Optimizing an On-Demand Passive Fertigation System for Microgravity

Dixon, Chihiro; Massa, Gioia D.; Jones, Scott B.

doi:10.2478/gsr-2025-0006

Figures & Tables

Figure 1.

Calcined clay with three particle size ranges: Profile (0.300–0.850 mm), Turface (1.19–2.38 mm) and Mix (0.300–2.38 mm).

(A) Top-down view and (B) schematic illustration of the passive fertigation system. Key components include the growth medium, porous cup, check valve and Mariotte bottle reservoir.

Illustration of hydraulic potential (H) dynamics in the fertigation system. Enlarged diagrams of the check valve show the opening/closing mechanism during drying and wetting of the porous medium, with inlet (Hi) and outlet (Ho) hydraulic potentials, as well as threshold hydraulic potential differences (ΔHvo and ΔHvc).

(A–C) Hysteretic water retention curves for different media, modeled using VG parameters from Table 1. (D–F) Temporal variation of hourly average h measurements. Red star symbols indicate manual maintenance events; black solid lines show hourly averages of h; blue dashed lines mark the computed ht corresponding to 60% effective saturation (0.6Se) (from A–C, Table 1).

Figure 5.

Diurnal h measurements in three Profile containers and corresponding H values for the irrigation system during (A) 0–10 days and (B) 18–28 days of the plant cultivation trial.

Passive fertigation system with potential diagrams at different positions (a–c: growth medium at different heights, d: check valve outlet, e: check valve inlet, f: water reservoir) under (A) Earth and (B) microgravity conditions.

Threshold ΔH value for opening (ΔHvo) and closing (ΔHvc) of the check values_

	ΔH_vo	ΔH_vc
	cm	cm
Profile	9.8 ± 0	7.0 ± 0.87
Turface	8.7 ± 0.058	5.8 ± 0.75
Mix	8.7 ± 0.68	5.8 ± 0.64

Physical properties, including particle size distribution, particle density (ρs), bulk density (ρb), the computed porosity (φ = 1 – ρb/ρs), and hysteretic water retention parameters for the VG (1980) model and the computed target volumetric water content (θt) and matric potential (ht) in Profile, Turface, and Mix

			Profile	Turface	Mix
Physical Properties
Particle size distribution		mm	0.25–1	1–2	0.25–2
Particle density^†	ρ_s	g cm⁻³	2.52	2.52	2.52
Bulk density	ρ_b	g cm⁻³	0.63	0.64	0.69
Porosity (φ = 1 – ρb/ρs)	φ		0.75	0.75	0.73
Hydraulic properties
Drying process
VG model parameters^‡	θ_r	cm³ cm⁻³	0.34	0.34	0.32
	θ_s	cm³ cm⁻³	0.72	0.73	0.72
	α	cm⁻¹	0.099	0.19	0.11
	n		7.7	5.6	3.9
Computed parameters	θ_t	cm³ cm⁻³	0.57	0.57	0.56
	h_t	cm	−9.8	−5.1	−9.1
Wetting process
VG model parameters^‡	θ_r	cm³ cm⁻³	0.34	0.34	0.32
	θ_s	cm³ cm⁻³	0.69	0.68	0.64
	α		cm⁻¹	0.19	0.32
	n		4.4	4.1	2.9
Computed parameters	θ_t	cm³ cm⁻³	0.55	0.54	0.51
	h_t	cm	−5.2	−3.1	−6.2

Computed hydraulic potential components in the fertigation system under Earth's gravity at quasi-hydrostatic condition in profile_

	Gravitational Potential	Matric Potential	Hydraulic Potential	ΔH across the Check Valve
Components	z	h	H (=z + h)	ΔH =H_i–H_o
	cm	cm	cm
Profile	z_t = 5	h_t = −9.8	−4.8
Check valve outlet	10	−14.8	H_o = −4.8	H_i–H_o = 8.6
Check valve inlet	10	h_i = −6.2	H_i = 3.8
Mariotte bottle	z_m = 3.8	Atmosphere = 0	3.8

Average and standard error values of the fresh- and dry-leaf mass per container (surface area 86_6 cm2) filled with Profile, Turface, and Mix_

	Fresh Mass		Dry Mass
	1st trial	2nd trial	1st trial	2nd trial
	g	g	g	g
Profile	49.5 ± 16.1	32.0 ± 7.79	2.78 ± 0.80	2.72 ± 0.50
Turface	45.2 ± 20.0	38.0 ± 19.2	2.49 ± 1.06	2.07 ± 0.20
Mix	57.5 ± 7.15	46.6 ± 9.32	2.96 ± 0.37	2.86 ± 0.58

Computed air-inlet tube position (zm) in the Mariotte bottle using Eq_ (3), the ht, and the expected h values in the center of each porous medium by substituting ΔHvo and ΔHvc into Eq_ (3) in Profile, Turface, and Mix_

	Computed z_m	h_t	Expected threshold porous media's h
	Computed z_m	h_t	Valve opening	Valve closing
		cm	cm	cm
Profile	3.8	−9.8	−11	−8.2
Turface	7.3	−5.1	−6.4	−3.5
Mix	3.5	−9.1	−10.2	−7.3

Optimizing an On-Demand Passive Fertigation System for Microgravity

Figures & Tables

Figure 1.

Figure 2.

Figure 3.

Figure 4.

Figure 5.

Figure 6.

Threshold ΔH value for opening (ΔHvo) and closing (ΔHvc) of the check values_

Computed hydraulic potential components in the fertigation system under Earth's gravity at quasi-hydrostatic condition in profile_

Average and standard error values of the fresh- and dry-leaf mass per container (surface area 86_6 cm2) filled with Profile, Turface, and Mix_

Computed air-inlet tube position (zm) in the Mariotte bottle using Eq_ (3), the ht, and the expected h values in the center of each porous medium by substituting ΔHvo and ΔHvc into Eq_ (3) in Profile, Turface, and Mix_

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