NoTill Seeding into Pasture Ground
Chris McDonough, Rural Solutions SA, Loxton
Key messages
· NoTill out-yields Early Cultivation in Wynarka pasture trial
· Early grass removal in pastures improves success in following NoTilled cereals
· Don’t get put off by early crop performance, as more N kicks in later in the season when required.
Why do the trial?
This paddock demonstration trial aims to better understand why many SA mallee farmers find it difficult to Notill into pasture ground, and to give them practical management options that will help increase crop success, and reduce the risk of wind erosion.
Results from farmers surveys conducted by the SA MDB NRM in 2010 reveal that approx. 44% of mallee farmers were generally Notill, while 43% practiced Minimum Tillage. 72% described themselves as mixed farmers, with cropping paddocks and pastures for livestock. While many of these farmers have used Notill, generally they find that crops perform better after a cultivation, when coming out of a pasture phase. Often these paddocks are worked up in summer or autumn, leaving an extended period when the paddock may be susceptible to wind erosion, particularly in years that have a late break to the season.
This project is designed to look at what farmers can practically do in both the pasture phase and the cropping year to reduce risks, improve yields and better manage their farming systems. It also hopes to give farmers some better indicators for recognising when a paddock coming out of pasture may be right for Notill cropping or not.
How was it done?
Two pasture paddocks were chosen in 2010 for this trial, in the southern (Wynarka) and northern (Bakara) Mallee: The Wynarka paddock was a good medic pasture consisting of about 25% barley grass. It’s soil is mainly loamy sand with shallow calcrete stone evident in most areas, and has been regularly cropped in recent years. This paddock was generally considered well set up for Notill seeding.
The Bakara site, however, was generally a less fertile paddock of dune / swale, ranging from deep sands to sandy loam flats. This paddock had been left out to volunteer pasture for 4 years, and had a large burden of well established weeds, with mainly onion weed and barley grass on the flats, while the sandhills were mainly covered with onion weed, false caper, and a generally low level of brome grass scattered throughout. Farmers would almost always consider cultivation as necessary to succeed in cropping a paddock like this, and it was not thought to be “set up for notill”.
Each paddock was divided into areas of early selective grass removal and spraytopping. Soil testing was done in December that year to assess the initial affect of treatments on root disease inoculum.
In 2011, 4 crop establishment treatments were used across the original pasture treatments. This included:
1. early worked (after rains in early March) and worked again 1 week prior to seeding
2. late worked 1 week prior to sowing
3. NoTill
4. NoTill with higher inputs
The comparison of cultivation timing was used to assess whether a late working may be as effective as an early working, and therefore decrease the time that a paddock susceptible to wind erosion. Notill with higher fertiliser was used to assess whether this could help counteract the extra soil mineralisation of nutrients that occurs after a cultivation prior to seeding.
At the Bakara site it was necessary to prickle chain the treatments 2-4 in March, due to high presence of large onion weed, which are difficult to kill chemically or for the farmers modified notill seeding machine to handle.
All treatments were soil tested for root disease and nutrients at seeding time. The crop was then monitored for root disease affects, and grain yield and quality measurements were taken at the end of the season. The Bakara site was monitored separately between the sand and the flats.
Trials were paddock scale using the farmers equipment with and repeated once. Each plot (approx 0.4 ha) was divided into 2 and monitored separately.
What happened?
The Wynarka site was a good medic pasture in 2010, with half of the paddock grass removed, while the other half was spray topped. This area had 24% barley grass in Sept at the time of spray topping.
Table 1 shows more rhizoctonia inoculum build up in the paddock at the end of the pasture year where spray topping was used, most likely due to the longer growth period of the grassy weeds, as opposed to the grass removal area. While summer rainfall has clearly helped reduce the rhizoctonia inoculum in the soil in both areas, the levels were still clearly higher in the spraytopped area at seeding time 2011. The majority of tests showed levels in the medium and high ranges, while the grass removed area far more consistently gave readings the low risk range.
In February there was a clear germination of barley grass in the spraytopped treatment that was not present in the grass removal area which remained very clean. While this volunteer growth was controlled in early March there were a few strips of grass missed that continued to grow through to seeding time. The opportunity was taken to disease test these areas, showing rhizoctonia had clearly built up to high levels there (Table 1).
Table 1 Root Disease Testing result, post pasture year and seeding time, Wynarka Site 2010-2011.
Treatment / Nov 2010 / May 2011Ave DNA Scores
pgDNA/g / No. of Tests / Rhizoctonia
Risk Scores / Ave DNA Score
pgDNA/g / Ave. Risk Rating
Grass Removal 2010 / 96 / 16 / 1 BDL,
13 Low,
2 Med / 32 / Low
Spray Top
2010 / 135 / 16 / 1 BDL,
4 Low,
8 Med
3 High / 86 / Medium
Spray Top 2010, where
no Autumn Spray in 2011 / 130 / 2 / 2 High / 257 / High
BDL = Below Detection Limit
Table 2 shows that the early tillage treatments at Wynarka, which were worked in both early March and one week prior to sowing on 17th May 2011, showed the highest amount of soil nutrition at seeding time (20kg/ha higher nitrogen in the top 30cm over NoTill) due to the early soil mineralisation caused by the soil disturbance. Interestingly, there was no real difference in the amount of rhizoctonia inoculum in the soil between these tillage treatments at this time.
Table 2 Seeding time soil Nitrogen (kg/ha) and root disease, Wynarka Site 2011
Surface / Deep / Total N / Ave. Rhizoctonia Levels0-10cm / 10-30cm / 0-30cm / pgDNA/g
Early Worked / 35 / 35 / 70 / 69
Late Worked / 31 / 29 / 60 / 54
Notill / 26 / 21 / 47 / 56
Figure 1 Visual root disease damage in crop, Wynarka Site 2011
Figure 2 Root score in crop Wynarka Site 2011
Figure 1 gives the average of visual estimation of the % of the crop showing weakness attributable to root disease, taken from transect monitoring across the plots (there were also of poor crop growth to areas of shallow stone). Interestingly, there was little evidence of classic rhizoctonia patches, except in the areas where the volunteer Autumn grass growth was left. Instead most affected areas were mainly uneven and appeared less vigorous in growth. This graph shows that grass removed and early worked areas had less visual disease symptoms than the spraytopped and Notill areas. This pattern was also evident in the root score results shown in Figure 2, although the differences between the two pasture treatments were far less. Clearly the best result, in terms of minimising crop damage from rhizoctonia, came from grass removal followed by early working of the soil.
It was remarkable that this crop was still showing good yield potential despite having significant root damage, with 30-60% root loss on average. Many plants were still performing well with few good roots compensating for the many roots lost.
Despite the increased mid season crop damage, the Notill plots out yielded the early worked plots and late worked plots in every section of the trial, averaging 22% higher than early working (Table 3). The NoTill sections did average lower protein than the worked sections, but this was attributed to the higher yield (0.6t/ha). When calculating N removal based on crop yield and protein, the Notill have actually found an extra 20kg/ha N overall.
Early grass removal in the pasture phase also resulted in crop yields 18% higher than those from the spray topped section.
With this protein level averaging just below 11.5% the gross margin has been based on the APW price achieved by the farmer of $195/t, compared with the Hard Wheat price achieved by the farmer of $220 for loads above 11.5%. Even with this price difference, Table 3 still show that Notill into pastures at this site lead to the highest gross margin, followed by Late Working, then Notill High, and finally Early Working.
Table 3 Treatment harvest data, Wynarka Site 2012
Yield / % Yld / Protein / N Removal / Extra Nused / Screen. / GM increase
t/ha / of EW / % / kg/ha / over EW kg/ha / % / over EW $/ha
Early Work (EW) / 2.76 / 100 / 12.2 / 148 / 0 / 2.43 / 0 / Hard @
Late Work / 2.92 / 106 / 12.0 / 153 / 6 / 2.51 / 39 / $220
Notill / 3.36 / 122 / 11.4 / 167 / 20 / 2.34 / 48 / APW @
Notill High / 3.29 / 119 / 11.4 / 165 / 17 / 2.01 / 8 / $195
The second site at Bakara was monitored separately between the two distinct soil types sandy loam flats and the deeper sand rises. Table 4 shows a much higher rhizoctonia inoculum level in the flats after grass removal than the spray topped area at the end of the year after the pasture phase. Because this section was a mostly barley grass pasture, the grass removed area was left almost bare for the second half the year. While there is no clear explanation for this, it is possible that this could have been detrimental to any competitive soil organisms against rhizoctonia. By seeding time the following year, after a high level of summer rain, results showed far less rhizoctonia inoculum in the grass removal areas of the loamy flats, and overall very low levels in the sands.
Table 5 shows that the late working and early working plots increase soil N mineralisation available to the crop in the top 30cm by 18-26kg/ha on the flat, which was a similar result to the Wynarka site results. The less fertile sandy soils however, only increased N after cultivation by 1-7kg/ha.
Table 4 Root Disease Testing result, post pasture year and seeding time, Bakara Site 2010-2011.
Treatment / Nov 2010 / May 2011Ave DNA Scores
pgDNA/g / No. of Tests / Rhizoctonia
Risk Scores / Ave DNA Score
pgDNA/g / Ave. Risk Rating
Grass Removal 2010 / Flats / 253 / 8 / 6 Low,
1 Med
1 High / 55 / Med
Sand / 133 / 8 / 2 BDL
6 Low / 14 / Low
Spray Top
2010 / Flats / 159 / 8 / 1 BDL,
2 Med
5 High / 146 / High
Sand / 73 / 8 / 3 BDL
4 Low
1 Med / 24 / Low
Table 3 Seeding time soil Nitrogen (kg/ha), Bakara Site 2011
Surface / Deep / Total / Ave Rhizoctonia0-10cm / 10-30cm / 0-30cm / Levels. pgDNA/g
Sand / Flat / Sand / Flat / Sand / Flat / Sand / Flat
Early Worked / 18 / 29 / 7 / 18 / 25 / 47 / 17 / 106
Late Worked / 14 / 23 / 5 / 15 / 19 / 38 / 14 / 161
Notill / 13 / 17.5 / 5 / 6.5 / 18 / 20.5 / 36 / 111
Figure 4 Area visually affected root disease damage in crop by pasture treatment, Bakara Site 2011
Figure 5 Area visually affected root disease damage in crop by tillage treatment, Bakara Site 2011
Figure 6 Average seed root loss by tillage treatment and soil type, Bakara 2011
Figure 7 Average surface root loss by tillage treatment and soil type, Bakara 2011
Figures 4-7 show generally lower levels of visual root disease affects on the crop than the Wynarka site, as well as far less actual root damage. The sandy areas of the paddock had lower disease ratings than the flats, most likely due to fact that there was a much lower grassy weed history in these areas, compared to the flat that were thick with barley grass. Figure 4 shows generally that the grass removal showed slightly lower disease carryover than spray topping.
All the visual disease ratings and root damage scores generally reflected the levels of rhizoctonia inoculum measured at seeding time (Table 4). Because of the general soil variation at this site and the patchy nature of rhizoctonia, it was not clear that the differences shown in Figures 5-7 are entirely due to tillage treatments. It is interesting that the surface root loss was consistently higher than the seed roots across all treatments. This is reflective of seedlings roots growing quickly down the path of the deep narrow points away from the rhizoctonia, which often takes affect later, when the soil temperature drops, and the surface roots are forming.