Potassium-supplying power of selected Pallic soils of New Zealand 1. Pot trial study

Examination of the non-exchangeable K (K-nex) supplying power of selected Pallic soils of the North and South islands, New Zealand, revealed a wide variation in the measured reserve K (K-c) values. A glasshouse pot trial showed that the supply of K-nex to ryegrass grown on 13 North Island Pallic soils ranged from 0 to 409 mg kg(-1) and from 33 to 353 mg kg(-1) on 6 South Island Pallic soils. There were lower levels of Knex supply in developed soils that had been used for agriculture compared with corresponding undeveloped soils for the South Island soils. The results have implications for the fertiliser models that are used in New Zealand to assist prediction of the fertiliser K requirements of pastures.