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Determination of the water requirement and crop coefficient values of sugarcane by field water balance method in semiarid region
Agricultural Water Management 232 (2020) 106042
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Determination of the water requirement and crop coefficient values of sugarcane by field water balance method in semiarid region
T
S.K. Dingre*, S.D. Gorantiwar Mahatma Phule Krishi Vidyapeeth, Rahuri, Maharashtra, India
A R T I C LE I N FO
A B S T R A C T
Keywords: Crop coefficient (Kc) Crop evapotraspiration (ETc) Days after planting (DAP) FAO 56 Field water balance Growth stage Sugarcane
Sugarcane is a major agro-industrial crop in semiarid regions and generally has high evapotranspiration. Standardized reference evapotranspiration (ET) and location specific crop coefficients are used to estimate crop evapotranspiration. However, precise information on crop coefficient (Kc) is a major impediment in semiarid environments. Field studies were conducted during two seasons of 2015 and 2016 in clay soils to determine crop evapotranspiration and crop coefficients (Kc) of sugarcane for semiarid India.The experimental area was cultivated with irrigation applied at 7–10 days interval by a drip irrigation system in addition to rainfall and the irrigation scheduling was based on field water balance approach. The crop evapotranspiration was determined by field water balance, reference evapotranspiration (ETo) by the Penman-Monteith approach while crop coefficient were computed through the standard FAO-56 methodology.On an annual basis, the total reference evapotranspiration (ETo) and crop evapotranspiration (ETc) were 1318−1426 mm and 1291−1388 mm respectively. Two years average sugarcane crop evapotranspiration estimated by field water balance method was 1339 mm year−1. The irrigation water requirement andeffective rainfall was 991 mm year-1 and 424 mm year-1 respectively. Two years results showed that there was a notable symmetry between Kc obtained from field water balance measurements and FAO-56 reported Kc. The determined Kc values for tillering, grand growth and maturity stages of sugarcane were 0.70, 1.20 and 0.78, respectively. The Kc values were found 25.5 %, 4 % and 20.4 % less during the tillering, grand growth and maturity stage respectively over the FAO-56 Kc values. The 2nd order polynomial equation was fitted with crop coefficient as the dependent variables and ratio of days after transplanting to total crop period as the independent variable. The daily values of Kc from equation is very useful towards efficient management of irrigation water in terms of making a Decision Support System, Soil Moisture based Crop Yield Modeling, Crop Water Requirement based Computer programme or Mobile Application, Automation of irrigation system in the major sugarcane growing countries of semi arid regions.
1. Introduction Globally agriculture contributes to more than 80 % share of available water. In many countries, especially for developing countries this share is reducing continuously due to realization of increased need of water for industries and domestic (urban and rural) water supply. On the other hand, there is limitation on developing new water resources due to technical and economic reasons: reduced availability of appropriate sites for the storage reservoir as we have utilized almost all the sites; increased cost of developing new water resources and social and environmental concerns. The climate change and variability also contribute reduced water availability due to increased frequency of extreme events. Thus, in context of global water scarcity for agriculture, the precise management of available water for irrigation is important.
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Sugarcane is the crop that contributes immensely to the regional economics of many countries including Brazil, India, China, Pakistan, Mexico and in many of these regions, water is the limiting factor for agriculture. Incidentally in these countries, water consumption for sugarcane is disproportionate compared to other crops. For example, in the western state of India (Maharashtra), sugarcane is cultivated over 6 % of the total cropped area and consumes almost 70 % of the total water available (Commission for Cost and Prices (CACP) (2015)). Thus, there is large inequality in water utilization for sugarcane compared with other crops. Ironically, around 80 % of the sugarcane is grown in regions that have a history of water scarcity. On an average 3000–4000 mm of water is applied to sugarcane depending on the method of irrigation while water requirement based on evapotranspiration is less than 2000 mm (Shrivastava et al., 2011).
Corresponding author. E-mail addresses: sachindingre@rediffmail.com (S.K. Dingre), [email protected] (S.D. Gorantiwar).
https://doi.org/10.1016/j.agwat.2020.106042 Received 12 August 2019; Received in revised form 19 January 2020; Accepted 21 January 2020 0378-3774/ © 2020 Elsevier B.V. All rights reserved.
Agricultural Water Management 232 (2020) 106042
S.K. Dingre and S.D. Gorantiwar
Flood irrigation is mostly adopted to irrigate sugarcane in canal command areas providing 2–3 times excess water than required. This is mainly due to the beliefs among farmers that more the water is applied to sugarcane, more yield is obtained. Of course, this is not true; therefore there is a need to provide the information to sugarcane farmers on precise water measurement. On other hand, the improved irrigation methods such as drip irrigation are being increasingly adopted but the lack of knowledge on the periodical water requirement for which the information such as crop evapotranspiration and crop coefficient is needed. The knowledge of crop evapotranspiration (ETc) and periodical or stagewise crop coefficients is important to improve water use efficiency in sugarcane (Inman-Bamber and McGlinchey, 2003). A variety of approaches are available for estimating crop evapotranspiration. The most widely accepted two step approaches which includes the quantification of the atmospheric demand through the calculation of reference evapotranspiration (ETo), and the incorporation of the surface characteristics through a crop factor called as crop coefficient (Kc), is generally followed in the estimation of crop evapotranspiration (Doorenbose and Pruitt, 1979). Doorenbos and Kassam (1979) suggested Kc value of 0.50, 1.00, 1.30, 0.80 and 0.60 for establishment, crop development, mid-season, late season and at harvest for sugarcane; however, these values are based on global averages of Kc and that too mostly from temperate regions. They emphasized the strong need for local calibration of crop coefficients since the climatic conditions encountered in the field differ from the standard conditions. Omary and Izuno (1995) in the south Florida, USA derived crop coefficients by Penman Eo estimate (1948 version), with a peak mid-season value of 1.27. Allen et al. (1998) further proposed Kc values for sugarcane in the range 0.40–1.25 for the initial (low canopy) and mid (full canopy) periods of crop development to 0.75 for the end (harvest) of development without providing the information on the derivation of these values (Inman-Bamber and McGlinchey (2005)). Inman-Bamber and McGlinchey (2003) determined Kc for sugarcane as 0.40, 1.25 and 0.70 during the initial stage, mid-season and at harvestusing the Bowen ratio energy balance method in Australia and Swaziland. In lysimeter studies at tropical Brazil, Cardoso et al. (2015) obtained sugarcane crop coefficients values as 0.31, 1.15, 1.25, and 0.90 for initial, development, mid and late sugarcane growth stages, respectively. However, for similar study in Myanmar, Win et al. (2014) reported these Kc values as 0.53, 0.81, 1.25, and 1.27 respectively. Silva et al. (2012) derived crop coefficients from field water balance measurements at tropical Brazil and reported Kc values for initial, mid-season and late stages as 0.56; 1.43 and 1.32, respectively. On the whole, all above studies emphasized the strong need for determination of crop coefficients since the climatic conditions and its interaction with crop vary in their spatial/temporal scale. The crop coefficients for calculating sugarcane evapotranspiration have not been developed for semi-arid environments hence, this study taken. The field water balance method was used for this purpose.
Table 1 Soil moisture constants (%) for different soil layers of experimental site. Soil layer depth, cm
0-15
15-30
30-45
45-60
60-75
Average
Field capacity (%) Permanent wilting point (%) Available water (%) Allowable deficit (%) Bulk density, Mg m−3
39.1 16.4 22.7 24.3 1.24
40.3 16.6 23.7 24.9 1.27
43.7 17.3 26.4 26.5 1.3
42.1 17.8 24.3 26.3 1.28
41.8 16.7 25.1 25.5 1.27
41.4 17.0 24.4 25.5 1.27
mean maximum and minimum relative humidity range from 59 to 90 % and 21–61 %, respectively. The annual mean pan evaporation ranges from 2.3–14.9 mm day−1 while, the sunshine hours range from 7 to 9 day−1. The annual mean wind speed ranges from 3.2–13.09 kmhr−1. Agro-climatically, the area falls under the scarcity zone of country.The local climate is semiarid with subtropical sugarcane cultivation. 2.2. Soil measurements A trench was opened in the experimental site for extracting soil samples that were used to determine the textural class, bulk density, field capacity and wilting point. The groundwater level at the experimental site dropped down to 2.0 m during the growing season. The experimental area was cultivated with irrigations applied at 7–10 days interval by a drip irrigation system, in addition to rainfall. Table 1 shows the main soil moisture constant of experimental soil. The textural class of the soil of experimental site was clay. The soil was medium alkaline in reaction (pH 8.36) with electrical conductivity of 0.40 dS m−1. The depth of soil was 1.8 m. The average field capacity and permanent wilting point were 41.4 and 17 %, respectively, and bulk density was 1.27 Mg m-3. Doorenbos and Kassam (1979) reported a maximum root penetration of the sugarcane plant of 100 cm, whereas most of the roots were concentrated in the top 75−80 cm of soil with only few roots below 20 cm. Therefore, a root zone depth of 75 cm was considered for planning the observations. 2.3. Root zone depth The observations of root length were recorded by destructive method upto tillering stage or development stage (135 days after planting). For each moisture content observation, the effective root zone was determined by carefully uprooting one healthy plant. Before uprooting, the soil surrounding the plant was fully made saturated and then removed slowly (FAO 24). The root length was measured with tape and approximately, the soil depth in which 80 % of the water intake takes place was taken as the effective root zone for irrigation purpose (Michael, 2010). For further measurements five root study plots were prepared by growing sugarcane in closed soil filled plastic tanks above the ground and effective root zone was measured directly by noting the root length in different soil layers.
2. Materials and methods
2.4. Soil moisture content
2.1. Site characterization
Soil moisture content were measured prior to every irrigation and in between two irrigations approximately at midpoint of irrigation interval during the entire crop season. Gravimetric method was used for determination of the soil moisture content. The soil samples were collected upto root zone depth at the depths of 15, 30, 45, 60 and 75 cm. The soil moisture was also monitored whenever the soil profile was recharged by precipitation.
The field experiment was carried out during the Annual seasons of 2015 and 2016 at Experimental Farm of Department of Irrigation and Drainage Engineering, Mahatma Phule Krishi Vidyapeeth, Rahuri located in the western region of Maharashtra state, India (latitude 19° 48’ N; longitude 19° 57′ E; altitude 657 m). The average annual precipitation is 555 mm. Out of total annual rainfall, about 80 percent rains are during South-West monsoon (June to September), while the rest is from North-East monsoon(October-November). The distribution of rain is erratic, uneven and ill distributed over 15–37 rainy days. The annual mean maximum and minimum temperature range between 21.2 °C–41.8 °C and 3.0 °C–24.6 °C, respectively. The annual
2.5. Application of irrigation water The scheduling of irrigation was based on soil moisture content in the root zone. The irrigation was done to refill the profile to field capacity. The irrigation was initiated when soil water in the root zone 2
Agricultural Water Management 232 (2020) 106042
S.K. Dingre and S.D. Gorantiwar
following equation (FAO-56);
approached, but never depleted more than 65 % (FAO-56) of available soil water. The depth of water applied for irrigation was calculated by equation formulated as below;
ETc = I + R e − RO − DP + CR ± ΔSF ± ΔS Where, ETc is crop evapotranspiration, I is depth of irrigation applied, R e is effective portion of rainfall, RO is runoff from the soil surface, DPis deep percolation below the root zone, CR is capillary rise (In case of a shallow water table), ΔSF is horizontal subsurface flow in or out of the root zone and ΔSis change in soil profile water storage respectively. All parameters were expressed in mm.The soil water balance equation based on the above stated simplified equation was formulated as below;
When R e ≤ (θft × Zt × BDt − θt × Zt × BDt ) n
dt =
∑ (θft
× Zt × BDt − θt × Zt × BDt ) − R e
i=1
When Re ≥ (θft × Zt × BDt − θt × Zt × BDt ) dt = 0 θft =
n
n
n
n
∑i =1 θfi ; θt = ∑i =1 θi; Zt = ∑i =1 Zi ; BDt = ∑i =1 BDi
t
(θt × Zt − 1 × BDt − 1) = (θt − 1 × Zt − 1×BDt − 1) + It − 1 +
Where dt is depth of irrigation water to be required in the active root zone at tth is the day of irrigation event (mm), θft and θt is soil watercontentsat field capacity and at before irrigation for ith layer of the root zone at tth day respectively (%), Zt is the depth of effective root zone at tth day (mm);i the incremental root depth (150 mm) and n is number of i layers, R e the effective rainfall (mm). BDt is bulk density of effective root zone on tth day (Mg m−3).The soil moisture contents at 33 Kpa and 1500 Kpa were worked out for different soil layers of experimentation with Pressure Plate Apparatus.
t−1
Σtt − 1ETc
2.6. Soil moisture storage
ΔS = S1 − S2 or ΔSt = (θt − 1 × Zt − 1 − θt × Zt-1) × BDt -1 n
n
∑ θi Zt-1 = ∑ Zi BDt−1 = ∑ BDi i=1
i=1
m
∑ j=1 ETcj
Where, jis the period for which ETc measured between two successive moisture content observation events (from t-1to t); mis the total number of two successive events in entire growth period. The effective rainfall was computed by criteria mentioned in FAO Document No. 25 (Dastane (1974)). Surface runoff was considered nil as experimental site had flat topography and no runoff was observed during the periods of irrigation or precipitation. In addition, to overcome runoff problem in irrigation process, drip-irrigation system was used which did not produced surface runoff in irrigation process. No shallow water table existed at the study site, thus only percolation below the root zone was of concern. However, to attain this purpose, drip irrigation system was used for irrigation water supply as it has distinct advantage of slow water supply rate which produced no deep percolation and equaling it as zero for analysis. Capillary rise was assumed to be zero because moisture table was more than 1 m below the bottom of root zone at experimental site. For prevention entry of subsurface flow, a 1 m deep interceptor drain was dug around the entire periphery of experimental plot. In addition to this, the mole drains were laid at 4.5 m lateral distance in entire experimental field
The changes in soil moisture storage (ΔS) were determined by considering the soil layers from soil surface down to the depth of effective root zone. The depth of moisture depleted from each layer viz. 0–15, 15–30, 30–45, 45–60, 60–75 cm during each soil moisture measurement were computed. The change in soil moisture storage (ΔS) was determined for successive observation days i.e. soil moisture storage at the previous observation day minus soil moisture storage at next observation day, as:
n
t−1
Σtt − 1R e
Where ETc is the crop evapotranspiration from in the active root zone (mm)between t-1 and tth day time interval, R e the effective rainfall (mm) betweent-1 and tth day time interval, It − 1 the supplemental irrigation (mm)given on t-1 day. The total evapotranspiration was expressed as;
ETc =
θt − 1 =
= (θt − 1 − θt ) × (Zt − 1 − BDt − 1) + It − 1 +
t
∑ Re − ∑ ETc
i=1
Where, S1 and S2 are the soil moisture storage at previous observation day and soil moisture storage at next observation day respectively. θt − 1 and θt are the soil moisture storages between two consecutive observation days (%). In other means, t-1 and t are the previous and successive day of observation (t followed by t-1). Zt − 1 is the depth of effective root zone at t-1 day (mm), i the incremental root depth (150 mm) and n is number of i layers.BDt-1 is bulk density of effective root zone at t-1 day (Mg m−3). The FAO-56 has suggested that soil water balance method can only give evapotranspiration estimates over long periods of the order of week-long or ten-day periods. Therefore, the interval between two successive soil moisture measurements was maintained between 7–10 days however, during rainy days it was extended to 15 days (Allen et al., 1998).
2.8. Reference evapotranspiration Daily measurements of air temperature, wind speed, solar radiation and relative humidity for estimating ETo as well as rainfall were made from automatic weather station observatory, situated at sugarcane experimental site for period from 12thDecember 2014 to 23rd December 2015 and 24th December 2015 to 31st December 2016. The reference evapotranspiration (ETo) which was obtained by the Penman-Monteith approach (Allen et al., 1998). 900
2.7. Crop evapotranspiration
ETo = The simplified soil moisture balance method was used to estimate crop evapotranspiration (ETc) in root zone between consecutive soil moisture measurement days. For this, water content in root zone depletion was calculated which essentially involves adding and subtracting of losses and gains of various parameters of the soil water budget expressed in terms of water depth. Rainfall, irrigation and capillary rise of groundwater towards the root zone was considered to decrease the root zone depletion in root zone whereas, crop evapotranspiration and percolation losses were considered to increase depletion in root zone. The moisture balance, expressed in terms of depletion at the end consecutive soil moisture measurement days was calculated by
0.408Δ (Rn − G ) + γ T + 273 u (es − ea ) Δ + γ (1 + 0.34u2 )
Where, ETo is Reference evapotranspiration (mm day−1); Rn isNet radiation at the crop surface (MJ m-2 day−1); G is Soil heat flux density (MJ m-2 day−1); T is Mean daily air temperature at 2 m height (°C); u2 is Wind speed at 2 m height (m s−1); es is Saturation vapour pressure (kPa); ea is actual vapour pressure (kPa); Δ is slope of vapour pressure curve (kPa °C-1) and γ is psychrometric constant (kPa °C-1). 2.9. Computation of crop coefficients The crop coefficients were computed for different growth stages of sugarcane. The growth period was divided into four stages: 3
Agricultural Water Management 232 (2020) 106042
S.K. Dingre and S.D. Gorantiwar
increase in soil layer depth upto 45 cm and thereafter it slightly decreased at 60 cm and lowest moisture content was observed at 75 cm depth (Fig. 2). During tillering stage, more soil moisture depletion was observed, however, when plant canopy fully developed after tillering, the soil moisture depletion was uniform in all layers (Singh and Mohan, 1994; Raghuvanshi and Wallender, 1998).The particular growth stage and incident of rainfall greatly influenced the soil moisture content. Invariably of growth stages and barring rainfall events, the moisture content was closer to field capacity.
establishment (0–45 days after planting), Tillering (60–135 DAP), grand growth (135–300 DAP) and maturity (300–360 DAP). The initial stage was assumed from the beginning of planted sugarcane to the full expansion of root volume in nursery; Tillering stage is just after 15 days of transplanting the seedlings when tillers are starts to emerge from mother shoot and ends when tiller starts to elongate at the beginning of grand growth; the grand growth stage is from then upto the timing when cane has achieved its full growth; the maturity stage continues from then until harvest. These four growth stages correspond to those defined in FAO-56 (Allen et al., 1998) respectively as initial, development, mid-season and end season. In this investigation, later three stages were considered and initial stage i.e. initial stage was skipped with a view that all the farmers of this region essentially raised nursery to attain good germination at initial stage. Further, nursery planting of sugarcane has distinct advantages like spare time for field preparation, saving of three irrigations and healthy plant selection, etc. The crop evapotranspiration values obtained by monitoring the soil moisture balance in the crop root zone and ETo values estimated using climatic data for specified periods. The crop coefficient (Kc) were computed as the ratio of crop evapotranspiration and reference evapotranspiration (ETc / ETo) for the respective period(7–10 daysinterval).The polynomial equation was fitted with Kct as the dependent variables and (t/T) as the independent variables.
3.3. Field water balance 3.3.1. Irrigation water applied The irrigation depth differed for a particular growth stage in a season due to differences in crop water use and duration of stage (Table 2). This was probably caused mostly by differences in annual weather conditions (Wiedenfeld, 2004). Invariably in both seasons, grand growth stage identified as high water requirement stage due to its long duration (165–170 days). This followed by tillering stage (75–80 days) and maturity stage (65–70 days). The irrigation water applied in grand growth stage of 2016 was less than half (372.4 mm) compared to 2015 (799 mm), because of the higher contribution of rainfall in crop water use in 2016. However, irrigation water amount in tillering stage (277.6 mm) was higher in 2016 than in 2015 (211.1 mm); because of the higher evaporative demands. In both the seasons, the lowest irrigation water was required during the maturity stage. This happened because of decline in crop water use (ETc) with crop maturity during this period, and may also indicate that the crop was taking advantage of moisture stored in the soil profile from off-season rainfall (Wiedenfeld Robert, 2000).
t 0 t 1 t 2 Kct = ao ⎛ ⎞ + a1 ⎛ ⎞ + a2 ⎛ ⎞ ⎝T ⎠ ⎝T ⎠ ⎝T ⎠ Where, Kct is crop coefficient of tth day; a0, a1, a2 are constants of equations; t is day considered; T is total period of crop growth from planting to harvesting (days). The regression coefficients were estimated and tested for its significance to decide upon the validity of the particular equation.Using best fit equation, the daily Kc values were estimated for both seasons and average daily Kc values (from 50 DAP i.e. from 10 days after transplanting) were then estimated by taking the average of estimated daily Kc values of 2015 and 2016.
3.3.2. Effective rainfall The rainfall received during 2015 and 2016 was 313.2 mm (38 rainy days) and 534.3 mm (40 rainy days), respectively. In both the years all rainfall received was effective (Table 2). The occurrence of rainfall affected the depth of irrigation in different growth stages. In 2015, the effective rainfall was 43.6 % less than average rainfall (555 mm) therefore; more irrigation water applied in that season. However, in 2016, effective rainfall (534.3 mm) contributed almost 41 % of crop consumptive use and therefore demands of irrigation water reduced to half in 2016. Among different growth stages, more irrigation applied in tillering stage (February-Mid May) in 2016 due to high evaporative demand. The respective years grand growth stages coincided with rains, that contributed consumptive use and therefore demand of irrigation water was differed in 2015 and 2016 season. In maturity stage, no rainfall received in both the season and thus, irrigation amounts for both the seasons were almost for this stage.
2.10. Agronomic practices The sugarcane seedlings rose in nursery and transplanted after 35 days in a 6 × 27 m field. Sugarcane seedlings transplanted at the spacing of 1.5 m × 0.6 m. During nursery, irrigations applied at 2 days interval as per measured crop evapotranspiration (ETc) values through climatological method (Allen et al., 1998). After transplanting, the common irrigation was applied continued upto15 days until the seedling was established. The value of crop coefficient for common irrigation was referred as 0.40 (FAO-56). The other agronomic practice viz. weeding, off barring, earthing up fertigation schedule and operation to prevent lodging were followed as per recommended by parent Agricultural University. 3. Results and discussion
3.3.3. Crop evapotranspiration The total depths of water use during 2015, 2016 and average of two seasons were 1386.8 mm, 1291 mm and 1338.9 mm respectively (Table 2). The sugarcane evapotranspiration (ETc) varies considerably from place to place depending on weather conditions, texture of soil and duration of the crop. Numerous approaches have been used by different researchers to measure or estimate sugarcane evapotranspiration (Thompson and Boyce, 1967; Omary and Izuno (1995); Allen et al., 1998; Wiedenfeld Robert (2000); Wiedenfeld, 2004; Chabot et al., 2005; Silva et al., 2012; Win et al., 2014; Anderson et al., 2015; Cardoso et al., 2015). Nevertheless, its estimate largely depends upon type of approach used by researchers. In some studies, evaporation from a USWB Class A pan (Allen et al., 1998) is common reference for measuring evapotranspiration in many crops including sugarcane. Using this method, Wiedenfeld (2004) reported crop evapotranspiration of sugarcane as 1021 mm including annual effective rainfall in semiarid south Texas, whereas, Wiedenfeld
3.1. Root zone depth The root zone depth at the time of transplanting was 50 mm at 53 and 47 DAP in 2015 and 2016, respectively (Fig. 1). During both the years, the root length of sugarcane increased linearly with advancement in age of crop. The rate of root length expedites at the end of tillering stage (115–125 DAP). Thereafter, effective root zone increased approximately up to 204 days and 217 days in 2015 and 2016, respectively and then root zone becomes constant at 750 mm and subsequent samples were taken up to 750 mm. 3.2. Soil moisture The soil moisture content increased with crop evapotranspiration during the growth period. The moisture content found increased with 4
Agricultural Water Management 232 (2020) 106042
S.K. Dingre and S.D. Gorantiwar
Fig. 1. Measured root zone depth (mm) of sugarcane during 2015 and 2016 season.
Fig. 2. Moisture content in the soil profile for sugarcane during the 2015 and 2016 growing seasons. Table 2 Field water balance components (mm) during the growth stages for sugarcane observed at the experimental site in a subtropical climate, India. Growth stage
Initial Tillering Grand growth Maturity Total
Days
55 75 170 65 365
2015
2016
Average
I
Pe
ΔS
ETc
I
Pe
ΔS
ETc
I
Pe
ΔS
ETc
52.1 211.3 799.4 110.5 1173.3
– 53.2 243.8 16.2 313.2
– 2.8 −104.5 2.0 −99.7
52.1 267.3 938.7 128.7 1386.8
49.3 277.6 372.4 109 808.3
– 0 534.3 0 534.3
– −16.5 −72.2 37.1 −51.6
49.3 261.1 834.5 146.1 1291
50.7 244.4 585.9 109.8 990.8
– 26.6 389.1 8.1 423.8
– −6.9 −88.4 19.6 −75.7
50.7 264.2 886.6 137.4 1338.9
Pe = Effective rainfall, I = Irrigation, ETc = Crop evapotranspiration (I + Pe + ΔS), ΔS = Soil moisture storage change.
two irrigated sugarcane fields (1191 mm and 1389 mm) of Maui, Hawaii, USA in contrasting climates by eddy covariance towers. They used the short (ET0) and tall (ETr) vegetation versions of the American Society for Civil Engineers (ASCE) equation. The only field water balance study reported sugarcane evapotranspiration as 1686.7 mm for tropical condition of Brazil (Silva et al., 2012). Thus, on an annual basis, the sugarcane evapotranspiration ranges from 950 to 1700 mm depending on the location from different parts of the world. Therefore, sugarcane evapotranspiration amounting 1339 mm derived by field water balance in this study seems to be appropriate for semiarid conditions.
Robert (2000) obtained its value as 968 mm using Jensen-Haise equation for same region. In few lysimetric studies, Thompson and Boyce, 1967 at Pongola, South Africa found sugarcane evapotranspiration similar to USWB Class pan evaporation, suggesting a ‘pan factor’ (i.e. the ratio of ETC to pan evaporation) of 1.0. Likewise, Win et al. (2014) at Myanmar and Cardoso et al. (2015) at tropical Brazil reported sugarcane evapotranspiration as 1369.84 mm and 1438.23 mm respectively. Omary and Izuno (1995) in south Florida, USA used a novel way of measuring actual sugarcane evapotranspiration by monitoring daily changes in the height of the water table and estimated annual ETc of sugarcane as 1060 mm. Differently, Chabot et al. (2005) measured transpiration of sugarcane in Gharb plain, Morocco using the sap flow technique and found that sugarcane evapotranspiration were 30 % more than those predicted from the Penman-Monteith equation. However, they believed that the sap flow technique is an inappropriate method for determining transpiration rates from a heterogeneous canopy like that of sugarcane because of uncertainties in the methodology. Anderson et al. (2015) measured sugarcane evapotranspiration at
3.4. Crop coefficients of sugarcane The Kc values with confidence bounds for both the years are shown graphically in the form of polynomial equation, with respect to the ratio of days to total crop period (Fig. 3). The average Kc of two years ranged from 0.31 to 1.29 (Table 3). In both the seasons, Kc consistently increased from 0.43 to 1.03 during 50–130 days after planting (DAP). Thereafter, it showed gradual increases due to crop development in 5
Agricultural Water Management 232 (2020) 106042
S.K. Dingre and S.D. Gorantiwar
Fig. 3. a and 3b 2nd order polynomial crop coefficient curve for sugarcane crop during 2015 and 2016 season.
days i.e. at 90 DAP. The average Kc value for tillering stage was found lower (0.70) than FAO-56 value (0.94). Earlier, Win et al. (2014) also reported the lower Kc value for development stage as 0.81 estimated from lysimeters for Myanmar. The trend of curves for mid season of both the seasons showed very close association with FAO-56 Kc curve, however average Kc value for grand growth (mid season) stage was estimated slight lower (1.20) over 1.25 (FAO-56). The lower Kc obtained in this investigation may be due to different climatic conditions of semi arid region which primarily altered the reference crop evapotranspiration i.e. ETo. Differently, Inman-Bamber and McGlinchey (2003) and Cardoso et al. (2015) confirmed the current 1.25 value whereas, Omary and Izuno (1995) and Silva et al. (2012) reported higher value over 1.25. Nevertheless, this difference was mainly to due to variation in ET measurement approaches, weather conditions, duration of the crop, methodological assumptions and accuracy. The decline phase of estimated Kc curve showed early fall with lower Kc values (0.78) over FAO-56 values (0.98). Overall, there was a good association between Kc-developed and KcFAO in average of both seasons. However, some variations observed along the growth stages in both seasons. It was revealed that %
form of cane elongation (mid season stage). During the mid-season i.e. 130–300 DAP, Kc increased from 1.08 and then remain same in the range of 1.13-1.04 with peak value as 1.29. The highest Kc value occurred during 200–220 DAP. The Kc values during the late season (300–360 DAP) decreased gradually from 1.04 to 0.56. Thompson and Boyce (1971) in a lysimeter study observed that ETc rates declined by about 30 % after crops lodged, an effect that lasted upto crop maturity. The two years average Kc values are represented in the form of following second order polynomial equation. The variation of Kc is shown in Fig. 4
t 2 t Kct = − 4.695 ⎛ ⎞ + 5.566 ⎛ ⎞ − 0.360 ⎝T ⎠ ⎝T ⎠
3.4.1. Comparison with FAO- 56 The crop coefficient values derived from field soil water balance during the tillering, grand growth and maturity stages for sugarcane in a semi-arid region were 0.70; 1.20 and 0.78, respectively. The corresponding values of FAO-56 are 0.90, 1.25 and 0.98, respectively (Table 4). It is pointed out that at 60 DAP, low Kc value (0.43) was attained as against 0.65 of FAO-56. However, it hiked up after 25–30 6
Agricultural Water Management 232 (2020) 106042
S.K. Dingre and S.D. Gorantiwar
reduction observed between FAO Kc and developed Kc was 25.5 %, 4 % and 20.4 % for tillering stage, grand growth stage and maturity stage respectively (Table 2). The average % reduction was 16.6 %. This may be due to the conditions of the study area, soil conditions and crop variety etc. whereas; FAO Kc equation is developed for global climatic conditions. Pereira Luis et al. (2015) also reported the advances in adopted Kc research included techniques to estimate Kc based on the architecture of crops, notably height and fraction of ground cover. In practice, results reported here showed that FAO-Kc could lead to over estimation in irrigation scheduling of sugarcane in semi-arid conditions and the use of Kc values developed in this study would lead in correction of water requirement for sugarcane. Further, in this study the Kc value measured over the growth period of sugarcane have been converted in the equation form leading to estimation of Kc for any specific day and its use in decision support system.
Table 3 Average estimated crop coefficients (Kc) of sugarcane from best fit regression equations of 2015 and 2016. S. No.
Period, days
Average estimated Kc
Growth stagewise Kc
FAO56 Kc
Growth stagewise FAO Kc
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33
0-40 40-50 50-60 60-70 70-80 80-90 90-100 100-110 110-120 120-130 130-140 140-150 150-160 160-170 170-180 180-190 190-200 200-210 210-220 220-230 230-240 240-250 250-260 260-270 270-280 280-290 290-300 300-310 310-320 320-330 330-340 340-350 350-360
0.40 0.31 0.43 0.53 0.63 0.73 0.81 0.89 0.96 1.03 1.08 1.13 1.18 1.21 1.24 1.26 1.28 1.29 1.29 1.28 1.27 1.25 1.22 1.19 1.15 1.10 1.04 0.98 0.91 0.83 0.75 0.66 0.56
– – 0.70 (Tillering stage)
0.4 0.55 0.65 0.75 0.85 0.95 1.05 1.15 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.17 1.09 1.02 0.94 0.86 0.79
– – 0.90 (Tillering stage)
1.20 (Grand growth stage)
0.78 (Maturity stage)
1.25 (Grand growth stage)
4. Conclusion Sugarcane have immense role in economy of sugarcane growing countries but its water consumption scenario represents the unfavorable perspective. In irrigated agriculture, underestimation of its crop evapotranspiration (ETc) can lead to suboptimal yield due to water stress whereas overestimation can lead to excessive applied water, thus reducing water available for other uses or additional acreage and decreasing economic competitiveness. The crop coefficient (Kc) is the important parameter influencing the estimation of crop evapotranspiration (ETc) of any crop; and knowledge of periodical or stagewise crop coefficients of sugarcane is important. This investigation addressed the important issue of irrigation scheduling; provided the information of crop evapotranspiration and crop coefficients for sugarcane by field water balance method under semi arid conditions. The crop evapotranspiration of sugarcane was 1339.4 mm including irrigation water requirement and effective rainfall as 991 mm and 424 mm respectively. The determined sugarcane Kc values for tillering (development stage), grand growth (mid-season) and maturity stage (end season) was 0.70, 1.20 and 0.78, respectively. The Kc values are 16.6 % lesser than those suggested by FAO-56 for sugarcane. The study pointed out that FAO-Kc could lead to over estimation in irrigation scheduling of sugarcane in semi-arid conditions and the use of Kc values developed in this study would lead in correction of water requirement. The sugarcane Kc values converted in 2nd order polynomial equation form leading to estimation of Kc for any specific day. The daily values of Kc from equation is very useful to researchers working in area of sugarcane water management especially making a Decision Support System, Soil Moisture based Crop Yield Modeling, Crop Water Requirement based Computer programme or Mobile Application, Automation of irrigation system etc. Overall this study provided the adoptable information for sugarcane toward efficient management of irrigation water leading to proportionalities appropriately the imbalance of sugarcane cultivated area and use of irrigation water in the major sugarcane growing countries of semi arid regions.
0.98 (Maturity stage)
Fig. 4. 2nd order polynomial crop coefficient curve for estimating crop coefficients of sugarcane for total growth period. Table 4 Comparison of FAO-56 and field soil water balance derived sugarcane crop coefficient values for each crop growth stage. Growth stage
Initial Stage Tillering stage Grand growth stage Maturity stage Averagea a
FAO Kc
0.40 0.94 1.25 0.98 1.1
Developed Kc
Declaration of Competing Interest There is no conflict of interest for this study.
% variation
2015
2016
Average
2015
2016
Average
0.40 0.67 1.20 0.73 0.9
0.40 0.75 1.23 0.80 0.9
0.40 0.70 1.20 0.78 0.9
0.0 28.5 4.0 25.5 19.3
0.0 20.4 1.2 18.4 13.3
0.0 25.5 4.0 20.4 16.6
Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.agwat.2020.106042. References
Average values not included initial stage value. Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop Evapotranspiration. FAO
7
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table data in the Everglades agricultural area. Agric. Water Manage. 27, 309–319. Pereira Luis, S., Allen Richard, G., Martin, S., Raes, D., 2015. Crop evapotranspiration estimation with FAO56: past and future. Agric. Water Manage. 147 (1), 4–20. Raghuvanshi, N.S., Wallender, W.W., 1998. Optimization of furrow irrigation schedules, designs and net return to water. Agric. Water Manage. 35 (3), 209–226. Shrivastava, A.K., Srivastava, A.K., Solomon, S., 2011. Sustaining sugarcane productivity under depleting water resources. Current Sci. 101 (6), 748–754. Silva, V., Borges, C., Farias, C., Singh, V., Albuquerque, W., Silva, B., 2012. Water requirements and single and dual crop coefficients of sugarcane grown in a tropical region. Brazil. Brazil. Agril. Sci. 3 (2), 274–286. Singh, P.N., Mohan, S.C., 1994. Water use and yield response of sugarcane under different irrigation schedules and nitrogen levels in a subtropical region. Agric. Water Manage. 26, 253–264. Thompson, G.D., Boyce, J.P., 1967. Daily measurements of potential evapotranspiration from fully canopied sugarcane. Agric. Meteorol. 4, 267–279. Thompson, G.D., Boyce, J.P., 1971. Comparisons of measured evapotranspiration of sugarcane from large and small lysimeters. Proceedings of the South African Sugar Technologists Association 45, 169–176. Wiedenfeld, B., 2004. Scheduling water application on drip irrigated sugarcane. Agric. Water Manage. 64, 169–181. Wiedenfeld Robert, P., 2000. Water stress during different sugarcane growth periods on yield and response to N fertilization. Agric. Water Manage. 43, 173–182. Win, S.K., Zamora, O.B., Thein, S., 2014. Determination of the water requirement and kc values of sugarcane at different crop growth stages by lysimetric method. Sugar Tech 16 (3), 286–294.
irrigation and drainage Paper No. 56., Rome, Italy, pp. 102–106. Anderson, R.G., Wang, D., Tirado- Corbalá, R., Zhang, H., Ayars, J.E., 2015. Divergence of actual and reference evapotranspiration observations for irrigated sugarcane with windy tropical conditions. Hydrol. Earth Syst. Sci. Discuss. 19, 583–599. Cardoso, G.G.G., Campos de Oliveira, R., Teixeira, M.B., Dorneles, M.S., Domingos, R.M.O., Megguer, C.A., 2015. Sugar cane crop coefficient by the soil water balance method. Afr. J. Agric. Res. 10 (24), 2407–2414. Chabot, R., Bouarfa, S., Zimmer, D., Chaumont, C., Moreau, S., 2005. Evaluation of the sap flow determined with a heat balance method to measure the transpiration of a sugarcane canopy. Agric. Water Manage 75, 10–24. Commission for Cost and Prices (CACP), 2015. Price Policy for Sugarcane, 2016-17 Sugar Season. Department of Agriculture and Cooperation. Ministry of Agriculture, Government of India, New Delhi, pp. 26–27. Dastane, N.G., 1974. Effective Rainfall in Irrigated Agriculture. FAO Irrigation and Drainage Paper No. 25., Rome. Doorenbos, J., Kassam, A.H., 1979. Yield Response to Water. FAO Irrigation and Drainage Paper No. 33., Rome, Italy Pp193. Inman-Bamber, N.G., McGlinchey, M.G., 2003. Crop coefficients and water-use estimates for sugarcane based on long-term Bowen ratio energy balance measurements. Field Crops Res. 83, 125–138. Inman-Bamber, N.G., McGlinchey, M.G., 2005. Water relations in sugarcane and response to water deficits. Field Crops Res. 92 (2-3), 185–202. Michael, A.M., 2010. Irrigation: Theory and Practice (3rd Ed.). Vikas Publishing House Pvt. Ltd., New Delhi, pp. 465–472. Omary, M., Izuno, F.T., 1995. Evaluation of sugarcane evapotranspiration from water
8
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Determination of the water requirement and crop coefficient values of sugarcane by field water balance method in semiarid region
T
S.K. Dingre*, S.D. Gorantiwar Mahatma Phule Krishi Vidyapeeth, Rahuri, Maharashtra, India
A R T I C LE I N FO
A B S T R A C T
Keywords: Crop coefficient (Kc) Crop evapotraspiration (ETc) Days after planting (DAP) FAO 56 Field water balance Growth stage Sugarcane
Sugarcane is a major agro-industrial crop in semiarid regions and generally has high evapotranspiration. Standardized reference evapotranspiration (ET) and location specific crop coefficients are used to estimate crop evapotranspiration. However, precise information on crop coefficient (Kc) is a major impediment in semiarid environments. Field studies were conducted during two seasons of 2015 and 2016 in clay soils to determine crop evapotranspiration and crop coefficients (Kc) of sugarcane for semiarid India.The experimental area was cultivated with irrigation applied at 7–10 days interval by a drip irrigation system in addition to rainfall and the irrigation scheduling was based on field water balance approach. The crop evapotranspiration was determined by field water balance, reference evapotranspiration (ETo) by the Penman-Monteith approach while crop coefficient were computed through the standard FAO-56 methodology.On an annual basis, the total reference evapotranspiration (ETo) and crop evapotranspiration (ETc) were 1318−1426 mm and 1291−1388 mm respectively. Two years average sugarcane crop evapotranspiration estimated by field water balance method was 1339 mm year−1. The irrigation water requirement andeffective rainfall was 991 mm year-1 and 424 mm year-1 respectively. Two years results showed that there was a notable symmetry between Kc obtained from field water balance measurements and FAO-56 reported Kc. The determined Kc values for tillering, grand growth and maturity stages of sugarcane were 0.70, 1.20 and 0.78, respectively. The Kc values were found 25.5 %, 4 % and 20.4 % less during the tillering, grand growth and maturity stage respectively over the FAO-56 Kc values. The 2nd order polynomial equation was fitted with crop coefficient as the dependent variables and ratio of days after transplanting to total crop period as the independent variable. The daily values of Kc from equation is very useful towards efficient management of irrigation water in terms of making a Decision Support System, Soil Moisture based Crop Yield Modeling, Crop Water Requirement based Computer programme or Mobile Application, Automation of irrigation system in the major sugarcane growing countries of semi arid regions.
1. Introduction Globally agriculture contributes to more than 80 % share of available water. In many countries, especially for developing countries this share is reducing continuously due to realization of increased need of water for industries and domestic (urban and rural) water supply. On the other hand, there is limitation on developing new water resources due to technical and economic reasons: reduced availability of appropriate sites for the storage reservoir as we have utilized almost all the sites; increased cost of developing new water resources and social and environmental concerns. The climate change and variability also contribute reduced water availability due to increased frequency of extreme events. Thus, in context of global water scarcity for agriculture, the precise management of available water for irrigation is important.
⁎
Sugarcane is the crop that contributes immensely to the regional economics of many countries including Brazil, India, China, Pakistan, Mexico and in many of these regions, water is the limiting factor for agriculture. Incidentally in these countries, water consumption for sugarcane is disproportionate compared to other crops. For example, in the western state of India (Maharashtra), sugarcane is cultivated over 6 % of the total cropped area and consumes almost 70 % of the total water available (Commission for Cost and Prices (CACP) (2015)). Thus, there is large inequality in water utilization for sugarcane compared with other crops. Ironically, around 80 % of the sugarcane is grown in regions that have a history of water scarcity. On an average 3000–4000 mm of water is applied to sugarcane depending on the method of irrigation while water requirement based on evapotranspiration is less than 2000 mm (Shrivastava et al., 2011).
Corresponding author. E-mail addresses: sachindingre@rediffmail.com (S.K. Dingre), [email protected] (S.D. Gorantiwar).
https://doi.org/10.1016/j.agwat.2020.106042 Received 12 August 2019; Received in revised form 19 January 2020; Accepted 21 January 2020 0378-3774/ © 2020 Elsevier B.V. All rights reserved.
Agricultural Water Management 232 (2020) 106042
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Flood irrigation is mostly adopted to irrigate sugarcane in canal command areas providing 2–3 times excess water than required. This is mainly due to the beliefs among farmers that more the water is applied to sugarcane, more yield is obtained. Of course, this is not true; therefore there is a need to provide the information to sugarcane farmers on precise water measurement. On other hand, the improved irrigation methods such as drip irrigation are being increasingly adopted but the lack of knowledge on the periodical water requirement for which the information such as crop evapotranspiration and crop coefficient is needed. The knowledge of crop evapotranspiration (ETc) and periodical or stagewise crop coefficients is important to improve water use efficiency in sugarcane (Inman-Bamber and McGlinchey, 2003). A variety of approaches are available for estimating crop evapotranspiration. The most widely accepted two step approaches which includes the quantification of the atmospheric demand through the calculation of reference evapotranspiration (ETo), and the incorporation of the surface characteristics through a crop factor called as crop coefficient (Kc), is generally followed in the estimation of crop evapotranspiration (Doorenbose and Pruitt, 1979). Doorenbos and Kassam (1979) suggested Kc value of 0.50, 1.00, 1.30, 0.80 and 0.60 for establishment, crop development, mid-season, late season and at harvest for sugarcane; however, these values are based on global averages of Kc and that too mostly from temperate regions. They emphasized the strong need for local calibration of crop coefficients since the climatic conditions encountered in the field differ from the standard conditions. Omary and Izuno (1995) in the south Florida, USA derived crop coefficients by Penman Eo estimate (1948 version), with a peak mid-season value of 1.27. Allen et al. (1998) further proposed Kc values for sugarcane in the range 0.40–1.25 for the initial (low canopy) and mid (full canopy) periods of crop development to 0.75 for the end (harvest) of development without providing the information on the derivation of these values (Inman-Bamber and McGlinchey (2005)). Inman-Bamber and McGlinchey (2003) determined Kc for sugarcane as 0.40, 1.25 and 0.70 during the initial stage, mid-season and at harvestusing the Bowen ratio energy balance method in Australia and Swaziland. In lysimeter studies at tropical Brazil, Cardoso et al. (2015) obtained sugarcane crop coefficients values as 0.31, 1.15, 1.25, and 0.90 for initial, development, mid and late sugarcane growth stages, respectively. However, for similar study in Myanmar, Win et al. (2014) reported these Kc values as 0.53, 0.81, 1.25, and 1.27 respectively. Silva et al. (2012) derived crop coefficients from field water balance measurements at tropical Brazil and reported Kc values for initial, mid-season and late stages as 0.56; 1.43 and 1.32, respectively. On the whole, all above studies emphasized the strong need for determination of crop coefficients since the climatic conditions and its interaction with crop vary in their spatial/temporal scale. The crop coefficients for calculating sugarcane evapotranspiration have not been developed for semi-arid environments hence, this study taken. The field water balance method was used for this purpose.
Table 1 Soil moisture constants (%) for different soil layers of experimental site. Soil layer depth, cm
0-15
15-30
30-45
45-60
60-75
Average
Field capacity (%) Permanent wilting point (%) Available water (%) Allowable deficit (%) Bulk density, Mg m−3
39.1 16.4 22.7 24.3 1.24
40.3 16.6 23.7 24.9 1.27
43.7 17.3 26.4 26.5 1.3
42.1 17.8 24.3 26.3 1.28
41.8 16.7 25.1 25.5 1.27
41.4 17.0 24.4 25.5 1.27
mean maximum and minimum relative humidity range from 59 to 90 % and 21–61 %, respectively. The annual mean pan evaporation ranges from 2.3–14.9 mm day−1 while, the sunshine hours range from 7 to 9 day−1. The annual mean wind speed ranges from 3.2–13.09 kmhr−1. Agro-climatically, the area falls under the scarcity zone of country.The local climate is semiarid with subtropical sugarcane cultivation. 2.2. Soil measurements A trench was opened in the experimental site for extracting soil samples that were used to determine the textural class, bulk density, field capacity and wilting point. The groundwater level at the experimental site dropped down to 2.0 m during the growing season. The experimental area was cultivated with irrigations applied at 7–10 days interval by a drip irrigation system, in addition to rainfall. Table 1 shows the main soil moisture constant of experimental soil. The textural class of the soil of experimental site was clay. The soil was medium alkaline in reaction (pH 8.36) with electrical conductivity of 0.40 dS m−1. The depth of soil was 1.8 m. The average field capacity and permanent wilting point were 41.4 and 17 %, respectively, and bulk density was 1.27 Mg m-3. Doorenbos and Kassam (1979) reported a maximum root penetration of the sugarcane plant of 100 cm, whereas most of the roots were concentrated in the top 75−80 cm of soil with only few roots below 20 cm. Therefore, a root zone depth of 75 cm was considered for planning the observations. 2.3. Root zone depth The observations of root length were recorded by destructive method upto tillering stage or development stage (135 days after planting). For each moisture content observation, the effective root zone was determined by carefully uprooting one healthy plant. Before uprooting, the soil surrounding the plant was fully made saturated and then removed slowly (FAO 24). The root length was measured with tape and approximately, the soil depth in which 80 % of the water intake takes place was taken as the effective root zone for irrigation purpose (Michael, 2010). For further measurements five root study plots were prepared by growing sugarcane in closed soil filled plastic tanks above the ground and effective root zone was measured directly by noting the root length in different soil layers.
2. Materials and methods
2.4. Soil moisture content
2.1. Site characterization
Soil moisture content were measured prior to every irrigation and in between two irrigations approximately at midpoint of irrigation interval during the entire crop season. Gravimetric method was used for determination of the soil moisture content. The soil samples were collected upto root zone depth at the depths of 15, 30, 45, 60 and 75 cm. The soil moisture was also monitored whenever the soil profile was recharged by precipitation.
The field experiment was carried out during the Annual seasons of 2015 and 2016 at Experimental Farm of Department of Irrigation and Drainage Engineering, Mahatma Phule Krishi Vidyapeeth, Rahuri located in the western region of Maharashtra state, India (latitude 19° 48’ N; longitude 19° 57′ E; altitude 657 m). The average annual precipitation is 555 mm. Out of total annual rainfall, about 80 percent rains are during South-West monsoon (June to September), while the rest is from North-East monsoon(October-November). The distribution of rain is erratic, uneven and ill distributed over 15–37 rainy days. The annual mean maximum and minimum temperature range between 21.2 °C–41.8 °C and 3.0 °C–24.6 °C, respectively. The annual
2.5. Application of irrigation water The scheduling of irrigation was based on soil moisture content in the root zone. The irrigation was done to refill the profile to field capacity. The irrigation was initiated when soil water in the root zone 2
Agricultural Water Management 232 (2020) 106042
S.K. Dingre and S.D. Gorantiwar
following equation (FAO-56);
approached, but never depleted more than 65 % (FAO-56) of available soil water. The depth of water applied for irrigation was calculated by equation formulated as below;
ETc = I + R e − RO − DP + CR ± ΔSF ± ΔS Where, ETc is crop evapotranspiration, I is depth of irrigation applied, R e is effective portion of rainfall, RO is runoff from the soil surface, DPis deep percolation below the root zone, CR is capillary rise (In case of a shallow water table), ΔSF is horizontal subsurface flow in or out of the root zone and ΔSis change in soil profile water storage respectively. All parameters were expressed in mm.The soil water balance equation based on the above stated simplified equation was formulated as below;
When R e ≤ (θft × Zt × BDt − θt × Zt × BDt ) n
dt =
∑ (θft
× Zt × BDt − θt × Zt × BDt ) − R e
i=1
When Re ≥ (θft × Zt × BDt − θt × Zt × BDt ) dt = 0 θft =
n
n
n
n
∑i =1 θfi ; θt = ∑i =1 θi; Zt = ∑i =1 Zi ; BDt = ∑i =1 BDi
t
(θt × Zt − 1 × BDt − 1) = (θt − 1 × Zt − 1×BDt − 1) + It − 1 +
Where dt is depth of irrigation water to be required in the active root zone at tth is the day of irrigation event (mm), θft and θt is soil watercontentsat field capacity and at before irrigation for ith layer of the root zone at tth day respectively (%), Zt is the depth of effective root zone at tth day (mm);i the incremental root depth (150 mm) and n is number of i layers, R e the effective rainfall (mm). BDt is bulk density of effective root zone on tth day (Mg m−3).The soil moisture contents at 33 Kpa and 1500 Kpa were worked out for different soil layers of experimentation with Pressure Plate Apparatus.
t−1
Σtt − 1ETc
2.6. Soil moisture storage
ΔS = S1 − S2 or ΔSt = (θt − 1 × Zt − 1 − θt × Zt-1) × BDt -1 n
n
∑ θi Zt-1 = ∑ Zi BDt−1 = ∑ BDi i=1
i=1
m
∑ j=1 ETcj
Where, jis the period for which ETc measured between two successive moisture content observation events (from t-1to t); mis the total number of two successive events in entire growth period. The effective rainfall was computed by criteria mentioned in FAO Document No. 25 (Dastane (1974)). Surface runoff was considered nil as experimental site had flat topography and no runoff was observed during the periods of irrigation or precipitation. In addition, to overcome runoff problem in irrigation process, drip-irrigation system was used which did not produced surface runoff in irrigation process. No shallow water table existed at the study site, thus only percolation below the root zone was of concern. However, to attain this purpose, drip irrigation system was used for irrigation water supply as it has distinct advantage of slow water supply rate which produced no deep percolation and equaling it as zero for analysis. Capillary rise was assumed to be zero because moisture table was more than 1 m below the bottom of root zone at experimental site. For prevention entry of subsurface flow, a 1 m deep interceptor drain was dug around the entire periphery of experimental plot. In addition to this, the mole drains were laid at 4.5 m lateral distance in entire experimental field
The changes in soil moisture storage (ΔS) were determined by considering the soil layers from soil surface down to the depth of effective root zone. The depth of moisture depleted from each layer viz. 0–15, 15–30, 30–45, 45–60, 60–75 cm during each soil moisture measurement were computed. The change in soil moisture storage (ΔS) was determined for successive observation days i.e. soil moisture storage at the previous observation day minus soil moisture storage at next observation day, as:
n
t−1
Σtt − 1R e
Where ETc is the crop evapotranspiration from in the active root zone (mm)between t-1 and tth day time interval, R e the effective rainfall (mm) betweent-1 and tth day time interval, It − 1 the supplemental irrigation (mm)given on t-1 day. The total evapotranspiration was expressed as;
ETc =
θt − 1 =
= (θt − 1 − θt ) × (Zt − 1 − BDt − 1) + It − 1 +
t
∑ Re − ∑ ETc
i=1
Where, S1 and S2 are the soil moisture storage at previous observation day and soil moisture storage at next observation day respectively. θt − 1 and θt are the soil moisture storages between two consecutive observation days (%). In other means, t-1 and t are the previous and successive day of observation (t followed by t-1). Zt − 1 is the depth of effective root zone at t-1 day (mm), i the incremental root depth (150 mm) and n is number of i layers.BDt-1 is bulk density of effective root zone at t-1 day (Mg m−3). The FAO-56 has suggested that soil water balance method can only give evapotranspiration estimates over long periods of the order of week-long or ten-day periods. Therefore, the interval between two successive soil moisture measurements was maintained between 7–10 days however, during rainy days it was extended to 15 days (Allen et al., 1998).
2.8. Reference evapotranspiration Daily measurements of air temperature, wind speed, solar radiation and relative humidity for estimating ETo as well as rainfall were made from automatic weather station observatory, situated at sugarcane experimental site for period from 12thDecember 2014 to 23rd December 2015 and 24th December 2015 to 31st December 2016. The reference evapotranspiration (ETo) which was obtained by the Penman-Monteith approach (Allen et al., 1998). 900
2.7. Crop evapotranspiration
ETo = The simplified soil moisture balance method was used to estimate crop evapotranspiration (ETc) in root zone between consecutive soil moisture measurement days. For this, water content in root zone depletion was calculated which essentially involves adding and subtracting of losses and gains of various parameters of the soil water budget expressed in terms of water depth. Rainfall, irrigation and capillary rise of groundwater towards the root zone was considered to decrease the root zone depletion in root zone whereas, crop evapotranspiration and percolation losses were considered to increase depletion in root zone. The moisture balance, expressed in terms of depletion at the end consecutive soil moisture measurement days was calculated by
0.408Δ (Rn − G ) + γ T + 273 u (es − ea ) Δ + γ (1 + 0.34u2 )
Where, ETo is Reference evapotranspiration (mm day−1); Rn isNet radiation at the crop surface (MJ m-2 day−1); G is Soil heat flux density (MJ m-2 day−1); T is Mean daily air temperature at 2 m height (°C); u2 is Wind speed at 2 m height (m s−1); es is Saturation vapour pressure (kPa); ea is actual vapour pressure (kPa); Δ is slope of vapour pressure curve (kPa °C-1) and γ is psychrometric constant (kPa °C-1). 2.9. Computation of crop coefficients The crop coefficients were computed for different growth stages of sugarcane. The growth period was divided into four stages: 3
Agricultural Water Management 232 (2020) 106042
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increase in soil layer depth upto 45 cm and thereafter it slightly decreased at 60 cm and lowest moisture content was observed at 75 cm depth (Fig. 2). During tillering stage, more soil moisture depletion was observed, however, when plant canopy fully developed after tillering, the soil moisture depletion was uniform in all layers (Singh and Mohan, 1994; Raghuvanshi and Wallender, 1998).The particular growth stage and incident of rainfall greatly influenced the soil moisture content. Invariably of growth stages and barring rainfall events, the moisture content was closer to field capacity.
establishment (0–45 days after planting), Tillering (60–135 DAP), grand growth (135–300 DAP) and maturity (300–360 DAP). The initial stage was assumed from the beginning of planted sugarcane to the full expansion of root volume in nursery; Tillering stage is just after 15 days of transplanting the seedlings when tillers are starts to emerge from mother shoot and ends when tiller starts to elongate at the beginning of grand growth; the grand growth stage is from then upto the timing when cane has achieved its full growth; the maturity stage continues from then until harvest. These four growth stages correspond to those defined in FAO-56 (Allen et al., 1998) respectively as initial, development, mid-season and end season. In this investigation, later three stages were considered and initial stage i.e. initial stage was skipped with a view that all the farmers of this region essentially raised nursery to attain good germination at initial stage. Further, nursery planting of sugarcane has distinct advantages like spare time for field preparation, saving of three irrigations and healthy plant selection, etc. The crop evapotranspiration values obtained by monitoring the soil moisture balance in the crop root zone and ETo values estimated using climatic data for specified periods. The crop coefficient (Kc) were computed as the ratio of crop evapotranspiration and reference evapotranspiration (ETc / ETo) for the respective period(7–10 daysinterval).The polynomial equation was fitted with Kct as the dependent variables and (t/T) as the independent variables.
3.3. Field water balance 3.3.1. Irrigation water applied The irrigation depth differed for a particular growth stage in a season due to differences in crop water use and duration of stage (Table 2). This was probably caused mostly by differences in annual weather conditions (Wiedenfeld, 2004). Invariably in both seasons, grand growth stage identified as high water requirement stage due to its long duration (165–170 days). This followed by tillering stage (75–80 days) and maturity stage (65–70 days). The irrigation water applied in grand growth stage of 2016 was less than half (372.4 mm) compared to 2015 (799 mm), because of the higher contribution of rainfall in crop water use in 2016. However, irrigation water amount in tillering stage (277.6 mm) was higher in 2016 than in 2015 (211.1 mm); because of the higher evaporative demands. In both the seasons, the lowest irrigation water was required during the maturity stage. This happened because of decline in crop water use (ETc) with crop maturity during this period, and may also indicate that the crop was taking advantage of moisture stored in the soil profile from off-season rainfall (Wiedenfeld Robert, 2000).
t 0 t 1 t 2 Kct = ao ⎛ ⎞ + a1 ⎛ ⎞ + a2 ⎛ ⎞ ⎝T ⎠ ⎝T ⎠ ⎝T ⎠ Where, Kct is crop coefficient of tth day; a0, a1, a2 are constants of equations; t is day considered; T is total period of crop growth from planting to harvesting (days). The regression coefficients were estimated and tested for its significance to decide upon the validity of the particular equation.Using best fit equation, the daily Kc values were estimated for both seasons and average daily Kc values (from 50 DAP i.e. from 10 days after transplanting) were then estimated by taking the average of estimated daily Kc values of 2015 and 2016.
3.3.2. Effective rainfall The rainfall received during 2015 and 2016 was 313.2 mm (38 rainy days) and 534.3 mm (40 rainy days), respectively. In both the years all rainfall received was effective (Table 2). The occurrence of rainfall affected the depth of irrigation in different growth stages. In 2015, the effective rainfall was 43.6 % less than average rainfall (555 mm) therefore; more irrigation water applied in that season. However, in 2016, effective rainfall (534.3 mm) contributed almost 41 % of crop consumptive use and therefore demands of irrigation water reduced to half in 2016. Among different growth stages, more irrigation applied in tillering stage (February-Mid May) in 2016 due to high evaporative demand. The respective years grand growth stages coincided with rains, that contributed consumptive use and therefore demand of irrigation water was differed in 2015 and 2016 season. In maturity stage, no rainfall received in both the season and thus, irrigation amounts for both the seasons were almost for this stage.
2.10. Agronomic practices The sugarcane seedlings rose in nursery and transplanted after 35 days in a 6 × 27 m field. Sugarcane seedlings transplanted at the spacing of 1.5 m × 0.6 m. During nursery, irrigations applied at 2 days interval as per measured crop evapotranspiration (ETc) values through climatological method (Allen et al., 1998). After transplanting, the common irrigation was applied continued upto15 days until the seedling was established. The value of crop coefficient for common irrigation was referred as 0.40 (FAO-56). The other agronomic practice viz. weeding, off barring, earthing up fertigation schedule and operation to prevent lodging were followed as per recommended by parent Agricultural University. 3. Results and discussion
3.3.3. Crop evapotranspiration The total depths of water use during 2015, 2016 and average of two seasons were 1386.8 mm, 1291 mm and 1338.9 mm respectively (Table 2). The sugarcane evapotranspiration (ETc) varies considerably from place to place depending on weather conditions, texture of soil and duration of the crop. Numerous approaches have been used by different researchers to measure or estimate sugarcane evapotranspiration (Thompson and Boyce, 1967; Omary and Izuno (1995); Allen et al., 1998; Wiedenfeld Robert (2000); Wiedenfeld, 2004; Chabot et al., 2005; Silva et al., 2012; Win et al., 2014; Anderson et al., 2015; Cardoso et al., 2015). Nevertheless, its estimate largely depends upon type of approach used by researchers. In some studies, evaporation from a USWB Class A pan (Allen et al., 1998) is common reference for measuring evapotranspiration in many crops including sugarcane. Using this method, Wiedenfeld (2004) reported crop evapotranspiration of sugarcane as 1021 mm including annual effective rainfall in semiarid south Texas, whereas, Wiedenfeld
3.1. Root zone depth The root zone depth at the time of transplanting was 50 mm at 53 and 47 DAP in 2015 and 2016, respectively (Fig. 1). During both the years, the root length of sugarcane increased linearly with advancement in age of crop. The rate of root length expedites at the end of tillering stage (115–125 DAP). Thereafter, effective root zone increased approximately up to 204 days and 217 days in 2015 and 2016, respectively and then root zone becomes constant at 750 mm and subsequent samples were taken up to 750 mm. 3.2. Soil moisture The soil moisture content increased with crop evapotranspiration during the growth period. The moisture content found increased with 4
Agricultural Water Management 232 (2020) 106042
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Fig. 1. Measured root zone depth (mm) of sugarcane during 2015 and 2016 season.
Fig. 2. Moisture content in the soil profile for sugarcane during the 2015 and 2016 growing seasons. Table 2 Field water balance components (mm) during the growth stages for sugarcane observed at the experimental site in a subtropical climate, India. Growth stage
Initial Tillering Grand growth Maturity Total
Days
55 75 170 65 365
2015
2016
Average
I
Pe
ΔS
ETc
I
Pe
ΔS
ETc
I
Pe
ΔS
ETc
52.1 211.3 799.4 110.5 1173.3
– 53.2 243.8 16.2 313.2
– 2.8 −104.5 2.0 −99.7
52.1 267.3 938.7 128.7 1386.8
49.3 277.6 372.4 109 808.3
– 0 534.3 0 534.3
– −16.5 −72.2 37.1 −51.6
49.3 261.1 834.5 146.1 1291
50.7 244.4 585.9 109.8 990.8
– 26.6 389.1 8.1 423.8
– −6.9 −88.4 19.6 −75.7
50.7 264.2 886.6 137.4 1338.9
Pe = Effective rainfall, I = Irrigation, ETc = Crop evapotranspiration (I + Pe + ΔS), ΔS = Soil moisture storage change.
two irrigated sugarcane fields (1191 mm and 1389 mm) of Maui, Hawaii, USA in contrasting climates by eddy covariance towers. They used the short (ET0) and tall (ETr) vegetation versions of the American Society for Civil Engineers (ASCE) equation. The only field water balance study reported sugarcane evapotranspiration as 1686.7 mm for tropical condition of Brazil (Silva et al., 2012). Thus, on an annual basis, the sugarcane evapotranspiration ranges from 950 to 1700 mm depending on the location from different parts of the world. Therefore, sugarcane evapotranspiration amounting 1339 mm derived by field water balance in this study seems to be appropriate for semiarid conditions.
Robert (2000) obtained its value as 968 mm using Jensen-Haise equation for same region. In few lysimetric studies, Thompson and Boyce, 1967 at Pongola, South Africa found sugarcane evapotranspiration similar to USWB Class pan evaporation, suggesting a ‘pan factor’ (i.e. the ratio of ETC to pan evaporation) of 1.0. Likewise, Win et al. (2014) at Myanmar and Cardoso et al. (2015) at tropical Brazil reported sugarcane evapotranspiration as 1369.84 mm and 1438.23 mm respectively. Omary and Izuno (1995) in south Florida, USA used a novel way of measuring actual sugarcane evapotranspiration by monitoring daily changes in the height of the water table and estimated annual ETc of sugarcane as 1060 mm. Differently, Chabot et al. (2005) measured transpiration of sugarcane in Gharb plain, Morocco using the sap flow technique and found that sugarcane evapotranspiration were 30 % more than those predicted from the Penman-Monteith equation. However, they believed that the sap flow technique is an inappropriate method for determining transpiration rates from a heterogeneous canopy like that of sugarcane because of uncertainties in the methodology. Anderson et al. (2015) measured sugarcane evapotranspiration at
3.4. Crop coefficients of sugarcane The Kc values with confidence bounds for both the years are shown graphically in the form of polynomial equation, with respect to the ratio of days to total crop period (Fig. 3). The average Kc of two years ranged from 0.31 to 1.29 (Table 3). In both the seasons, Kc consistently increased from 0.43 to 1.03 during 50–130 days after planting (DAP). Thereafter, it showed gradual increases due to crop development in 5
Agricultural Water Management 232 (2020) 106042
S.K. Dingre and S.D. Gorantiwar
Fig. 3. a and 3b 2nd order polynomial crop coefficient curve for sugarcane crop during 2015 and 2016 season.
days i.e. at 90 DAP. The average Kc value for tillering stage was found lower (0.70) than FAO-56 value (0.94). Earlier, Win et al. (2014) also reported the lower Kc value for development stage as 0.81 estimated from lysimeters for Myanmar. The trend of curves for mid season of both the seasons showed very close association with FAO-56 Kc curve, however average Kc value for grand growth (mid season) stage was estimated slight lower (1.20) over 1.25 (FAO-56). The lower Kc obtained in this investigation may be due to different climatic conditions of semi arid region which primarily altered the reference crop evapotranspiration i.e. ETo. Differently, Inman-Bamber and McGlinchey (2003) and Cardoso et al. (2015) confirmed the current 1.25 value whereas, Omary and Izuno (1995) and Silva et al. (2012) reported higher value over 1.25. Nevertheless, this difference was mainly to due to variation in ET measurement approaches, weather conditions, duration of the crop, methodological assumptions and accuracy. The decline phase of estimated Kc curve showed early fall with lower Kc values (0.78) over FAO-56 values (0.98). Overall, there was a good association between Kc-developed and KcFAO in average of both seasons. However, some variations observed along the growth stages in both seasons. It was revealed that %
form of cane elongation (mid season stage). During the mid-season i.e. 130–300 DAP, Kc increased from 1.08 and then remain same in the range of 1.13-1.04 with peak value as 1.29. The highest Kc value occurred during 200–220 DAP. The Kc values during the late season (300–360 DAP) decreased gradually from 1.04 to 0.56. Thompson and Boyce (1971) in a lysimeter study observed that ETc rates declined by about 30 % after crops lodged, an effect that lasted upto crop maturity. The two years average Kc values are represented in the form of following second order polynomial equation. The variation of Kc is shown in Fig. 4
t 2 t Kct = − 4.695 ⎛ ⎞ + 5.566 ⎛ ⎞ − 0.360 ⎝T ⎠ ⎝T ⎠
3.4.1. Comparison with FAO- 56 The crop coefficient values derived from field soil water balance during the tillering, grand growth and maturity stages for sugarcane in a semi-arid region were 0.70; 1.20 and 0.78, respectively. The corresponding values of FAO-56 are 0.90, 1.25 and 0.98, respectively (Table 4). It is pointed out that at 60 DAP, low Kc value (0.43) was attained as against 0.65 of FAO-56. However, it hiked up after 25–30 6
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reduction observed between FAO Kc and developed Kc was 25.5 %, 4 % and 20.4 % for tillering stage, grand growth stage and maturity stage respectively (Table 2). The average % reduction was 16.6 %. This may be due to the conditions of the study area, soil conditions and crop variety etc. whereas; FAO Kc equation is developed for global climatic conditions. Pereira Luis et al. (2015) also reported the advances in adopted Kc research included techniques to estimate Kc based on the architecture of crops, notably height and fraction of ground cover. In practice, results reported here showed that FAO-Kc could lead to over estimation in irrigation scheduling of sugarcane in semi-arid conditions and the use of Kc values developed in this study would lead in correction of water requirement for sugarcane. Further, in this study the Kc value measured over the growth period of sugarcane have been converted in the equation form leading to estimation of Kc for any specific day and its use in decision support system.
Table 3 Average estimated crop coefficients (Kc) of sugarcane from best fit regression equations of 2015 and 2016. S. No.
Period, days
Average estimated Kc
Growth stagewise Kc
FAO56 Kc
Growth stagewise FAO Kc
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33
0-40 40-50 50-60 60-70 70-80 80-90 90-100 100-110 110-120 120-130 130-140 140-150 150-160 160-170 170-180 180-190 190-200 200-210 210-220 220-230 230-240 240-250 250-260 260-270 270-280 280-290 290-300 300-310 310-320 320-330 330-340 340-350 350-360
0.40 0.31 0.43 0.53 0.63 0.73 0.81 0.89 0.96 1.03 1.08 1.13 1.18 1.21 1.24 1.26 1.28 1.29 1.29 1.28 1.27 1.25 1.22 1.19 1.15 1.10 1.04 0.98 0.91 0.83 0.75 0.66 0.56
– – 0.70 (Tillering stage)
0.4 0.55 0.65 0.75 0.85 0.95 1.05 1.15 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.17 1.09 1.02 0.94 0.86 0.79
– – 0.90 (Tillering stage)
1.20 (Grand growth stage)
0.78 (Maturity stage)
1.25 (Grand growth stage)
4. Conclusion Sugarcane have immense role in economy of sugarcane growing countries but its water consumption scenario represents the unfavorable perspective. In irrigated agriculture, underestimation of its crop evapotranspiration (ETc) can lead to suboptimal yield due to water stress whereas overestimation can lead to excessive applied water, thus reducing water available for other uses or additional acreage and decreasing economic competitiveness. The crop coefficient (Kc) is the important parameter influencing the estimation of crop evapotranspiration (ETc) of any crop; and knowledge of periodical or stagewise crop coefficients of sugarcane is important. This investigation addressed the important issue of irrigation scheduling; provided the information of crop evapotranspiration and crop coefficients for sugarcane by field water balance method under semi arid conditions. The crop evapotranspiration of sugarcane was 1339.4 mm including irrigation water requirement and effective rainfall as 991 mm and 424 mm respectively. The determined sugarcane Kc values for tillering (development stage), grand growth (mid-season) and maturity stage (end season) was 0.70, 1.20 and 0.78, respectively. The Kc values are 16.6 % lesser than those suggested by FAO-56 for sugarcane. The study pointed out that FAO-Kc could lead to over estimation in irrigation scheduling of sugarcane in semi-arid conditions and the use of Kc values developed in this study would lead in correction of water requirement. The sugarcane Kc values converted in 2nd order polynomial equation form leading to estimation of Kc for any specific day. The daily values of Kc from equation is very useful to researchers working in area of sugarcane water management especially making a Decision Support System, Soil Moisture based Crop Yield Modeling, Crop Water Requirement based Computer programme or Mobile Application, Automation of irrigation system etc. Overall this study provided the adoptable information for sugarcane toward efficient management of irrigation water leading to proportionalities appropriately the imbalance of sugarcane cultivated area and use of irrigation water in the major sugarcane growing countries of semi arid regions.
0.98 (Maturity stage)
Fig. 4. 2nd order polynomial crop coefficient curve for estimating crop coefficients of sugarcane for total growth period. Table 4 Comparison of FAO-56 and field soil water balance derived sugarcane crop coefficient values for each crop growth stage. Growth stage
Initial Stage Tillering stage Grand growth stage Maturity stage Averagea a
FAO Kc
0.40 0.94 1.25 0.98 1.1
Developed Kc
Declaration of Competing Interest There is no conflict of interest for this study.
% variation
2015
2016
Average
2015
2016
Average
0.40 0.67 1.20 0.73 0.9
0.40 0.75 1.23 0.80 0.9
0.40 0.70 1.20 0.78 0.9
0.0 28.5 4.0 25.5 19.3
0.0 20.4 1.2 18.4 13.3
0.0 25.5 4.0 20.4 16.6
Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.agwat.2020.106042. References
Average values not included initial stage value. Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop Evapotranspiration. FAO
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