Joint International Conference on Long-term Experiments ...

classified according to the soil texture groups. The correlation between soil test (AL-K)
values and responses to K, using Bray's relative index method, was investigated. The
AL-method has been widely used in the Scandinavian countries, in the Netherlands, in
Portugal and in some Central European countries, and is still the official soil PK test
method in many of these countries.
RESULTS AND DISCUSSIONS
Evaluating the results of Hungarian 1- to 10-years-old potassium field experiments with
maize, winter wheat, and alfalfa found in literature between 1960 and 2000, conclusions
were made as follows:
As a result of previous NPK experiment series in Hungary with cereals and row
crops, N-responses were highest in both groups, which was followed by the Kresponses
in row crops and P-responses in cereals. N-responses were twice as high as
K- or P-responses (Várallyay sr 1950, Denke 1974a and 1974b, Debreczeni and
Debreczeni 1994).
Regarding the texture of Hungarian soils, 16% are sands, 10% sandy loams, 43%
loams, 19% clay loams and 7% are clayey soils.
The soils of the experimental fields did not receive previous significant potassium
doses so the results of the trials helped in estimating the original K supplying power of
the soils with different soil texture.
Soils with higher clay contents provided a better original (native) K-supplying power.
Among clay minerals, usually smectite was dominant in heavy soils, and illite in light
ones.
For estimating the extractable K-contents of the soils in Hungary, the AL-method
(0.1 mol/L ammonium lactate + 0.4 mol/L acetic acid, pH = 3.7, according to Egnér,
Riehm and Domingo (1960) has been official since the 60's.
On the basis of K field experiments with winter wheat, maize and alfalfa, carried
out between 1960 and 2000, the AL-method indicated the native K-supplying power of
the soils quite accurately (Figures 1 to 3). By this method probably not only the K
adsorbed and in the soil solution, but also some parts of fixed K was extracted.
According to the results of Sárdi and Németh (1993), AL- or neutral NH4-acetate extractants dissolve similar amounts of K from the same soil samples, resp.
The connection between the AL-K content of K-control (NP) plots and the
responses to K, expressed in relative yields (100Yield in NP plot/ Yield in NPK plot,%)
could be described by a Mitscherlich-like equation, modified by Bray (1944): / Y'= 100
(1-10 -cx ) /, where x = AL-K content in the K-control (NP) plots; Y' = relative yield in
the trials, having "x" AL-K contents in the K-control plots; and c = proportional
constant (Mitscherlich's "working factor").
The "c" values - similarly to the findings of Bray (1944) - were different for maize
(0.0083 and for the other crops: alfalfa (0.0109) and for winter wheat (0.0153),
respectively.
The determination coefficient (R2) for maize and alfalfa trials was higher (0.77*** and
0.80***) than winter wheat trials (0.67***), respectively.
The connection between the AL-K contents of K-controls and surplusses (yield in
NPK-NP, t/ha) for the same crops could be described by a hyperbolic curve.
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