The amount of potassium leached after rain on 10 of 11 days

Monthly soil and leaf samples were collected from the 11^th green at Keya Golf Club during the 2019 growing season. Andrew McDaniel and I wanted to look at the annual range of values, and changes over time, for soil and leaf nutrients.

Samples were taken on 21 August, just before the start of the KBC Augusta Tournament. On 21 August, the soil test K, measured by a Mehlich 3 extraction, was 89 mg/kg (ppm).

Then it rained a lot—a total of 374 mm (14.7 inches) fell between 21 August and the time another soil sample was collected on 1 September. There was rain on 10 of those 11 days between samplings, averaging 34 mm per day (1.33 inches per day).

So what happened with the soil K? Did a lot of it leach?

No. The soil test K from the sample taken on 1 September was 88 ppm, down just 1 ppm from the amount in the soil on 21 August.

Most of the K extracted by Mehlich 3 is on cation exchange sites. And no matter how much it rains, cation exchange capacity won’t be affected.

For more about this, see:

• After 17 inches of rain, how much K leached?
• I’d be applying potassium all the time: Part 1
• I’d be applying potassium all the time: Part 2