The numbered points on the triangle mark where each soil typically falls — most cluster toward the sandy corner, the defining challenge of arid-zone agriculture.
A soil's position on the triangle sets, directly or in part, three of the seventeen land qualities:
Loams in the centre hold water well and work easily. Sands drain too fast to retain water; heavy clays hold water but seal, crack and resist tillage. Texture is the single most influential physical property of a soil — which is why it anchors the whole soil-physical group.
Read the three axes toward their labelled corners — % sand along the bottom, % clay up the left, % silt down the right. Follow the gridline for each value; where the three lines meet is the soil's texture class. The three percentages always sum to 100.
In a wet climate, poor texture can be forgiven — rain refills the soil often. In Saudi Arabia, where almost every drop is irrigated and water is the scarcest input, a soil that cannot hold water wastes it. A sandy soil may need watering every two or three days; a loam holds enough to stretch that to a week. Across a national irrigation budget, that difference is decisive — which is why texture, not fertility, is the first thing the capability assessment reads.
Rises from almost nothing in pure sand to high in loams, then stays high but harder to release in clays.
Best in loams. Sands are loose but blow away; clays are heavy, sticky when wet and brick-hard when dry.
Low in sands, high in silts and clays — a surface crust after rain blocks infiltration and stops seedlings emerging.