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).
Table 1.
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† | ρs | g cm−3 | 2.52 | 2.52 | 2.52 |
| Bulk density | ρb | 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‡ | θr | cm3 cm−3 | 0.34 | 0.34 | 0.32 |
| θs | 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 | θt | cm3 cm−3 | 0.57 | 0.57 | 0.56 |
| ht | cm | −9.8 | −5.1 | −9.1 | |
| Wetting process | |||||
| VG model parameters‡ | θr | cm3 cm−3 | 0.34 | 0.34 | 0.32 |
| θs | 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 | θt | cm3 cm−3 | 0.55 | 0.54 | 0.51 |
| ht | cm | −5.2 | −3.1 | −6.2 | |
Figure 2.
(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.
Figure 3.
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).
Table 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 =Hi–Ho |
| cm | cm | cm | ||
| Profile | zt = 5 | ht = −9.8 | −4.8 | |
| Check valve outlet | 10 | −14.8 | Ho = −4.8 | Hi–Ho = 8.6 |
| Check valve inlet | 10 | hi = −6.2 | Hi = 3.8 | |
| Mariotte bottle | zm = 3.8 | Atmosphere = 0 | 3.8 |
Figure 4.
(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).
Table 3.
Threshold ΔH value for opening (ΔHvo) and closing (ΔHvc) of the check values.
| ΔHvo | ΔHvc | |
|---|---|---|
| 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 |
Table 4.
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 zm | ht | Expected threshold porous media's h | ||
|---|---|---|---|---|
| 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 |
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.
Table 5.
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 |
Figure 6.
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.