Quantifying uptake rate of potassium from soil in a long-term grass rotation experiment

Abstract

Soil-plant potassium (K) dynamics were studied using a long-term field experiment in order to evaluate the plant performance and K delivering capacity of the soil parent material. Rye grass (Lolium perenne L.) based rotations on a loamy sand derived from granitic bedrock were studied over 30 years with two K-fertilisation regimes, nil (K0) and 65 kg K ha −1 yr −1 . Mineralogical and chemical methods were combined to identify and quantify soil K resources including the partitioning of K between minerals. Two or three cuts were taken annually and herbage yield and composition together with exchangeable soil K were analysed. Herbage yield declined with time and significantly reduced when the K concentrations approached 1%. The grass K concentration also declined over time and stabilized at around 0.5-0.7% (dw) in K0 in all cuts. Input-output mass balances showed an accumulated net K off-take (deficit) of 1,100 kg ha −1 , i.e. 35 kg ha −1 yr −1 . With an exchangeable K pool of 100 kg ha −1 (in the rooting zone 0-40 cm) this indicated a substantial release of K from mineral sources, most probably biotite and hydrobiotite. Assuming a similar net off-take was continued then this particular mineralogical K source would be depleted within two centuries. The study illustrates the strength of combining long-term field experimental data with state of the art quantitative mineralogical methods in order to assess site-specific resources which can form a basis to evaluate the sustainability of different management practices.

Comparison of silicate minerals as sources of potassium for plant nutrition in sandy soil

“…In particular, the BET surface area of the nepheline syenite is about 60% of the value for microcline, indicating that dissolution rate is more important than surface area as a control on K availability. The greater growth rate observed for biotite is consistent with previous work that has long shown the ability of biotite to weather in planted soils (consistent with Figure ; Mortland et al , ; Öborn et al , ). Biotite used in this experiment has the largest BET surface area, but also the largest equivalent spherical diameter (Table ), which reflects the platey (non‐spherical) nature of the mineral grains.…”

Potassium fertilization of timothy‐based cut grassland—Effects on herbage yield, mineral composition and critical K concentration on soils with different K status

“…There were small yield responses for K even after 20 years at two fields with a high content of acid‐soluble K (Håland & Bakken, ). These soils delivered more than 100 kg K/ha per year throughout this period, and high long‐term release of K has also been found in other studies (Öborn et al., ). The ability of soils to sustain a long‐term delivery of K is dependent upon their mineral composition and the soil‐weathering conditions (Holmquist et al., ).…”

Estimating weathering rates using base cation budgets in a Norway spruce stand on podzolised soil: Analysis of fluxes and uncertainties

“…Cation budgets have been calculated at the scale of catchments (e.g., Koseva et al, 2010) as well as experimental plots (e.g., Andrist-Rangel et al, 2007;Simonsson et al, 2007;Öborn et al, 2010). In a soil cation budget, weathering is estimated by the difference from other independently measured element fluxes.…”