Agriculture Reference
In-Depth Information
Fig. 4.9.1.
Soil organic matter level changes over time.
The lower nutrient offtakes in rotation A were as a result of poorer
yields. The potato crop accounted for 46% of nitrogen, 58% of phosphorus
and 81% of the potassium exported from rotation B. The field beans
exported 150 kg N ha −1 from an average yield of 3.5 t ha −1 . This is
comparable with the export of N for field beans reported by Sprent and
't Mannetje in 1996. The subsequent wheat crop exported as much N as
the first wheat crop in rotation C; therefore, despite the large export of N by
the bean crop, it has to be assumed that a significant account of N had been
fixed.
Discussion
It commonly has been reported that during the period of conversion to
organic production there is a fall in soil organic matter levels and other soil
nutrients (Wander et al ., 1994). Similarly, it is well documented within
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