Effect of Systematic Mineral Fertilization on Available Potassium in Pellic Vertisol

  • V. Koteva


The long-term field experiment at the Institute of Agriculture in Karnobat, Bulgaria, encompasses 47 years of systematic fertilization of field crops in rotation on Pellic vertisol with low, moderate and high levels of NPK fertilizer and, in a control experiment, without fertilizer. Cropping without addition of fertilizer decreased available potassium by 5.7 kgK2O/decare(daa)/year. Annual application of 4 and 8 kg/daa of potassium did not compensate for potassium removed by the crops – there remains a deficit of 5.5 and 3.5 kg/daa, respectively; only annual application of 12 kg/daa achieves a positive balance in the rotation. Despite the deficit, the levels of available potassium in the soil remain high under all treatments. Low and moderate fertilization levels do not significantly change the soil’s reserve of available potassium compared to the unfertilized control; under the high fertilization level, available potassium increases in the 0–40 cm horizon compared to the unfertilized control, but changes in the deeper layers are insignificant and reserves remain high.

For our 47-year trial, available potassium determined by Milcheva’s method gives better idea of the potassium nutrient for plants than exchangeable potassium determined by Ivanov’s method.


Positive Balance Mineral Fertilization Potassium Fertilizer Unfertilized Control Exchangeable Potassium 
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Copyright information

© Springer Science+Business Media Dordrecht 2014

Authors and Affiliations

  1. 1.Institute of AgricultureKarnobatBulgaria

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