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  • Writer's pictureWayne

30t/ha of lime is enough, right? Nope.

It is so important to remember that the pH scale is on a negative logarithmic scale. A pH of 5 is 10 times worse then 6. A pH of 4 is 100 times worse than 6. And we had a pH of 3.1 on one area. A pH of 3 is 1,000 times worse than 6.

I received our soil test results back this week. Some eye opener results for me, until I reminded myself about the -ve logarithmic scale for pH. When we started with this farm, one location was 3.4 (CaCl2) in the 0-10cm layer, and 3.1 at 30-40cm. Since 30 t/ha of high quality of lime was added, it is now only 4.2 at 0-10cm and 3.4cm at 20-30cm.

A few very important points here. Some research says it takes many years (decades) to increase the pH at depth. That is not correct in the high rainfall areas with high earthworm activity. Yes, cultivating the lime into the soil would speed things up, but as you can see, in just over 2 years, we have increased the pH at depth a little. We have a long way to go. In other areas that were not as acidic, the sub-soil pH has increased significantly.

But, after 30t/ha of high quality lime, our surface pH is still extremely acidic at this location. If you have been reading these blogs, you will have seen some very lush pasture in Alpha paddock where this 3.1 pH was. It is very encouraging to me to know there is so much more pasture production waiting for me when we get the pH up above 5.5.

On about 90% of the farm, the pH is now where I want it to be (5.5-6.5) on the surface. A few spots are still too acidic at depth, but it will take some time for the lime to keep making its way down, with the help of masses of earthworms and plant roots.

Phosphate levels still need building on about half of the farm, and potassium levels at depth are still abit too low on about 20% of the farm. However, I will not be applying more potassium for awhile because as you can see in the photos below, we are still quite green here. Kikuyu is such an amazing grass and it is brilliant at bringing potassium up from depth.

We have only had a few millimetres of rain this January (3mm to be exact when these photos were taken) but the kikuyu is still recovering rapidly from grazing. It will keep getting better as the pH and nutrition continues to improve, and when we get enough sheep. The pastures have not been grazed hard enough since August 2020.

If you want to be part of Caluka Farms, you are welcome to. Please come and have a look and a chat.

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