The effects of superphosphate and potassium fertilizer and salts on the nitrogen mineralization of incubated meadow soil

Abstract

Three experiments were carried out to study the effect of superphosphate, potassium fertilizer salts on the extent of N mineralization and on the nitrification rate with increasing time of incubation of soil samples from a meadow.

Experiment 1: Increasing amounts of superphosphate, up to 96 mg per 30 g soil (equivalent to 174 kg P per ha) had only a small effect on the N mineralization. The samples treated with potassic fertilizer, up to 126 mg per 30 g soil (equivalent to 996 kg K per ha), reached values up to 65% higher than the control without any fertilizer. There was a positive and significant P × K interaction. The nitrification decreased with applications of any fertilizer.

Experiment 2: The addition of potassium as chloride, sulfate and carbonate increased the amount of mineralized N to the same extent. Chloride and sulfate reduced the nitrification rate, whereas carbonate promoted it.

Experiment 3: The addition of potassium chloride to soil sterilized with thimerosal had no effect on the amount of N released. With increasing time of incubation the content of mineral N in the samples increased. The abiotical release of N without K addition amounted to nearly 1.9 mg N per 100 g soil after 3 days of incubation and 15 days later to 6.0 mg N per 100 g soil.