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Lower stems Plants grown in 0.3 and 1000 mmol m-3 Ca2+, respectively

Leaves of terminal shoot, stated value below which deficiency symptoms occur

One cultivar, in 0.3 and 1000 mmol m-3 Ca2+, respectively

Poor seed set below first value, good seed set above second value

Soil pH 5.6

Soil pH 5.9

Soil pH 6.2

Values for days 45 and 96

Plants grown in 0.3 and 1000 mmol m-3 Ca2+, respectively 21-day-old plants

One cultivar, in 0.3

and 1000 mmol m-3 Ca2+, respectively

One cultivar, in 0.3

and 1000 mmol m-3 Ca2+, respectively

Plants grown in 0.3 and

1000 mmol m-3 Ca2+, respectively

5.4 ASSESSMENT OF CALCIUM STATUS IN SOILS 5.4.1 Forms of Calcium in Soil

Calcium is the main exchangeable base of clay minerals and, as such, is a major component of soils. One of the most important natural sources of calcium is underlying limestone or chalk, where it occurs as calcium carbonate (calcite). Calcium in rocks also occurs as a mixture of calcium and magnesium carbonates (dolomite). Soils over such rocks often contain large amounts of calcium carbonate, although not invariably so. The soils may not have been derived from the rock, but have

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