form the proposed polynomial equations (models) and ET0 estimated by PM were compared with Lysimeter measured ETc in the form of scatter plots as shown in Fig. 2 and, also comparison plots as presented in Fig. 3. The performance indicators of these models are given in Table 4. The slope and intercept, respectively, close to one and zero of scatter plots and closeness of computed ETc values with those of observed ETc as observed from comparison plots indicate the satisfactory performance of the models. The high values of R2 and EC and low values of RMSE also represent the satisfactory performance of the models.
References Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop evapotranspiration Guidelines for computing crop water requirements. In: FAO Irrigation and Drainage Paper 56. FAO, Rome. Doorenbos, J., Pruitt, W.O., 1977. Guidelines for predicting crop water requirements. Irrigation and Drainage Paper, 24. FAO, Rome, Italy. Jensen Marvin, E., 1968. Water consumption by agricultural plants. In: Kozlowski, T.T. (Ed.), Plant Water Consumption and Response. Water Deficits and Plant Growth, Vol. II. Academic Press, New York, pp. 1–22. Kashyap, P.S., Panda, R.K., 2001. Evaluation of evapotranspiration estimation methods and development of crop coefficients for potato crop in a sub- humid region. Agric. Water Manage. 50 (1), 9–25. Shah, S.B., Edling, R.J., 2000. “Daily evapotranspiration prediction from Louisiana flooded rice field. ”. J. Irrig. Drain. Eng. ASCE 126 (1), 8–13. Tyagi, N.K., Sharma, D.K., Luthra, S.K., 2000. Evapotranspiration and crop coefficients of wheat and sorghum. J. Irrig. Drain. Eng. ASCE 126 (4), 215–222.
Contents lists available at ScienceDirect
European Journal of Agronomy journal homepage: www.elsevier.com/locate/eja
Development of crop coefficient models of castor and maize crops K. Chandrasekhar Reddy ∗ Siddharth Institute of Engineering & Technology, Puttur, Andhra Pradesh, India
a r t i c l e
i n f o
Article history: Received 21 April 2015 Received in revised form 29 May 2015 Accepted 15 June 2015 Available online 24 June 2015 Keywords: Reference evapotranspiration Crop coefficients Polynomial equations, FAO-56 Penman-Monteith method
a b s t r a c t Castor and maize are the most commonly cultivated crops in the Rajendranagar region of Andhra Pradesh, India. The study aims to develop a crop coefficient (Kc ) models for these crops, using Lysimeter measured daily crop evapotranspiration (ETc ) data and daily reference evapotranspiration (ET0 ) computed using FAO-56 Penman-Monteith (PM) method. Kc values obtained using relationship Kc = ETc /ET0 , crop coefficient curves were derived as a function of days after sowing and polynomial model was fitted. The performances of the models were tested using performance indicators. The models performed well for both the crops. These models can, therefore, be used for estimating Kc values of castor and maize crops for any day after sowing in the study region. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Accurate estimation of the crop water requirement (crop evapotranspiration) is a vital part of agricultural planning. The water requirement varies widely from crop to crop and also during the growth period of the crop. Field measurement (with Lysimeter) of crop evapotranspiration (ETc ) is not so easy and it is often expensive and impractical. The most common and practical approach extensively used for estimating crop evapotranspiration (ETc ) is the crop coefficient (Kc ) approach (1977, Allen et al., 1998) which consists of multiplying reference evapotranspiration (ET0 ) with crop coefficients (Kc ) to find ETc (i.e., ETc = ET0 x Kc ). Reference evapotranspiration (ET0 ) is defined as the rate of evapotranspiration from a hypothetical reference green grass of actively growing, completely shading the ground, uniform height, and not short of water (Allen et al., 1998). Accurate field measurements of ET0 are also difficult and it is usually estimated using weather data. There are several empirical or semi-empirical equations are available to assess ET0 from meteorological data. Depends upon the data availability, climatic conditions of the area and degree of accuracy, we may choose the appropriative empirical equation to estimate ET0 . However, FAO-56 Penman-Monteith (PM) equation, which yields the results nearer to Lysimeter measured data, may be used as the standard method in all climatic conditions to estimate ET0. Experimentally determined ratios of ETc /ET0 called crop coefficients (Kc ) (Allen et al., 1998). The crop coefficients depend on the
∗ Corresponding author. Fax: +91 8577224888. E-mail address: [email protected] http://dx.doi.org/10.1016/j.eja.2015.06.003 1161-0301/© 2015 Elsevier B.V. All rights reserved.
type of crop and its varieties, crop height, leaf characteristics, soil properties, climate conditions, irrigation methods and so on. Different crops will have different crop coefficients (Kc ), even for the same crop Kc varies throughout the growth period due to changes in vegetation and ground cover. The growing period of the crop is generally divided into four phenological stages (initial, development, mid and late) for the purpose of stage-wise development of crop coefficients. The variations in Kc during the growing period are described in the form of a crop coefficient curve. Initially the concept of crop coefficients (Kc ) was introduced by Jensen Marvin (1968) and later many researchers (Doorenbos and Pruitt, 1977; Allen et al., 1998) are carried out investigations and recommended crop coefficient values for various crops grown under different climatic conditions. These values are normally used at places where local data are not available. However, there is a strong need for local calibration of crop coefficients because the climatic conditions in the field differ from the standard conditions. Shah and Edling (2000) evaluated PM, FAO-Penman and 1963 Penman combination models for their capabilities to predict rice ET using daily weather data. Crop coefficients of rice for the vegetative, flowering, and yield formation stages were found 1.39, 1.51, and 1.43, respectively. Tyagi et al., (2000) developed crop coefficients (Kc ) for wheat and sorghum from ETc measurements and weather data. It was pointed out that actual Kc values are significantly different from those suggested by the UN FAO indicating the need for generating these values at local/regional level. The relationships between standard UN FAO PM and other ET0 methods were also investigated. Kashyap and Panda (2001) made an attempt to develop regional relationships between the evapotranspiration measured by the Lysimeter and that estimated by the climatological
K.C. Reddy / Europ. J. Agronomy 69 (2015) 59–62
KC
60
2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0
Center: Rajendranagar Crop: Castor
1
11
21
31
41
51
61
71
81
101
91
111
121
131
2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0
Crop: Maize
1
11
21
31
41
51 Days
61
71
81
91
Fig. 1. Variation of daily Kc values.
7
Center: Rajendranagar Crop: Castor
6
ETc observed, mm/day
ETc observed, mm/day
7
5 4 3 2 1 0
Center: Rajendranagar Crop: Castor
6 5 4 3 2 1 0
0
1
2
3
4
5
6
7
0
ETc estim ated, m m /day
1
2
3
4
5
6
7
ETc estim ated, m m /day
8
8
Center: Rajendranagar Crop: Maize
7 6
ETc observed, mm/day
ETc observed, mm/day
KC
Days
5 4 3 2 1 0
Center: Rajendranagar Crop: Maize
7 6 5 4 3 2 1 0
0
1
2
3
4
5
6
7
8
0
1
2
3
4
5
6
7
ETc estim ated, m m /day
ETc estim ated, m m /day
Training period
Testing period
Fig. 2. Scatter plots of daily ETc observed with that estimated using polynomial Kc models and PM ET0 .
8
K.C. Reddy / Europ. J. Agronomy 69 (2015) 59–62
61
Table 1 Details of FAO-56 Penman-Monteith ET0 estimation method. Basic reference
Equation
ET0 =
Allen et al. (1998)
Input data
0.408(Rn −G)+
900 (e −e˛ ) Tmean +273 2 s
+(1+0.342 )
Primary
Secondary
Tmin , Tmax , RHmin , u2 , n
–
Table 2 Crop details and period of data collected. Crop
Crop varieties
Crop season
Crop period (days)
Period of data
Training period
Testing period
Castor (Ricinus communis) Maize (Zea mays)
ARUNA B21, CM202, CM119, CM104, GANGA5
Jun–Nov July–Oct
135 100
1978–1993
1978–1988
1989–1993
methods. The crop coefficients for potato crop were also estimated at different stages of growth and Kc value at the maturity stage was found to be considerably higher than the corresponding FAO recommended Kc value. This study deals with the derivation of crop coefficients and development of crop coefficient (Kc ) models of castor and maize crops in the Rajendranagar region of the study area.
Table 3 Polynomial regression Kc models. Crop
Regression equation
Castor
Kc = −9E-06 x3 + 0.001 x2 − 0.0212 x + 0.5032 (1 ≤ x ≤ 70) Kc = 1E-05 x3 − 0.0032 x2 + 0.3181 x − 9.0549 (x >70) Kc = −2E-05 x3 + 0.0017 x2 − 0.0229 x + 0.5192 (1 ≤ x ≤ 60) Kc = −4E-05 x3 + 0.0084 x2 − 0.5879 x + 14.9834 (x >60)
Maize
2.1. Crop coefficient models 2. Materials and methods Rajendranagar region, Rangareddy district, Andhra Pradesh, India, has been selected as the study area. The meteorological data in the study area for the period 1978–1993 was collected from IMD, Pune. Data from 1978 to 1988 is used for the purpose of training the Kc model and rest of data for testing the Kc model. Details of FAO56 Penman-Monteith method used for ET0 estimation and crops selected for the study are shown in Tables 1 and 2, respectively.
The crop coefficients for castor and maize crops were determined, as the ratio of Lysimeter measured ETc values to reference evapotranspiration (ET0 ) values computed using FAO-56 PenmanMonteith method, in the region of the study area. Lysimeter measured daily ETc data were used to derive daily crop coefficients for the crops. These Kc values were plotted with respect to days after sowing (x) and a dual polynomial function each for rising and falling trends of the curve was fitted to the data.
7 Center: Rajendranagar Crop: Castor
ETc (mm/day)
6 5 4 3 2 1
ETc observed
ETc estimated
0 1
11
21
31
41
51
61
71
81
91
101
111
121
131
Days
8 Center: Rajendranagar Crop: Maize
7 ETc (mm/day)
6 5 4 3 2 1
ET observed
ETc estimated
0 1
11
21
31
41
51
61
71
81
91
Days Fig. 3. Comparison of observed daily ETc values with those estimated using polynomialKc models and PM ET0 during testing period.
62
K.C. Reddy / Europ. J. Agronomy 69 (2015) 59–62
Table 4 Performance indicators of ETc models. Crop
Castor Maize
Slope of the scatter plot
Intercept of the scatter plot
R2
Training period
Testing period
Training period
Testing period
Training period
Testing period
Training period
Testing period
Training period
Testing period
0.8887 1.0233
1.0554 0.9273
0.1177 0.0456
0.0307 0.1587
0.8392 0.9090
0.8972 0.8623
0.48 0.46
0.47 0.58
83.92 90.90
89.72 86.23
RMSE (mm)
EC (%)
2.2. Performance evaluation criteria
4. Conclusion
The performance evaluation indices used in the present study, namely, Coefficient of Determination (R2 ), root mean square error (RMSE) and efficiency coefficient (EC).
The crop coefficient (Kc ) values were calculated for castor and maize crops in the Rajendranagar region and a third order polynomial Kc models were fitted. The performances of the models were tested using performance indicators. The models performed well for both the crops. It has been observed that crop evapotranspiration (ETc ) values computed based on these polynomial Kc models are comparable with those of Lysimeter measured ETc. These models can, therefore, be used for estimating Kc values of castor and maize crops for any day after sowing in the study region. These models are also suggested for other areas having similar climatic conditions and same crop varieties.
3. Results and discussion The daily crop coefficients for the crops in the region selected for the present study plotted against time i.e., days after sowing (x) are as shown in Fig. 1. It may be observed from these plots that Kc values showed an increasing trend with the advancement in crop growth up to physiological development and after that started declining. A dual polynomial function each for rising and falling trends of the curve was fitted to the data. A third order polynomial equation was fitted to both rising and falling trends as presented in Table 3. The ETc values for the crops calculated as the product of Kc estimated form the proposed polynomial equations (models) and ET0 estimated by PM were compared with Lysimeter measured ETc in the form of scatter plots as shown in Fig. 2 and, also comparison plots as presented in Fig. 3. The performance indicators of these models are given in Table 4. The slope and intercept, respectively, close to one and zero of scatter plots and closeness of computed ETc values with those of observed ETc as observed from comparison plots indicate the satisfactory performance of the models. The high values of R2 and EC and low values of RMSE also represent the satisfactory performance of the models.
References Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop evapotranspiration Guidelines for computing crop water requirements. In: FAO Irrigation and Drainage Paper 56. FAO, Rome. Doorenbos, J., Pruitt, W.O., 1977. Guidelines for predicting crop water requirements. Irrigation and Drainage Paper, 24. FAO, Rome, Italy. Jensen Marvin, E., 1968. Water consumption by agricultural plants. In: Kozlowski, T.T. (Ed.), Plant Water Consumption and Response. Water Deficits and Plant Growth, Vol. II. Academic Press, New York, pp. 1–22. Kashyap, P.S., Panda, R.K., 2001. Evaluation of evapotranspiration estimation methods and development of crop coefficients for potato crop in a sub- humid region. Agric. Water Manage. 50 (1), 9–25. Shah, S.B., Edling, R.J., 2000. “Daily evapotranspiration prediction from Louisiana flooded rice field. ”. J. Irrig. Drain. Eng. ASCE 126 (1), 8–13. Tyagi, N.K., Sharma, D.K., Luthra, S.K., 2000. Evapotranspiration and crop coefficients of wheat and sorghum. J. Irrig. Drain. Eng. ASCE 126 (4), 215–222.