Efficient Sand Integration

Crop

Irrigation - Lettuce

Irrigating lettuce on sand

Following the principles of good irrigation practice lettuce crops can be watered using the following guideline crop factors.

Water requirement (mm) = Evaporation (mm) x Crop factor

Crop factors for transplanted lettuce

Week

1 - 2

2 - 3

4

5

6

7 until harvest

Crop factor

1.0

1.1

1.3

1.4

1.5

1.5

After transplanting a watering of 4mm is sufficient to “bed” the plants. Apply at least four light waterings of more than 1 mm each per day for the first week to achieve crop factor of at least 1.0.

To achieve maximum yields of lettuce the soil must be maintained close to its maximum water holding capacity. In sand this is achieved by watering daily when the water requirement is less than 6mm and at least twice when the requirement exceeds 8mm. Apply the bulk of the water early to mid morning; late afternoon watering promotes disease and applying water at night can be wasteful.

Split applications may be needed to cool a crop or control wind blown sand but at least one application should be sufficient to penetrate the soil to a depth which encourages deeper rooting. During cooler months additional night and early morning irrigation may be required for frost control.

The above table relates to crops grown on Karrakatta sand low in organic matter at the Medina Research Station and represents a guide for achieving optimum yield on this soil type.

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