Grains Research and Development

Esperence Crop Updates 2011

Using mouldboard ploughs and rotary spaders to ameliorate water repellent sandplain soils - where do they fit?

Stephen Davies WA Department of Agriculture and Food, Geraldton.

Key Messages

  1. In 9 on-farm grower trials in 2010 both rotary spading and mouldboard ploughing successfully overcame water repellence and both resulted in large grain yield increases mostly in the order of 500- 1200 kg/ha.
  2. Spading and ploughing of water repellent sandplain soils that have reasonable subsoil water holding capacity is more beneficial than for the pale deep sands whose low water holding capacity limits the opportunity to realise the improved yield potential, particularly in seasons with a dry finish.
  3. For the pale deep sands cheaper methods for improving crop establishment may be more cost effective such as improved furrow sowing and use of in-furrow banded soil wetters (surfactants).
  4. Rotary spaders would be the preferred implement if incorporation of clay-rich subsoil (claying) or lime into acid subsoils is a priority whereas complete soil inversion using a mouldboard plough is preferred if weed control and is a priority plus it is cheaper and water repellence amelioration benefits may last longer.

Aims

To assess the impact of full inversion mouldboard ploughing and partial inversion rotary spading on soil water repellence, crop growth and grain yield using large scale on-farm trials.

Background

For the past three years researchers and grower in the northern agricultural region have been assessing the role of soil inversion using mouldboard ploughs as a tool to bury weeds, overcome nonwetting and remove compaction and if required bury lime into acid subsoils. Results of this research has been very promising with weed control of >90% always achieved when plough setup and soil conditions were right, improved crop establishment on water repellent sands and large increases in grain yield (Newman and Davies 2009 and 2010). In 2008 growers started using rotary spaders to incorporate clay-rich subsoil after claying operations but also found that spading water repellent soils in the absence of additional clay improved crop and pasture establishment and growth. In 2009 DAFWA researchers in collaboration with the West Midlands and Northern Agri grower groups established some trials that included both spading and mouldboard ploughing of water repellent sandplain soils with some promising results (Davies et. al. 2010).

Method

In 2010 numerous growers in the Northern Agricultural Region implemented on-farm trials to test the value of one-off rotary spading or mouldboard ploughing of water repellent sandplain soils. Nine of these on-farm trials were selected and monitored (Table 1). The implements used in the trials were 4m wide rotary spaders with working depths of 25-30 cm or 7-9 furrow one-way or reversible mouldboard ploughs with working depths of 30-35 cm. In most instances the trials were grower-scale unreplicated strip trials with untreated control crops either side of the treatment strips. In most cases the strips were wide enough to accommodate header cuts and ranged from 500 to 1500 m long. Establishment counts and sampling for soil analyses, crop biomass and yield were all conducted at paired sampling sites to account for soil variation. Those parts of the paddock most strongly exhibiting water repellence were targeted for sampling as the primary aim was to test the capacity of the tools to overcome water repellence. Samples for water repellence testing were collected from 0-5cm. Dried samples were assessed for water droplet penetration time (WDPT) under standard laboratory conditions. Handharvest cuts were taken at crop maturity with crops harvested at ground-level so measures of aboveground biomass, head numbers, grain yield, harvest index and grain quality could be measured. The soil types in these trials fell into two broad groups: one group was the highly repellent pale, yellow and brown deep sands with low clay content to depth (typically <5%) and poor water holding capacity. The other group includes soils with highly repellent sandy topsoils but with reasonable subsoil water holding capacity. This included the yellow loamy sands (also known as sandy earths) that have subsoil clay contents of ~5-10% and the sand over gravel soils with subsoil having high gravel content typically in a loamy or clayey soil matrix.

Table 1. Details of on-farm rotary spader and mouldboard plough trials that were monitored in 2010.

Grower Location Soil Type Treatment Type Year Treated 2010 Crop Sowing Date Growing Season Rainfall (mm)
Harris Binnu Yellow deep sand Spader 2010 Magenta wheat 23-May 165
O'Callaghan Marchagee Yellow loamy sand Spader 2010 Magenta wheat 22-May 177
Hayes Warradarge Pale deep sand Spader 2010 Mace wheat 7-Jun 241
Hayes Badgingarra Pale deep sand Spader 2009 Magenta wheat 15-May 218
McTaggart W. Moora Sand over gravel Spader 2010 Calingiri wheat 31-May 220
Smart E. Nabawa Yellow loamy sand Mouldboard 2010 Wyalkatchem wheat 25-May 211
Fordham Badgingarra Brown deep sand Mouldboard 2010 Wyalkatchem wheat 15-Jun 270
Kenny Badgingarra Sand over gravel Mouldboard 2010 Calingiri wheat 15-Jun 300
Kenny Badgingarra Pale deep sand Mouldboard 2010 Baudin barley 14-Jun 300

Results

Water droplet penetration time (WDPT) measures were used to compare the water repellence of the control and treated soils at each site. The control treatments had severe water repellence with WDPT exceeding 600 seconds (10 minutes) at all the sites apart from a loamy sand site at Marchagee (WDPT = 182 secs, moderate repellence; Table 2). The water repellence of the spader and mouldboard plough treated soils was variable, ranging from 2 to > 600 seconds. Spading tends to have higher WDPT than mouldboard ploughing as spading leaves some topsoil near the surface. Mouldboard ploughing typically results in very low WDPT measures except in those cases where the soil conditions (too dry) or plough setup results in incomplete inversion. The brown deep sand site at Badgingarra is an example of this although crop establishment was still much improved at this site. Lower WDPT measures are also achieved on soils that have higher clay contents in the subsurface soil, such as the loamy sands at Marchagee and East Nabawa (Table 2). For example at the Marchagee site the clay content of the topsoil increases from 4.6 to 6.2% as a result of the spading alone which would further improve soil wettability.

Table 2. Impact of rotary spading or mouldboard ploughing on water droplet penetration time (WDPT;
seconds) for 0-5cm soil samples.

 

Grower (Crop) Location Soil Type Treatment Type Year treated WDPT Control WDPT Treated
Harris (wheat) Binnu Yellow deep sand Spader 2010 >600 470
O'Callaghan (wheat) Marchagee Yellow loamy sand Spader 2010 182 5
Hayes (wheat) Warradarge Pale deep sand Spader 2010 >600 418
Hayes (wheat) Badgingarra Pale deep sand Spader 2009 >600 8
Smart (wheat) E. Nabawa Yellow loamy sand Moudlboard 2010 >600 2
Fordham (wheat) Badgingarra Brown deep sand Moudlboard 2010 >600 >600
Kenny (barley) Badgingarra Pale deep sand Moudlboard 2010 >600 38

* This site was rotary spaded in 2009 so this represents a second year response to spading.

Substantial biomass and grain yield increases were seen at all the sites (Figs. 1 and 2). Mature shoot biomass was increased by both spading and mouldboard ploughing by an average of 2 t/ha (Fig. 1), and there was an average increase of over 100 heads/m2 as a result of the use of spaders or mouldboard ploughs (data not shown). These results are largely a result of improved (earlier) and more even establishment resulting in more dense crops, which was particularly evident on the most severely water repellent deep sands.

 

A comparison of the change in shoot biomass of various types of water repellent soil, after treatment with a rotary spader or mouldboard plough. Pale sand yielded a change of 2.1 and 1.3 tonnes per hectare when treated with a rotary spader, coloured sand at 2 t/ha, loamy sand at 2.4 t/ha and sandy gravel had the strongest response with a cahnge of 3.9 t/ha. Mouldboard ploughing was most effective on pale sand, with a change of 3.5 t/ha, then sandy gravel at 2.3, coloured sand at 1.6 and loamy sand at 1.2.

Figure 1. Average increase shoot biomass (t/ha) in response to rotary spading or mouldboard ploughing for a number of
on-farm field trials conducted in 2010 across a variety of sandplain soil types. Data are for wheat unless otherwise indicated.

 

On average grain yield was increased by around 400-700 kg/ha on the deep sands whereas on soil with water repellent topsoil but reasonable water holding capacity subsoil the yield responses tended to be higher with all but the Smart site having increases of 1000 kg/ha or more (Fig. 2). This result isn’t surprising given that all the sites experienced a dry finish to the season and the deep sands would have had little stored water for grain filling making crops prone to haying off. The pale sand site at Warradarge is an example of this with rotary spading increasing crop biomass at maturity by 2.1 t/ha (Fig. 1) yet grain yield only increased by 0.4 t/ha (Fig. 2; 0.7 to 1.1 t/ha) with a large increase in screenings from 22 to 48% (Fig. 3). By comparison at the loamy sand site at Marchagee biomass was increased by 2.4 t/ha (Fig. 1) with grain yield increased by 1.1 t/ha (Fig. 2; 2.4 to 3.5 t/ha) and screenings only increased from 1.7 to 3% (Fig. 3).

 

A comparison of increase in grain yield for various water repellent soil types treated with a rotary spader or mouldboard plough. Rotary spader treated pale sand achieved 0.4 and 0.5 tonnes per hectare increase, coloured sand achieved 0.7, loamy sand 1.1 and sandy gravel 2.0 tonnes per hectare. Mouldboard ploughing achieved a greater increase than rotary spading for pale sand at 1.25, and 1.25 for sandy gravel, a significantly lower increase in grain yield than achieved with rotary spading. Coloured and loamy sand both had a lower increase with mouldboard ploughing than rotary spading at 0.5 tonnes per hectare increase.

Figure 2. Average increase in grain yield (t/ha) in response to rotary spading or mouldboard ploughing for a number of on-farm
 field trials conducted in 2010 across a variety of sandplain soil types. Data are for wheat unless otherwise indicated.

 

A comparison of wheat screenings percentage for various soil types rotary spaded, mouldboard ploughed or untreated. Screenings dramatically increased from 22 to 47% for one trial of rotary spaded pale sand, but decreased from 27 to 25% for the other trial. A 1% increase in screenings was observed with rotary spading from 2 and 1% for coloured and loamy sand, and the screenings percentage was negligible for rotary spaded sandy gravel, compared to 2% untreated. Mouldboard ploughing reduced the screenings percentage by 1% for loamy sand from 6% untreated, from 11% untreated sandy gravel to 5%, but increased screenings for coloured sand from 4 to 5%.

Figure 3. Screenings (%) for wheat in response to rotary spading or mouldboard ploughing for a number of on-farm field trials
conducted in 2010 across a variety of sandplain soil types..

Conclusion

Yield response to amelioration

There are many possible factors that may be resulting in the large grain yield responses measured
after using these tillage tools including:

  • reduced water repellence;
  • improved and earlier (more even) crop emergence;
  • improvements in the pH profile through burial of higher pH topsoil and lifting of low pH subsoil and incorporation of surface applied lime;
  • reduced soil strength through a soil loosening effect (deep ripping effect);
  • reduced weed competition (see Newman 2010 Weed response to inversion – this proceedings);
    changes in nutrient and organic carbon distribution;
  • increased N mineralisation;
  • reduced occurrence of stubble and soil-borne pest and disease;
  • reduced carryover of residual herbicides in water repellent soil.

It is likely that the relative importance of these factors may vary from site to site and it may be difficult to determine which of these factors are the main drivers of the yield response in any given situation. Several of these factors, including the impacts of these techniques on pests and disease and carryover of residual herbicides, have received no research attention to date. At this stage use of both the spader and the mouldboard plough seem to result in similar yield increases in the first year.

The results from the trials monitored in 2010 confirm previous observations that while the use of these tillage tools can ameliorate water repellence on pale deep sands the benefits in terms of final grain yield are not as large as it is on sandplain soils high better water holding capacity. The pale deep sands have very low water holding capacity and whilst spading or ploughing might increase the crop biomass there is often limited soil water available for grain filling making these crops prone to haying off. It may be possible to reduce this risk of haying off caused by excess biomass by reducing the seeding rate, reducing post-seeding N applications or even grazing the crops to reduce the biomass. Otherwise alternative more cost effective management options for the pale deep sands may still be needed, such as improved furrow sowing methods and/or use of banded surfactants to improve crop establishment or alternative land uses.

Impact on soil water repellence

Both implements ameliorate water repellence. The mouldboard plough does this by completely inverting and burying the water repellent topsoil and bringing to the surface wettable topsoil. Rotary spading is different in that it does not evenly mix the subsoil and topsoil. Some clumps of topsoil tend to get moved to depth while seams of subsoil are lifted to the surface but there are still significant amounts of repellent topsoil near the surface. Overall approximately 2/3 of the topsoil is buried through spading with the remaining 1/3 being mixed through the topsoil. It was observed following reasonable rains after a mid-season dry spell in 2010 that the seams of subsoil created by spading provided many more preferential pathways for water entry into the spaded soil, so any additional mixing or homogenisation of these soils may destroy these preferred pathways and needs to be avoided or the benefits might be lost. Because of these different mechanisms it is suspected that amelioration of water repellence by mouldboard ploughing may last longer than the amelioration by spading but we have no data to confirm this yet. In those soils where spading or ploughing results in an increase in topsoil clay content, such as occurs with the deep loamy sands the water repellence amelioration benefits should last longer. The impact of these tools on improved establishment and increased shoot and hence stubble biomass may under a subsequent zero till, full stubble retention system provide more opportunities for water entry through biological pathways such as intact stubble, root systems and plant crowns in the long term. These mechanisms are being explored by Margaret Roper (CSIRO) and additional research is being established to gather evidence on the whether spading or ploughing prior to commencing a zero-till, full retention system is an advantage.

Which impliment to choose

Deciding which of the implements is best to use comes down to each individual growers priorities and what they want to use the tools for. A mouldboard plough is the best tool if weed control is a high priority plus it is cheaper and faster to use but can require more technical skill to get the plough setup right and the inverted soil is very soft and will need to be rolled in a seperate operation. Previous research has shown that the spader can control 60-70% of the weeds compared with >90% for the mouldboard plough. The spader is the better tool for incorporating amendments, including clay-rich subsoil (claying) or lime into acid subsoils. Spading leaves some water repellent topsoil near the surface so emerging crops do have access to some soil nutrients, including P in the surface soil but it may also mean that water repellence can re-develop more rapidly on spaded soils compared with those inverted by the plough. Many growers and contractors prefer to deep rip the soil prior to spading to decrease the soil strength and remove rocks or stumps but this is an additional cost.

Fitting spading and mouldboard ploughing into the system

Given the higher yields, improved weed control and reduced water repellence many growers are keen to undertake more rotary spading and mouldboard ploughing on their farms. The problems and concerns raised by growers in regards to the use of these tools are:

  • High erosion risk associated with burying all soil cover is the biggest problem and the only reason why some growers are not adopting large mouldboard ploughing or spading programs. It is not possible to remove this risk, it can only be minimised by ploughing or spading the soil when it is wet and sowing a cereal cover crop immediately. It should be remembered that spading or ploughing is a one-off amelioration event and may only need to be repeated once every 10 years or more so the erosion risk is confined to a short period between cultivation and establishment of the cover crop. The improved crop establishment and higher stubble loads as a result of ploughing or spading is likely to reduce erosion risk over the summer on some of the most highly repellent sands.
  • Soil softness can result in poor trafficability in ploughed soils that haven’t had adequate rolling the soil can be very soft even at harvest. Rolling the soil after mouldboard ploughing is a necessity. In most cases where there have been no or negative yield responses to mouldboard ploughing or spading it is s result of crops being sown too deep resulting in poorer establishment.
  • Many growers do not have access to tractors with 3-point linkage that have sufficient horsepower for these implements. This may be mitigated somewhat as tool carriers are available for mouldboard ploughs and more trailing spaders are becoming available.
  • Timing of ploughing and spading is a huge constraint. Contractors are only likely to come at a growers preferred time if they have a large renovation program planned and the demand for contract ploughing and spading services is likely to grow. The cost of large renovation program may make purchasing a plough or spader more attractive to a grower but then they may also need to purchase a suitable tractor and will need to find an operator at a time when there is competition from other seeding and spraying operations.
  • The implications of these cultivation tools on crop nutrition is an area which requires more research. Inversion ploughing can result in subsoil very low in nutrients and sometime with low pH being brought to the surface into which the crop is grown. This may be particularly critical for P which is required early during crop growth. Soil testing to depth is critical and some growers believe treating ploughed or spaded soil as new land with extra nutrition is a good strategy and lime may need to be applied post-cultivation if acid subsoil is brought to the surface.

References

Newman P and Davies S (2009) Mouldboard plough – the answer to all of the problems with sandplain
farming! Agribusiness Crop Updates, Perth, 24-25 February 2009.

Davies S, Newman P, Best B (2010) Impact of soil inversion, soil dilution and claying on non-wetting
sandplain soils. Agribusiness Crop Updates, Perth, 25-26 February 2010.

Newman P, Davies S (2010) Mouldboard plough continues to kick goals. Agribusiness Crop Updates,
Perth, 25-26 February 2010.

Key words

Water repellence, rotary spading, mouldboard ploughing.

Acknowledgements

Thanks to all the growers who allowed us access to their trials: Damian Harris (Binnu); Simon Smart (E. Nabawa); Michael O’Callaghan (Marchagee); David and Paul Hayes (Badgingarra); Jeff Fordham (Badgingarra); Andrew Kenny (Badgingarra) and Ben McTaggart (West Moora). Thanks to the West Midlands, Northern Agri and Liebe grower groups and Breanne Best (DAFWA) for technical support. This research was funded by GRDC through the ‘Delivering agronomic strategies for water repellent soils in WA’ (DAW00204) and ‘Putting Precision Agriculture on the ground in WA’ (CSA00016 – O’Callaghan site) projects.

Project No.:  DAW00204 (GRDC) and CSA00016 (GRDC)

Page reviewed by: Peter Newman (DAFWA Geraldton)