『Abstract
In agriculture there is a growing need to use phosphorus (P)
fertilizer more efficiently because of P related environmental
problems and diminishing P reserves. A key factor to achieve this
is an accurate prediction of the P supply potential of a soil.
To improve the choice of soil tests and interpretation of the
corresponding results a new methodology is proposed. The methodology
is derived based on the continuous removal of P from soils using
an artificial P sink (Fe oxide-impregnated paper) and linking
the results to standard soil tests. To achieve this, the desorption
results are modeled based on the adsorption characteristics of
the P sink and a soil specific Langmuir desorption isotherm in
which the parameters are calculated a priori from standard soil
tests. To be able to make any prediction of the P supply potential
a minimum of two parameters is needed: a measure for the reversibly
adsorbed P (Q) and for the P concentration in solution (C). The
best prediction is obtained when Q was approximated by P-Olsen,
followed by PAL and Pox. The measure for C is an indication of
the rate with which P can be removed from the soil and is approximated
by P-CaCl2. The ratio Q over C is an indication
of the capacity of the soil to buffer C, and thus the capacity
to maintain the flux from the soil to a sink. The accuracy of
this prediction increases for soils with high buffer power, i.e.
with low P saturation of the reactive surface area associated
with the readily desorbable P. In this case the Langmuir isotherm
is linear. To increase the accuracy of this prediction for soils
that do not have a high buffer power, and the Langmuir isotherm
is thus nonlinear, a measure for the reactive surface area (e.g.
Feox and Alox) of the
soil must also be taken into account. In addition, to be able
to extend the prediction of the soil P supply potential to an
amount of P exceeding the amount of readily desorbable P, a measure
for the total desorbable P content must be included (e.g. Pox). This total desorbable P content dictates
the level at which C is highly buffered once the reversibly adsorbed
P has been depleted.
The methodology was verified in pot- and field experiments. Implementation
of the methodology based on two parameters in a Dutch routine
soil laboratory has resulted in a more accurate P fertilizer recommendation
for grassland.
Keywords: Phosphorus; Langmuir isotherm; Soil processes; Soil
tests』
1. Introduction
2. Theory and data interpretation
3. Materials and methods
Desorption experiments
Pot experiments
Field experiments
4. Results and discussion
4.1. General soil characteristics and P status
4.2. Modeling soil P desorption to an artificial P sink
4.2.1. Choice of soil tests to estimate model parameters
4.2.2. Modeling P transfer from soil to Pi-paper and decrease
in P concentration in solution
4.2.3. Modeling soil P desorption isotherms
4.2.4. Methodology to predict soil P supply potential
4.2.5. Verification of methodology in pot experiments
4.2.6. Testing the methodology in field trials
4.2.7. Practical implications and applicability
5. Conclusions
Acknowledgements
References