Tillage impacts in no-till systems

Author: Yash Dang1, Anna Balzer1, Mark Crawford2, Vivian Rincon-Florez1, Hongwei Liu1, Alice Melland3, Dio Antille3, Shreevasta Kodur3, Mike Bell1, Jeremey Whish4, Yunru Lai1, Nikki Seymour5, Lilia Carvalhais1, Peer Schenk1 | Date: 18 Jul 2017

1School of Agriculture and Food Sciences, University of Queensland; 2Department of Natural Resources and Mines;  
3University of Southern Queensland; 4CSIRO; 5Department of Agriculture and Forestry

Take home messages

  1. One-time tillage in continuous no-tillage (NT) system reduced weed populations and improved crop productivity and profitability in the first year after tillage, with no impact in subsequent four years.
  2. Soil properties were not impacted in Vertosols, however Sodosols and Dermosols suffered short-term negative soil health impacts. A Sodosol and Dermosol also posed higher risks of runoff, and associated loss of nutrients and sediment during intense rainfall after tillage.
  3. Tillage reduced plant available water in the short-term which could result in unreliable sowing opportunities for the following crop especially in semi-arid climate.
  4. Generally there were no significant differences in crop productivity and soil health between tillage implements and tillage frequencies between tillage and NT.
  5. The study suggests that occasional tillage can be a viable strategy to manage constraints of NT systems, with few short-term soil and environmental costs and some benefits such as short-term farm productivity and profitability and reduced reliance on herbicides.

Introduction

No-tillage (NT;seeding with low soil disturbance and no prior tillage) is a key component of conservation agricultural systems which has provided tangible, economic, environmental and social benefits as compared to conventional tillage which involves intensive disturbance of soil prior to crop sowing. The adoption of NT has progressed globally and in Australia, particularly within north-eastern cropping regions. However, there are concerns regarding long-term sustainability of such systems due to build-up of herbicide-resistant weed populations, increased incidence of soil and stubble-borne diseases, and stratification of nutrients and organic carbon in the top soil. There is an increased interest in the use of an occasional tillage to combat both biotic and abiotic constraints in NT system. The impact of tillage in an otherwise NT farming system on agronomic, soil and environmental factors has either been shown to be inconsistent or studied for a relatively short period. Only a few studies have examined the impact of occassional tillage for periods of four to five years, and these yielded inconsistent results.

Materials and methods

A total of 14 field experiments were established in four different phases in northern NSW and Queensland during 2012-15 on sites with a long-term history of continuous NT and controlled-traffic farming:

(i) five sites with or without tillage treatments in otherwise NT fields in winter 2012;

(ii) three sites with treatments involving different timing, frequency and type of tillage implements with each treatment factor (timing or, frequency or type of tillage) in a separate experiment in a complete randomised block design in winter 2013,

(iii) two sites with different types of tillage implements (strip tillage, narrow chisel, and disc) and one experiment to quantify soil water loss and recovery with one-time tillage in summer 2013, and

(iv) three sites with or without tillage treatments to quantify runoff and loss of soluble nutrients immediately following tillage under simulated rainfall in winter 2015.  
All tillage operations were shallow to an approximate soil depth of 0-15 cm.

A randomised, complete-block design was used for all sites except at Warwick. At Warwick, a long-term experiment consisting of a factorial combination of tillage practice (NT vs conventional tillage), crop residue management (burnt or retained) and nitrogen (N) ferilizer rates (0, 30 and 90 kg N/ha) was longitudinally split into two, with half of the NT section receiving chisel and the remaining half left un-tilled as a control. In the present study, we reported results for no-till-stubble retained-N90 treatments only and analysed as randomised complete block design. All sites had a minimum of three replicates. A detailed description of each site, and tillage implement used, timing and frequency is given in Table 1. The most commonly tillage implements used included chisel, disc, offset disc, scarifier and ‘Kelly’ prickle chain. We determined short-term soil water loss due to evaporation on a Vertosol (100 m x 12 m plots with 9 m buffer space between plots) at Felton A site (Table 1) on day 1, 2, 3, 4, 7, 9, 17, 30, 44, 60, and 65 post tillage using an EM38 (Geonics MKII) in both vertical and horizontal modes. Volumetric water content was estimated using a pre-calibrated linear relationship between volumetric water content and EM38 readings recorded at the site.

At rainfall simulation sites during 2015; runoff was generated for at least 30 min at a rainfall intensity of 70 mm h-1 from four plots of NT and tillage on three soil types. Samples of runoff from rainfall simulations were analysed for volume, sediment and nutrient contents. Nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) fluxes were measured to quantify short-term greenhouse gases (GHG) emissions. Gases were extracted manually from chambers at 0, 25, 50 and 75 min after enclosure once per day before rainfall, within 3 h post-rainfall, and then 1, 2 and 3 days after rainfall. Soil samples were obtained yearly prior to sowing and analysed for physical, chemical and biological properties.

Results and discussion

Soil impacts

Soil water storage and crop water supply are the major factors affecting grain production in the semi-arid region of north-eastern Australia. Tillage in a NT farming system would potentially increase soil evaporation. In the present study, tillage initially reduced the soil water content, due to evaporation. Within 4 weeks of tillage, however, sufficient rainfall replenished soil water loss and helped to recover the soil moisture to pre-till moisture status (Fig. 1). Evaporation losses due to tillage can be as high as 20 to 30 mm. Evaporation can be affected by climatic conditions above the soil surface, depth of the tilled layer, time and nature of tillage, the nature of induced surface structure and the pore geometry of the tilled layer.

Following one-time tillage, soil water content in the 0-0.1 m layer was not significantly impacted at any site or time; except at Warwick 3 months after tillage (Table 2). Soil water recovery was due to substantial rain (80 - 99 mm) received in the first 3 months after tillage operations during 2012 and 2013 at most sites. The exception was a significantly negative impact at the Warwick site, despite 118 mm rainfall between tillage and the time of soil sampling after 3 months. High clay content soils, like that at Warwick (65%), require more rain to refill the soil profile. No significant differences in soil water content due to tillage treatments were observed prior to seeding in subsequent years i.e. after 12, and 24 months after the tillage operation. Given that crop production in north-eastern Australia heavily relies on stored soil moisture during the fallow period, the initial loss of soil water in extreme cases could present either unreliable sowing opportunities or a poor crop establishment. No-till farming systems, especially in high clay soils, usually have a much wider sowing window due to retention of adequate water for crop establishment. In most circumstances, the occurrence of rain after the tillage operation would determine the success of tillage in NT farming systems. This raises the importance of timing of tillage in the farming systems context in relation to the seasonal forecast. Overall, the climatic conditions throughout the season will influence soil water, aeration and temperature and thus will have a marked influence on crop responses and yields in different seasons.

Immediately following a tillage operation, there was significantly higher cumulative CO2 emissions over 2 days on the Sodosol (67 mg C m-2 and 37 µg C m-2 from tillage and NT plots, respectively) but not on the Vertosol (209 µg C m-2 and 215 µg C m-2 from tillage and NT plots, respectively). However, the impact of one-time tillage on SOC was not significant (P<0.05) after 3, 12 or 24 months tillage on any of the soil types studied (Table 2). There are a number studies that indicate large amounts of CO2 are lost from the soil immediately following tillage due to an increase in microbial respiration, typically occurring with a release of trapped CO2.  However, in the long-term, there is no consistent effect of one-time tillage on soil TOC in long term NT systems. Particulate organic carbon (POC) is considered to be more easily decomposed and is preferentially degraded over humic TOC by tillage. In the present study, POC ranged from 10% of TOC in the Black Vertosol at Warwick to 30% of TOC in the brown Sodosol at Condamine. The POC content was significantly decreased in the Black Vertosol at Biloela 3 months after tillage. There was no significant impact on POC at other sites. The decrease in POC with tillage may be due to changes in incorporation of residue into soil, redistribution and decomposition, or where aggregate breakdown results in increased mineralisation. In the present study, surprisingly there was an increasing trend in POC in black Vertosol at Warwick with tillage after 3 months. This could be due sampling anomalies and/or the high spatial variability associated with carbon distribution in field conditions and/or high stubble load prior to tillage leading to incorporation. Available soil P tended to be lower in the surface soil (0 – 0.1 m) at all sites 3 months after tillage, however, the reduction was significant only on the Vertosol at Biloela A. At 12 and 24 months after tillage, available P was similar at all sites. Most studies have reported a general decrease in available P in the surface soil due to tillage. However, in the present study, use of shallow tillage and low P mobility did not result in redistribution of nutrients into the nutrient-poor subsoil.

Total microbial activity (TMA) in the top 0.1 m soil depth was quite variable and not significantly affected at any site three months after one-time tillage operation. However, there was a significant decrease in TMA 12 months after tillage as compared to 3 months after tillage in the Black Vertosol at Warwick (Table 2). Differences may be associated to changes in seasons between the collection times. Generally, FDA as a measure of TMA is considered to be a ’broad-scale’ measurement for enzymatic activities and may not be sensitive enough to detect changes in specific processes due to functional redundancy of soil microbial communities. Alternatively, the result suggests the soil communities were functionally stable in these soils. Furthermore, one-time tillage did not affect the mycorrhizal associations or Pratylenchus thornei nematode populations measured in Black Vertosols at Warwick and Jimbour 12 months after tillage. There was no incidence of crown rot at most sites. However, at the Jimbour site with crown rot infection, one-time tillage did not result in a significant decrease in crown rot (results not shown).

Environmental impacts

On the Dermosol at Moonie B and the Sodosol at Billa Billa there was significantly higher runoff from tillage plots than from NT plots. Runoff volume was highly variable and similar between tillage and NT treatments on the Vertosol at Felton B (Fig. 2). Consistent with these effects on runoff volume, infiltration rates were significantly higher on the NT plots than the tillage plots on the Dermosol and Sodosol (Fig. 3). Erosion and total N loads were highest after tillage on the Sodosol however there were no significant differences due to tillage on the Dermosol or Vertosol. Total P loads in runoff were also significantly higher from tillage than from NT on both the Sodosol and Dermosol. The impact of tillage on runoff and nutrient loads was largely attributed to removal of groundcover by tillage and an increased vulnerability to erosion. Soluble P losses were low overall (<12% of total P) and rather than reducing surface soil enrichment with P and associated soluble P concentrations in runoff, TILLAGE increased soluble P concentrations in runoff at two sites (Fig. 3).

As well as the higher cumulative CO2 emissions over 2 days after tillage on the Sodosol, approximately three and four times more CH4 was absorbed over the sampling periods by the NT treatment than the tillage treatment in the Vertosol and Sodosol, respectively. There were no significant impacts on cumulative N2O fluxes due to tillage, with 111 µg N m-2 and 100 µg N m-2 measured from the Vertosol and 61 N m-2 and 56 µg N m-2 measured from the Sodosol, from tillage and NT plots, respectively. The N2O fluxes were low relative to higher input cropping systems, and emissions from both the tillage and NT treatments may have been limited by soil mineral N availability. An increased risk of runoff, erosion and nutrient loss from Sodosols and Dermosols after tillage for weed control in cropping systems typical of the NGR are trade-offs that need consideration in tillage decisions. However, the low GHG emissions measured, despite intense rainfall, suggests that tillage practices in these farm systems have a low global warming potential.

Agronomic impacts

Weed populations on all the sites were significantly decreased 3 months after one-time tillage in 2012 and a trend toward decreased weed density at two sites established in 2013 (Table 2). Twelve months after tillage, weed populations were significantly lower on the black Vertosol at Biloela and the grey Dermosol at Moonie. On the brown Sodosol at Condamine, there was an increase in weed density, in particular African turnip weed (Sysibrium thellungii). Twenty-four and 36 months’ post tillage, there were indications of lower weed populations in TILLAGE as compared to NT but results were not significant. Most studies suggest a positive impact of tillage on reducing weed density. However, tillage has the potential to move buried weed seed to the surface soil, thus providing a more favourable environment for germination by breaking seed dormancy.

The first year after tillage operation generally provided higher productivity at all the sites compared to NT, however these results were not significant. On average, one-time tillage resulted in 0.1 t ha-1 higher yield as compared to NT. The Brown Sodosol at Condamine recorded a marginally significant increase in chickpea yield (1.07 – 1.16 t ha-1) after a single chisel treatment (P = 0.08). In the second year of tillage operation, slight positive trends were observed on the Black Vertosol at Biloela, Grey Dermosol at Moonie and the Black Vertosol at Warwick. The Brown Sodosol at Condamine recorded a decrease in yield when compared to NT, likely resulting from a significant increase in the weed population. 24 and 36 months after the tillage operation, no significant differences were observed between NT and tillage treatments. It appears that reduced weed population in the tillage treatments resulted in improved grain yield, as also observed elsewhere. Net return with one-time tillage was generally positive at most sites ($10-$35 ha-1) except from Vertosol at Biloela (-$3 ha-1), Jimbour (-$17 ha-1) and Moree (-$5 ha-1). However, overall total net return over the 4 years was positive for all sites. Most studies conducted in North America (USA and Canada) and Europe suggests that introducing occasional tillage in continuous NT systems could improve productivity and profitability in the short term. However in the long-term, the impact is negligible or even negative.

Table 1. Site description and tillage timing, frequency and implements used in a single factor randomised block design

Site

Soil type

NT history

Tillage frequency

Tillage implement

Tillage

timing

Crops

2012

2013

2014

2015

Biloela A

Vertosol

18

1,2

Chisel

29 Mar, 20 Apr 2012, 28 Jan, 10 Feb 2013

Wheat

Chickpea

Sorghum
Wheat

Wheat

Condamine

Sodosol

19

1,2

Chisel

6 Mar, 18 Apr 2012

Chickpea

Wheat

Wheat

Wheat

Wee Waa

Vertosol

16

1

Chisel, prickle chain

26 Mar 2012

Chickpea

   

Moonie A

Dermosol

7

1

Chisel, Disc

3 Mar 2012

Barley

Chickpea

Chickpea

 

Warwick

Vertosol

43

1

Chisel

3 Mar 2012

Wheat

Wheat

Wheat

Wheat

Biloela B

Vertosol

18

1,2,3

Chisel

Dec 2012, Jan, Feb 2013

 

Chickpea

Sorghum
Wheat

 

Jimbour

Vertosol

9

1,2,3

Chisel, Disc

4 Dec 2012, 23 Jan, 20 Mar 2013

 

Wheat

Chickpea

 

Moree

Vertosol

5

1

Kelly chain, chisel

12 Mar 13, 5 Apr 2013

 

Wheat

  

Felton A

Vertosol

5

1

Disc

12 Aug 2013

 

Sorghum

  

Emerald

Vertosol

7

1

Narrow chisel, offset disc

29 May 2013

 

Sorghum

  

Yelarbon

Vertosol

5

1

Tyne, offset disc

29 May 2013

 

Sorghum

  

Felton B

Vertosol

9

1

Scarifier

20 May 2015

  

Linseed
Mung beans

 

Billa Billa

Sodosol

15*

1

Cultivator, Kelly Prickle Chain

31 May 2015

 

Fallow

Sesame

 

Moonie B

Dermosol

9*

1

Cultivator, Kelly Prickle Chain

4 Jun 2015

 

Mung beans

Wheat

 

*The Billa Billa and Moonie B sites were strategically cultivated to shallow depths (≤ 150 mm) for weed control or pupae busting after cotton cropping once or twice, respectively, in the four years prior to the experiment

Table 2. Short- and long-term impacts of one-time chisel tillage in an otherwise continuous no-till system on agronomic and  soil health indicators in 0-0.1 m soil layer
 

Biloela A
(Vertosol)

Condamine
(Sodosol)

Moonie A (Dermosol)

Warwick
(Vertosol)

Wee Waa (Vertosol)

Moree (Vertosol)

Jimbour (Vertosol)

 

3m

12m

24m

36m

3m

12m

24m

36m

3m

12m

24m

3m

12m

24m

36m

3m

3m

12m

3m

12m

BD

-

-

~

 

-

-

 

-

+

~

-

-

+

~

-

-

~

-

~

SW

-

+

+

~

-

+

-

~

-

+

+

+

-

-

-

-

~

-

~

TOC

-

-

-

~

-

-

-

~

-

-

-

-

-

+

+

-

-

~

-

~

POC

~

~

 

~

-

~

 

~

-

~

~

+

~

 

~

~

~

~

~

P

-

+

+/-

-

-

-

-

-

-

-

-

-

-

~

-

-

~

-

~

TMA

+

-

~

 

-

+

~/+

 

-

-

-

-

-

-

 

~

+

~

-

~

MBC

~

~

~

 

~

+

~

 

~

+

~

~

~

~

 

~

+

~

+

~

Weeds

-

 

-

 

+

-

+

+

-

 

+

-

+

-

Grain yield (t/ha)

+

+

~

~

-

~

 

+

+

-

+

+

+

~

+

~

+

~

Net return ($)

-

+

~

~

+

+

-

 

+

+

-

+

+

+

~

+

-

 

-

-

↓ or ↑ indicate a significant decrease or increase, respectively at p<0.05; NS, non-significant  (+) NS increase; (-) NS decrease; (~) no result; 3m, 3 months after tillage; 12m, 12 months after tillage; 24m, 24 months after tillage; TMA, total microbial activity (µg/mL FDA/g soil/hour); MBC, microbial biomass (μg C g-1 soil); BD, bulk density (g/cc); SW, soil water (mm); TOC, total organic carbon (t/ha); POC, particulate organic carbon (t/ha); P, available P (Colwell-P) mg/kg.

Table 3. Impacts of tillage frequency on soil health quality parameters indicators in 0-0.1 m soil layer
  

Biloela A1

Condamine1

Biloela B1

Jimbour1

Jimbour2

 

Months

3122436312243631236312312

SW

1

-

-

+

 

-

-

-

 

+

+

 

-

+

+

+

 

2

-

-

+

 

-

-

-

 

+

-

 

-

+

+

+

 

3

        

+

-

 

+

+

+

+

SOC

1

-

~

-

~

-

~

-

~

+

-

 

-

-

+

+

 

2

-

-

-

~

-

+

-

-

+

-

 

~

+

~

+

 

3

        

+

-

 

~

+

+

+

P

1

-

+

+

-

-

-

-

~

~

-

 

-

+

-

 

2

-

-

+

+

-

-

-

-

+

-

 

~

+

-

 

3

        

~

+

 

-

+

-

↓ or ↑ indicate significant decrease or increase, respectively at p<0.05; NS, non-significant  (+) NS increase; (-) NS decrease; (~) no result; 3m, 3 months after tillage; 12m, 12 months after tillage; 24m, 24 months after tillage; BD, bulk density (g/cc); SW, soil water (mm); SOC, soil organic carbon (t/ha); P, available (Colwell-P) mg/kg. 1chisel type tillage, 2disc type tillage.

Table 4. Changes in weed populations (number/m2) with increasing tillage operation frequency. Values within a row with different superscript letters indicate significant difference  at P<0.05 from NT at each site (n=4)

Site

Year

No-till

Tillage frequency

Once

Twice

Thrice

Biloela A1

2012

10.5a

1.3b

4.3c

 

Biloela A1

2013

3.0 a

0.3 b

0.2 b

 

Biloela A1

2014

14.5 a

19.4a

25.5 a

 

Condamine1

2012

14.5 a

2.3c

6.5 b

 

Condamine1

2013

4.5 a

23.4 b

15.6 a

 

Condamine1

2014

0.75 a

1.6a

0.9 a

 

Jimbour1

2013

2.3 a

0.6 a

0.5 a

0.8a

Jimbour1

2014

1.1 a

0.3 a

1.0 a

0.9 a

Jimbour2

2013

2.3 a

2.0 a

0.1 a

0.8 a

Biloela B1

2013

0.0 a

0.0 a

0.0 a

0.0 a

Biloela B1

2014

4.0 a

4.7 a

4.8 a

9.2 a

1chisel type tillage, 2disc type tillage
Table 5. Changes in grain yield (t/ha) with increasing tillage operation frequency. Values within a row with different superscript letters indicate significant difference at P<0.05 from NT at each site

Crop

Site

Year

No-till

Tillage frequency

Once

Twice

Thrice

Wheat

Biloela A1

2012

2.66 a

2.75 a

2.72 a

 
 

Biloela A1

2012

2.66 a

2.75 a

2.72 a

 
 

Biloela A1

2014

1.49 a

1.55 a

1.42 a

 
 

Biloela B1

2014

1.11 a

1.40 b

1.46 b

1.64 b

 

Condamine1

2013

1.51 a

1.48 a

1.39 a

 
 

Condamine1

2014

0.73 a

0.71 a

0.71 a

 
 

Jimbour1

2013

2.92 a

2.67 a

2.81 a

3.11
 

Jimbour2

2013

2.92 a

2.93 a

3.00 a

3.03 a

Chickpea

Biloela A1

2013

2.02 a

2.13 a

2.16 a

 
 

Biloela B1

2013

1.88 a

2.03 a

2.14 a

2.24 b

 

Condamine1

2012

1.05 a

1.14

1.16 b

 
 

Jimbour1

2014

1.16 a

1.10 a

1.13 a

1.16 a

 

Jimbour2

2014

1.16 a

1.14 a

1.07 a

1.13 a

Sorghum

Biloela A1

2014

2.48 a

2.43 a

2.53 a

 
 

Biloela B1

2014

2.44 a

2.51 a

2.44 a

2.36 a

1chisel type tillage, 2disc type tillage.

Table 6. Impacts of tillage with different strategic tillage implements on soil health quality parameters indicators in 0-0.1 m soil layer
  

Moonie

Wee Waa

Jimbour

Emerald

Yelarbon

  31224312243631233

SW

Chisel

~

+

+

-

 

-

 

+

+

~

~

 

Disc

~

+

+

-

 

+

 

-

+

+

+

SOC

Chisel

-

-

-

~

  

+

-

-

+

~

 

Disc

-

+

-

+

  

-

+

+

+

+

P

Chisel

-

-

-

-

 

+

-

-

+

+

 

Disc

-

-

-

+

 

~

+

-

+

-

~

TMA

Chisel

-

+

-

-

-

  

-

   
 

Disc

~

~

-

-

-

  

~

   

↓ or ↑ indicate significant decrease or increase, respectively at p<0.05; NS, non-significant  (+) NS increase; (-) NS decrease; (~) no result; 3m, 3 months after tillage; 12m, 12 months after tillage; 24m, 24 months after tillage; SW, soil water (mm); SOC, soil organic carbon (t/ha); P, available (Colwell-P) mg/kg.

Table 7. Changes in weed populations (number/m2) with different tillage implements (Values within a row with different superscript letters indicate significant difference at P<0.05 from NT at each site (n=4))

Crop

Site

Year

No-till

Tillage implements

Chisel

Disc

Kelly chain

Barely

Moonie

2012

9.2 a

1.0 b

1.2 b

 

Chickpea

Moonie

2013

0.75 a

0.13a

0.3 a

 

Chickpea

Moonie

2014

0.5 a

0.6 a

1.5 a

 

Wheat

Moree

2013

2.4 a

0.9 a

 

0.9 a

Wheat

Jimbour

2013

2.3 a

0.6 a

2.0 a

 

Chickpea

Jimbour

2014

1.1 a

0.3 a

0.3 a

 

Sorghum

Yelarbon

2013

0.4 a

0.0 a

0.0 a

 
Table 8. Changes in grain yield (t/ha) with different tillage implements  (Values within a row with different superscript letters indicate significant difference at P<0.05 from NT at each site)

Crop

Site

Year

No-till

Tillage implements

Chisel

Disc

Kelly Chain

Wheat

Jimbour

2013

2.92 a

2.88 a

2.89 a

 
 

Moree

2013

3.51 a

3.56 a

 

3.57 a

Chickpea

Moonie

2013

0.66 a

0.71 a

0.64 a

 
 

Moonie

2014

3.60 a

3.31 a

3.34 a

 
 

Jimbour

2014

1.16 a

1.12 a

1.17 a

 
 

Wee Waa

2012

1.45 a

1.54 a

 

1.47 a

Sorghum

Emerald

2013

4.80 a

4.47 a

5.41 a

 
 

Yelarbon

2013

2.09 a

2.01 a

2.05 a

 

Barley

Moonie

2012

2.27 a

2.42 a

2.37 a

 
Table 9. Impacts of tillage operation at increasing number of days prior to sowing of crops soil health quality parameters indicators in 0-0.1 m soil layer
 

Tillage time

Jimboura

Jimbourb

Moreea

Moreec

Biloelaa

 312312312312312

SW

T1

-

+

+

+

-

+

~

+

+

+

T2

-

+

+

+

+

+

-

+

-

T3

+

+

+

+

    

+

-

OC

T1

-

-

+

+

-

~

+

-

+

-

T2

+

+

~

+

~

-

-

~

+

-

T3

+

+

+

+

    

-

-

P

T1

-

+

-

-

-

-

+

~

-

T2

-

+

~

+

+

+

+

-

T3

~

+

-

    

+

+

Table 10. Changes in weed populations (number/m2) with tillage operation at increasing number of days prior to sowing of crops. Values within a row with different superscript letters indicate significant difference at P<0.05 from NT at each site (n=4)(↑) significant increase; (↓) significant decrease; (+) increase; ( -) decrease; (~) no change; 3m, 3 months after tillage; 12m, 12 months after tillage; 24m, 24 months after tillage; TMA, total microbial activity (µg/mL FDA/g soil/hour); MCB, microbial biomass (μg C g-1 soil); BD, bulk density (g/cc); SW, soil water (mm); OC, organic carbon (t/ha); POC, particulate organic carbon (t/ha); P, available (Colwell-P) mg/kg. a denotes Chisel tillage, b denotes disc tillage, c denotes Kelly disc chain tillage; T1, tillage operation 7 months before sowing; T2, tillage operation 5 months before sowing, T3, tillage operation 3 months before sowing

Crop

Site

Year

No-till

Strategic tillage operation (days prior to sowing)

<14

14-40

40-90

90-120

120-200

>200

Wheat

Biloela B1

2014

4.0 a

  

9.2 a

4.8 a

4.7 a

 
 

Jimbour1

2013

2.3 a

   

1.0 a

1.0 a

0.6 a

 

Jimbour2

2013

2.3 a

   

0.9 a

1.1 a

2.0 a

 

Moree2

2013

2.4 a

0.9 a

0.8 a

    
 

Moree3

2013

2.4 a

0.9 a

0.8 a

    

Chickpea

Biloela B1

2013

0.1 a

  

0.0 a

0.0 a

0.0 a

 
 

Jimbour1

2014

1.1 a

   

0.1 a

1.0 a

0.3 a

 

Jimbour2

2014

1.1 a

   

0.4 a

0.8 a

0.3 a

1chisel type tillage, 2disc type tillage, 3Kelly chain tillage.

Table 11. Changes in grain yield (t/ha) with tillage operation at increasing number of days prior to sowing of crops. Values within a row with different superscript letters indicate significant difference at P<0.05 from NT at each site (n=4)

Crop

Site

Year

No-till

Strategic tillage operation (days prior to sowing)

<14

14-40

40-90

90-120

120-200

>200

Wheat

Biloela B1

2014

1.11 a

  

1.29 b

1.35 b

1.35 b

 
 

Jimbour1

2013

2.92 a

   

3.04a

2.92 a

2.67 a

 

Jimbour2

2013

2.92 a

   

2.91 a

2.82 a

2.93 a

 

Moree1

2013

3.51 a

3.54 a

3.58 a

    
 

Moree3

2013

3.51 a

3.63 a

3.51 a

    
 

Biloela B1

2013

1.88 a

  

1.88 a

1.98 a

2.03 a

 
 

Jimbour1

2014

1.16 a

   

1.20 a

1.14 a

1.10 a

          

Chickpea

Jimbour2

2014

1.16 a

   

1.09 a

1.12 a

1.14 a

Sorghum

Biloela B1

2013

1.11 a

  

2.33 a

2.40 a

2.51 a

 

1chisel type tillage, 2disc type tillage, 3Kelly chain tillage

Line chart showing changes in the soil water content following disc tillage to a depth of 0-0.1 m in a Black Vertosol at Felton, with rainfall events indicated.Figure 1. Changes in the soil water content following disc tillage to a depth of 0-0.1 m in a Black Vertosol at Felton, with rainfall events indicated.

Bubble chart showing suspended sediment (t/ha) and total nitrogen (kg/ha) in runoff after strategic tillage (ST) and no-tillage (NT) on a Vertosol, Sodosol and Dermosol. Bubble sizes and labels indicate the total runoff (mm) generated over 80 minutes of rainfall.

Figure 2. Suspended sediment (t/ha) and total nitrogen (kg/ha) in runoff after strategic tillage (ST) and no-tillage (NT) on a Vertosol, Sodosol and Dermosol. Bubble sizes and labels indicate the total runoff (mm) generated over 80 minutes of rainfall.

Figure 3. Infiltration rates (mm h-1) measured in the final stages of rainfall simulation events on strategic tillage (ST) and no-tillage (NT) plots on the Vertosol at Felton B, the Sodosol at Billa Billa and the Dermosol at Moonie B.  Letters that differ denote means that are significantly different (P<0.05).Figure 3. Infiltration rates (mm h-1) measured in the final stages of rainfall simulation events on strategic tillage (ST) and no-tillage (NT) plots on the Vertosol at Felton B, the Sodosol at Billa Billa and the Dermosol at Moonie B.  Letters that differ denote means that are significantly different (P<0.05).

Bar chart showing event-mean soluble P concentrations in runoff (mg/L) after strategic tillage (ST) and no-tillage (NT) on a Vertosol, Sodosol and Dermosol. Letters that differ denote means that are significantly different (P<0.05).

Figure 4. Event-mean soluble P concentrations in runoff (mg/L) after strategic tillage (ST) and no-tillage (NT) on a Vertosol, Sodosol and Dermosol. Letters that differ denote means that are significantly different (P<0.05).

Line graph showing probability of rainfall exceedance during 1960-2014 at Dalby, Moree, and Biloela.

Figure 5. Probability of rainfall exceedance during 1960-2014 at Dalby, Moree, and Biloela.

Conclusions and recommendations

Generally, a trend was observed for negative effects of tillage on soil water and TOC stocks in the short-term. However, these effects were often not significant, even for short term (3 months) and were minimal in the intermediate period (12 months after tillage). The latter indicates a relatively quick recovery of soil water in most soils, with the exception of high clay soils. Provided tillage is shallow, as in the present study and not on-going, the recovery of most measured parameters is relatively rapid under tillage and is unlikely to undo the long term beneficial changes associated with NT systems. In poorly structured soils, greater impacts and longer recovery periods can be expected. The major benefit of occasional tillage is the control of herbicide-resistant and hard-to-kill weeds except at some sites (e.g. Sodosol at Condamine).

Our results indicate that tillage has a place in conservation farming, provided that appropriate consideration and implementation is achieved. Single tillage events appear insufficient to significantly alter the long term benefits of NT in the vast majority of cases. In some circumstances tillage will assist in overcoming certain issues associated with NT, thus improving the productivity of fields. Examples include deep banding of immobile nutrients like P and K to address a subsoil nutrient depletion, or using tillage during a fallow to control hard-to-kill weeds. However, the implementation of tillage requires many considerations for its success. This includes the knowledge on (i) the weed history and potential seed bank so that emergence of other weed species can be prevented, (ii) soil water status and the time required for its replenishment prior to planting, (iii) nature of soil types relative to tillage e.g. risks of smearing (reducing infiltration), compaction, and aggregate breakdown and (iv) subsoil constraints, especially salinity and sodicity where use of any tillage implements that invert soil may bring salts nearer the soil surface and may cause yield loss.

If tillage is deemed necessary, the most important question to address is the best timing, frequency and implement for the tillage operation. Timing of tillage has major implications for the success or failure of tillage operations. Limited research on the tillage timing in continuous NT suggests that farmers should analyse long-term historical rainfall data and risk-management tools that have been developed. Tillage too close to sowing and/or immediately after the harvest of the previous crop should be avoided. Use of inversion tillage with implements such as mouldboard plough is rare in Queensland and northern New South Wales. Most growers use non-inversion shallow tillage based on tyne and disc implements that do not invert the soil and differences between these tillage implements and frequencies of tillage passes were in general non-significant.

It is clear that different tillage systems have their own advantages and disadvantages. There are a number of interacting factors involved in comparing the performance of tillage systems. The challenge for strategic tillage (ST) operation in the NT systems is to maintain economic levels of production and at the same time reduce environmental damage such as soil erosion and water pollution. Future research needs to focus on how and when ST might fit into cropping sequence to obtain maximum benefits and minimise the potential negative consequences.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, the author would like to thank them for their continued support. We are indebted to our collaborative growers, Nev and Ron Boland, Darren and Tanya Jensen, Rod and Sam Hamilton, Paul and Samantha Fulbohm, Brian and Val Gregg, Geoff Manchee, Warakirri Farming Co., Ken and John Stump for providing field sites, managing the trials and providing their generous support. Thanks are also due to Paul McNaulty, Paul Caster and Stuart Thorn for their support. The authors would like to thank the DSITI Ecoscience precinct soil laboratory for their skilful soil analysis, and Suzette Argent, Don Browne, Ram Dalal, Maria Harris, Tony King, Phil Moody, Clement Ng, Rod Obels, and Micheal Widderick for their substantial contributions to the design, setup, acquisition, analysis, or interpretation of data and continuing support

Contact details

Yash Dang
The University of Queensland
Mb: 0427 602 099
Email: y.dang@uq.edu.au