AgMemo - Grains news, December 2018

Page last updated: Thursday, 13 December 2018 - 1:43pm

Topsoil slotting plates boost yields on sandy soils

DPIRD research officer Wayne Parker assesses root development in a red non-cracking sodic clay, three years after it was deep ripped with topsoil inclusion, as part of a research project to investigate the use of topsoil slotting plates.

Grain growers with compacted sandy soils could achieve yield improvements of more than 35% by using topsoil slotting plates in association with deeper ripping, according to recent research.

The Department of Primary Industries and Regional Development’s (DPIRD) field trials, with co-investment from the Grains Research and Development Corporation (GRDC), showed topsoil slotting plates provided an additional boost to large yield increases produced by deep ripping.

Topsoil slotting is thought to enhance and prolong the effect of deep ripping, when combined with controlled traffic farming, enabling plant roots to penetrate into the clay.

There has been increasing interest from growers in the use of topsoil slotting plates; however, questions remain regarding the benefits relative to the additional cost.

The department’s trials used topsoil slotting plates, 28cm long and 43.5cm deep, bolted behind ripping tines and working 100mm below the soil surface, allowing topsoil to fall down into the ripping slot.

Department research officer Wayne Parker said three years of trials at Moora and Binnu showed a significant yield response in the first two years from deep ripping at 550mm with topsoil slotting plates. The results varied depending on crop type and seasonal conditions.

Topsoil slotting provided a positive response at both sites in 2015, allowing plant roots to access moisture at depth during a hot spring, resulting in an 83% yield increase in canola at Moora and an 18% yield improvement in wheat at Binnu.

In 2016 there was a 33% increase in barley yields at Moora, while at Binnu the increased lupin biomass generated by deep ripping ended up producing excess shade that limited yield improvement to 9%.

In 2017 the yields in the northern trial were compromised by the late start to the season, low rainfall and hail damage, resulting in a negative response in wheat at Binnu, however, there was a 54% increase in lupins at Moora.

The department is preparing to harvest the final year of these trials, while complementary trials on different soil types will continue in Ravensthorpe and Salmon Gums.

While topsoil slotting plates had a role to play when ameliorating soil compaction, their use would have to be considered carefully alongside the cost of the application.

In addition to the cost of the plates, the extra drag adds 20% to the energy cost of towing the ripper, not to mention the extra wear and tear on machinery.

It is also important to note that soil compaction is only one of the soil constraints present in sandy soils. Subsoil acidity and soil water repellence continue to be costly constraints, which are not remedied by deep ripping.

To get the most from the increased cost of plates, it is better to have the topsoil pH amended prior to slotting to assist subsoil pH amelioration.

More information about the department’s soil management research is available on the website.