The old tennis courts at Tammin
Background
For years the grass tennis courts at Tammin were kept ready for use by regular fertilising, mowing and marking of the lines with chalk. After they were decommissioned and left unkept, the lines of the courts were still marked by growth differences in the grass and invading weeds (Figure 1).
Acidification and liming
The two major causes of soil acidification - product removal from mowing and nitrate leaching from fertiliser - would have acted to acidify the soil of the courts. This can be seen in the off-line pH values in Table 1. The soil profile is acidic down to at least 30cm. In the topsoil, the availability all major nutrients would be reduced.
The activity of beneficial microbes would be reduced and if any legumes had come in as weeds nodulation would be poor. In the subsurface, aluminium would be toxic and root growth restricted. It is not surprising that the growth of the grass and weeds is so poor in the areas of the court that don't make up the lines.
| Sample depth (cm) | Soil pHCa | Soil pHCa |
|---|---|---|
| N/A | On lines | Off lines |
| 0-10 | 4.3 | 3.9 |
| 10-20 | 4.9 | 3.6 |
| 20-30 | 5.5 | 3.8 |
Chalk used for marking lines on tennis courts is primarily calcium carbonate and acts in the same way as agricultural lime. Consequently, the pH of the soil on the lines is much higher than off the lines. The topsoil is a quarter as acidic on the lines compared to off the lines, but even so, is still well below pHCa 5.5 which is the recommended topsoil target for farming.
Although growth of the grass and weeds is substantially greater on the lines, it could be even better if the pH was higher. The subsurface pH on the lines is above the recommended target for agriculture (pHCa 4.8) and would not be causing aluminium toxicity. The roots of the plants would be able to explore a greater depth of soil to access moisture and nutrients.