APPENDIX III

## 1. Soil and terrain constraint classifications for soil units according to FAO’74 Legend

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TERRAIN SLOPE CONSTRAINTS

| Rain-fed | Gravity irrigation* | Sprinkler irrigation
Severe constraints | slopes > 30% | slopes > 8% | slopes > 16%
Constraints | slopes 16-30% | slopes 5-8% | slopes 8-16%
Slight constraints | slopes 8-16% | slopes 2-5% | slopes 5-8%
No constraints | slopes 0-8% | slopes 0-2% | slopes 0-5%

*Applicable to non-terraced land

SOIL DEPTH CONSTRAINTS

Severe constraints: All soils with depth limitations within 50 cm of the surface caused by the presence of coherent hardrock or hard-pans (shallow soils): Lithosols (I), Renzinas (E), Rankers (U), all soils with Lithic phase.

Constraints: All soils with depth limitations within 100 cm of the surface by presence of Petrocalcic, Petrogypsic, Petroferric and Duripan phases.

No constraints: Deep soils: all other soils.

NATURAL FERTILITY CONSTRAINTS

Severe constraints: Soils with low natural fertility and soils where a major land improvement is required before cultivation is possible: all other soils.

Constraints: Soils with moderate natural fertility: Jd, Gh, Gd, Rd, Q, Qc, Ql, T, To, Th, Xy, M, Mo, Mg, Bc, Bd, Bh, Bg, Bf, Lf, Lp, Lc, Lg, D, De,Dg, Pl, W, We, Wh, A, Ao, Ah, Nd, Nh, Fr and Fh.

No constraints: Soils with high natural fertility: J, Je, G, Ge, Gc, Gm, R, Re, Rc, E, Tm, V, VP, Vc, Sm, Y, Yh, Yk, Yl, X, Xh, Xk, Xl, K, Kh, Kk, Kl, C, Ch, Ck, Cl, Cg, H, Hh, Hc, Hl, Hg, B, Be, Bk, Bv, L, Lo, Lk, Lv, Wm, N and Ne.

SOIL DRAINAGE CONSTRAINTS

Severe constraints: Poorly and imperfectly drained soils: All Gleysols (G, Ge, Gc, Gd, Gm, Gh, Gp and Gx), all Planosols (W, We, Wd, Wm, Wh, Ws, Wx) and all gleyic sub-groups (Zg, Sg, Mg, Hg, Lg, Dg, Pg and Ag), except Bg.

No constraints: Excessively and well drained soils: all other soils.

SOIL TEXTURE CONSTRAINTS

Severe constraints: Coarse textured soils. Soils with less than 18% clay, more than 65% sand, or which have stones, boulders or rock outcrops in the surface layer or at the surface: All Arenosols (Q, Qc, Ql, Qf, Qa), all Regosols (R, Re, Rc, Rd, Rx) and Vitric Andosols (Tv) with coarse texture, and all soils with petric and stony phase.

Constraints Soils with heavy cracking clays: Soils with 30% or more clay to at least 50 cm deep, with cracks at least 1 cm wide and 50 cm deep at some period in most years (unless irrigated), and high bulk density between the cracks: All Vertisols (V, Vp, Vc) and vertic sub-groups (Bv and Lv).

No constraints: Soils with medium and fine textures: all other soils.

SOIL CHEMICAL CONSTRAINTS

Severe constraints: Soils with severe salinity, sodicity, or gypsum limitations.

(a) Soils with a high salt content or exchangeable sodium saturation within 100 cm of the surface: All Solonchaks (Z, Zo, Zm, Zt, Zg), all Solonetz (S, So, Sm, Sg) and Solodic Planosols (Ws);

(b) Soils with gypsic horizons: Gypsic Xerosols (Xy), Gypsic Yermosols (Yy);

(c) Soils with saline and sodic phases.

No constraints: All other soils.

MICELLANEOUS LAND UNITS

The miscellaneous land units of the DSMW are considered as severe constraints. They include: dunes, shifting sands, salt flats, rock debris, desert detritus, glaciers and snow caps.

## 2. Soil and terrain constraint classifications for soil units according to FAO’90 Revised Legend

TERRAIN SLOPE CONSTRAINTS

| Rain-fed | Gravity irrigation * | Sprinkler irrigation
Severe constraints | slopes > 30% | slopes > 8% | slopes > 16%
Constraints | slopes 16-30% | slopes 5-8% | slopes 8-16%
Slight constraints | slopes 8-16% | slopes 2-5% | slopes 5-8%
No constraints | slopes 0-8% | slopes 0-2% | slopes 0-5%

* Applicable to non-terraced land

SOIL DEPTH CONSTRAINTS

Severe constraints: All soils with depth limitations within 50 cm of the surface caused by the presence of coherent hardrock or hard-pans (shallow soils): Leptosols (LP), all soils with Lithic phase

Constraints: All soils with depth limitations within 100 cm of the surface by presence of Petroferric and Duripan phases.

No constraints: Deep soils: all other soils

NATURAL FERTILITY CONSTRAINTS

No constraints: Soils with high natural fertility: FL, FLe, FLc, FLm, FLu, GL, GLe, GLk, GLa, GLm, GLu, RG, RGe, RGc, Rgu, AN, ANm, ANh, ANu, VR, VRe, VRk, CM, CMe, CMu, CMc, CMx, CMv, KS, KSh, KSl, KSk, CH, CHh, CHk, CHl, CHw, PH, PHh, PHc, PHl, GR, GRh, LV, LVh, LVx, LVk, LVv, PD, PDe, NT, NTh, NTr, AT, ATa, Atc.

Constraints: Soils with moderate natural fertility: FLd, FLs, GLd, RGd, AR, ARh, ARb, ARl, ARc ARg, ANg, VRd, CMd, CMg, CMo, CL, CLh, CLl, CHg, PHg, PHj, GRg, LVf, LVa, LVg, LVj, PL, PLe, PLd, PLm, PLu, PDd, PDg, PDj, PZ, PZh, LX, LXh, AC, ACh, ACu, NTu, FR, FRh, FRr, FRu, HS, HSl, HSs, HSf, ATf.

Severe constraints: Soils with low natural fertility and soils where a major land improvement is required before cultivation is possible: all other soils.

SOIL DRAINAGE CONSTRAINTS

Severe constraints: Poorly and imperfectly drained soils: All Gleysols (GL, GLe, GLk, GLd, GLa, GLm, Glu, GLt, GLi), all planosols (PL, PLe, PLd, PLm, PLu, PLi) and soils with antraquic phases.

Constraints All soil with gleyic and stagnogleyic subgroups (ARg, ANg, CMg, SNg, SNj, SCg, CHg, PHg. PHj, GRg, LVg, LVj, PDg, PDj, PZg, LXg, LXj, ACg, ALg, ALj).

No constraints: Excessively and well drained soils: all other soils.

SOIL TEXTURE CONSTRAINTS

Severe constraints: Coarse textured soils, soils with less than 18% clay, more than 65% sand, or have stones, boulders or rock outcrops in the surface layer or at the surface: All Arenosols (AR, ARh, ARb, Arl, ARo, ARa, ARc, ARg), all Regosols (RG, RGe, RGc, RGy, RGd, RGu, RGi), all Podzols (PZ, PZh, PZb, PZf, PZc, PZg, PZi) and Vitric Andosols (ANz) with texture “1”, and soils with skeletic, yermic, rudic, desert and Gobi phases.

Constraints Soils with heavy cracking clays: Soils with 30% or more clay to at least 50 cm deep, with cracks at least 1 cm wide and 50 cm deep at some period in most years (unless irrigated), and high bulk density between the cracks: All Vertisols (VR, VRe, VRd, VRk, VRy) and vertic sub-groups (CMv, LVv).

No constraints: Soils with medium and fine textures: all other soils.

SOIL CHEMICAL CONSTRAINTS

Severe constraints: Soils with severe salinity, sodicity, or gypsum limitations:

(a) Soils with a high salt content or exchangeable sodium saturation within 100 cm of the surface: All Solonchaks (SC, SCh, SCm, SCk, SCy, SCn, SCg, SCi), all Solonetz (SN, SNh, SNm, SNk, SNy, SNj, SNg) and Salic Fluvisols (FLs);

(b) All Gypsisols (GY, GYh, GYk, GYl, GYp) and soils with gypsic horizons: (RGy, VRy, SNy, SCy, Ksy);

(c) Soils with salic and sodic phases.

No constraints: All other soils.

MICELLANEOUS LAND UNITS

Miscellaneous land units are considered as severe constraints. They include: dunes, shifting sands, salt flats, rock debris, desert detritus, and glaciers/snow caps.