Agriculture Reference
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Fig. 4.2.
The seasonal dynamics from October 1996 to September 1997 of mineral N and
soluble organic N in the surface soil (0-23 cm) under (a) an 8-year grass ley ploughed immediately
after the first sampling and planted with wheat, and (b) a continuous arable plot ploughed at the
same time.
obtained with FYM; recent yields show that the trend has reversed and
FYM, with or without fertilizer or residues, gives the best yields. However,
the data in Table 4.4 suggest that this is not because there is more 'available
P' in this plot; available P levels are quite low in the FYM-treated plot.
It is possible that, where manure was added, the inorganic P was
converted into labile organic and microbial forms rather than fixed as
inorganic P. Also, organic matter sorbs on to P-fixing surfaces, blocking
fixation. The cause would appear to be linked to SOM because the organic
carbon content has been maintained more effectively where manures were
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