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| Author: | W.J. Conradie |
Abstract:
Fertilization trials, using cv.
Barlinka grafted onto Ramsey, were carried out on three soils in the Hex River Valley.
The 0 - 600 mm layer of the first soil (S1) contained 1.15% C and 6.7% clay, in comparison to 0.59% C and 2,8% clay for the second (S2), while the third (S3) contained 0,43% C and 4,1% clay.
Annual N and K applications ranged from 0-180 kg ha-1 and 0-120 kg. ha-1, respectively.
All soils showed NO3-N contents of less than 3 mg. kg-1 at budbreak.
From this stage up to flowering, active mineralization occurred for S1 and S2, resulting in NO3-N contents of approximately 8 mg. kg-1 in the control treatments.
Due to grapevines having a relatively large N - demand after flowering, NO3--N content for these treatments was reduced to 7 mg. kg-1 at véraison.
Even though N fertilization increased NO3-N content in S1 and S2, cane mass and grape yield were not affected.
The NO3+-N content of S3 never exceeded 5 mg. kg-1, even at the highest N application rate, pointing to a low N - supplying capacity and the necessity for N fertilization.
Potassium accumulated in the soil with the highest clay content (S1. Leaching of K from the sandlier soils (S2 and S3) necessitated annual fertilization.
Leaf analyses (total N, NO3-N and K) differed between the three soils.
For each individual soil, however, leaf analyses were fairly constant, in spite of large differences in N and K applications.
Soil analyses appeared to be a better guideline for N and K fertilization than leaf analyses.
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