Soil varies in its potassium (K + ) content and ability to supply K + to crops. Site-specific K + management aims to optimize crop production and minimize K + loss from the soil. The spatial variation of available K + prior to fertilizer application, the K + fixation capacity of soil and soil texture need to be taken into account for variable-rate K + application. This study was done to measure the spatial variation of the fertilizer K + availability index (A I ), which shows the potential for K + fixation, and to develop a strategy that takes the spatial distribution of this index into account for site-specific K + application. To determine the fixation capacity, the linear relation between the amount of K + added to soil and the amount of K + fixed was determined on 40 topsoil samples. Samples of soil were equilibrated in a moist condition for 3 weeks after the addition of 0, 25, 75, 225 and 675 mg K + kg -1 . The increase in exchangeable K + was described by a linear relationship. The fertilizer K + availability index (slope) varied from 0.20 to 0.49, indicating 51-80% of added K + was converted to the non-exchangeable form. Principal component analysis (PCA) showed that the first two components accounted for most of the variation, 48.7 and 26.3% of total variation, respectively. A non-hierarchical cluster analysis (k-means clustering) identified four groups and the amounts of fertilizer K + required were calculated for each group. The results suggested that such classes could form a basis for variable-rate application to maintain an adequate K + status for crop production and to reduce potential K + loss from soil by leaching.
Soil varies in its potassium (K + ) content and ability to supply K + to crops. Site-specific K + management aims to optimize crop production and minimize K + loss from the soil. The spatial variation of available K + prior to fertilizer application, the K + fixation capacity of soil and soil texture need to be taken into account for variable-rate K + application. This study was done to measure the spatial variation of the fertilizer K + availability index (A I ), which shows the potential for K + fixation, and to develop a strategy that takes the spatial distribution of this index into account for site-specific K + application. To determine the fixation capacity, the linear relation between the amount of K + added to soil and the amount of K + fixed was determined on 40 topsoil samples. Samples of soil were equilibrated in a moist condition for 3 weeks after the addition of 0, 25, 75, 225 and 675 mg K + kg -1 . The increase in exchangeable K + was described by a linear relationship. The fertilizer K + availability index (slope) varied from 0.20 to 0.49, indicating 51-80% of added K + was converted to the non-exchangeable form. Principal component analysis (PCA) showed that the first two components accounted for most of the variation, 48.7 and 26.3% of total variation, respectively. A non-hierarchical cluster analysis (k-means clustering) identified four groups and the amounts of fertilizer K + required were calculated for each group. The results suggested that such classes could form a basis for variable-rate application to maintain an adequate K + status for crop production and to reduce potential K + loss from soil by leaching.
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