View of Water Footprint Analysis of Paddy Cultivation by Subsurface Irrigation in a Greenhouse

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Jurnal Teknik Pengairan: Journal of Water Resources Engineering, 2023, 14(1) pp. 1-12 https://jurnalpengairan.ub.ac.id/ | p-ISSN : 2086-1761 | e-ISSN : 2477-6068

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Water Footprint Analysis of Paddy Cultivation by Subsurface Irrigation in a Greenhouse

I Gede Pande Mahardika¹, Chusnul Arif^1*)

1Department of Civil and Environmental Engineering, Faculty of Agricultural Engineering and Technology, IPB University, Bogor 16680, Indonesia

Article info: Research Article

DOI :

10.21776/ub.pengairan.2023.014.01.01

Keywords:

dry irrigation; flooded irrigation;

greenhouse; water footprint; wet irrigation

Article history:

Received: 27-07-2022 Accepted: 10-01-2023

*)Correspondence e-mail:

Creative Commons License

This work is licensed under a Creative Commons Attribution-Non-

commercial 4.0 International License.

Abstract

Water is one of the main elements that rice plants require to grow and develop. The problem related to agricultural land is the shift in the function of agricultural land to become non-agricultural land due to competition in water usage. The water footprint approach can assess the amount of water required for production or yields. This study aims to analyze the water footprint value of rice cultivation with various treatments of irrigations. The research was conducted at the Kinjiro Farm Greenhouse, Gunung Batu, Bogor, West Java from March to July 2022. There were three treatments of irrigation systems based on water level, flooded irrigation (IT) with the water level above the soil surface, wet irrigation (IB) with the water level parallel to the soil surface, and dry irrigation (IK) with the water level below the soil surface. The total water footprint obtained for all treatments during rice cultivation activities was 9.73 m³/kg. The water footprint values of IT, IB, and IK were 1.92 m³/kg, 1.66 m³/kg, and 6.14 m³/kg, respectively. IB had the largest water productivity of 0.60 kg/m³. Wet irrigation (IB) had the highest growth of rice plants based on the parameters of average growth of rice plant height, number of leaves, rice tillers, productive tillers, and rice panicles. Therefore, wet irrigation (IB) is the most optimal irrigation system for rice cultivation in a greenhouse.

Cite this as: Mahardika, I, G, P., Arif, C. (2023). Water Footprint Analysis of Paddy Cultivation Using Subsurface Irrigation in a Greenhouse. Jurnal Teknik Pengairan: Journal of Water Resources Engineering, 14(1), page.1-12 https://doi.org/10.21776/ub.pengairan.2023.014.01.01

1. Introduction

The staple food of most people of Indonesia is rice, which is grown in paddies and has become one of the parameters of national food stability. Rice as a plant commodity has a high economic value because Indonesian people require rice as their staple food throughout the year. [1] Indonesia produced 54.65 million tons of GKG (ground dry rice grains) in 2020, and an increase in paddy production occurred in 2021 to 55.27 million tons of GKG. Thus paddy production increased by 1.14% from 2020 to 2021. The population of Indonesia which continues to experience growth from year to year has the effect of the increased demand for rice on the market. An increase in the area of agricultural lands in Indonesia does not balance out the increasing number of people. The area of rice harvests in 2021 decreased by 1.33% compared to the area in 2020 from 10.66 million hectares to 10.52 million hectares [1].

A problem that is often encountered concerning agricultural lands is the shift in the function of agricultural land to become non-agricultural lands due to competition in the usage of water resources for other needs, such as domestic and non-domestic needs [2]. The concept of water footprint allows for the discovery of the amount of water usage that is required for an activity of production. The water footprint concept is implemented to measure savings in water usage needs for the cultivation of rice paddies to increase the productivity of yields without having to use water resources in excess [3]. Water becomes one of the essential elements useful for rice paddies for their growth and

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2 Mahardika, Arif: Water Footprint Analysis of Paddy Cultivation Using Subsurface Irrigation in a Greenhouse

development. A lack of water during the rice paddies' cultivation period affects the plants' development, such as by decreasing photosynthetic activity [4].

Efforts to develop rice paddy cultivation methods to increase the productivity of agricultural yields may be conducted through approaches such as the development of irrigation technologies or systems. Irrigation plays an important role in the activity of cultivating rice paddies. Sub-surface irrigation is a method for distributing water under the soil surface, which may utilize open channels or closed channels (a pipe system). In a system of sub-surface irrigation, water is made to penetrate under the root zones of plants in the ground. The application of a sub-surface irrigation system is appropriate to be applied in areas with little available water, and thus efforts of implementing subsurface irrigation can increase savings of water usage for cultivation, specifically of rice paddies [5].

Therefore, optimal irrigation is important and necessary for the cultivation of rice paddies, as is the allocation of water resources that is effective and efficient. Therefore, this research aims to determine the water footprint value for cultivating rice paddies through various sub-surface irrigation system treatments in a greenhouse and to analyze optimal irrigation system with the highest water productivity and greatest plant height growth.

2. Materials and Methods

The research was conducted at Kinjiro Farm, which has the address of Jl. Hegarmanah IV, RT.01/RW.08, Gunung Batu, Bogor, West Java. The research location is situated at the coordinate point of 7° 24' 24.5" South Latitude and 106° 46' 17.7" East Longitude (Figure 1). This research required tools that comprised 3 water tubs of 125 liter capacity, paddy growth medium as 18 pots of 19 liter capacity, PVC pipes, pipe connectors, 3 water level sensors, 3 water gauges, 3 faucets, 3 EC 5 soil moisture sensors, Em50 data logger, weather station, open pan evaporimeter, ruler, measuring tape, and tray for the sowing of rice paddy seedlings. In addition, this research used the materials of IPB 3S of rice paddy seedlings, irrigation water, urea fertilizer, KCL fertilizer, TSP fertilizer, and soil. This research also used applications, such as the ECH2O and Sketch Up applications. The conducted research activities are generally divided into several activity stages, covering planting media and irrigation instrument preparation, rice planting and cultivation, data collection, data processing, and water footprint analysis.

Figure 1. Research Location

2.1. Preparation of planting media and irrigation instruments

Planting rice paddies was conducted in a greenhouse building measuring 5.4 m x 3.3 m. The greenhouse functioned to hold back the influence of rainwater that can impede the growth of the plants, prevent the cultivation soil from becoming soggy, and anticipate the entry of rainwater into

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the planting media. Furthermore, the web covering of the greenhouse can protect plants from pests and serve as synthetic ventilation to regulate temperature conditions [6]. Pots as the planting media were filled with soil to a height of 20 cm from the base of the pots. The design for the planting media can be seen in Figure 2. Each row of pots represented one treatment, for which the treatments were differentiated by the water level height in the planting media.

In this research, there were three treatments of irrigation systems, Flooded Irrigation (IT), Wet Irrigation (IB), and Dry Irrigation (IK). Traditional rice paddy cultivation systems generally use Flooded Irrigation (IT) when there is an abundance of available irrigation water. At the same time, Wet Irrigation is a more economical form of irrigation, particularly for rice paddy cultivation by the System of Rice Intensification (SRI) [7]. Dry Irrigation is used when water resources are limited for water stress treatment. The IT treatment's planting tub was flooded, with the water surface height being 3 cm above the soil surface. The planting tub for the IB treatment was wet, with the water surface height being level with the soil surface. The planting tub for the IK treatment was of dry condition, with the water surface height being 3 cm below the soil surface. The illustration of the regulation of water surface height and distribution of water to the planting tubs for the IT, IB, and IK treatments is depicted in Figure 3. A water level sensor functioned to control the water level height for each treatment. The water level sensor worked by closing the water inlet if the water level condition in the water pot is under the established set point and automatically opening to allow the water level height for each treatment to be controlled according to the set point. The water pressure in the control tub distributed water from the control tub to all planting tubs until their water surfaces were at the same level. Capillary in the soil moved water to become distributed and fill the entire pot.

Figure 2. Design of planting media

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Figure 3. Regulation of water level height for treatments (a) IT, (b) IB, and (c) IK

2.2. Rice cultivation

Rice cultivation activity was divided into four stages: the sowing of rice paddy seedlings, planting of rice paddy seedlings, care of rice paddies, and harvest of rice paddies. The utilized rice seedlings were of the IPB 3S variety. Before sowing, the rice paddy seedlings were first soaked. After soaking, the rice paddy seedlings were sprinkled into a container filled with soil and in moist condition. The sowing process required approximately 14 days. The rice paddy seedlings ready to be planted were

Dry Irrigation (IK)

Wet Irrigation (IB)

Flooded Irrigation (IT)

Outlet Pipe Inlet Pipe

Water Gauge

Water Containment Tub

Water level 3 cm

above soil surface Water surface level

with soil surface

Water level 3 cm below soil surface

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then moved to the planting media as pots in the greenhouse. Plant care activities involved fertilization and weeding or weed control of the plants. Fertilization during rice paddy cultivation referred to [8], is conducted three times when the rice paddies are 7 days, 20 days, and 40 days after planting.

Harvesting was reaping the resulting rice paddy grains that were conducted when the grains and leaves had turned yellow. Harvesting aims to obtain the weight of grains that are yielded from the conducted rice paddy production. The resulting weight of grains was used to analyze the water footprint.

2.3. Data collection and processing

The primary data utilized in this research were obtained through direct measurement and were collected from the weather station at the research location. The primary data that were collected from the research location were the reduction of water level in the containment tub, changes of water level height in the planting pots, soil moisture, average daily temperature, amount of daily sunlight radiation, several plant growth parameters, and the weight of grains at harvest time. Primary data such as average temperature and sunlight radiation were obtained by utilizing a weather station that had been set up at the research location. Additionally, there were primary data in the form of rice paddy growth parameters that cover plant height, number of leaves, number of tillers, number of panicles, and the weight of grains obtained after the harvest. The primary data were used to analyze water footprint and effects of land conditions on the growth of rice paddies.

2.3.1. Water Balance

Water balance is the comparison of the available water with the water required to meet the irrigation needs. Water used for rice paddy cultivation on agricultural lands generally comes from rainwater and irrigation water. Water escaping the activity of rice paddy cultivation may occur through evapotranspiration, percolation, leakage, and runoff. Based on these details, the equation for water balance can be written out in a more complex form, as equation (1) [9].

ΔS = (P + I) - (ETc + Pk + Sp + R) (1) The rice cultivation activity was performed on planting media inside a greenhouse; thus the influence of rainwater as a water input source was not accounted for. The utilized planting media were pots, which leads to the processes of percolation and leakage not influencing the amount of water that escapes, and thus the equation for water balance changes to the form as in equation (2) below. The available water is considered to fulfill water needs, and there are no water reserves, thus irrigation water needs can be calculated through equation (3).

ΔS = I – Etc (2) I = ETc (3) Remarks:

ΔS = Water reserves (mm) P = Rainfall (mm) I = Irrigation (mm)

ETc = Crop evapotranspiration (mm) Pk = Percolation (mm)

Sp = Seepage (mm) R = Runoff (mm) 2.3.2. Crop Water Requirements

Crop water requirement is the amount of water used in fulfilling water needs that have been used up in processes that occur in plants, such as evapotranspiration. Evapotranspiration value covers potential evapotranspiration and crop evapotranspiration [10]. Referring to [11], the calculation of potential evapotranspiration may be performed using the Hargreaves model with equation (4) below.

Crop evapotranspiration is affected by the crop coefficient, for which the kinds of plants affect the

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value of the coefficient. Therefore, the crop evapotranspiration value is calculated by using equation (5) [9].

ETo = 0.0135(Tmean+17.78)Rs[ ^238.8

595.5−0.55 𝑥 𝑇𝑚𝑒𝑎𝑛] (4) ETc = ETo x Kc (5) Remarks:

ETo = Potential evapotranspiration (mm/day) ETc = Crop evapotranspiration (mm/day) Tmean = Average air temperature (°C) Rs = Solar radiation (MJ/m²/day) Kc = Crop coefficient

2.3.3. Water Productivity

Water productivity indicates the optimal quality of water usage to yield certain products. Water productivity can be calculated through equation (6) [12].

WP = ^Y

∑ WU (6) Remarks:

WP = Water productivity (kg grains/m³ water) Y = Harvest yield (kg/m²)

WU = Water usage (m³/m²)

2.3.4. Water Footprint

The water footprint is the entire amount of water that is used in a process to yield a certain product.

There are three components for water footprint: green water footprint, blue water footprint, and grey water footprint [13]. The green water footprint value measurement refers to the amount of rainwater that evaporates during plant cultivation. The rice paddy cultivation was fully conducted inside a greenhouse building, and thus the usage of rainwater as a supply of water needs did not occur. It causes the green water footprint value to be not included in the overall total water footprint value that was analyzed. The total water footprint value can be calculated with equation (7).

WF = WF blue + WF grey (7) The blue water footprint value refers to using surface water and groundwater as irrigation that evaporates during production. The blue water footprint value during production is obtained from irrigation water that evaporates [14]. The blue water footprint value can be calculated through equation (8), referring to [13].

WF blue = ^{CWU blue}

Y (8) The grey water footprint value indicates the amount of water used to reduce pollutants such as those that originate from the usage of pesticides and chemical fertilizers in plant cultivation for its quality to be appropriate to the ambient water quality criteria [15]. The greywater footprint value can be calculated through equation (9) [13].

WF grey = (α x AR) / (Cmax−Cnat)

Y (9)

Remarks:

WF = Water footprint of plants (m³/kg) WF blue = Blue water footprint of plants (m³/kg) CWU blue= Blue crop water use (m³/m²)

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WF grey = Grey water footprint of plants (m³/kg) α = Times the leaching-run-off fraction

AR = Chemical application rate to the field (kg/ha) Cmax = Maximum acceptable concentration (kg/m³)

Cnat = Natural concentration for the pollutant considered (kg/m³) Y = Crop yield (kg/m³)

3. Results and Discussion

3.1. Conditions of Water Level Height and Actual Soil Moisture

Figure 4 shows the actual water level height for the three treatments. The actual water level height approached the planned water level height. The water level height affected the soil moisture for land conditions. Based on the chart of moisture changes in Figure 5, the highest soil moisture occurred for the IT land condition, with an average soil moisture of 0.57 ± 0.008 m³/m³. The IB land condition had an average soil moisture of 0.54 ± 0.008 m³/m³. The lowest soil moisture occurred for IK, with 0.53 ± 0.012 m³/m³. The soil moisture that resulted from the three treatments during the cultivation period fulfilled the optimal soil moisture for the cultivation of rice paddies. According to [16], the optimal soil moisture for cultivating rice paddies using the SRI method with the wet condition is from 0.62 m³/m³to 0.35 m³/m³ at the end of the season with the dry condition.

Figure 4. Water level height in various treatments

During the cultivation, the temperature and solar radiation conditions inside and outside the greenhouse are presented in the charts in Figure 6 and Figure 7. The average daily temperature measured inside the greenhouse was 27.08 ± 1.07 °C, while the average daily temperature measured outside the greenhouse was 26.63 ± 1.16 °C. Heat energy originates from solar radiation absorbed by and mostly trapped inside the greenhouse (the greenhouse effect), which causes an increase in temperature [17]. According to [18], the optimal average daily temperature for rice paddy cultivation ranges from 25-29 °C. Thus the average daily temperature during the cultivation period inside the greenhouse fulfilled the condition for rice paddy cultivation to be conducted. In addition to temperature, the factor of solar radiation inside the greenhouse also plays a role in the evapotranspiration process. The average daily amount of radiation outside the greenhouse was greater than the average daily amount of radiation inside the greenhouse, where the average daily amount of radiation measured inside the greenhouse was 4.34 ± 1.31 MJ/m²/day. In comparison, the average daily amount of radiation measured outside the greenhouse was 12.09 ± 2.72 MJ/m²/day.

-20 -15 -10 -5 0 5

0 20 40 60 80 100 120

Height of water level from soil surface (cm)

Days after planting

Irigasi Tergenang Irigasi Basah Irigasi Kering Flooded Irrigation Wet Irrigation Dry Irrigation

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Figure 5. Soil moisture in various treatments

Figure 6. The daily average temperature inside and outside the greenhouse

Figure 7. Daily average radiation inside and outside the greenhouse

0,4 0,5 0,6 0,7

0 20 40 60 80 100 120

Average soil moisture (m3/m3)

Days after planting

Irigasi Tergenang Irigasi Basah Irigasi Kering

0,00 5,00 10,00 15,00 20,00 25,00 30,00 35,00

0 20 40 60 80 100 120

Temperature (°C)

Days after Planting

di dalam greenhouse di luar greenhouse

0,00 2,00 4,00 6,00 8,00 10,00 12,00 14,00 16,00 18,00 20,00

0 20 40 60 80 100 120

Rs (MJ/m2/day)

Days after Planting

di dalam greenhouse di luar greenhouse Flooded Irrigation Wet Irrigation Dry Irrigation

inside greenhouse outside greenhouse

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3.2. Crop Evapotranspiration for Various Irrigation Systems

The potential evapotranspiration (ETo) affected crop evapotranspiration (ETc). The average ETo value during the planting period of 113 days was found to be 1.08 ± 0.35 mm/day. However, the ETo value fluctuated during planting (Figure 8). It was because of fluctuations in measured daily temperature and solar radiation inside the greenhouse as indicated by Figures 6 and 7.

Figure 8. Daily potential evapotranspiration

With different conditions for irrigation water, ETo for the three treatments also differed (Figure 9). Results of measuring indicated that the IT treatment had the highest average fluctuation, while the IK treatment had the lowest average fluctuation. The average daily ETc value for the IT treatment was 1.78 ± 1.22 mm/day, for the IB treatment was 1.46 ± 0.82 mm/day, and for the IK treatment was 1.13 ± 0.57 mm/day. The obtained average ETc value was directly proportional to the reduction of the water level in the reservoir. The water level reduction in the reservoir illustrated the amount of water expended by each land condition during the rice paddy cultivation activity. According to [19], the inundation treatment has the highest average ETc value. It was because the inundation of land is carried out continuously, and thus the resulting evapotranspiration was higher.

Figure 9. Rate of daily crop evapotranspiration for the three treatments of land conditions The total irrigation water usage for the three treatments is presented in Table 1. IT, IB, and IK's total irrigation water usage was 161.37 L, 132.30 L, and 102.00 L, respectively. Therefore, it indicated that IT used the most water compared to the other two treatments. Considering growth phases, the vegetative phase required the greatest water usage based on measurement results; the total amount of water expended during the vegetative phase for the three treatments was 140.10 L.

Meanwhile, the least expended water occurred for the maturing phase, with 68.66 L. In the vegetative phase, the plants still had small leaf and stem sizes, and thus the soil evaporation value mostly

0,00 0,20 0,40 0,60 0,80 1,00 1,20 1,40 1,60 1,80 2,00

0 20 40 60 80 100 120

ETo (mm/day)

HST (days)

Evapotranspirasi Potensial

0,00 1,00 2,00 3,00 4,00 5,00 6,00 7,00 8,00

0 20 40 60 80 100 120

ETc (mm/day)

Days after Planting

Irigasi TergenangFlooded Irrigation Irigasi BasahWet Irrigation Irigasi KeringDry Irrigation Potential

Evapotranspiration

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affected the crop evapotranspiration value [20]. Therefore, the maturing phase requires an amount of water that is even smaller and progressively decreases to a dry condition until the harvest period or the mature yellow stage is reached.

Table 1. Water usage based on growth phases of rice paddies Phase

Total Evapotranspiration (mm/phase)

Total Irrigation Water Needs (liters)

IT IB IK IT IB IK

Vegetative 76.46 58.93 40.88 60.77 46.84 32.49

Advanced Vegetative 43.98 33.16 28.85 34.96 26.35 22.93

Generative 49.99 44.70 34.49 39.73 35.53 27.41

Maturing 32.60 29.67 24.12 25.91 23.58 19.17

Total 203.03 166.45 128.34 161.37 132.30 102.00

3.3. Analyses of Water Footprint and Water Productivity

Water footprint was calculated based on the total water usage in fulfilling plant needs to produce products (harvest). From Table 2, it can be seen that the IB treatment resulted in the highest production compared to the others. When converted into ton/ha, with the assumption from a previous study [21], the IB treatment produced 2.60 ton/ha. However, this production result is still below average in Indonesia at 4.50 ton/ha [22]. This low production result was because the cultivation was performed inside a greenhouse, which caused solar radiation to decrease significantly (Figure 7), causing the ETo to decrease significantly.

Table 2. Yields of all three irrigation system treatments

Irrigation Type Land Area Weight of Grains Yield

(m²) (kg) (kg/m²)

Flooded Irrigation (IT) 0.79 0.076 0.095

Wet Irrigation (IB) 0.79 0.081 0.101

Dry Irrigation (IK) 0.79 0.020 0.025

Total 2.39 0.177 0.222

The total blue water footprint can be calculated from harvest data, as presented in Table 3. Based on Table 3, the largest percentage of the water usage resulted from IT treatment, with 40% of the entire water usage. The IK treatment contributed the smallest percentage of the entire water usage, with 25%. The total blue water footprint value obtained from the three treatments was obtained 3.48 m³/kg. The IK treatment resulted in the largest percentage of the total blue water footprint at 57%, while the smallest percentage resulted from the IB treatment, with 18%. The blue water footprint value that resulted from the IB treatment (0.64 m³/kg) is smaller in comparison to the blue water footprint value for the other two treatments, indicating that the IB treatment used the least amount of irrigation water but resulted in the greatest product compared to the IT and IK treatments.

Table 3. Results of Blue Water Footprint Calculation

Irrigation Type Land Area Yield* CWU blue WF blue

m² (kg/m²) (m³/m²) (m³/kg)

Flooded Irrigation (IT) 0.79 0.243 0.20 0.83

Wet Irrigation (IB) 0.79 0.259 0.16 0.64

Dry Irrigation (IK) 0.79 0.064 0.13 2.00

Total 0.566 0.49 3.48

Remarks: *Yield has been converted according to the SRI rice paddy planting distance of 25 cm x 25 cm.

Meanwhile, the results of calculating the greywater footprint from fertilizer usage are presented in Table 4. The grey water footprint value resulting from fertilizer usage for the three treatments was

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6.10 m³/kg. The largest greywater footprint value was obtained from the IK treatment, with a percentage of 66% of the total greywater footprint value. In contrast, the IB treatment resulted in the smallest greywater footprint value, with 16%. Therefore, the grey water footprint values obtained based on the IT, IB, and IK treatments were 1.06 m³/kg, 1.00 m³/kg, and 4.04 m³/kg.

Table 4. Results of Grey Water Footprint Calculation for Fertilizer Usage Mineral AR (mg) α Cmax

(mg/L) Cnat

(mg/L) WU grey

(m³/m²) GWF IT

(m³/kg) GWF IB

(m³/kg) GWF IK (m³/kg)

N 13800 0.1 20 0.1 0.09 0.36 0.34 1.36

P 4500 0.03 1 0.01 0.17 0.71 0.66 2.68

Total 0.26 1.06 1.00 4.04

The results of calculating the greywater footprint from EM4 are presented in Table 5. The grey water footprint resulting from EM4 usage for the three treatments was 0.14 m³/kg. As with the greywater footprint value from fertilizer usage, the largest greywater footprint from EM4 usage was obtained from the IK treatment (0.098 m³/kg), with a percentage of 67% of the entire total of the greywater footprint from EM4 usage. Meanwhile, the IB treatment resulted in the smallest grey water footprint value (0.024 m³/kg), with a percentage of 16%. Therefore, the total grey water footprint value from the usage of fertilizer and EM4 from the IT, IB, and IK treatments, respectively, were found to be 1.09 m³/kg, 1.02 m³/kg, and 4.14 m³/kg, and thus the total grey water footprint value for the entirety of production was found to be 6.25 m³/kg.

Table 5. Results of Grey Water Footprint Calculation for the Usage of EM4

Irrigation Type Yield* WU grey WU grey WF grey

(kg/m²) (L) (m³/m²) (m³/kg)

Flooded Irrigation (IT) 0.243 5 0.0063 0.025

Wet Irrigation (IB) 0.259 5 0.0063 0.024

Dry Irrigation (IK) 0.064 5 0.0063 0.098

Total 0.566 15 0.0189 0.148

Remarks: *Yield has been converted according to the SRI rice paddy planting distance of 25 cm x 25 cm The calculation of the total water footprint and water productivity of the rice paddy cultivation that had been conducted can be seen in Table 6. The total water footprint from rice paddy cultivation activities inside a greenhouse with usage of three kinds of treatments was found to be 9.73 m³/kg.

Wet irrigation (IB) had the smallest water footprint value at 1.66 m³/kg, while dry irrigation (IK) had the largest at 6.14 m³/kg. The water footprint is the total amount of water that was used to yield certain products, for which in rice paddy cultivation, the resulting product is in the form of grains after the harvest period. A larger obtained value for water footprint also means a larger amount of water that has been used to yield a certain product. Thus wet irrigation (IB) used the least amount of water compared to flooded irrigation (IT) and dry irrigation (IK) in yielding products with the same mass. When converted, the water footprint value obtained for IB is equal to 1,660 m³/ton. Total water productivity in the production of grains from the entirety of the treatments was found to be 1.28 kg/m³. Wet irrigation (IB) had the largest value of water productivity compared to the other treatments, with 0.60 kg/m³; therefore, water was more optimally used in rice paddy cultivation inside a greenhouse using wet irrigation.

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Table 6. Results of Total Water Footprint and Water Productivity Calculation

Irrigation Type Yield* WF blue WF grey Total WP Total WF (kg/m²) (m³/kg) (m³/kg) (kg/m³) (m³/kg)

Flooded Irrigation (IT) 0.243 0.83 1.09 0.52 1.92

Wet Irrigation (IB) 0.259 0.64 1.02 0.60 1.66

Dry Irrigation (IK) 0.064 2.00 4.14 0.16 6.14

Total 0.566 3.48 6.25 1.28 9.73

Remarks: *Yield has been converted according to the SRI rice paddy planting distance of 25 cm x 25 cm.

4. Conclusion

Total irrigation water needs for flooded irrigation (IT), wet irrigation (IB), and dry irrigation (IK), respectively, are 161.37 L, 132.30 L, and 102.00 L. The water footprint values obtained from rice paddy cultivation inside a greenhouse using sub-surface irrigation are 1.92 m³/kg for treatment of IT, 1.66 m³/kg for IB, and 6.14 m³/kg for IK. With the lowest value, IB then becomes the most efficient irrigation system that yields products (paddies). Additionally, IB has the highest water productivity value compared to IT and IK. This situation further supports the results of the water footprint value, in that IB represents the best irrigation treatment for using irrigation water to yield the maximum amount of products.

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