National Land Capability Framework · Kingdom of Saudi Arabia · All 13 Regions

KSA National
Land Capability Framework

A systematic national evaluation of the inherent physical limitations of agricultural land across all 13 regions of the Kingdom of Saudi Arabia. Based on internationally recognised UN/FAO parameters for land evaluation. Land capability describes what the land can physically support — independent of any specific crop or use. Classification follows the C1–CN hierarchy with limiting factor subclasses. Water supply is assessed separately as a national resource allocation decision.

FrameworkFAO Bulletin 32 & 2007 Rev.
Groups5 Land Quality Groups
Land Qualities17 Assessed
OutputC1 / C2 / C3 / C4 / CN
LogicMaximum Limitation
© TEC SOLUTION 2026
FAO Class C1 — Highly Capable C2 — Moderately Capable C3 — Marginally Capable C4 — Currently Not Capable CN — Not Capable
Subclasses: s = soil   w = water/wetness   e = erosion   c = climate   t = topography   n = nutrient   z = salinity   f = flood   d = sand drift/encroachment

Soil Physical Limitations

Inherent physical properties of the soil that determine its capacity to support plant growth and withstand agricultural use. Largely permanent — cannot be corrected economically at field scale.
s — soil limitations
Group A

Soil Chemical Limitations

Chemical properties that control nutrient availability, ion toxicity, and soil-water-plant relationships. Semi-permanent — some can be managed with amendment programmes over time.
z — salinity/sodicity n — nutrient limitations
Group B

Water & Drainage Conditions

Availability of water for plant use and the ability of the land to remove excess water. Conditions that govern the movement and retention of water within the land unit — drainage condition, flood hazard, and waterlogging risk. Water supply (aquifer availability, depletion trajectory, alternative sources) is assessed separately as a national resource allocation decision and reported alongside the capability class, not within it.
w — water/wetness f — flood hazard
Group C

Topography & Erosion Hazard

Terrain characteristics that determine workability, erosion risk, and mechanisation feasibility. Permanent limitations — slope cannot be changed at agricultural scale.
t — topographic e — erosion hazard d — sand drift/encroachment
Group D

Climate Limitations

Fixed climatic conditions that define what the land can support regardless of management. Assessed nationally across all 13 regions — from the hyper-arid Rub' al Khali to the rain-fed highlands of Asir, Jazan, and Al-Baha. Temperature regime, aridity, radiation, and length of growing period are immutable characteristics that vary significantly across the Kingdom's diverse landscapes.
c — climate limitations
Group E

Select a land quality card to view its FAO class thresholds, limiting factor logic, and references.

FAO Land Capability Framework — adapted from internationally recognised UN/FAO parameters for land evaluation (Bulletin No. 32 [1] and the 2007 Revised Framework [6]) for national application across all 13 regions of the Kingdom of Saudi Arabia. Thresholds from the Al Lith pilot are retained as illustrative worked examples; national calibration across the full KSA range of soil types, climates, and geomorphological units is a deliberate next step in the national methodology.

The Maximum Limitation — the capability class of any land parcel is determined by its single most severe limitation. A site with excellent soils and climate but ECe of 9 dS/m is classified CN regardless of all positive attributes. This is the maximum limitation method. FAO Bulletin 32 defines the classes but does not prescribe how seventeen ratings are combined into one; parametric alternatives — the Storie index, the square-root method — are equally established. This study applies maximum limitation deliberately, because a severe physical constraint is not compensated by favourable conditions elsewhere, and because the resulting class names the quality that produced it.

Subclass notation — letters appended to the class indicate the nature of the limitation: C3sz means marginally capable due to both soil physical (s) and salinity/sodicity (z) limitations. Multiple subclass letters indicate multiple concurrent limitations.

How a class is actually decided. The full method — every quality rated against its own thresholds, the five alternative approaches compared on one worked hectare, and why maximum limitation was chosen — is set out in a dedicated section.
Core FAO Principle: "The capability of the land is determined by its most severe limitation, not by its average condition. All limitations must be identified; the final class reflects the worst single constraint regardless of how many positive qualities the land possesses."
FAO Soils Bulletin No. 32 — A Framework for Land Evaluation (FAO, 1976) fao.org
Full Reference Library — All sources cited in this framework
Crop Production
17 / 17
Livestock & Grazing
4 / 17
Aquaculture
2 / 17
Agro-industry & Facilities
3 / 17
Land Management
11 / 17

Capability by Sector answers the question the capability class alone cannot: this land is C2 — or CN — so what can go on it? The matrix maps each of the nineteen land qualities against five main sectors, stating whether that sector responds to that quality and in which direction. No thresholds, no class boundaries, no per-sector scoring — there remains one capability class per hectare. This matrix says which sectors that class routes to.

How to read it by column: a dense column means that sector is sensitive to physical land conditions and will benefit strongly from a national classification. An empty column means the sector uses its own assessment parameters, not the nineteen land qualities.

Mark
● Responds — this quality can limit this sector
○ Does not respond — assessed and deliberately excluded
◐ Inverted — severe rating selects rather than rules out
▲ Conditional — depends on sub-sector or production system
○ is not a blank — it means assessed and excluded, not unevaluated
ID Land Quality Sub Crop
Production▼		 Livestock
& Grazing▼		 Aqua­culture▼ Agro­industry
& Facilities▼		 Land
Management▼
A · Soil Physical
LQ-SP-01Available Water Capacitys●○○○○
LQ-SP-02Soil Workabilitys●○○○▲
LQ-SP-03Rooting Conditionss●○▲○●
LQ-SP-04Surface Sealing & Crustings●○○○●
B · Soil Chemical
LQ-SC-01Salinity Hazardz●○○○○
LQ-SC-02Sodicity Hazardz●○○○○
LQ-SC-03Nutrient Availabilityn●○○○○
LQ-SC-04Toxicity Riskn●○○○○
C · Water & Drainage
LQ-W-01Drainage Conditionw●○○○○
LQ-W-02Flood Hazardf○†○○●●
LQ-W-04Waterlogging Riskw○○○○●
D · Topography & Erosion
LQ-T-01Terrain Workabilityt●○▲●●
LQ-T-02Water Erosion Hazarde●●○○◐
LQ-T-03Wind Erosion Hazarde●●○○◐
LQ-T-04Sand Encroachment Hazardd●○○●◐
E · Climate
LQ-C-02Thermal Suitabilityc●●○○●
LQ-C-03Radiation & Solar Energyc●○○○○
Qualities responded to — of 17 16 of 173 of 172 of 173 of 1710 of 17
CN Routing — What the Subclass Letter Unlocks

A capability class alone discards land. CN says not capable and stops. CN with its subclass letter says why — and the matrix says who does not care. This routing table prevents a national run from marking the entire Red Sea coastal plain as not capable land while Saudi Arabia actively develops aquaculture along it.

Capability ResultWhy Land Cannot Support General CroppingSectors That Remain Open
C1 – C4 Varying degrees of limitation — all manageable for at least some crop types
Crop production Livestock & grazing Aquaculture Agro-industry Land management
CNz Salinity Soil ECe or progressive salinisation beyond reclamation threshold. Conventional crops cannot establish or sustain yield.
Aquaculture Saline-tolerant restoration Agro-industry (off-site)
CNt Terrain Slope exceeds mechanisation threshold (>15%). No commercial-scale field crop production viable.
Rangeland & grazing Forestry & conservation Marine aquaculture
CNe Erosion Catastrophic water or wind erosion rate. Topsoil depletion irreversible at agricultural timescales.
Restoration — selected by this constraint Rangeland with management
CNd Sand encroachment Active dune advance >15 m/year. Infrastructure burial within project lifetime.
Dune stabilisation & conservation Offshore aquaculture
CNs Soil physical Rooting depth, texture or structure permanently precludes soil-based crop production.
Protected agriculture (substrate) Agro-industry & facilities Aquaculture
○† Flood Hazard — Crop Production: Marked ○ per the current governing set: irrigated cropping in KSA's arid interior basins is genuinely flood-remote and flood hazard was not in any crop sub-sector's governing definition. Flagged for review — the governing set may have been written before wadi-margin spate irrigation zones were explicitly included. If spate irrigation is confirmed as a national sub-sector, this cell becomes ●.
◐ Inverted cells — Land Management only: Water Erosion, Wind Erosion, and Sand Encroachment are inverted for the Land Management sector. A severe erosion rating does not disqualify land from restoration — it is precisely what selects land for restoration. Forestry responds to these qualities as limitations; restoration and conservation respond to them as qualifications. No other sector column contains inverted cells.
Aquaculture column: All nineteen land qualities return ○ except two conditional cells (Rooting Conditions and Terrain Workability — relevant for land-based pond construction only). This is not an omission: aquaculture is assessed on its own sector-specific parameters (water-body regime, effluent assimilation capacity, tidal range, current velocity, accessibility) which are not land qualities and sit outside the national land capability framework.
Livestock & Grazing — Group A and B cells: All soil physical and soil chemical qualities return ○ for livestock. This is correct and deliberate: grazing value is assessed directly from satellite vegetation productivity records rather than predicted from soil chemistry or texture. The row of ○ marks across Groups A and B is a finding, not a gap — it demonstrates that the capability framework does not score all land on a single ladder.

Click a sector column heading to view its description, assessed qualities, and key references.

Note on element numbering. LQ-W-03 is an inherited numbering gap. LQ-C-01 moisture deficit and LQ-C-04 length of growing period were retired from capability at version 10.1. Their measurements are now SQ-E-01 and SQ-E-04 in the Suitability module, where they are crop-keyed.

Both are relational. A deficit is a deficit of something and a growing period is long enough for something — neither carries meaning until a crop is named, which is what suitability does and capability does not. Thermal regime (LQ-C-02) and radiation (LQ-C-03) remain, because degree-days accumulated and megajoules received are absolute properties of a location, true whatever is planted.

Testing confirmed the need. With both in capability, every hectare in the Kingdom returned CN — the terminal class — with one of the two always governing. Rainfed growing period is zero across almost the whole country, and aridity runs 0.02–0.09 against a C1 boundary of 0.50. Under maximum limitation the national capability map was uniformly terminal and the other fifteen qualities carried no influence anywhere.
Classification Method · How a Capability Class is Decided
Every land quality is rated. The worst one becomes the class.

FAO Bulletin 32 defines the capability classes. It does not prescribe the arithmetic. The framework establishes what C1 to CN mean, what a land quality is, and how land is matched against a land use requirement — but the method for combining seventeen individual ratings into a single class is left to the evaluator, and the literature offers two distinct families.

Limitation methods take the most severe constraint as the class. Parametric methods — the Storie index, the square-root method, the Sys land index — convert each rating to a percentage and combine them arithmetically. Both are established, and both appear in Sys et al. (1993). This study applies the maximum limitation method, for the reasons set out below.

This section concerns capability only — the 17 land qualities and the C1–CN classes. The Suitability module applies the same limitation rule to its own 26 diagnostic factors and the S1–N2 classes; the reasoning is identical and is not repeated there.

Start with one hectare. Its 17 land qualities sit in five groups. Group A is expanded below — click any row to see how its class and rating were obtained.

Capability assessment — one hectare17 land qualities · 5 groups
Click any group to expand its qualities — then click a quality to see how its class and rating were derived.
ASoil Physicalsubclass s4 qualitieslimited by rootingC4▾
LQ-SP-01Available water capacity147 mm/m90%C1
LQ-SP-01 · Available water capacity — how the class and rating are obtained
i
How much water the soil can hold for the plant to use between waterings.
A soil that holds more water needs watering less often and carries a crop through a missed irrigation. Sandy soils hold little; loams hold a lot.
1 · Class table for this quality — in mm/m  (higher is better)
C1
> 120
C2
90–120
C3
60–90
C4
30–60
CN
< 30
147 mm/m falls in band C1. This is the assessment result — the study stops here.
2 · The same bands on a common 0–100 scale
85–100%
60–85%
40–60%
25–40%
0–25%
band C1 = 120–200 mm/m  maps to  85–100%
position in band = ( 147 − 120 ) ÷ ( 200 − 120 ) = 0.338
rating = 85 + ( 0.338 × 15 ) = 90%
Why a percentage exists at all. Depth is in centimetres, salinity in dS/m, slope in percent — they cannot be combined until they share a scale. This conversion is required only by the scoring methods compared below. The method this study applies never uses it.
LQ-SP-02Soil workability88 index91%C1
LQ-SP-02 · Soil workability — how the class and rating are obtained
i
How easy the soil is to plough, level and prepare a seedbed in.
Hard, cloddy or sticky soils cost more fuel and machinery time, and a poor seedbed means uneven germination.
1 · Class table for this quality — in index  (higher is better)
C1
> 80
C2
60–80
C3
40–60
C4
20–40
CN
< 20
88 index falls in band C1. This is the assessment result — the study stops here.
2 · The same bands on a common 0–100 scale
85–100%
60–85%
40–60%
25–40%
0–25%
band C1 = 80–100 index  maps to  85–100%
position in band = ( 88 − 80 ) ÷ ( 100 − 80 ) = 0.400
rating = 85 + ( 0.400 × 15 ) = 91%
Why a percentage exists at all. Depth is in centimetres, salinity in dS/m, slope in percent — they cannot be combined until they share a scale. This conversion is required only by the scoring methods compared below. The method this study applies never uses it.
LQ-SP-03Rooting conditions42 cm35%C4
LQ-SP-03 · Rooting conditions — how the class and rating are obtained
i
How deep roots can actually grow before hitting something they cannot pass.
Rock, hardpan or calcrete stops roots. A shallow root zone means the plant reaches less water and less nutrient, whatever else is favourable.
1 · Class table for this quality — in cm  (higher is better)
C1
> 100
C2
75–100
C3
50–75
C4
25–50
CN
< 25
42 cm falls in band C4. This is the assessment result — the study stops here.
2 · The same bands on a common 0–100 scale
85–100%
60–85%
40–60%
25–40%
0–25%
band C4 = 25–50 cm  maps to  25–40%
position in band = ( 42 − 25 ) ÷ ( 50 − 25 ) = 0.680
rating = 25 + ( 0.680 × 15 ) = 35%
Why a percentage exists at all. Depth is in centimetres, salinity in dS/m, slope in percent — they cannot be combined until they share a scale. This conversion is required only by the scoring methods compared below. The method this study applies never uses it.
LQ-SP-04Surface sealing & crusting92 index94%C1
LQ-SP-04 · Surface sealing & crusting — how the class and rating are obtained
i
Whether the soil surface forms a hard crust after watering.
A crust blocks water from soaking in and can physically trap emerging seedlings underneath it.
1 · Class table for this quality — in index  (higher is better)
C1
> 80
C2
60–80
C3
40–60
C4
20–40
CN
< 20
92 index falls in band C1. This is the assessment result — the study stops here.
2 · The same bands on a common 0–100 scale
85–100%
60–85%
40–60%
25–40%
0–25%
band C1 = 80–100 index  maps to  85–100%
position in band = ( 92 − 80 ) ÷ ( 100 − 80 ) = 0.600
rating = 85 + ( 0.600 × 15 ) = 94%
Why a percentage exists at all. Depth is in centimetres, salinity in dS/m, slope in percent — they cannot be combined until they share a scale. This conversion is required only by the scoring methods compared below. The method this study applies never uses it.
Group A resolves to C4. Three of its four qualities are excellent. Rooting conditions at 42 cm is not. The group takes the worst of its members.
BSoil Chemicalsubclass z / n4 qualitiesno limitationC1▾
LQ-SC-01Salinity (ECe)1.6 dS/m88%C1
LQ-SC-01 · Salinity (ECe) — how the class and rating are obtained
i
How salty the soil is.
Salt makes it harder for roots to draw water, even when water is present. Above a crop’s tolerance, yield falls and eventually the crop fails.
1 · Class table for this quality — in dS/m  (lower is better)
C1
< 2
C2
2–4
C3
4–8
C4
8–16
CN
> 16
1.6 dS/m falls in band C1. This is the assessment result — the study stops here.
2 · The same bands on a common 0–100 scale
85–100%
60–85%
40–60%
25–40%
0–25%
band C1 = 0–2 dS/m  maps to  85–100%
position in band = ( 2 − 1.6 ) ÷ ( 2 − 0 ) = 0.200
rating = 85 + ( 0.200 × 15 ) = 88%
Why a percentage exists at all. Depth is in centimetres, salinity in dS/m, slope in percent — they cannot be combined until they share a scale. This conversion is required only by the scoring methods compared below. The method this study applies never uses it.
LQ-SC-02Sodicity (ESP)4.7 %93%C1
LQ-SC-02 · Sodicity (ESP) — how the class and rating are obtained
i
How much sodium is held on the soil particles.
Sodium breaks down soil structure. The soil seals up, water stops soaking in, and the surface turns to a hard pan.
1 · Class table for this quality — in %  (lower is better)
C1
< 10
C2
10–15
C3
15–25
C4
25–40
CN
> 40
4.7 % falls in band C1. This is the assessment result — the study stops here.
2 · The same bands on a common 0–100 scale
85–100%
60–85%
40–60%
25–40%
0–25%
band C1 = 0–10 %  maps to  85–100%
position in band = ( 10 − 4.7 ) ÷ ( 10 − 0 ) = 0.530
rating = 85 + ( 0.530 × 15 ) = 93%
Why a percentage exists at all. Depth is in centimetres, salinity in dS/m, slope in percent — they cannot be combined until they share a scale. This conversion is required only by the scoring methods compared below. The method this study applies never uses it.
LQ-SC-03Nutrient availability72 index86%C1
LQ-SC-03 · Nutrient availability — how the class and rating are obtained
i
Whether the soil can supply and hold the nutrients a crop needs.
Poor soils can be fertilised, but low-fertility soils also lose fertiliser quickly, which raises the running cost every season.
1 · Class table for this quality — in index  (higher is better)
C1
> 70
C2
50–70
C3
30–50
C4
15–30
CN
< 15
72 index falls in band C1. This is the assessment result — the study stops here.
2 · The same bands on a common 0–100 scale
85–100%
60–85%
40–60%
25–40%
0–25%
band C1 = 70–100 index  maps to  85–100%
position in band = ( 72 − 70 ) ÷ ( 100 − 70 ) = 0.067
rating = 85 + ( 0.067 × 15 ) = 86%
Why a percentage exists at all. Depth is in centimetres, salinity in dS/m, slope in percent — they cannot be combined until they share a scale. This conversion is required only by the scoring methods compared below. The method this study applies never uses it.
LQ-SC-04Toxicity (boron)0.2 mg/L97%C1
LQ-SC-04 · Toxicity (boron) — how the class and rating are obtained
i
Whether boron in the soil or water is high enough to poison the crop.
Boron is needed in trace amounts and toxic slightly above them. The safe range is narrow, and it differs sharply between crops.
1 · Class table for this quality — in mg/L  (lower is better)
C1
< 1.0
C2
1.0–2.0
C3
2.0–4.0
C4
4.0–6.0
CN
> 6.0
0.2 mg/L falls in band C1. This is the assessment result — the study stops here.
2 · The same bands on a common 0–100 scale
85–100%
60–85%
40–60%
25–40%
0–25%
band C1 = 0–1 mg/L  maps to  85–100%
position in band = ( 1 − 0.2 ) ÷ ( 1 − 0 ) = 0.800
rating = 85 + ( 0.800 × 15 ) = 97%
Why a percentage exists at all. Depth is in centimetres, salinity in dS/m, slope in percent — they cannot be combined until they share a scale. This conversion is required only by the scoring methods compared below. The method this study applies never uses it.
Group B resolves to C1. Every quality in this group rates C1. The group carries no limitation and does not constrain the hectare.
CWater & Drainagesubclass w / f3 qualitiesno limitationC1▾
LQ-W-01Drainage condition82 index89%C1
LQ-W-01 · Drainage condition — how the class and rating are obtained
i
How quickly excess water drains away from the root zone.
Roots need air as well as water. Slow-draining soil suffocates them and invites root disease.
1 · Class table for this quality — in index  (higher is better)
C1
> 75
C2
55–75
C3
35–55
C4
18–35
CN
< 18
82 index falls in band C1. This is the assessment result — the study stops here.
2 · The same bands on a common 0–100 scale
85–100%
60–85%
40–60%
25–40%
0–25%
band C1 = 75–100 index  maps to  85–100%
position in band = ( 82 − 75 ) ÷ ( 100 − 75 ) = 0.280
rating = 85 + ( 0.280 × 15 ) = 89%
Why a percentage exists at all. Depth is in centimetres, salinity in dS/m, slope in percent — they cannot be combined until they share a scale. This conversion is required only by the scoring methods compared below. The method this study applies never uses it.
LQ-W-02Flood hazard0.3 events/10 yr96%C1
LQ-W-02 · Flood hazard — how the class and rating are obtained
i
How often the site is likely to flood.
Flooding can drown a crop, wash away topsoil, and damage irrigation infrastructure. In spate systems it is a resource instead.
1 · Class table for this quality — in events/10 yr  (lower is better)
C1
< 1
C2
1–2
C3
2–4
C4
4–7
CN
> 7
0.3 events/10 yr falls in band C1. This is the assessment result — the study stops here.
2 · The same bands on a common 0–100 scale
85–100%
60–85%
40–60%
25–40%
0–25%
band C1 = 0–1 events/10 yr  maps to  85–100%
position in band = ( 1 − 0.3 ) ÷ ( 1 − 0 ) = 0.700
rating = 85 + ( 0.700 × 15 ) = 96%
Why a percentage exists at all. Depth is in centimetres, salinity in dS/m, slope in percent — they cannot be combined until they share a scale. This conversion is required only by the scoring methods compared below. The method this study applies never uses it.
LQ-W-04Waterlogging risk5 days/yr92%C1
LQ-W-04 · Waterlogging risk — how the class and rating are obtained
i
How long water sits in the root zone after rain or irrigation.
Short waterlogging is survivable. Sustained saturation starves roots of oxygen and kills the plant from below.
1 · Class table for this quality — in days/yr  (lower is better)
C1
< 10
C2
10–25
C3
25–50
C4
50–90
CN
> 90
5 days/yr falls in band C1. This is the assessment result — the study stops here.
2 · The same bands on a common 0–100 scale
85–100%
60–85%
40–60%
25–40%
0–25%
band C1 = 0–10 days/yr  maps to  85–100%
position in band = ( 10 − 5 ) ÷ ( 10 − 0 ) = 0.500
rating = 85 + ( 0.500 × 15 ) = 92%
Why a percentage exists at all. Depth is in centimetres, salinity in dS/m, slope in percent — they cannot be combined until they share a scale. This conversion is required only by the scoring methods compared below. The method this study applies never uses it.
Group C resolves to C1. Every quality in this group rates C1. The group carries no limitation and does not constrain the hectare.
DTopography & Erosionsubclass t / e / d4 qualitiesno limitationC1▾
LQ-T-01Terrain / slope0.5 %96%C1
LQ-T-01 · Terrain / slope — how the class and rating are obtained
i
How steep and even the ground is.
Steep or uneven ground blocks machinery, prevents centre-pivot irrigation, and makes water run off instead of soaking in.
1 · Class table for this quality — in %  (lower is better)
C1
< 2
C2
2–5
C3
5–10
C4
10–16
CN
> 16
0.5 % falls in band C1. This is the assessment result — the study stops here.
2 · The same bands on a common 0–100 scale
85–100%
60–85%
40–60%
25–40%
0–25%
band C1 = 0–2 %  maps to  85–100%
position in band = ( 2 − 0.5 ) ÷ ( 2 − 0 ) = 0.750
rating = 85 + ( 0.750 × 15 ) = 96%
Why a percentage exists at all. Depth is in centimetres, salinity in dS/m, slope in percent — they cannot be combined until they share a scale. This conversion is required only by the scoring methods compared below. The method this study applies never uses it.
LQ-T-02Water erosion hazard2.3 t/ha/yr93%C1
LQ-T-02 · Water erosion hazard — how the class and rating are obtained
i
How fast rain and runoff strip topsoil from the site.
Topsoil is where the fertility and the water-holding capacity live. Once it is gone it takes centuries to replace.
1 · Class table for this quality — in t/ha/yr  (lower is better)
C1
< 5
C2
5–10
C3
10–25
C4
25–50
CN
> 50
2.3 t/ha/yr falls in band C1. This is the assessment result — the study stops here.
2 · The same bands on a common 0–100 scale
85–100%
60–85%
40–60%
25–40%
0–25%
band C1 = 0–5 t/ha/yr  maps to  85–100%
position in band = ( 5 − 2.3 ) ÷ ( 5 − 0 ) = 0.540
rating = 85 + ( 0.540 × 15 ) = 93%
Why a percentage exists at all. Depth is in centimetres, salinity in dS/m, slope in percent — they cannot be combined until they share a scale. This conversion is required only by the scoring methods compared below. The method this study applies never uses it.
LQ-T-03Wind erosion hazard16 index88%C1
LQ-T-03 · Wind erosion hazard — how the class and rating are obtained
i
How fast wind strips soil from the site.
Wind removes the fine fraction, sandblasts young seedlings, and buries irrigation lines. Windbreaks reduce it but cost money.
1 · Class table for this quality — in index  (lower is better)
C1
< 20
C2
20–40
C3
40–60
C4
60–80
CN
> 80
16 index falls in band C1. This is the assessment result — the study stops here.
2 · The same bands on a common 0–100 scale
85–100%
60–85%
40–60%
25–40%
0–25%
band C1 = 0–20 index  maps to  85–100%
position in band = ( 20 − 16 ) ÷ ( 20 − 0 ) = 0.200
rating = 85 + ( 0.200 × 15 ) = 88%
Why a percentage exists at all. Depth is in centimetres, salinity in dS/m, slope in percent — they cannot be combined until they share a scale. This conversion is required only by the scoring methods compared below. The method this study applies never uses it.
LQ-T-04Sand encroachment0.7 m/yr90%C1
LQ-T-04 · Sand encroachment — how the class and rating are obtained
i
How fast mobile sand is advancing onto the site.
Moving dunes bury crops, roads and canals. Holding them back is a permanent, recurring cost on the operation.
1 · Class table for this quality — in m/yr  (lower is better)
C1
< 1
C2
1–3
C3
3–6
C4
6–12
CN
> 12
0.7 m/yr falls in band C1. This is the assessment result — the study stops here.
2 · The same bands on a common 0–100 scale
85–100%
60–85%
40–60%
25–40%
0–25%
band C1 = 0–1 m/yr  maps to  85–100%
position in band = ( 1 − 0.7 ) ÷ ( 1 − 0 ) = 0.300
rating = 85 + ( 0.300 × 15 ) = 90%
Why a percentage exists at all. Depth is in centimetres, salinity in dS/m, slope in percent — they cannot be combined until they share a scale. This conversion is required only by the scoring methods compared below. The method this study applies never uses it.
Group D resolves to C1. Every quality in this group rates C1. The group carries no limitation and does not constrain the hectare.
EClimatesubclass c2 qualitiesno limitationC1▾
LQ-C-02Thermal regime3500 GDD91%C1
LQ-C-02 · Thermal regime — how the class and rating are obtained
i
Whether the site accumulates enough warmth for the crop to complete its cycle.
Too little heat and fruit never ripens. Too much and flowers drop. Every crop has its own window.
1 · Class table for this quality — in GDD  (higher is better)
C1
> 2500
C2
1800–2500
C3
1200–1800
C4
800–1200
CN
< 800
3500 GDD falls in band C1. This is the assessment result — the study stops here.
2 · The same bands on a common 0–100 scale
85–100%
60–85%
40–60%
25–40%
0–25%
band C1 = 2500–5000 GDD  maps to  85–100%
position in band = ( 3500 − 2500 ) ÷ ( 5000 − 2500 ) = 0.400
rating = 85 + ( 0.400 × 15 ) = 91%
Why a percentage exists at all. Depth is in centimetres, salinity in dS/m, slope in percent — they cannot be combined until they share a scale. This conversion is required only by the scoring methods compared below. The method this study applies never uses it.
LQ-C-03Radiation28 MJ/m²/day98%C1
LQ-C-03 · Radiation — how the class and rating are obtained
i
How much sunlight energy reaches the crop each day.
Sunlight drives photosynthesis and therefore yield. Saudi Arabia is among the sunniest places on earth, so this rarely limits.
1 · Class table for this quality — in MJ/m²/day  (higher is better)
C1
> 18
C2
14–18
C3
10–14
C4
6–10
CN
< 6
28 MJ/m²/day falls in band C1. This is the assessment result — the study stops here.
2 · The same bands on a common 0–100 scale
85–100%
60–85%
40–60%
25–40%
0–25%
band C1 = 18–30 MJ/m²/day  maps to  85–100%
position in band = ( 28 − 18 ) ÷ ( 30 − 18 ) = 0.833
rating = 85 + ( 0.833 × 15 ) = 98%
Why a percentage exists at all. Depth is in centimetres, salinity in dS/m, slope in percent — they cannot be combined until they share a scale. This conversion is required only by the scoring methods compared below. The method this study applies never uses it.
Group E resolves to C1. Every quality in this group rates C1. The group carries no limitation and does not constrain the hectare.
Total assessed 17 qualities worst group governs C4s
?
This hectare is excellent at almost everything.
One quality is not. So what class does it get?

Sixteen of seventeen land qualities rate favourably. The soil holds water well, the chemistry is sound, drainage is adequate, the terrain is nearly flat, the climate suits cultivation, and there is no erosion or encroachment hazard. By almost every measure this is good agricultural ground.

One quality is not favourable. Effective rooting depth is 42 cm — a calcrete horizon sits just below. No crop assessed in this study can establish a working root system in 42 cm of soil. Not date palm, not wheat, not tomato, not forage. The constraint is not partial and it does not vary by sector: it closes off every agricultural activity the study evaluates.

So the question the classification method must answer is simple, and everything below turns on it:

Does sixteen favourable qualities out of nineteen make this good land — or does the one that fails decide it?

This is not a rhetorical question. Established land evaluation methods answer it differently, and the same hectare can emerge as C1 or C4 depending purely on which is applied. The five below are worked against these identical readings.

Five ways to answer it. Each is defined below with its formula and reference, worked against the identical 17 readings from the hectare above. Four are published alternatives; the fifth is the method this study applies.

01
Arithmetic mean
Simple averaging — not a published land-evaluation method
FAILS
Definition. Every quality rating is summed and divided by the number of qualities. All qualities count equally. This is the method most readers assume when they see seventeen ratings, which is why it is shown first.
Formula
LI = ( Σ Ri ) ÷ n
where Ri = rating of quality i as % of optimal  ·  n = 17
= ( 90 + 91 + 35 + 94 + 88 + … + 89 ) ÷ 17  =  1,506 ÷ 17
Reference
No primary reference — arithmetic averaging is not an established land-evaluation method. It is included here as the intuitive baseline that the limitation and parametric families both reject.—
FAO Bulletin 32 rejects simple averaging implicitly by defining classes through limitation rather than aggregate score.
Open source
Result88.6% C1 The single C4 quality is diluted by sixteen favourable ones. The hectare reports as highly capable when a crop cannot root in it.
02
Weighted mean
Weights as implemented in ALUES 0.2.1 (scale 1–3)
FAILS
Definition. Each rating is multiplied by an importance weight before averaging, so qualities judged more critical carry greater influence. The ALUES database loaded in this study carries exactly such a weight column. The test below gives rooting conditions the maximum weight of 3 — the most favourable possible case for the method.
Quality (first six of 17)RwR × w
Available water capacity903270
Soil workability912182
Rooting conditions353105
Surface sealing942188
Salinity (ECe)883264
Sodicity (ESP)932186
… 11 more  ·  Σ(R×w) = 3,217  ·  Σw = 37
Formula
LI = Σ( Ri × wi ) ÷ Σ wi
where wi = importance weight, 1 (minor) to 3 (critical)
= 3,217 ÷ 37
Reference
ALUES: Agricultural Land Use Evaluation System, v0.2.1 — Mariano, A.J. et al. CRAN R package. Implements weighted parametric scoring; the weight column is present in every crop requirement record loaded by this study.CR-03
See also the ALUES Reference Manual and the suit function vignette for the scoring implementation.
Open source
Result86.9% C1 Weighting does not rescue averaging. Even with the limiting quality at maximum weight the result moves only 1.5 points and the class is unchanged. The failure is in the averaging operation, not the weights.
03
Storie index
Parametric — multiplicative
AGREES
Definition. Ratings are expressed as decimal fractions of optimal and multiplied rather than averaged. Because multiplication compounds, any single low factor pulls the whole product down regardless of how favourable the others are. Storie applies it across four governing factor groups.
Formula
SI = A × B × C × X  × 100
each factor expressed 0–1 as a fraction of optimal
= 0.90 × 0.35 × 0.88 × 0.96 × 100
Reference
Storie Index Soil Rating — Storie, R.E. (1978). Special Publication 3203, Division of Agricultural Sciences, University of California. The original multiplicative parametric soil rating.ST-78
Method also summarised in O’Geen, A.T. et al. (2008), Revised Storie Index for Use with Digital Soils Information, UC ANR Publication 8335.
Open source
Result26.6% C4 Reaches the correct class — the 0.35 factor dominates the product. But the output is a number that does not say which factor produced it.
04
Square-root method
Parametric — anchored on the minimum
AGREES
Definition. The index is anchored on the lowest rating, then modified by the square root of the next two lowest. Widely applied in arid-zone land evaluation because it retains the severity of the worst constraint while allowing secondary constraints to moderate the result.
Formula
LI = Rmin × √( Ra/100 × Rb/100 )
where Rmin = lowest rating  ·  Ra, Rb = next two lowest
= 35 × √( 0.86 × 0.88 ) = 35 × 0.869
Reference
Assessment of the agricultural potential of the soils of Sudan — Khiddir, S.M. (1986). PhD thesis, State University of Ghent, Belgium. Origin of the square-root parametric method.CR-02
The method is set out and applied in Sys, C., Van Ranst, E. & Debaveye, J. (1991), Land Evaluation Part II: Methods in Land Evaluation, Agricultural Publications No. 7, Brussels.
Open source
Result30.4% C4 Also reaches C4, because it is built on the minimum. Closest of the parametric family to the limitation result — still a value rather than a diagnosis.
05
Maximum limitation
Limitation family — applied in this study
IN USE
Definition. No arithmetic is performed. Each quality is classified against its own thresholds, each group takes the worst class among its members, and the hectare takes the worst class among the groups. The subclass letter of the governing quality group is appended to the result.
Rule
Chectare = max( C1, C2, … C17 )
where max selects the most severe class, not the largest number
= max( C1, C1, C4, C1, … C1 ) = C4
subclass = letter of the governing quality group = s
Reference
A Framework for Land Evaluation — FAO (1976). FAO Soils Bulletin No. 32. Defines the class and subclass structure and the limitation principle by which a class is assigned.LE-01
Applied through Land Evaluation Part III: Crop Requirements — Sys, C., Van Ranst, E., Debaveye, J. & Beernaert, F. (1993), which presents the limitation tables alongside the parametric alternatives.
Open source
ResultC4s C4 Same class as both parametric methods, and the only result that names the limiting quality. A planner reads not just how limited the land is, but what to address.

Applying it to the hectare. The chosen method resolves each group to the worst class among its members, then the hectare to the worst class among the groups.

Rolling up to the hectare class
A → C4· B → C1· C → C1· D → C1· E → C1→ HECTARE = C4s

Four of the five groups return C1. One returns C4. The hectare is C4s — class 4, subclass s for a soil physical limitation. Eighteen of seventeen qualities are favourable and none of them changes the outcome, because no crop can establish a root system through calcrete at 42 cm.

Step 1
Each quality has its own class table
All 17 land qualities carry an independent set of thresholds. Rooting depth has one, salinity another, slope another. A measurement is looked up against its own bands, in its own units — never against a shared scale.
Step 2
Rate every quality, then every group
Each quality is classified individually. Each of the five groups then takes the worst class among its own members. At the end of this step there are five group results and still no hectare class.
Step 3
The hectare takes the worst group
The hectare adopts the most severe of the five group classes, and the subclass letter records which group produced it — C4s is class 4, limited by a soil physical quality.

What the comparison actually shows

The three methods that reach the correct class do so because each is governed by the minimum — the square-root method anchors on it, multiplication is compounded downward by it, and maximum limitation takes it outright. Only the averaging methods fail, and they fail because averaging is the one operation that permits a severe constraint to be paid for by favourable conditions elsewhere. Weighting does not repair this: raising the limiting quality to the maximum weight moved the result by 1.5 points and left the class unchanged.

So the choice is not about which method reaches the right class — on this hectare three of five agree. The choice is about what the result tells you. A parametric index returns 26.6. The limitation method returns C4s: class four, limited by a soil physical quality. One is a number; the other is an instruction.

01
Severe constraints are not compensated
A crop cannot root through calcrete at 42 cm because the radiation is excellent. The binding constraint binds, whatever else is favourable.
02
The class names its own cause
The subclass letter travels with the class, so a planner reads not only how limited the land is, but which group of qualities is limiting it.
03
A reviewer can verify it
Any class can be checked by locating the single worst quality. A parametric result requires reproducing the entire calculation to audit.
Where these methods are set out
A Framework for Land EvaluationFAO (1976) · Soils Bulletin 32
Defines the class and subclass structure, land qualities, and the matching principle. Does not prescribe an aggregation arithmetic — the choice of method rests with the evaluator.
Land Evaluation Part III: Crop RequirementsSys, Van Ranst, Debaveye & Beernaert (1993)
Presents both families — limitation tables and a parametric land index. The source of the threshold tables used in this study, and the reason both approaches are treated here as legitimate.
Storie Index Soil RatingStorie (1978) · University of California
The original multiplicative parametric rating. Factor fractions are multiplied rather than averaged, which is why a single low factor governs the product.
Square-root parametric methodKhiddir (1986)
Anchors the index on the minimum rating, modified by the square root of the next two lowest. Widely applied in arid-zone land evaluation.
Guidelines: Land Evaluation for Rainfed AgricultureFAO (1983) · Soils Bulletin 52
Applies the framework through limitation-based matching of land use requirements against land qualities.
One consequence must be stated plainly. Because a single quality decides the class, the assessment is sensitive to any one erroneous input — an incorrect soil depth value moves a hectare from C1 to C4 on its own, with no other reading to offset it. This is agronomically correct behaviour and it raises the stakes on data quality rather than lowering them. It is why every input layer carries a recorded source and validation status, and why the class always names the quality that produced it: a surprising result can be traced immediately to the single measurement responsible.

Note on the ALUES weight values. The crop threshold records loaded in this study carry a weight column, because the ALUES package implements a parametric method. Those weights are retained in the database for provenance but are not applied — weighting belongs to the parametric family, and mixing the two approaches would produce a class that is neither.