Grassland potassium balance in a pot experiment using soils with different management histories

Potassium (K) management is important in grassland systems, especially in dairy farming. The interactions of potassium with other nutrients, such as magnesium (Mg), and enhanced potassium levels can have impacts on yields, product quality and on metabolic health issues of dairy cattle. A deeper understanding of potassium cycling is thus necessary for sustainable management. We used four sandy soils of similar genesis but with contrasting concentrations of available K and combined these with different levels of mineral K fertilisation in a glasshouse pot trial. A mass balance approach was used to examine soil K history and treatment fertiliser K effects on plant K and Mg uptake. The duration of the experiment was 5 months, growing Italian Ryegrass (Lolium multiflorum Lamark). Potassium concentrations in shoots were relatively high and were influenced by initial soil K and K input. Magnesium concentrations decreased the most in the soil with the lowest initial K and with increasing K input. Uptake of K by shoots and retention in soil were the main sinks for input K. The short- term reaction of the plant-available soil K pool seemed to be very dynamic but limited for soils with high initial K.