Success with no-till into pasture ground

Take home messages:

• Early grass control in pastures is best.
• Choose sown cereal pasture varieties with good disease resistance.
• Chemically control summer and autumn weeds well, don't just rely on grazing.
• Cultivation increases seeding nutrition rather than reduces disease inoculum.

Why do the trial?

The paddock trial aim was to better understand why many farmers with livestock find it difficult to no-till into pasture ground, and to give them practical management options for both the pasture and cropping phases that will help maximise outcomes, while reducing the risk of wind erosion.

How was it done?

Part A of this three year G&G2 project compared 2011 wheat crops that followed 2010 grass free and spray topped pastures in 2010 (for full report go to https://msfp.org.au/docs/research_74.pdf ). Part B compared 2012 wheat crops that followed sown cereal pastures and volunteer pastures in both the southern (Wynarka) and northern (Wunkar) Mallee last season. The Wynarka paddock used cereal rye as the cereal pasture and was very clean of other grassy or broadleaf weeds, while the Wunkar site had oats trashed in and brome and barley grass, wild turnip and capeweed. In that dry season both sites’ volunteer pasture sections of capeweed, wild turnip and grass were poor, leading to increased erosion risk from these sections. Observations suggested that the bulk of the paddock feed was obtained from the sown cereal sections (although areas were not separately fenced or measured).

In 2011 and 2012, 4 crop establishment treatments were used across the original pasture treatments:

1. Early worked (EW) after rains in late February and worked again 1 week prior to seeding.
2. Late worked (LW) 1 week prior to sowing.
3. No-till (NT).
4. No-till with higher inputs (NTH).

The trials were paddock scale using farmer equipment with all treatments replicated, and main soil types measured separately. The conclusions drawn from this trial reflect the clear and consistent results obtained irrespective of the variation across the paddock. This paper mainly presents 2012 results (Part B) but will also draw recommendations based on Part A and the overall project results and observations.

What happened?

Previously, Part A of the project had clearly shown low rhizoctonia build up after grass free pasture, medium levels following spray topping and very high levels where autumn growth was not controlled. In last years’ trial, however, the low/medium level in December at Wynarka, and the medium/high levels at Wunkar had a greater than 80% reduction in rhizoctonia inoculum to low levels (Table 1). This was thought to be mainly due to significant summer rainfall events in both December and February. While seeding into these low levels, crop monitoring still showed an average of 30-35% root loss at both sites.

Table 1. Effects of 2011 pasture type on disease inoculum and 2012 wheat yield following.

(L) Low; (M) Med; (H) High. VP (Volunteer Pasture), BR (Bevy Rye), MO (Marion Oats)

Bipolaris inoculum levels at the Wynarka site after Bevy rye averaged 88 pgDNA/g in December compared to 18 pgDNA/g following the volunteer pasture. By seeding time these levels had grown to an average 163 pgDNA/g after the Bevy rye and only 35 pgDNA/g after volunteer pasture across 32 soil tests (Table 1). As the wheat crop ripened in mid-October, white heads marked the cereal rye strips, resulting in a 33% yield loss compared to the volunteer pasture. It was also noted that the root loss measured from rhizoctonia averaged 39% from these rye areas compared to 24% from the volunteer pastures area, suggesting a link between the disease affects. Generally cereal rye is used as an important break crop in the mallee to improve soil health, and bipolaris is generally not a strong consideration when planning rotations, so it was quite unexpected that this problem arose, and suggests that further work needs to be done in this area.

Table 2. Available nitrogen (kg/ha) at seeding time after different cultivation treatments.

As in the previous years’ trial (Part A), the early tillage treatments had little impact on the levels of rhizoctonia inoculum in the soil come seeding time, but did result in large differences in available nitrogen to 30cm depth.  Early worked areas last year had between 13-35kg/ha higher N availability at seeding compared to the no-till areas (Table 2), and 23-27kg/ha higher N at seeding in 2011.

Figure 1. Tillage treatments into pasture, GG2 trial, Blackets 2011.

Figure 2. Spray topped versus grass removal, GG2 trial, Blackets 2011.

Yields results from the Wynarka site last season were inconsistent between tillage treatments across replications, and there was no clear advantage to cultivation apparent.  However, in 2011 the Wynarka results consistently showed a yield benefit from no-till over early working across the site (Figure 1). In both years these sites were well set up for no-till with summer and autumn chemical weed control as required.

Table 3. Yield, protein and nitrogen use results from 2012 Wunkar site.

SCP = Sown Cereal Pasture of Marion Oats, VP = Volunteer Pasture

*N use refers to nitrogen extracted by crop based on yield and protein levels

Results from Wunkar in 2012 (130mm GSR) showed a consistent yield advantage for the early worked plots (Table 3). There are a few thoughts on this. The first is that this paddock did not have any chemical summer weed control, but rather just grazing of summer weeds. This was also found at similar trial work conducted at Parilla (Figure 3) where only grazing summer weeds lead to decreased no-till yield results. Last year many Mallee farmers commented on the large difference in crops between those paddocks that had excellent summer weeds control (i.e. that conserved moisture), and those that didn’t.

Any no-till farmer knows that one of the keys to success is having good summer weed control. My feeling is that many livestock farmers tend to use grazing for summer weed control more than chemical control. This is a logical compromise for getting some valuable feed as well as keeping summer growth down to a manageable size. However, if you are not killing the plants, roots and all, then you will be compromising the potential of your following crop and certainly diminishing your chances of success with no-till seeding into this ground.

Figure 3. 2012 Yields from aligned Caring for our Country project trials (courtesy of Tanja Morgan).

The second thought regarding results presented in Table 3, is that while we are keen to promote no-till seeding over cultivation (where it may lead to potential erosion issues (both sites, particularly Wynarka, suffered wind erosion from the worked areas)), the reality is that there are some seasons and situations where cultivation may prove to be advantageous, particularly in relation to the availability and timing of N mineralisation. In 2011(Part A) at the Wynarka site the no-till plots started with around 20-25kg less N available at seeding time, yet then appeared to mineralise far more N throughout the growing season, leading to higher yields and resulting in about 20kg/ha more N being found and used at harvest. This extra N mineralisation (also measured in CSIRO trials) is attributed to the higher microbial activity that occurs in no-till systems throughout the growing season as the crops need it, predominantly when the soil is moist and the temperatures are warmer.

In 2012, however, this extra N boost in no-till systems did not appear to kick in as well, possibly due to the cold winter and almost complete lack of rainfall after mid-August to the end of the season when increased microbial activity normally occurs. This appears consistent with the generally low proteins from continuous cropping systems across the region. More work needs to be done to better understand these nutritional relationships within various farming systems and seasons.

The NTH plots (Table 3) were designed to try and account for the extra nutrient mineralisation at seeding from cultivation. In 3 of the 4 trials over the 2 years, while the farmer applied an extra 25-50kg/ha of fertiliser, this only equated to an extra 4.5-9 kg/ha N which generally showed no consistent advantage. However, at Wynarka in 2012 the NTH plots received an extra 23kg/ha N, which averaged a 0.4t/ha yield increase over NT plots and 0.8% higher protein across the loamy sand main trial area. These yield and protein benefits were higher in the plots suffering from bipolaris. While I would like to see more work done in this area, I feel that farmers starting no-till from a more traditional base with pastures may benefit from extra N, unless coming off a good legume pasture.

Differences in protein levels between the soil types in dune swale landscape at Wunkar were high (Table 3). If achieving APW was borderline, then there may well have been a good case for harvesting and marketing the flats separate to the sand hills, to help maximise returns.

Keys to successful no-till into pasture ground

Based on results from these 2 years of trials, other mallee research and anecdotal observations, the following recommendations have been made:

• Early grass removal from pasture phase is better than just spray topping.
• If using sown cereal pastures, choose disease resistant varieties.
• Use chemical summer weed control that kills weeds and optimises moisture conservation, rather than just relying on grazing management.
• Keep autumn a weed free zone, not allowing for disease build up on volunteer growth.
• Use proven no-till seeding systems with good breakout pressure, deeper working narrow points, good seed and fertiliser placement and press wheels creating a water harvesting furrow.
• Sow early as practical before soil temperatures decline, with adequate N, P and Zn.
• Don’t despair if no-till looks poor early, as generally nutrient mineralisation as the crops require it throughout the season will be advantageous.

My observations are that farmers that have been successfully no-tilling in more intensive cropping systems with the right set ups and management generally have more success with no-till into pasture ground. Farmers that are generally coming from a more traditional crop pasture situation will have bigger challenges in trying to move toward best practice no-till management after pasture. Remember, no-till systems will help protect your paddocks from potential erosion and will help increase biological activity in the soil that will improve crop nutrition in the long term.

Acknowledgements

Co-operating farmers Daniel Evans, Peter Blacket and workman Brian Pedler with the “Improving no-till crop performance when transitioning from pasture to crop in Mallee environments” project funded through Grain&Graze2 and GRDC.

Tanja Morgan and co-operating farmers from the “Increasing adoption of no-till technology following the pasture phase” project funded through Caring for our Country. Jeremy Nelson of SA MDB NRM.

Viterra Loxton for assistance in grain testing.

Gupta Vadakattu of CSIRO Ecosystem Sciences, Alan MacKay of SARDI Plant and Soil Health, Mallee Sustainable Farming Inc and Ag Excellence Alliance.

Contact details

Chris McDonough
Rural Solutions SA, Loxton Research Centre
(08) 85959136
0408 085 393
www.ruralsolutions.sa.gov.au
chris.mcdonough@sa.gov.au