Geoscience Reference
In-Depth Information
experiment, and another for root crops at Barnfield, continue to the present day.
In addition to unmanured and FYM plots, there were two main groups of treat-
ments. One group tested the effects of phosphorus, potassium, sodium and magnesi-
um separately and in various combinations in the presence of nitrogen, while the other
compared different amounts and forms of nitrogen (NO
3
versus
NH
4
) in the presence
of all these other four nutrients together. The yields of wheat from the Broadbalk plots
have been summarized from time to time. They make fascinating reading for anyone
with a statistical bent.
Some of the results are shown diagrammatically here in increasing order of yield
through the introduction of better varieties of wheat during this 120 year period,
coupled with better pest and weed control. It is interesting to note that yields have
been maintained and even increased somewhat on the plots which have received noth-
ing since 1843. This is the level sustainable with natural inputs alone. It is similar to
the world average.
Scanning across the columns, one sees the enormous response to artificial fertil-
izers especially with modern wheat varieties. Recent yields from the NPK plots are
a little above the national average. The last column on the right gives the yield from
the use of FYM. The next chapter discusses organic farming. For the moment, it is
enough to note that 35 tons of FYM contain about twice as much N, about three times
as much K, and a little more P than the levels in the artificial fertilizers supplied to
plots 13 and 7.
One of the reasons why the early experiments were so difficult to understand was
because one cannot always predict the combined effect of two nutrients from a know-
ledge of their separate effects.
Figure 56
shows an example in which K increased the
yield of sugar-beet by about 0.14 tonnes/ha, N increased it by 0.36 t/ha, and both to-
gether increased it by 0.57 t/ha. This suggests that the individual effects are roughly
additive; the dashed lines in the figure show the predicted additive effect. However, if
one doubles the dose of both N and K, the picture changes: the two together 'interact'
to produce much more than one would expect from their separate effects. The third
figure shows an even greater interaction when N is combined with a cocktail of other
essential nutrients in increasing the yields of potatoes.
