APPENDIX III

Appendix III-Soil and terrain constraint classifications for soil units

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.

Miscellaneous 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.