101 Questions answered
Growing Pulses in Ameliorated Soil: Lime Depends on Post-Amelioration p
This largely depends on the pH of the soil once it has been ameliorated, as pulses don’t like acidic soil. If the soil was not acidic before amelioration, then lime is not needed – the bigger concern is crop establishment in soft soil in the year after amelioration.
If the soil is acidic, then the depth of acidity, pH of the subsoil, and method of amelioration need consideration. You might be able to get ‘free’ lime from an alkaline subsoil if enough of it is mixed in during amelioration.
If, for example, the topsoil is acidic and you are ripping and only scratching the top of an alkaline subsoil, you will probably need lime as the physical amelioration won’t do much to the topsoil pH.
Spading or ploughing that mixes alkaline subsoil into the topsoil might not need any further lime. Spading straight acidic sand won’t change the pH.
Table 1 shows how soil pH at Lameroo changed three years after various treatments including surface spreading lime, ripping, and cultivation with a rotary hoe. The initial soil was acidic from 5 – 25 cm depth. Ripping alone did little to improve soil pH. Liming then ripping had more of an impact.
Claying
Spreading and incorporating nearby clay improved soil pH. As the clay itself was alkaline and contained carbonate (1.4%), spreading at 100t/ha is equivalent to applying 1.4 t/ha of lime.
If you are looking to spade or delve to incorporate alkaline clay, do soil tests first to a) check the depth to clay and b) check the subsoil doesn’t have other issues such as salinity or sodicity. Also balance the lime rates if liming and adding clay as too much alkaline material can lead to nutrient deficiencies.
To see if you’ll get free alkalinity from deeper soil layers, check soil pH in 10 cm increments to the depth of amelioration.
