Introduction

• In my Internship I studied the current GRUD, particularly Mg, P and K

• Fertilizer requirement models imply \(Y\sim STP + Clay\) & \(P-\text{Export}\sim STP + Clay\)

• Currently only stationary measurement of STP are considered

• Could a kinetic desorption-model better explain the soil status and yield data?

Experimental Setup

• LTE STYCS, all treatment conditions equal except P-fertilization, which is in 6 Levels, 3 were considered(\(P0\),\(P100\),\(P166\))
• 5 Sites regarded; Cadenazzo, Ellighausen, Rümlang-Altwi, Oensingen, Zürich-Reckenholz
• 5 Sites, 4 blocks per site, 6 Treatment-Levels, 4 Repetitions
• Years 2017-2022 were observed, kinetic data was collected for year 2022 and used to predict 2017-2022
• kinetic data worth one year vs STP worth 6 years to predict the same data-set

Kinetic Model

Flossmann & Richter conducted in 1982 experiments that should:

• improve the classification of P-supply in soils
• work in tandem with a current STP-method e.g. CAL or Olsen

The net-desorption was observed, a kinetic of first order was assumed: \[\frac{dP}{dt}=k\times(P^S-P)\] When solved with \(P(0)=0\), the following equation was obtained: \[P(t)=P^S\times(1-e^{-kt})\] The researchers estimated the plateau \(P^S=P_\text{CAL/Olsen}-P_{H_2O}\) and linearized as follows: \[log(1-\frac{P(t)}{P^S})=-kt\] \(PS\), \(k\) and \(k*PS\) were extracted, \(k*PS\) being the average net-release speed.

Kinetic-Experiment Setup

Could a kinetic desorption-model better explain the soil status and yield data?

Relevant Variables

Soil Variables:

• \(P-CO_2\) & \(P-AAE10\) stand for the GRUD STP-measurements in [\(g~P/kg ~ Soil\)]
• \(k\)(\(s^{-1}\)) can be interpreted as the relative speed of net-desorption of orthophosphate
• \(k*PS\)(\(g~Ps^{-1}\)) can be interpreted as the average net-release speed
• \(PS\)(\(mg~P/L~H_2O\)) is the equilibrium concentration of \(PO_4^{3-}\) of the net-desorption experiment
• From the 0-20cm Horizon: Clay-, Silt-,\(C_{org}\)-content and pH

Yield Variables:

• For a year \(X\) and crop \(C\) \(Y_{main-rel}\) stands for \(Y_{main-rel}:=Y_C^{X}/mean(Y_C~\text{in year}~X~\text{in CH})\)
• For every year:site:crop combination the yield was normalised using: \(Y_\text{norm}:=Y/median(Y_{P166})\)
• The P-Export was calculated as the P-Uptake of the main product
• The P-Balance was calculated as the difference \(P_{Fertilized}-\text{P-Export}\)

Research Questions

• I: Is the method presented by Flossmann and Richter (1982) with the double extraction replicable with the soils from the STYCS-trial?
• II: How do GRUD-measurements of STP correlate to the soil properties \(C_\text{org}\)-content, clay-content, silt-content and pH?
• III: Are the kinetic coefficients \(k\) and \(PS\) correlated to soil properties?
• IV: How well can current GRUD methods of STP (\(P-CO_2\) & \(P-AAE10\)) predict the Yield-parameters, P-Export and P-Balance?
• V: How well can the kinetic parameters \(k\) & \(PS\) predict Yield-parameters, P-Export and P-Balance?

QI: Replicability of kinetic model in STYCS

Observation

• The estimation \(PS=P_{Olsen}-P_{H_2O}\) did not deliver reasonable and significant models in terms of residuals and significance