Rainfed cultivation with supplemental irrigation modelling on seed yield and oil of Coriandrum sativum L. using precision agriculture and GIS moisture mapping Open Access

Globally, the herb and spice sector has been enjoying rapid growth for several decades on the back of burgeoning demand from the booming economies, alongside with increased recognition of the health and culinary benefits of herbs and spices (FAO 2018). The worldwide herb and spice trade currently represents a multibillion-dollar industry and one that is booming with international demand and expanding areas of production with a clear need for international standards (FAO 2018). A well known herb and spice plant is coriander (Coriandrum sativum L.) which is an annual herbaceous crop of the Apiaceae (Umbellifera) family and it is known to be a native plant of Mediterranean region, Western Europe and Asia. Coriander is also commonly referred to as cilantro when grown for its herbage, used in many foods.

The erect, glabrous, annual plant coriander is produced throughout the world for culinary, aromatic and medicinal uses (Diederichsen 1996; Evergetis & Haroutounian 2014; Mandal & Mandal 2015; Khodadadi et al. 2016; Wei et al. 2019). The plant of coriander has been used since ancient times for cooking, medication and flavouring (Nadeem et al. 2013).

The essential oil extracted from coriander fruits (commonly termed seeds) has numerous uses (Diederichsen 1996; Lenardis et al. 2000; Evergetis & Haroutounian 2014; Mandal & Mandal 2015; Wei et al. 2019).

The essential oil from coriander is most commonly isolated from the plant seeds (fruits) usually by either steam or hydrodistillation or by the new microwave-assisted hydrodistillation extraction method (Ghazanfari et al. 2020). The essential oil content in coriander seeds has been found to vary between 0.125 and 1.90% (v w⁻¹) essential oil, of which 60–70% is linalool, the compound that gives the pleasant characteristic odor (Diederichsen 1996; Anitescu et al. 1997; Jeliazkova et al. 1997; Lenardis et al. 2000; Smallfield et al. 2001; Ayanoglue et al. 2002; Msaada et al. 2007, 2009; Gil et al. 2009; Neffati et al. 2011; Mandal & Mandal 2015; Khodadadi et al. 2016; Beyzi et al. 2017; Ghazanfari et al. 2020).

Coriander plant has many therapeutic properties including as an anti-inflammatory, analgesic, anticonvulsant, blood pressure lowering, cholesterol lowering, antioxidant, anti-diabetic, anti-mutagenic, sedative-hypnotic, protective against lead toxicity and heavy metal detoxificier, (Asgharpanah & Kazemivash 2012; Momin et al. 2012; Laribi et al. 2015; Mandal & Mandal 2015).

Regarding soil moisture is the content of water in the soil, held in the spaces between soil particles. Soil moisture availability is considered essential for nutrient cycling, a pre-requisite for primary crop production (Filintas 2011). Moreover, soil moisture affects the land evapotranspiration which is a central process in the climate system and a nexus of the water, energy and carbon cycles (Allen et al. 1998; Wan et al. 2007; Filintas 2008, 2011; Garten et al. 2009; Koutseris et al. 2010; Falloon et al. 2011, Filintas et al. 2019, 2020; Stamatis et al. 2011). Soil moisture is the most important factor for enhanced growth and production of coriander under rainfed condition. Among different growth stages of coriander, reproductive stages (L_mid and L_late growth stages) are much more sensitive than vegetative stage.

As the main source of natural water for agriculture and natural vegetation, soil moisture influences a variety of processes related to plant growth and agricultural production (Allen et al. 1998; Rodriguez-Iturbe 2000; Filintas 2011), as well as a range of soil processes (Allen et al. 1998; Filintas 2011; Filintas et al. 2019). Rainfall and irrigation water supply the moisture in soil and are used for field crop production which will become increasingly limited at Mediterranean latitudes due to climate and land-use changes (Clarke 1993). It is evident that scarce water resources frequently limit crop production in semiarid lands. Decreases in and scarcity of water resources resulting from many environmental effects and sources, and especially from agricultural irrigation consumption, are major environmental issues worldwide (Filintas 2008; Dioudis et al. 2009a, 2009b; Koutseris et al. 2010).

Regarding precision agriculture (PA), is referred as a management strategy which gathers using various ways, means and processes, and analyzes temporal, spatial and individual geodata and combines it with other digital or analog information in order to support proper crop management decisions according to the estimated field's variability for improved resources use efficiency, productivity, quality, profitability and sustainability of agricultural production.

Properly used, supplemental drip irrigation cultivation vs. rainfed cultivation, in conjunction with soil moisture monitoring and geographical information system (GIS) precision agriculture moisture root zone profile geospatial modelling and two-dimensional (2-D) mapping, may constitute a method for improving seed yield, essential oil and plant's umbel heights and also water use efficiency of coriander's crops for sustainable management of resources, and can contribute to environmental protection and sustainability.

The aim of the present study was to determine the effects of rainfed and supplemental drip irrigation, and of sowing period treatments on coriander (Coriandrum sativum L.) (Figure 1) yield, essential oil content and umbel heights by applying new agro-technologies (TDR-sensors measured soil's moisture (SM), GIS, global positioning system (GPS), precision agriculture (PA), soil-hydraulic analyses and geostatistical models) for yield and SM root zone profile geospatial modelling and 2-D GIS mapping), adapted to the specific climatic conditions of Central Greece and also the Mediterranean, in order to increase the harvested seed yield and essential oil without reducing the quality of the final product.

The experiment was conducted at the farmland of Gaiopolis campus–University of Thessaly, in a typical soil-climatic environment of Thessaly plain, at Larisa city in Central Greece (coordinates: latitude 39°62′68″N, longitude 22°38′5 ″E). The study area (Central Greece) is characterized by a typical Mediterranean climate with a cold winter, hot summer and low precipitation in spring and summer. The soil of the experimental site is characterized as sandy clay loam (SCL), soil organic matter (SOM) content was found to be 1.70%, bulk specific gravity of soil was 1.42 g·cm⁻³, the plant available water (PAW) was 0.129 cm·cm⁻¹, the pH at (1:5) soil/water extract was 7.10 and the cation-exchange capacity (CEC) of soil was 19.3 cmol·kg⁻¹, all at a depth of 0–30 cm.

The coriander's (Figure 1) experimental plot design was a factorial split plot design with the main factor of the two irrigation treatments (IR1: rainfed, IR2: rainfed plus supplemental drip irrigation (100% ETo) using a surface drip irrigation system) and sub factor the two sowing periods (SP1: last week of October, SP2: first week of November) treatments.

The size of each experimental plot unit was 1.8 m² (0.9 m width × 2 m length) containing two rows of plants each and the total area cultivated was 28.80 m². The layout and size of the 16 plots were designed that way because it was suitable and easier for the correct application of the drip irrigation system, the water cleaning system (filters) and to achieve a high distribution uniformity of irrigation water.

Control of weeds in all plots was performed manually by hand and no pesticides were used.

The effective root depth of coriander plant is 0–30 cm, where in a typical water extraction pattern the root hairs absorb about 90% of the water (soil moisture) and available nutrients of the soil. So, in order to determine soil's physical, chemical and hydraulic characteristics at the effective root depth zone (0–30 cm) of coriander, a soil sampling survey was carried out at the experimental plot units.

Soil samples at depth 0–30 cm were collected and analysed at the laboratory of Applied Soil Science of Gaiopolis campus–University of Thessaly in order to determine SOM content, soil's texture, structure and classes, soil's hydraulic properties (plant available water, field capacity (FC, θ_fc), wilting point (θ_wp)), soil's pH and CEC. A GPS receiver was used to identify the sampling locations.

The ideal season for sowing coriander seeds is the last week of October to the first week of November (Meena et al. 2013). So, the seeding took place on two different sowing periods on October (last week) and November (first week) applying 20 kg·ha ⁻¹ of coriander (Coriandrum sativum var. microcarpum L.) seed in a row distance of 40 cm and plant distance of 10 cm. Two doses, basic and surface fertilization (A dose = 66.67 kg P₂O₅ and B dose = 74.44 kg N per hectare) were applied.

Soil moisture of the plots was measured by applying the time domain reflectometry (TDR) method. For the application of the TDR method, a TDR measuring instrument-model MP-917 ESI (Environmental Sensors INC 1997; Dioudis et al. 2010; Filintas 2011) and soil moisture TDR probes with five sensors each were used (Figure 3(a)). Each probe have five sensors (segments), placed at 0–15, 15–30, 30–45, 45–60 and 60–75 cm depths and each sensor was used for measuring volumetric soil water content (⁠ of coriander's root zone.

In TDR method, the propagation velocity (v) of an electromagnetic energy pulse in the soil is determined. In order to determine v in soil, very short electrical pulses are sent through a metallic two rod probe (Figure 2(a)) with one or more sensors (segments). From the travel time (t) and the length (l) of the probe, which has been travelled along twice, the propagation velocity v = 2 l/t is calculated (Worsching et al. 2006). When the pulse velocity changes in the soil, is a result of a change in soil moisture content due to the relatively large dielectric value of water (Muñoz-Carpena 2012). The pulse velocity in the probe sensors is measured by the instrument and correlated to the soil moisture. A lower velocity indicates a wetter soil. TDR has been used for measuring volumetric soil water by several researchers (Yu & Drnevich 2004; Filintas 2008, 2011; Dioudis et al. 2010; Filintas et al. 2010). TDR is a non-destructive and relatively less labour intensive technique; the TDR instrument used is portable, the sensors are easy to install and safe to operate. This technique allows reliable measurements of volumetric water content within a short time period. No soil specific calibrations are required (Topp & Davis 1985; Ferrara & Flore 2003). TDR technique gives accurate results within an error limit of ±1% and allows continuous measurements to be obtained over the full soil moisture range (profile) (Chandler et al. 2004; Filintas 2008, 2011; Dioudis et al. 2010; Filintas et al. 2010), along with measurements of the electrical conductivity of the soil (Thomsen et al. 2007). The TDR measurements data of soil moisture were imported daily in a digital geodatabase and used in a GIS utilizing precision agriculture and geostatistics in order to model and produce digital soil moisture 2-D maps of coriander's root zone soil profile of the experimental plots.

Meteorological data were obtained from a meteorological station near to experimental field. The effective rainfall for the experimental site conditions was calculated according to USDA-SCS (1970).

The fruits (seeds) of Coriandrum sativum var. microcarpum L. were harvested in June at the stage of full maturity, where only brown fruits were present. Post-harvest processing results found that the fruits' mean diameter was D_f <3 mm, while the mean weight of 1000 fruits was found to be 9.26 g. After air drying fruits in a shady place (humidity 9%) at the laboratory, a commercial grain crusher with two rotating rollers was used to crush the fruits and subsequently were sieved with a 2.0 mm metallic sieve, before distillation.

Essential oil content determination was performed by extraction from coriander seeds with hydro-distillation using a Clevenger-type distillation apparatus. Twelve and a half gram of dried coriander seeds were subjected into 250 mL of water for 105 min of hydrodistillation. The extraction procedure was repeated three times for each sample and the essential oil content was estimated on dry weight basis (DW) of coriander seed material (ml·100 g⁻¹).

At the experimental cropfield, soil samples (0–30 cm) were collected in an grid pattern of 0.9 m × 2 m to determine exture [(clay content (Cl), silt (Si) content, sand (Sa) content and gravel (Gr) content)], SOM content, pH and CEC, soil's structure and texture classes, bulk specific gravity of soil and PAW (% vol.) that was determined by FC water content (θ_fc) (or water holding capacity) (% vol.) and wilting point water content (θ_wp) (% vol.) measurements.

A satellite GPS receiver was used to identify and register the sampling locations. A total of 16 soil samples were air-dried and passed through a 2 mm mesh to determine soil texture by the Bouyoucos-hydrometer method (Page et al. 1982; Beretta et al. 2014).

Soil's pH was determined in a 1:5 soil/water extract, while pH value was measured by using glass electrode and a pH meter. Soil organic matter was analysed by chemical oxidation with 1 mol·L⁻¹ K₂Cr₂O₇ and titration of the remaining reagent with 0.5 mol·L⁻¹ FeSO₄. Soil's nitrogen inorganic forms were extracted with 0.5 mol·L⁻¹ CaCl₂ and estimated by distillation in the presence of MgO and Devarda's alloy, respectively (Page et al. 1982).

The PAW for plant growth is the difference between soil's FC and wilting point (WP) (⁠ water contents. The FC and WP water contents were measured with the porous ceramic plate method placed into a container that is pressurized with 1/3 atmospheres (about 5 psi) for FC and with 15 atmospheres (about 225 psi) for WP (Filintas 2008; Dioudis et al. 2009a; Filintas et al. 2010, 2019). Soil classification with USDA Soil Classification Triangle was performed according to USDA classification (Soil Survey Staff 1975).

Data analysis was performed using the IBM SPSS v.26 (Norusis 2011) statistical software package. The results are means of the samples and measurements of all measured and derived data groups. Mean separation was made using LSD_0.05 statistical test as the test criterion when significant differences (P = 0.05) between treatments were found (Steel & Torrie 1982).

The Zero Hypothesis (H0) for the main factor (irrigation treatments [IR1: rainfed, IR2: rainfed plus supplemental drip irrigation (100% ETo)], for the sub factor [sowing periods treatments (SP1: last week of October, SP2: first week of November)] and for irrigation treatments and sowing period treatments interaction effects on coriander's seed yield, essential oil content and plant's umbel heights were H0ir, H0sp and H0irxsp, respectively, as seen below.

H0ir = irrigation treatments [IR1: (rainfed), IR2: (rainfed plus supplemental drip irrigation)] have no significant effect on coriander's seed yield and/or on essential oil content and/or on plant's umbel heights.

H0sp = sowing period treatments [SP1 (last week of October), SP2 (first week of November)] have no significant effect on coriander's seed yield and/or on essential oil content and/or on plant's umbel heights.

H0irxsp = irrigation treatments and sowing period treatments interaction have no significant effect on coriander's seed yield and/or on essential oil content and/or on plant's umbel heights.

For the experimental farm field, spatial interpolation was used with the geostatistical models of CoKriging, which are used to estimate an unknown value, given the observed values at sampled plots (Lu & Wong 2008; Dioudis et al. 2009a; Filintas et al. 2010, 2019; Filintas 2011; Stamatis et al. 2011). The method is based on the assumptions that the attribution values of measured parameters at the unsampled soil sites are a weighted average of values at sampled soil sites of the experimental farm field. Using the parameters found from measurements and laboratory analyses (which were digitally mapped in a GIS geodatabase environment) as input auxiliary variables, we delineated soil moisture profile digital GIS maps of coriander's root zone with the help of spatial analysis and the use of a GIS software (ArcGIS^© version 10.2).

In addition, the evaluation of TDR measured soil moisture, require statistical analysis of residual errors, the difference between predicted and observed values and prediction characterization between over- and underestimates. To that end, we used the statistical parameters described by Loague & Green (1991); Filintas (2011); Filintas et al. (2019), such as the equations for the mean prediction error (MPE), mean standardized prediction error (MSPE) and the root mean square standardized error (RMSSE). The MPE and MSPE values should approach zero for an optimal prediction and the RMSSE should approach one.

The study area is characterized by a typical Mediterranean climate with cold humid winters and hot-dry summers. In particular, the average max air temperature ranged during the cultivation period (October to June) from 1.98 °C to 29.25 °C (mean 15.68 °C), during the autumn–winter (October–February) from 1.98 °C to 22.11 °C (mean 11.68 °C), during the spring (March–May) from 15.07 °C to 22.35 °C (mean 17.81 °C) and during the summer months (June and July) had a mean of 29.25 °C. Monthly relative humidity ranged during the cultivation period (October to June) from min 49.76% to max 82.11% (mean 68.07%), during the autumn–winter (October–February) from min 60.26% to max 82.11% (mean 71.29%), during the spring (March–May) from min 63.65% to max 76.48% (mean 68.82%) and during the summer month (June) had a mean of 49.76%.

Precipitation during the autumn–winter (October–February) was 184.00 mm, on spring (March–May) was 192.10 mm and only 1.00 mm on summer (June) with a total precipitation (October to June) of 377.10 mm. The various climatic parameters (max air temperature, mean air temperature, average max air temperature, average min air temperature, mean relative humidity, mean precipitation (rainfall), mean effective rainfall, and mean wind force) of the study area are presented in Figure 2.

The above, mentioned values of climatic data are very important because directly affect crop growth, evapotranspiration and crop water requirements (needs). A certain crop (in our case coriander) grown in a sunny and hot climate needs per day more water than the same crop grown in a cloudy and cooler climate.

However, there are – apart from air temperature and precipitation – other climatic factors which influence the crop water needs. These factors are the relative humidity, the wind force (see Figure 2) and sunshine. When the climate is dry, the crop water needs are higher than when it is humid. Moreover, in windy climates, the crops will use more water than in calm climates.

A first reading of the above climatic values indicates that the air temperature, relative humidity and wind force are acceptable values that permit the coriander proper growth. On the contrary, precipitation amount and its distribution through time on the four crop growth stages seems to be not enough to cover crop water needs as rainfed cultivation on all stages for the coriander's full growth.

According to the USDA (Soil Survey Staff 1975), soil texture was characterized as SCL. Results and statistical analysis of soil laboratory analysis at the laboratory of Applied Soil Science of Gaiopolis campus revealed that the soil of the experimental field (mean values) was characterized as SCL, SOM was 1.70%, bulk specific gravity of soil was 1.42 g·cm⁻³, the PAW was 0.129 cm·cm⁻¹, the pH at (1:5) soil/water extract was 7.10 and the cation-exchange capacity (CEC) of soil was 19.3 cmol·kg⁻¹.

The TDR sensor (Figure 3(a)) measurements (average of the soil moisture content measurements at five different soil depths [0–15 cm, 15–30 cm, 30–45 cm, 45–60 cm and 60–75 cm]) were used in order to monitor daily soil moisture and the depletion of available soil moisture (ASMD) (Dioudis et al. 2009a; Filintas et al. 2010; Filintas 2011) that was calculated and evaluated in relation to each rainfed and supplementary drip irrigation treatment.

The TDR measurements datasets (data of five different soil depths) of soil moisture were imported in a digital geodatabase and used in a GIS environment utilizing precision agriculture and geostatistics (Filintas et al. 2010, 2019, 2020; Filintas 2011) in order to model and produce digital soil moisture 2-D maps of coriander root zone soil profile of the plots. An example of the produced digital soil moisture GIS Model 2-D maps of coriander root zone soil profile of the supplemental drip irrigation plots is depicted in Figure 3(b).

In Table 1 is presented the rainfall, effective rainfall, supplemental irrigation and crop evapotranspiration ETc of the cultivation period of coriander's plant.

In Figure 4 are depicted the results of the daily soil-water balance model (Filintas 2011) with the daily monitoring of soil moisture (measured with TDR instrument and sensors (Dioudis et al. 2009a; Filintas et al. 2010; Filintas 2011)), effective rainfall, soil evaporation, crop ETc, field capacity ⁠, permanent wilting point (⁠⁠, saturation (soil moisture content at saturation), and coriander's crop height, through the four crop growth stages of treatment IR1: rainfed.

As it can be observed in Figure 4, in the middle of one of the most sensitive growth stages [the flowering (L_mid stage)] (Allen et al. 1998; Filintas 2008, 2011), the crop ETc almost gradually increases till the end of the flowering stage, while precipitation is deteriorating to very low amounts.

At the fourth crop growth stage (L_late stage) the crop ETc continues to increase furthermore, while precipitation is deteriorating to almost zero amounts.

In Figure 4, in the middle of one of the most sensitive growth stages [the flowering (L_mid stage)] a shortage of soil moisture occurs in the dry rainfed area of the experimental field's location due to increased crop ETc and the prevailing climatic conditions, driving soil moisture at the end of L_mid stage to drop down at very low levels of soil water content near the permanent wilting point ⁠, at the end of the flowering stage.

During the grain filling crop growth stage (L_late stage) of the coriander's crop, the soil moisture continues to be at low levels of soil water content which is dropping down gradually at the edge of the permanent wilting point due to increased crop ETc and to very low precipitation amount of the study area. This soil water content shortage situation at very low levels caused a serious water stress to the coriander plants and as a result, rainfed crop growth was poor and yield was consequently low (IR1: rainfed = 422.369 (±17.205) Kg·ha⁻¹).

Shortage of soil moisture in the dry rainfed areas often occurs during the most sensitive growth stages [flowering (L_mid stage) and grain filling (L_late stage)] of the coriander crop and in other crops also. As a result, rainfed crop growth is poor and yield is consequently low.

Productivity results of IR2: rainfed plus supplemental irrigation plots were superior because the soil water content shortage situation did not occur at IR2 and soil moisture distribution (see Figure 3(b)) as it can be observed in digital GIS 2-D maps of coriander's soil moisture root zone profile was ranged at high volumetric soil water contents, and it did not cause any water stress to the coriander plants. As a result, supplemental irrigation crop growth was increased in comparison to the rainfed and supplemental irrigation treatments yield was consequently high (IR2: rainfed plus supplementary irrigation = 1203.473 (±34.246) Kg·ha⁻¹).

The two-way ANOVA (analysis of variance) (Filintas 2011; Norusis 2011) statistical analysis (P = 0.05) results of the irrigation treatments, sowing periods and irrigation treatments*sowing period interactions effects on coriander's dry seed yield, essential oil contents and plant's umbel heights are presented in Table 2.

According to the two-way ANOVA results of Table 2, the zero hypothesis (H0ir) for the main factor irrigation treatments [IR1: rainfed, IR2: rainfed plus supplemental drip irrigation (100% ETo)], was rejected for coriander's dry seed yield, essential oil contents and plant's umbel heights. Statistically, this means that the irrigation treatments [IR1: rainfed, IR2: rainfed plus supplemental drip irrigation] have significant effect on coriander's dry seed yield, on essential oil contents and on the plant's umbel heights.

According to the two-way ANOVA results of Table 2, the zero hypothesis (H0sp) for the sub factor sowing period treatments (SP1: last week of October, SP2: first week of November), was rejected for coriander's dry seed yield and essential oil contents but it was not rejected for plant's umbel heights.

Statistically, this means that the sowing period treatments (SP1: last week of October, SP2: first week of November) have a significant effect on coriander's dry seed yield and on essential oil content but have no significant effect on the plant's umbel heights (P = 0.873). There is a 0.005% and a 0.117% chance of getting results by random chance for coriander's dry seed yield and essential oil contents respectively.

According to the two-way ANOVA results of Table 2, the zero hypothesis (H0irxsp) for irrigation's and sowing period's treatments interaction was rejected for coriander's dry seed yield but it was not rejected for essential oil contents and for the plant's umbel heights.

Statistically, this means that the irrigation treatments and sowing period treatments interaction have significant effect on coriander's dry seed yield but have no significant effect on essential oil contents (P = 0.993) and on the plant's umbel heights (P = 0.907). There is a 1.5% chance of getting results by random chance for coriander's dry seed yield.

The two-way ANOVA (Filintas 2011; Norusis 2011) statistical analysis (P = 0.05) results revealed that the irrigation treatments (IR1: rainfed, IR2: rainfed plus supplementary irrigation (100% ETo) [best]), significantly affects coriander's dry seed yields (IR1 = 422.369 (±17.205) Kg·ha⁻¹ and IR2 = 1203.473 (±34.246) Kg·ha⁻¹) essential oil contents (IR1 = 0.937 (±0.047) % v·w⁻¹ and IR2 = 1.175 (±0.034) % v·w⁻¹) and plant's umbel heights (IR1 = 73.746 (±2.849) cm and IR2 = 86.968 (±2.213) cm).

Supplemental irrigation, using a limited amount of water, if applied during the critical crop growth stages (especially on L_mid and L_late growth stages), can result in substantial improvement on coriander's seed yield (+284.934%), on essential oil contents (+125.396%) and on the plant's umbel heights (+117.929%).

Therefore, daily monitoring with TDR sensors and 2-D GIS geostatistical mapping of soil moisture root zone profile and calculation of the soil-water balance of coriander's root zone profile for the four crop growth stages, can outcome better decisions for supplemental drip irrigation which is an effective response to alleviate the adverse impact of soil moisture stress during dry spells on the yield of rainfed coriander (Coriandrum sativum L.) crop and probably in other rainfed crops.

The above advances in agriculture will let businesses be more profitable, efficient, safer, and environmentally friendly.

The two-way ANOVA statistical analysis (P = 0.05) results revealed that the irrigation treatments (IR1: rainfed, IR2: rainfed plus supplementary irrigation (100% ETo) [best]), significantly affects coriander's dry seed yields (IR1 = 422.369 (±17.205) Kg·ha⁻¹ and IR2 = 1203.473 (±34.246) Kg·ha⁻¹) essential oil contents (IR1 = 0.937 (±0.047) % v·w⁻¹ and IR2 = 1.175 (±0.034) % v·w⁻¹) and plant's umbel heights (IR1 = 73.746 (±2.849) cm and IR2 = 86.968 (±2.213) cm).

Statistical results revealed that the sowing period treatments (SP1: last week of October, SP2: first week of November [best]) have significant effect on coriander's dry seed yield and on essential oil content but have no significant effect on plant's umbel heights (P = 0.873).

Moreover, the two-way ANOVA statistical analysis also revealed that the irrigation treatments and sowing period treatments interaction have significant effect on coriander's dry seed yield but have no significant effect on essential oil contents (P = 0.993) and on plant's umbel heights (P = 0.907). There is a 1.5% chance of getting results by random chance for coriander's dry seed yield.

Supplemental irrigation, using a limited amount of water, if applied during the critical crop growth stages (especially on L_mid and L_late growth stages), can result in substantial improvement on coriander's seed yield (+284.934%), on essential oil contents (+125.396%) and on the plant's umbel heights (+117.929%).

Therefore, daily monitoring with TDR sensors and 2-D GIS geostatistical mapping of soil moisture root zone profile and calculation of the soil-water balance of coriander's root zone profile for the four crop growth stages, can provide better decisions for supplemental drip irrigation which is an effective response to alleviate the adverse impact of soil moisture stress during dry spells on the yield of rainfed coriander (Coriandrum sativum L.) crop and probably in other rainfed crops.

The significance of the results achieved is strongly indicative that farmers should adopt these management practises (rainfed plus supplementary irrigation, November sowing and 2-D TDR-GIS SM monitoring and precision agriculture GIS mapping) in order to achieve better management decisions, better dry seed yields, better essential oil contents, environmentally friendly agricultural management and increased income.

In the future, modern farms and various agricultural operations will work differently, primarily because of advancements in technology, such as soil, water and crop sensors, devices, farm machines, and information technology. Future agriculture will use sophisticated technologies such as GIS, precision agriculture, robots, temperature and moisture sensors, aerial and satellite images, drones equipped with various sensors, GPS technology, etc. These advances in agriculture will let businesses be more profitable, efficient, safer, and environmentally friendly.

Data cannot be made publicly available; readers should contact the corresponding author for details.