Estimation of Seasonal Evapotranspiration, Crop coefficient and Water Productivity of Maize and Sunflower under Drip Irrigation in Semi-arid Region of Telangana, India

Estimation of Seasonal Evapotranspiration, Crop coefficient and Water Productivity of Maize and Sunflower under Drip Irrigation in Semi-arid Region of Telangana, India

Kadasiddappa M. Ma^1* , Praveen Rao V² , Ramulu V²

¹Department of Agronomy, Agricultural College, Aswaraopet, Professor Jayashankar Telangana State Agricultural University (PJTSAU), Telangana, Hyderabad, India

²Professor Jayashankar Telangana State Agricultural University (PJTSAU), Telangana, Hydera-bad, India

Corresponding Author Email: kadasiddappa.m@gmail.com

DOI : http://dx.doi.org/10.53709/CHE.2021.v02i04.035

Abstract

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1. INTRODUCTION

The limited available water resources in the India demand its economic use which will be achievable only by adopting advanced technology of irrigation like micro irrigation. Water is the critical natural resource, which is often costly and limiting input particularly in arid and semi arid regions, hence needs judicious use to reap the maximum benefit from this limiting resource [1]. The importance of water resources management is due to the increase of the population and water demand especially in the Middle East and North Africa, which are classified as arid and semi-arid regions [2]. These are threatened by the water crisis in the future. India is classified among the countries that are facing high-water shortages. This is mainly due to the combination of persistent drought and the increase of water demand effects due toincreasing pressure on population and food demand, especially in the irrigation sector. With growing demand for water resources from competing sectors, great emphasis has been placed on water use efficiency in irrigated fields [3], particularly in semiarid environment condition. At present, paradigm shift from traditional practices to more modern technologies for crop production is the key for Indian farmers.

Maize and sunflower are two most important crops in India and grown on considerable area under irrigation. Yield of both crops depends upon the availability of adequate quantity of water, especially in areas where production suffers due to scarcity and/or irregular distribution of rainfall [4]. The irrigation water requirement of maize and sunflower generally varies according to evaporative demand and rainfall of that region [5]. Further, achieving highest water use efficiency is the prerequisite and which will frequently occur at relatively dry or deficit irrigation treatments having less than the highest economic yields. In a survey conducted in west Asian region during 1995 to 2000 revealed that 30 to 50% of irrigation water can be saved under drip irrigation compared with conventional irrigation practices without sacrificing crop yield or quality in annual crops [6]. Reduction in water consumption due to drip method of irrigation over the surface method of irrigation varied between 30 to 70% and productivity gain in the range of 20 to 90% for different crops [7]. Since, maize and sunflower is grown in mostly in irrigated condition, comprehensive knowledge of actual water requirement (ETc) of both crops is necessary for appropriate irrigation scheduling under drip irrigation. Optimization of water applied to the crops by drip irrigation is very essential as yields of the crops are adversely affected either with excess or deficit water supply. Crop water use varies substantially during the growing period due to variation in crop canopy and climatic conditions.

The prediction of seasonal actual evapotranspiration (ETa) and crop coefficients (Kc) as a function of growth period is very much important for determining crop water use and scheduling irrigation at regional level [8]. Referring to agricultural production, the measurement of ET is very important in arid and semiarid regions, where it is essential for determining crop water demand. ET is the process by which water is transported from the earth’s surface to the atmosphere by the evaporation from surfaces (soils and wet vegetation) and by the transpiration from plants through the stomata present in the plant leaves [9, 8]. Crop evapotranspiration is a fundamental variable in the hydrological cycle and is thus significant for the management of irrigation and water resources [10]. The quantification of ET is normally based on the determination of reference evapotranspiration (ETo). The United Nations Food and Agriculture Organization (FAO) proposed the FAO-56 Penman-Monteith reference ETo for irrigation schedule in 1998 [8]. This method has been widely used because it gives satisfactory results under various climate conditions across the world [11, 12 and 13]. Field water balance is commonly used to measure total water use or actual crop evapotranspiration (ETa) when lysimeter facilities are not available and it is found that ETa increase with increase in number of irrigation from one to adequate [14]. The seasonal evapotranspiration of wheat estimated by [15] using water balance method under humid tropical canal command area of West Bengal of eastern India. Although crop co-efficient values for different crops grown under different climatic conditions as suggested by [16] are used where locally measured data are not available. As suggested by [8], that these values need to be derived empirically for each crop based on the local conditions to determine the water requirement. Therefore, to alleviate the water scarce situationin agriculture crop production and acclimatize to the scientificwater management is one of the best choice ratherblanket uses of precious resource. In this direction, the present study will focus on estimation of evapotranspiration, crop co-efficient and water productivity as well as choice of suitable crop either maize or sunflower under semi-arid condition of Telangana region of India under limited water situation.

2. MATERIAL AND METHODS

A field experiment was carried out at Research & Development Farm, WALAMTARI, Himayatsagar, Hyderabad, Telangana, India (17⁰ 19’ 38.11” N-Latitude, 78⁰ 22’ 44.45” E-Longitude and an altitude of 520 m above mean sea level) during winter (rabi) season of 2013-14 and 2014-15.The experiment was laid out by following Randomized Block Design (RBD) which consists of six irrigation treatments and replicated four times. The six irrigation treatments consisting of five drip irrigation levels at 40%, 60%, 80%, 100% and 120% pan evaporation replenishments (Epan) and a surface furrow irrigation at 1.0 IW/CPE.The experimental soil for maize was sandy clay loam in texture, neutral in reaction, non saline, low in available nitrogen and medium in available phosphorus and potassium (Table 1). Likewise for sunflower, the soil was clayey in texture, neutral to slightly alkaline in soil reaction, non saline, low in available nitrogen, medium in available phosphorus and potassium (Table 2).The available soil moisture in the crop root zone depth of 60 cm was 104 mm for maize with a saturated hydraulic conductivity varying from 0.7 cm h⁻¹ to 1.4 cm h⁻¹ and 132 mm for sunflower with a saturated hydraulic conductivity of 0.2cm h⁻¹. The irrigation water was near neutral in reaction and was classified under the Class II (C₃S₁). The residual sodium carbonate (RSC) levels indicated that there was no residual alkalinity problem (Table 3). The climate of experimental site described as dry tropical and semi-arid with dry winter (Nov-Feb). With respect to pan evaporation, mean pan evaporation ranged from 2.5 to 6.2 mm day⁻¹and 1.7 to 4.9 mm day⁻¹in 2013-14 and 2014-15, respectively. The seasonal pan evaporation during the crop period was 442 mm in 2013-14 and 354 mm in 2014-15, respectively.

In drip method, irrigation was scheduled once in 2 days and total water applied along with effective rainfall in different growth development stages of crops are indicated in Table 4 and 5 for maize and sunflower, respectively. In surface furrow method, irrigation was applied as per 1.0 IW/CPE ratio when CPE reached 50 mm based on daily evaporation data recorded from USWB class ‘A’ pan evaporimeter in class ‘B’ agro-meteorological station, Research & Development Farm, WALAMTARI, Himayatsagar. For providing irrigation, inline drip laterals were fixed on the sub-mains as per the crop row spacing in the individual plots (1.20 m and 0.9 m apart for maize (paired row) and sunflower crop, respectively) with 0.4 m distance between two emitters having 4 LPH discharge rate. Simultaneously separate main line was laid out for furrow irrigated plots facilitating separate control valves and water meter.

Maize hybrid – DHM-117 with 110-120 days duration and sunflower hybrid – DRSH-1 with 90-100 days duration were used as test varieties during rabi season. Before conducting experiment Green gram variety MGG-295 (Madhira Green Gram-295), having 65-75 days duration was used for bulk sowing during kharif season. Recommended doses of N, P₂O₅ and K₂O (160:80:60 kg ha⁻¹ and 120:80:60 kg ha⁻¹ for maize and sunflower, respectively) were applied in the form of urea, mono-ammonium phosphate and potassium nitrate to both the crops through drip fertigation. Whereas, in surface furrow irrigation theses fertilizers were applied in the form of urea, single super phosphate and muriate of potash. Half dose of N and full dose of P₂O₅ and K₂O were applied as basal for both the crops. Remaining quantity of nitrogen was applied to soil in three equal splits at emergence, knee-height and tasseling stages in maize and emergence, vegetative and buttoning stages in sunflower crop.

Soil moisture content was estimated at fortnightly interval and at the time of harvesting upto 60 cm soil depth.The change in profile soil water storage (mm) was determined from the successive soil water sampling measurements.The moisture content at FC and PWP were estimated in the laboratory by Pressure plate and membrane apparatus (FC=26.9%, PWP=15.8% for maize field and FC=37.4%, PWP=24.1% for Sunflower field). The soil moisture content estimated by gravimetric method at fortnightly interval is furnished in table 6 and table 7 for maize and sunflower, respectively.

The daily reference evapotranspiration (ETo) was calculated following FAO 56- Penman -Monteith equation.

ETo=(0.408∆(Rn-G)+Y(900/(T+273))U2(es-ea))/(∆+Y(1+0.34 U2))————————–1.

Where: Rn- Measured net irradiance at the crop canopy (MJ/m2/day)
G- Soil heat flux density (MJ/ m2)
T- Measured Mean daily air temperature (oC)
U2-Mean daily wind speed at 2 m height (m/s)
es- Saturated vapourpressuer (kPa)
ea- Mean actual vepour pressure(kPa)
Δ – Slope of the saturation vapour pressure – Temperature curve (kPa/oC)
Y – Psychrometric constant (kPa/oC)
0.408 – Coefficient (M2 mm/MJ)

Seasonal crop evapotranspiration (ETc) was estimated based on water balance equation using soil water measured by gravimetric sampling method (FAO). Soil water contents were recorded atsowing, before irrigation, 24 hours after irrigation or rainfall and ETc was calculated with the following relationship;

For estimation of Kc values, the crop life was divided into germination and establishment (0-15 DAS), vegetative (16-45 DAS), tasseling and silking (46-75 DAS), kernel development (76-105 DAS) and maturity stage (106- Harvest) for maize and germination and establishment (0-15 DAS), vegetative (16-30 DAS), flowering and pollination (31-65 DAS), seed development (66-90 DAS) and maturity stage (91- Harvest) for sunflower.

The data obtained on grain/seed and straw/stalk yield were analyzed statistically by the method of analysis of variance as per the procedure for both the years and on pooled basis as outlined for randomized block design (RBD)given by [22]. Statistical significance was tested by P-value at 0.05 level of probability and critical difference was worked out where ever the effects were significant.

3. RESULT AND DISCUSSION

3.1. Grain and Stover Yield

3.1.1. Maize:

Average grain and straw yield of maize was greater (8456 and 13,734 kg ha⁻¹, respectively) when irrigation was scheduled at 100% Epan with drip but it was on par with 80% and 120% Epan drip irrigation schedules on pooled basis (Table 8). Drip irrigation at deficit levels of 40%, 60% Epan and surface furrow irrigation at 1.0 IW/CPE ratio caused significant reduction in grain yield of maize relative to drip irrigation at 100% Epan in both the years and on pooled basis.The grain yield increase in 120%, 100% and 80% Epan was to the tune of 172%, 180% and 171% over drip irrigation scheduled at 40% Epan, respectively, 39%, 43% and 39% over drip irrigation scheduled at 60% Epan, respectively and 37%, 41% and 37% over surface furrow irrigation, respectively on pooled basis. Similar results were reported by [23] in maize and [23] in wheat wherein the mean grain yield of crop increased with increasing water application in drip irrigation. The lowest grain yield of 3024 kg ha⁻¹ on pooled basis was recorded in 40% Epan drip irrigation treatment. The above trends in grain and straw yield levels registered under 80%, 100% and 120% Epan in comparison to other treatments could be traced to the favorable soil water balance (effective rainfall + applied water) near to field capacity (Table 6 and Figure 10a) as was observed by variation in soil moisture during the crop growing season [24]. Thus, favourable soil water balance under drip irrigation 80%, 100% and 120% Epan aided the plants to put forth improved performance over other treatments, since water plays a vital role in carbohydrate metabolism, protein synthesis, cell wall synthesis, cell enlargement and partitioning of photosynthates to sink for improved development of growth traits [25]. Therefore, crop plants in 80%, 100% and 120% Epan treatments had the crop growth, development and yield contributing characters resulting in higher yields. Further, the regression of maize grain yield on soil moisture (Figure 1) and crop ET (Figure 2) revealed a significant and positive correlation with a determination coefficient of 96.7% and 98.6%, respectively.

3.1.2. Sunflower:

The sunflower irrigated with drip irrigation at 100% Epan produced appreciably higher seed yield and stalk yield (2722 and 5650 kg ha⁻¹on pooled basis, respectively) over drip irrigation scheduled at 60%, 40% Epan and surface furrow irrigation at 1.0 IW/CPE ratio (Table 3). However, the seed and stalk yield produced at 80% Epan and 120% Epan in both the years and on pooled basis were statistically similar with that of drip irrigation scheduled at 100% Epan. These results are in tune with the finding of [26] who observed that, moderately deficit irrigation is beneficial for realizing higher economic yield. On the other hand, it was observed that drip irrigation at 60% Epan exhibited improved performance over surface furrow irrigation at 1.0 IW/CPE ratio treatment in both the years and on pooled basis. Comparison of drip irrigation at 40%, 60% Epan and surface furrow irrigation at 1.0 IW/CPE irrigation treatments indicated that they were significantly different from each other  in both the years and on pooled basis and the seed yield was in decreasing order of 60% Epan > surface furrow irrigation at 1.0 IW/CPE > 40% Epan. Significantly lowest seed and stalk yield was observed with the deficit drip irrigation at 40% Epan (1117 and 3851 kg ha⁻¹on pooled basis, respectively).

The increase in the seed yield of sunflower observed due to drip irrigation scheduled at 100% Epan was to the tune of 144%, 44% and 83% and with 80% Epan it was 137%, 40% and 78% over drip irrigation scheduled at 40%, 60% Epan and surface furrow irrigation at 1.0 IW/CPE, respectively. Such enormous increment in yield due to increased drip irrigation level was also observed by [27-31]. Similar, improvement in seed yield with increase in drip irrigation frequency by reducing the gap between water application and plant needs was also reported by [32].

The favourable water balance under 80% and 100% Epan could be the main driving force behind for realizing higher yield levels in comparison to other treatments and this was also evident from the variation in soil moisture during the crop growing season (Figure 10b). Further, the regression of sunflower seed yield on soil moisture (Figure 3) revealed that a significant (P = 0.05) and positive correlation existed between them with a coefficient of determination (R²) of 0.801.

3.2. Crop Evapotranspiration (ETc)

3.2.1. Maize:

The crop ETc at various crop growth periods i.e. germination and establishment to grain development was linear in all the treatments during 2013-14 (Table 9). However, during 2014-15, it increased linearly up to vegetative stage and thereafter it remains more or less similar up to grain development stage. During establishment stage the difference in crop ET was not varied much among the treatments and recorded average crop ET of 22 mm and 21 mm in 2013-14 and 2014-15, respectively owing to uniform water application during this period. The higher crop ET during vegetative stage in second year (2014-15) was traced to higher cumulative Epan values (Figure 4) recorded than the subsequent stages. From vegetative period until maturity due to variations in the water application levels as per the treatments a large difference in crop ET was observed. At maturity period due to withholding of irrigations after crop reaching physiological maturity, large reductions in crop ET was observed in all the treatments. The lower crop ET values observed in the maize with drip irrigation scheduled at 40% and 60% Epan from 15 DAS to maturity than rest of the treatments were due deficit irrigation water applications in these treatments. Lowest seasonal crop ET of 263.4 mm and 213.1 mm in 2013-14 and 2014-15, respectively was associated with 40% Epan owing to less water application. Highest seasonal crop ET (466 mm and 378 mm in 2013-14 and 2014-15, respectively) were observed with surface furrow irrigation at 1.0 IW/CPE treatment (Table 9). In the present experiment, reduction in seasonal crop ET with decreasing irrigation level was observed in the order of surface furrow irrigation at 1.0 IW/CPE > 120% Epan> 100% Epan> 80% Epan> 60% Epan> 40% Epan in both the years.

The seasonal crop ET of maize where irrigations were scheduled at higher pan evaporation replenishment ratio throughout the crop growing season was more than that registered in lower evaporation replenishment treatments. Linear increase in yield with increase in irrigation levels was also noticed by [33-34]. Reduction in irrigation levels (ETa/ETm< 1) caused appreciable reduction in crop ET in comparison to drip irrigation at 120% Epan treatment. The crop ET is a physical process takes place continuously from a periodically replenished source of water and variable potential viz., soil moisture reservoir to a sink of virtually unlimited capacity i.e. the atmosphere. As long as the water availability matches the rate of water loss through transpiration by the crop canopy and evaporation from soil surface the crop ET continues at potential rates as determined by the evaporative demand of the atmosphere [5] as witnessed in drip irrigation scheduled at 100%, 120% Epan and 1.0 IW/CPE treatments (Table 9). However, as the crop removes the water from the soil, the soil moisture content and soil water potential decreases leading to low soil water conductivity thereby resistance to water movement in the soil increases. This tend to decrease water flow in to the plant system causing marked reduction in crop ET as could be observed in deficit irrigation levels i.e. in drip irrigation at 40% and 60% Epan treatments.

3.2.2. Sunflower:

The crop evapotranspiration (mm) of sunflower increased with consequent increase in drip irrigation levels at all crop growth stages and recorded utmost in drip irrigation scheduled at 120% pan evaporation replacement (Epan) treatment (Table 10 and Figure 5). However, the crop evapotranspiration recorded in all the drip irrigation treatments were lower than surface furrow irrigation treatments at all crop growth stages in both the years of study. The crop evapotranspiration during germination and establishment period was not differed among different irrigation treatments in both the years owing to uniform application of water at this stage of crop development. However, crop ET increased with the ontogeny (time) of the crop and attained peak crop ET (103 mm and 118 mm in 2013-14 and 2014-15, respectively) during flowering and pollination period in all the treatments. Then onwards, the crop ET started declining towards maturity due to withholding of irrigation water after crop reaching physiological maturity in both the years.

Among the drip irrigation treatments, the highest seasonal crop ET (334.0 mm and 291.4 mm in 2013-14 and 2014-15, respectively) was evidenced with drip irrigation scheduled at 120% Epan (Table 5). On the other hand, surface furrow irrigation at 1.0 IW/CPE ration recorded the highest seasonal crop ET of 365.0 mm and 321.0 mm in 2013-14 and 2014-15, respectively over all the drip irrigation treatments. Crop evapotranspiration decreased steeply with the decrease in irrigation water levels and the lowest seasonal crop ET (237.0 mm and 210.7 mm in 2013-14 and 2014-15, respectively) was noticed with drip irrigation scheduled at 40% Epan. Reference crop evapotranspiration (ETo) estimated by pan evaporation method follows similar trend as that of crop ET calculated at different growth periods. However, the estimated ETo value was lower than the seasonal crop ET in all the irrigation treatments in both the years.

3.3.1. Maize:

The Kc values in all the treatments were low during the initial stages of crop establishment (0.71 on pooled basis) and then increased linearly with crop growth advancement and attained peak values at tasseling and silking stage (Figure 6). During vegetative stage and grain development stage the Kc values recorded were more or less same and slightly higher during tasseling and silking stage but with further advancement in crop age (maturity period) the Kc values decreased due to lower crop ET values in both the years. Such variation in Kc values with crop ontogeny was also reported by [8, 35]. Further, the Kc values decreased with decrease in irrigation levels. Maize crop drip irrigated at 40% Epan recorded lowest average Kc values (0.83 and 0.84 on pooled basis) than the rest of the treatments due to deficit water application. These results are in tune with finding of (23, 36-37). The mean Kc value for the total maize growing period (sowing to harvest from all the treatments) was 1.12 and 1.15 in 2013-14 and 2014-15, respectively. The variation in average Kc values in both the years (pooled basis) of study for all the treatments with time expressed as a linear line diagram shown in Figure 6. The curves were constructed based on the reference crop evapotranspiration (ETo) estimated (equation 1). The Kc values calculated with drip irrigation scheduled at 80% Epan treatment in the present experiment were found nearer to the FAO Kc values (0.4-0.71, 1.20-1.35 and 0.6-0.35, initial, mid and late season, respectively) suggesting the optimum Kc values at this treatment and interestingly, this is the treatment which has recorded optimum yield levels (Table 8 and 9). These results corroborate with the values obtained by [15,23,35, 38].

3.3.2. Sunflower :

Variation in drip irrigation levels had remarkable and positive influence on the crop coefficients (Kc) at different crop growth period (Figure 7). Among the drip irrigation levels, the data indicated that the highest Kc (1.70 and 1.89) was noticed at flowering and pollination stage of sunflower during both the years (2013-14 and 2014-15) with drip irrigation scheduled at 120% Epan treatment. Likewise, drip irrigation scheduled at 100% Epan, also registered crop coefficient values (Kc) of 1.52 and 1.67 during first and second year, respectively at flowering and pollination stage. However, the Kc values were low at the initial stages of crop establishment in all the treatments (0.67 on pooled basis) and then increased linearly with crop growth advancement and attained a peak values at vegetative stage and seed development period in first and second year, respectively. During vegetative stages and seed development stages the Kc values recorded were more or less same in higher drip irrigation treatments. With further increase in crop age (maturity period) the Kc values declined due to lower ETc values in both the years. On the other hand, the Kc values recorded at surface furrow irrigation at 1.0 IW/CPE ratio were higher over all the drip irrigation treatments in all the treatments in both the years. The highest Kc values of 1.99 was recorded on pooled basis at flowering and pollination stage and then declined with the time or age of sunflower crop.

Further, the Kc values decreased with decrease in drip irrigation levels from 120% Epan to 40% Epan and the lowest seasonal Kc values (0.96 on pooled basis) were associated with drip irrigation scheduled at 40% Epan treatment. The average Kc value for the total growing period (sowing to harvest) for all the treatments were 1.15 and 1.23 in 2013-14 and 2014-15, respectively. The Kc curve drawn with drip irrigation scheduled at 80% Epan treatment (Figure 7) resembles more or less same as that of FAO Kc curve (0.35-0.55, 1.15-1.30 and 0.41-0.6 for initial, mid and late season, respectively) suggesting the optimum Kc values for sunflower crop sat Himayatsagar, Hyderabad region for sunflower crop.  The Kc values in different oilseed crops were compared by [40-42] and they were all in the same range as obtained in the present experiment with drip irrigation scheduled at 80% Epan treatment.

3.4. Water Productivity (kg m⁻³)

3.4.1. Maize:

Drip irrigation recorded highest water productivity over surface check basin irrigation method. Application of water through drip at 80% Epan registered significantly highest water productivity (2.34, 2.67 and 2.49 kg m⁻³ in 2013-14, 2014-15 and on pooled basis) over rest of the drip irrigation treatments (Figure 8). However, the highest water productivity recorded at 80% Epan was found to be at par with the water productivity recorded at 100% Epan in both the years and on pooled basis. These findings are in corroboration with [43-47]. Generally water productivity decreases with increases in irrigation as yield gain is less than proportional increase in ET. Further, the incremental levels of irrigation from 80% Epan to 120% Epan did not show any marked variation in yield levels and thus water productivity started declining with increasing levels of water application.

3.4.2. Sunflower:

Significantly highest water productivity of sunflower was recorded with drip irrigated crop over the surface furrow irrigation at 1 IW/CPE ratio in both the years. Among the various drip irrigation treatments, irrigation scheduled at 80% Epan recorded the highest water productivity (0.93, 1.07 and 1.00 kg m⁻³ during 2013-14 and 2014-15 and on pooled basis, respectively) (Figure 9). The higher water productivity obtained at 80% Epan drip irrigated treatments could be due to higher seed yield obtained coupled with lower water application i.e. suboptimal irrigation as was also reported by [48]. However, the highest water productivity recorded at 80% Epan was found to be at par with the water productivity recorded at 100% Epan in both the years and on pooled basis. Significantly lowest water productivity was registered under surface irrigation at 1.0 IW/CPE ratio followed by drip irrigation at 40% Epan in both the years and on poled basis.

3.5. Variation in Soil Moisture Content with Crop Growth Stages

Soil moisture content in the soil is a dynamic process. It varies according to the prevailing weather conditions, type of soil, method of irrigation and management practices. The type of crop grown and stage of the crop also have tremendous influence on the moisture content in the soil at a given point of time. In the present experiment, different drip and surface furrow irrigation levels markedly influenced the average soil moisture content at 0-60 cm depth during both the years of experimentation in rabi season (Figure 10a and 10b).

In case of maize, drip irrigation levels exhibited uniform soil moisture depletion pattern as compared to surface furrow irrigation method which showed higher fluctuation between irrigation events during both the years. The soil moisture content in drip irrigation treatment viz., 120% and 100% pan evaporation replenishment (Epan) was higher throughout the crop life as compared to other treatments (40%, 60%, 80% Epan and IW/CPE=1). Likewise, the irrigation scheduled at 1.0 IW/CPE though had higher fluctuation between irrigation events maintained higher soil moisture contents over drip irrigation at 60% and 40% Epan. The effect of rain received at later period of crop growth was more illustrative showing higher effect on lower drip irrigation treatments than others (Figure 10a). Due to withholding of irrigation after physiological maturity in all the treatments, sharp fall in the soil moisture content was observed and the rate of decrease in soil moisture was higher in higher irrigation regimes.

While in case of sunflower, drip irrigation levels exhibited uniform soil moisture depletion pattern as compared to surface furrow irrigation method, which showed higher flux between irrigation events. The variation in soil moisture content observed in drip irrigation treatment viz., 120% and 100% pan evaporation replenishment (Epan) was much tapered throughout the crop life as compared to rest of the treatments. With the decrease in drip irrigation levels from 100% Epan to 40% Epan, there was distinctive variation in soil moisture content with depleting trend towards maturity period of the crop. Likewise, the irrigation scheduled at 1.0 IW/CPE though had higher fluctuation between irrigation events maintained higher soil moisture contents over drip irrigation at 60% and 40%. The rainfall received during later period (40-50 DAS) was of totally effective. However, its effect was seen only on lower drip irrigation levels (Figure 10b). Due to withholding of irrigation water application when crop reached physiological maturity, rapid fall in the soil moisture content was observed in all the treatments in both the years of study.

3.6. Comparison of Maize and Sunflower to Crop ET deficits and Use of Yield Sensitivity Coefficients (Ky) as a Basis for Crop Selection in Different Water Supply Circumstances, either in terms of Production or Profits

As shown in the Figure 11, which directly compares the yield sensitivity coefficients (Ky) found for maize (DHM- 117) and sunflower (DRSH-1) hybrids studied at      Himayatsagar, Hyderabad. The Stewarts S₂ function (linear functions) showed in Figure 11 for both the crops represent minimum relative yield loss expectations for each crop at all levels of drip irrigations relative to seasonal crop ET deficit. It may be noted that yield sensitivity coefficients may differ between hybrids/varieties as well as species. Therefore, a low yield sensitivity coefficient coupled with a high production potential is a characteristic to be sought when selecting crops for limited water situations or breeding crops for drought resistance. In the instance at hand, Figure 11 revels that sunflower is inherently 12.3%, 2.0% and 8.4% more sensitive to seasonal crop ET deficits than maize in 2013-14 and 2014-15 and on pooled basis respectively.

Yield sensitivity coefficient such as those in Figure 11 are the key to selecting either the most productive or profitable crop to be grown in specified water supply circumstances. Figure 12, which is based on Figure 11 compares the actual grain/seed yield expectations for maize and sunflower under a wide range of seasonal crop water supply levels. All that is needed to transform the yield sensitivity coefficients (Ky) in Figure 11 into actual “Water production functions” such as those in Figure 12 at another site or a given site is to estimate the maximum values for grain/seed yield (Ym) and ETa (ETm) when water is not limiting production. In Figure 12 these maximum values of sensitivity coefficients (Ky) for maize and sunflower crop under Himayatsagar, Hyderabad conditions illustrated.

The Figure 12 shows that maximum yield of sunflower can be achieved at the lowest crop ET level when compared to maize. However, in terms of tonnage, maize out yielded sunflower at all seasonal water supply levels through drip. Figure 11 and 12 also provide the essential technical input necessary for economic analysis, when commodity prices and crop production costs are considered, Figure 12 may be transformed to as shown in Figure 13.  In Figure 13 the net value of production per hectare is plotted against seasonal crop ET. For purposes of illustration the Figure 13 incorporates the prices and costs which prevailed in the Hyderabad in the month of July, 2015 following the harvest period of maize and sunflower. At that time the prices per 1.0 kg stood at ` 13.00 for maize and ` 35.00 for sunflower. While the cost of production per ha for maize and sunflower were ` 37630.00 and ` 36547.00, respectively.

The figure which emerged was that sunflower crop found to be profitable over maize when the seasonal crop ET exceeds a value of approximately 225 mm, 175 mm and 200 mm in 2013-14, 2014-15 and on pooled basis respectively. While a crop ET less than approximately 225 mm, 175 mm and 200 mm, and regardless of the degree of water control, for both the crops the rate of return per unit amount of crop ET was zero i.e. when seasonal crop ET falls to 225 mm, 175 mm and 200 mm none of these crops return any profit. Maize becomes unprofitable when crop ET fell approximately to 245 mm in 2013-14, 175 mm in 2014-15 and 210 mm in pooled basis. Likewise, sunflower becomes unprofitable when crop ET fell below 225 mm, 175 mm and 195 mm during 2013-14, 2014-15and on pooled basis. These crop ET levels shows that even though after assured crop ET levels which are mentioned above for both the crops, they are still under loss zone indicating that at this crop ET level, they could not translate it into real economic value and no economic returns can be anticipated. Whereas, after these levels, sunflower performed better than maize, but the limitation was that the sunflower reaches its potential yield levels before seasonal crop ET of 350 mm. On the other hand, under unlimited water situation, maize continued to put forth its yield levels even up to 425 mm and produced more than the sunflower yield.

The economic analysis shows that, at any given point of time, if water scarcity is anticipated, then it is better to go for sunflower crop than maize crop which requires higher water levels to realize same net returns. This type of analysis with different combination of field crops will help extension personnel for proper recommendation of suitable crop when harsh weather/weather aberrations are expected, and the farmers to decide and do contingent plans well in advance under drip or whichever method of irrigation and management practices to realize better income and sustain livelihood.

4. Conclusion:

Drip irrigation is an advantageous technique for getting higher yield of maize and sunflower in semi-arid tropics of India. Drip irrigation scheduled at 80% Epan (Pan evaporation replenishment) was found to be optimum in terms of growth and yield traits, and yield of maize and sunflower crop with highest water productivity over 40%, 60% Epan and surface furrow irrigation at 1.0 IW/CPE ratio. The study established precise information on ETc at different growth stages in both the crops. Crop coefficient, derived will facilitate prediction of crop ET and irrigation requirement of maize crop in advance of planting for planning irrigation strategies. The calculated Kc values for maize and sunflower were higher than FAO values which will be useful to estimate crop water requirement with further developing optimum irrigation schedules for achieving higher water productivity. Maximum profit of sunflower can be achieved at the lowest crop ET level when compared to maize. But in terms of tonnage, maize out yielded sunflower at all levels of seasonal evapotranspiration through drip. The outcome of such research is useful to draft guideline on crop selection and regional drip irrigation scheduling for scientist, farmers, stakeholders and policy makers under different models for profit maximization and resource conservation.

5. Acknowledgement

We sincerely thank and acknowledge support provided by WALAMTARI for providing funding support, facilities of conducting field experiment, manpower, technical information and other assets for conducting field experiment.

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References

1. Kadasiddappa M.M. and Praveen Rao V. 2018.Irrigation scheduling through drip and surface methods- A critical review on growth, yield, nutrient uptake and water use studies of rabimaize.Agricultural Reviews, 39(4) 2018: 300-306.
2. Farga, E., Arafata, S.M., Abd El-Wahedb M.S and L-Gindyc, A.M.E. 2012. Estimation of Evapotranspiration ETc and Crop Coefficient Kc of Wheat, in south Nile Delta of Egypt Using integrated FAO-56 approach and remote sensing data. The Egyptian Journal of Remote Sensing and Space Science. 15(1), 83-89.
3. Hatfield J.L., Prueger J.H., Reicosky D.C 1996 Evapotranspiration effects on water quality. In: Proc. ASAE Int. Conf. Evapotranspiration and Irrigation Scheduling, Nov 3–6, 1996, San Antonio: 536–546.
4. Kadasiddappa, M. M., Praveen Rao, V., Yella Reddy, K., Ramulu, V., Uma Devi., M and Narendar Reddy, S. 2017. Effect of irrigation (drip/surface) on sunflower growth, seed and oil yield, nutrient uptake and water use efficiency-A review. Agricultural Reviews. 38(2):152-158.
5. Bowman, J. A., Simmon, F. S and Kimpel, B. C. 1991. Irrigation in Midwest: Lessons from Illinois. Journal of Irrigation and Drainage Engineering, 117 (5): 700-715.
6. FAO/IAEA. 2002. Water balance and fertigation for crop improvement in West Asia. International Atomic Energy Agency, TECDOC-1266 ISSN- 1011-4289.
7. Anitta, F.S and Muthukrishnan, P. 2011. Effect of drip fertigation and intercropping on growth, yield and water use efficiency of maize (Zea mays L.). Madras Agriculture Journal, 98(7-9): 238-242.
8. Allen, R.G., Pereira, L.S., Raes, D and Smith, M. 1998. Crop evapotranspiration-Guidelines for computing crop water requirements. Irrigation and Drainage, Paper. No.56. FAO, Rome.
9. Rawat, K.S., Singh, S.K., Bala, A and Szabó, S. 2019 Estimation of crop evapotranspiration through spatial distributed crop coefficient in a semi-arid environment. Agricultural Water Management. 213, 922–933.
10. Guo, E.W and Zhang, L. J2019 Estimating Evapotranspiration Using SEBAL Model and Landsat-8 RS Data. Journal of Irrigation and Drainage. 38, 83–89.
11. Smith, M., Allen, R., Monteith, J. L., Perrier, A., Santos Pereira, L. and Segeren, A. 1992  Report on the Expert Consultation on Revision of FAO Methodologies for Crop Water Requirements Land and Water Development Division. – Food and Agriculture Organization of the United Nations, Rome
12. Allen, R.G 2000.Using the FAO-56 dual crop coefficient method over an irrigated region as part of an evapotranspiration intercomparison study. Journal of Hydrology. 229(1-2):27-41.
13. Bodner, G., Loiskandl, W and Kaul, H.P. 2007.Cover crop evapotranspiration under semi-arid conditions using FAO dual crop coefficient method with water stress compensation. Agricultural Water Management. 93(3):85-98.
14. Prihar, S.S and Sandhu, B.S., 1987. Irrigation of Field Crops-Principles and Practices. I.C.A.R., New Delhi, India.
15. Bandyopadhyay, P.K and Mallick, S. 2003. Actual evapotranspiration and crop coefficients of wheat (Triticumaestivum L.) under varying moisture levels of humid tropical canal command area. Agricultural Water Management, 59: 33-47.
16. Doorenbos, J and Pruitt, W.O. 1977. Crop water requirements. Irrigation and Drainage, No.  24, Food and Agriculture Organisation(FAO). Rome. Italy.
17. Piper, C.S. 1966. Soil and plant analysis. International Science Publication. New York, 47-49.
18. Saxton, K.E and W.J. Rawls. 2006. Soil water characteristic estimates by texture and organic matter for hydrologic solutions. Soil Science Society of American Journal. 70: 1569-1578.
19. Jackson, M.L. 1973. Soil chemical analysis.Prentice Hall of India, Pvt. Ltd. New Delhi. 498.
20. Subbaiah, B.V and Asija, G.L. 1956. A rapid procedure for determination of available nitrogen in soil. Current Science. 25: 259-260.
21. Olsen, S.R., Cole, C.W., Watanable, R.S and Dean, L.A. 1954. Estimation of available phosphorus in soils by extraction with sodium carbonate. US Department of Agriculture Proceedings. No. 939.
22. Panse, V.G and Sukhatme, P.V. 1978. Statistical methods for agricultural workers. IndianCouncil of Agricultural Research, New Delhi. 361.
23. Silungwe, F.R., Mahoo, H.F and Kashaigili, J.J. 2010.  Evaluation of water productivity for maize under drip irrigation. Second RUFORUM Biennial Meeting. 20-24, September 2010, Entebbe, Uganda. 725-728.
24. Bar-Yousef, B. 1999. Advances in fertigation. Advances in Agronomy, 65: 1.
25. Gardner, F.P., Pearu, R.B and Mitchell, R.L. 1985. Physiology of crop plants. Iowa State University press. Iowa. 327.
26. Unger, P.W. 1990. Sunflower. In: Irrigation of Agricultural Crops Eds. B.A. Stewart and D.R. Nielsen. American Society of Agronomy, Madison, Wikskinson, USA, 775-794.
27. Tolga, E and Lokma, D. 2003. Yield response of sunflower to water stress under Tekirdag conditions. HELIA, 26(38): 149-158.
28. Kazemeini, S.A., Mohsen, E and Avat, S. 2009. Interaction effects of deficit irrigation and row spacing on sunflower (Helianthus annuus L.) growth, seed yield and oil yield. African Journal of Agricultural Research, 4(11): 1165-1170.
29. Sezen, S.M., Yazar, A., Kapur, B and Tekin, S. 2011. Comparison of drip and sprinkler irrigation strategies on sunflower seed and oil yield and quality under Mediterranean climatic conditions. Agricultural Water Management, 98: 1153-1161.
30. Toll, J.A and Howel, T.A. 2012. Sunflower water productivity in four Great Plains soils. Field Crops Research, 127: 120-128.
31. Malve S. H., Praveen Rao V., Dhake A 2017 Estimation of seasonal evapotranspiration and crop coefficient of wheat (Triticumaestivum L.) under drip irrigation and N-fertigation scheduling at Jalgaon, Maharashtra. Journal of Agrometeorology, 19(4), 350-354.
32. Badr, M.A and Taalab, A.S. 2007. Effect of drip irrigation and discharge rate on water and soluble dynamics in sandy soil and tomato yield. Australian Journal of Basic and Applied Sciences,1 (4): 545-552.
33. Yazar, A., Gokcel, F and Sezen, M.S. 2009. Corn yield response to partial root zone drying and deficit irrigation strategies applied with drip system. Plant and Soil Environment, 55(11): 494-503.
34. Bozkurt, S., Yazar, A and Mansuroglu, G.S. 2011. Effects of different drip irrigation levels on yield and some agronomic characteristics of raised bed planted corn. African Journal, 6(23): 5291-5300.
35. Gao, Y., Duan, A., Sun, J., Li, F., Liu, Z., Liu, H and Liu, Z. 2009. Crop coefficient and water-use efficiency of winter wheat/spring maize strip intercropping. Field Crops Research, 111: 65-73.
36. Sharan, B. 2012. Performance of sweet corn hybrid under different levels of irrigation and nitrogen applied through drip system. M.Sc.(Ag.) thesis submitted to ANGRAU, Hyderabad.
37. Kumar, B.R., Rao. P.V., Avilkumar, K and Ramulu, V. 2013. Crop coefficients for drip and check basin irrigated castor for prediction of evapotranspiration. Journal of Research, ANGRAU. 41(2): 107-110.
38. Kar and Verma, H.N. 2005. Phenology based irrigation scheduling and determination of crop coefficient of winter maize (Zea mays L.) in rice fallow of eastern India. Agricultural Water Management, 75: 169-183.
39. Tekwa, I.J and Bwade, E.K. 2011. Estimation of irrigation water requirement of maize (Zea mays L.) using pan evaporation method in Maiduguri, North-Eastern Nigeria. Agricultural Engineering International, CIGR Journal, 13(1): 1552.
40. Tyagi, N.K., Sharma, D.K and Luthra, S.K. 2000. Evapotranspiration and crop coefficients of wheat and sorghum. Journal of Irrigation Drainage Engineering, 126: 215-222.
41. Kar, G., Kumar, A and Martha, M., 2007. Water use efficiency and crop coefficients of dry season oilseed crops. Agricultural Water Management, 87: 73-82.
42. De-Tar, W.R. 2009. Crop coefficients and water use for cowpea in the San Joaquin Valley of California. Agricultural Water Management, 96: 53-66.
43. Sharma, D.K., Kumar, A and Singh, K.N. 1990. Effect of irrigation scheduling on growth, yield and evapotranspiration of wheat in sodic soil. Agricultural Water Management, 18: 267-276.
44. Mahdi, M. Al-Kasi., Abdel Berrada and Mark Stack. 1997. Evaluation of irrigation scheduling programme and spring wheat yield response in South-Western Colorado. Agricultural Water Management, 34: 137-148.
45. Singh, V., Bhunia, S.R and Chauhan, R.P.S. 2003. Response of late sown wheat (TriticumaestivumL.) to row spacing cum- population densities and levels of nitrogen and irrigation in North-Western Rajasthan. Indian Journal of Agronomy, 48: 178-181.
46. Clinton, C., Shock Erik, Feibert, B.G., Lamont, D and Saunders. 2005. Water management for drip irrigated spring wheat. Malheur Experiment Station, Oregon State University Ontario, Dept. of crop and soil science.
47. Arora, V.K.,Harbakhshinder Singh and Bijay Singh, 2007. Analyzing wheat productivity responses to climatic, irrigation and fertilizer-nitrogen regimes in a semi-arid sub-tropical environment using the CERES-Wheat model. Agricultural Water Management, 94(1-3): 22-30.
48. Fanish, S.A., Muthukrishnan, P and Manoharan, S. 2011. Effect of drip fertigation in maize (Zeamays L.) based intercropping system. Indian Journal of Agricultural Research, 45(3): 233-238.