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applied (Table 4.4). However, soil carbon levels have decreased under
cultivation even on manured plots.
The efficiency of manures and fertilizers for supplying P and K have
been compared in three long-term experiments in Europe. Blake
et al
.
(2000a,b) measured P and K balances in the plough layers of the Broadbalk
Continuous Wheat Experiment at Rothamsted, a 97-year-old rotation
experiment at Bad Lauchstaedt in Germany, and a 76-year-old experiment
at Skierniewice in Poland on rotations and continuous rye. The P and K
were applied as fertilizers, FYM and a combination of both.
Figure 4.3 shows the efficiency of use of applied P and K (i.e. that
removed in the crop); that not used was fixed in the soil or leached below
the sampling depth (plough layer). Efficiencies of > 100% for K indicate
Table 4.2.
Organic carbon contents, available P contents and maize yields in the 23-year-old
Kabete Experiment at the Kenyan Agricultural Research Institute (KARI).
Organic carbon (%)
Maize yield (t ha
−
1
)
Available P
(mg kg
−
1
)
1998
Treatment
1976
1998
1976
1998
Nil
2.8
1.62
13.1
3.8
1.2
NP
1.63
88.0
4.3
2.3
FYM
1.99
38.2
3.9
3.2
FYM + NP
2.07
129.1
4.0
2.9
FYM + NP + crop residues
2.15
107.2
4.0
3.0
Fig. 4.3.
Efficiency of phosphorus and potassium applied to three soils from the UK, Germany
and Poland when applied as fertilizers, manures (FYM) or a combination of the two.
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