Deep ripping on deep white sands

Aims

To establish the value of ripping depth on compacted deep south coast sands. This trial aims to demonstrate that deep ripping to below the depth of compaction is required for the greatest economic benefit. Establishing the longevity of the ripping benefit is essential in this trial where the site is run in a fully controlled traffic system (CTF).

Background

Compaction of deep sands can be alleviated by deep ripping but it is not fully known how long the ripping effect lasts in south coast soils. Shallow ripping has been proven to have limited improvements on soil strength and grain yield in previous trials so ripping deeper on appropriate soils is essential. There are questions remaining about how long the ripping effect lasts for in a CTF system and when to repeat the deep ripping.

Method

A trial at East Gibson is investigating the longevity of deep ripping in deep sands in a controlled traffic paddock. Trial treatments were ripped with an Agroplow in March 2018 with treatment depths outlined in table 1. Plots are 1.7km long and 9.14m wide. Scepter wheat was grown in 2018 and GT-53 canola in 2019. The soil profile at the site is white sand over gravel and clay at 30 – 90cm depth.

In season data collection included taking establishment counts at crop emergence in 2019 in each plot along 6x 1mx2 rows. Penetrometer readings were taken across the same transect in August 2018 and September 2019. Harvest yield data was collected from the grower and interpreted using SMS.

Results

Yield results

Results from yield mapping in 2018 showed that ripping to 60cm significantly increased wheat yields by 0.5 to 1.15t/ha on different yield zones averaging 0.8t/ha over the full length of the plots when compared to both 40cm and nil ripped plots (Figure 1). There was no difference in grain yield between plots ripped to 40cm and the nil rip plots with an average grain yield for both of 4.3 t/ha (Figure 1). Average grain yield of plots ripped to 60cm was 5.1 t/ha. The ripping cost of about $100/ha was well covered by extra grain worth about $160 in the first year.

Figure 1- Average grain yield of Scepter wheat sown in 2018, the first season after ripping, from each ripping depth treatment. Different letters on the bars show a significant difference between treatments at P≤0.05

In 2019 when the site was sown to GT-53 canola there was no change in plant numbers between treatments calculated from establishment counts. No significant grain yield differences were found among the treatments with an average site yield of 2.1 t/ha (Figure 2). A potential yield of 2.07 t/ha was calculated at this site for canola using a modified French and Schultz method; therefore all treatments are near potential yield for the 2019 season regardless of deep ripping treatments. There was no change in plant numbers between treatments calculated from establishment counts taken in 2019.

Figure 2– Average yield of GT-53 canola sown in 2019, the second season after ripping, from each ripping depth treatments. Different letters on the bars show a significant difference between treatments at P≤0.05.

Soil strength results

Penetrometer readings were taken in August 2018 and September 2019 to assess changes in soil strength for the ripping depth treatments. 2018 penetrometer results show a significant reduction in soil strength when deep ripped to 60cm compared to the 40cm and nil ripped plots. There was no difference between the nil rip and the 40cm deep ripped plots. Severe soil compaction, of 2.5 MPa, occurs at 40cm depth at this site (Figure 3). This indicates that the 40cm ripped treatment was not deep enough to shatter this layer of compaction. It is important to understand the depth of compaction to ensure ripping depth is fully effective.

Figure 3 – Soil strength profiles from penetrometer readings taken in August 2018, four months after ripping to depths of 40cm and 60cm. The dotted line at 2.5MPa highlights severe compaction. LSDs are for soil strength at 10cm intervals down the profile at P≤0.05.

Penetrometer results in 2019 indicate a sustained reduction in soil strength in plots ripped to 60cm when compared to the nil and 40cm ripped plots (Figure 4). There is some natural re-compaction occurring at depths 50 – 60cm. This is indicated in figure 4 where there is no longer a significant difference in soil strength among treatments below about 55cm depth.

Figure 4 – Soil strength profiles from penetrometer readings taken in September 2019, four months after ripping to depths of 40cm and 60cm. The dotted line at 2.5MPa highlights severe compaction. LSDs are for soil strength at 10cm intervals down the profile at P≤0.05.

Conclusion

Results from both 2018 and 2019 indicate that deep ripping to a depth of 60 cm is economically worthwhile on deep white sands in the Esperance port zone. Although there was a sustained reduction in soil strength in the second year after ripping this was not reflected in yield, with no change across treatments in canola yield in 2019.It is important to understand where the depth of compaction is to ensure ripping depth will alleviate the problem.

This site will be sown to barley in 2020. Penetrometer readings and grain yield data will be taken again to assess the longevity and impact of the deep ripping. The secondary 40cm deep ripped plot will be re-ripped in 2022 to 60cm. This will be allow for a comparison of fresh and older deep ripping.

Acknowledgments

Thank you to the Lewis family for hosting this trial and to Jeremy Lemon, Tom Edwards and David Hall for professional guidance.

Reviewed by: Jeremy Lemon

GRDC Project Number: DAW000256

Important disclaimer
The Chief Executive Officer of the Department of Primary Industries and Regional Development and the State of Western Australia accept no liability whatsoever by reason of negligence or otherwise arising from the use or release of this information or any part of it.

Copyright © State of Western Australia (Department of Primary Industries and Regional Development), 2018