Acid layers can occur in a relatively thin zone that prevents root growth, and can be missed by traditional 0-10 cm soil sampling. Applying pH indicator dyes (available from hardware or gardening stores) can be an effective first step in identifying if there is an acid problem, and where in the profile it occurs.
“Where pH falls below the threshold targets, a liming plan should be part of a long-term amelioration strategy,” Dr Macdonald says. “Yield benefits to ripping alone may be limited where subsurface acidity constraints are not addressed.”
Water repellencyis common in sandy soils, leading to uneven soil moisture and poor establishment. Although providing some surface disruption in the year of implementation, most ripping practices do not provide enough surface mixing to overcome repellency for multiple years.
“Rather than ripping alone, repellency is better addressed through deep ploughing approaches that mix the repellent sand to dilute and/or bury the problem layer,” Dr Macdonald says.
“Where available, clay can provide a permanent solution to overcoming water repellency. Specific delving and mixing tine designs are required to effectively mix the surface soil layers, and can be applied with/without claying practices to overcome water repellency.
“If repellency is not overcome, the full yield benefits of ripping are unlikely to be achieved as issues of water infiltration, establishment and erosion risks will remain.”
Dr Macdonald says subsoil toxicities and nutrient deficienciesexist within sandy soil landscapes in the southern region and can change rapidly with topography. A subsoil ‘health’ check can be useful in enabling growers to avoid areas where deeper rooting depth may not bring yield returns due to subsoil toxicities.
“Diagnosing subsoil issues involves assessing pH, electrical conductivity, exchangeable sodium, boron or chloride and essential plant nutrients, and various packages are offered from commercial laboratories.”
Growers are also encouraged to consider the risk of erosion: “Ripping will loosen and soften the soil profile to depth, flattening and unanchoring standing stubble,” Dr Macdonald says.
“The reduction in soil cover, coupled with the loosened surface, will leave ripped areas prone to wind erosion. Rolling after deep ripping will help to consolidate the soil surface but a lack of standing stubble will make the site vulnerable.”
A successful ripping operation is likely to increase the potential of crops and pastures for several years and therefore management of ripped areas should be adjusted to match the new potential yield.
“For example, without higher N inputs the crop yields may not fully respond to the benefits from deep ripping,” Dr Macdonald says.