Studies on fertilization of field-grown irrigated alfalfa - I. Effect of potassium source and time of application

Alfalfa (Medicago sativa L.) yields of 20-25 ton/ha are obtainable in a Mediterranean climate, with 8-9 harvests each year. These high yields demand a large supply of potassium from the soil. Plant uptake of potassium reached 540 kg K ha, the majority being derived from the exchangeable form. A safety level of 2.5% K in the whole plant is needed to prevent yield declines. Fertilization with potassium chloride gave higher yields than with potassium sulfate. Splitting the K application over period of two cuts is recommended for sandy loam soils with a low cation exchange capacity.