Handbook for Irrigation of Wine Grapes in South Africa

Figure 3.2

ca. 2.5 cm diam. soil at the sticky point

Textural class

Comments

N

Sand (S)

Sandy feel. Hardly adheres to fingers.

Forms a cohesive ball?

Y

Y

Ball falls apart easily

Very sandy feel. Very little adhesion to fingers, but more than pure sand.

Loamy sand (LS)

N

N

Ball roll into short, thick cylinder?

Y

Y

N

Soapier feel than SL, but not as smooth and or less readily worked as Z . Adheres to at least one finger. Sandy feel. Adheres to at least one finger. Not soapy or sticky. Readily worked.

Ball rolls into thread?

Sandy loam (SL)

Sandy feel predominates?

N

Y

N

Y

Very silky/soapy feel?

Silty loam (Z L)

Silky/soapy feel predominates?

Y

N

Silt (Z )

Rare as a texture. Silky/soapy feel

N

Thread bends into U?

Loam (L)

No predominating feel. Roughly equal quantities of S, Z & C. Adheres to finger and thumb. Readily worked.

Y

N

N

Y

Is the “U” cracked?

Significantly silky/ soapy feel?

Significantly sandy feel?

Sand clay loam (SCL)

Moderately silky and sandy feel. Adheres to finger and thumb.

Y

N

Y

Thread rolls into a ring?

Silt clay loam (Z CL)

Moderately sticky with soapy feel. Adheres to finger and thumb. Moderately stiff workability.

N

Y

Y

Y

Is the ring cracked?

Significantly silky/ soapy feel?

Clay loam (CL)

Stickier and harder to work. Less soapy than Z CL and less sandy than SCL. Adheres to finger and thumb.

N

Y

Sticky with sandy feel. Takes a rough polish. Stiff to work.

Significantly sandy feel?

Sandy clay (SC)

N

Y

Significantly silky/ soapy feel?

Silty clay (Z C)

Very sticky with silty soapy feel. Takes a polish. Stiff workability.

N

Clay (C)

Extremely sticky and difficult to work.

Sticky point: Moisture content at which dry soil being wetted just begins to adheres to fingers. Workability: Ease with which the soil can be moulded between the fingers. Because consistency varies greatly with moisture, samples must be properly and uniformly wetted up.

Cylinder: Approx. 5 cm long and 2.5 cm diameter. Thread: Approx. 13 cm long and 0.6 cm diameter. Ring: Approx. 2.5 cm diameter formed from about 8 cm of thread as described above.

FIGURE 3.2. A hand identification chart for soil texture analysis as proposed by Northcliff and Lang (redrawn from Rowell, 1994).

If the soil texture is more or less homogeneous within the profile, it will not impede root development and distribution (Fig. 3.3). However, physical and/or chemical limitations such as compaction or low pH in the subsoil will restrict root development, although the texture is fairly homogeneous (Fig. 3.4). Where these limitations occur, it must be ameliorated by deep soil preparation before a vineyard is planted. This will ensure deep, well-developed root systems.

56 CHAPTER 3 – WATER RELATED SOIL PROPERTIES