Whole plants were separated into
shoots and roots for analysis. At ¯owering three
representative plants per plot (nine plants, shoots,
per treatment) were taken at 80 (1993/1995) or 70
(1997) days after sowing. Plant height and leaf area
index (LAI) were also determined during the crop
season. Leaf area index (leaf area (m
of soil) was measured by using a Sky Area Meter
(Sky Instruments, UK). Plant material was dried at
708C, after decontamination by washing, and then
ground. Nitrogen was determined by Kjeldahl diges-
tion, and S using Mg(NO3)2 (Helrich, 1990), with
turbidimetric determination of sulphate as BaSO4.
2
) of the crop per