FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY

Bray I extractions are consistently lower and for vineyard soils the accuracy thereof, regarding P availability, has not yet been confirmed.

TABLE 1: Minimum soil phosphorus concentrations required for grapevines grown in different soil pH regimes, as applicable for different extractants # .

Extractant Olsen Citric acid Mehlich III

Soil pH KCl

Soil texture class

Bray I

Bray II

mg kg –1

Sandy Loamy Clayey Sandy Loamy Clayey Sandy Loamy Clayey Sandy Loamy Clayey

– – –

25 30 35 25 30 35 25 30 35 25 30 35

25 30 35 20 25 30 20 25 30 18 21 25

20 25 30 15 20 25 10 12 15 10 12 15

20 25 30 20 25 30 20 25 30 15 18 21

< 5.0

12 14 16 10 12 15 10 12 15

5.0 – 6.0

6.0 – 7.0

> 7.0

Sandy (0 – 6% clay) / Loamy (6 – 15% clay) / Clayey (>15% clay) # Data on the relative extractability of P with different extractants was supplied by C.P. Beyers, Nitrophoska. Olsen: 0.5M NaHCO 3 Citric acid: 0.05M citric acid (C 6 H 8 O 7 ) Mehlich III: 0.2M acetic acid (CH 3 COOH) + 0.25M NH 4 NO 3 + 0.015M NH 4 F + 0.13M HNO 3 + 0.001M EDTA

Bray I: 0.025M HCl + 0.3M NH 4 F Bray II: 0.1M HCl + 0.3M NH 4 F

22 | INTERPRETATION OF SOIL ANALYSIS REPORTS FOR VINEYARDS