Strategic Tillage Research Articles

Effects of strategic tillage on short-term erosion, nutrient loss in runoff and greenhouse gas emissions

Occasional strategic tillage (ST) of long-term no-tillage (NT) soil to help control weeds may increase the risk of water, erosion and nutrient losses in runoff and of greenhouse gas (GHG) emissions compared with NT soil. The present study examined the short-term effect of ST on runoff and GHG emissions in NT soils under controlled-traffic farming regimes. A rainfall simulator was used to generate runoff from heavy rainfall (70mmh–1) on small plots of NT and ST on a Vertosol, Dermosol and Sodosol. Nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) fluxes from the Vertosol and Sodosol were measured before and after the rain using passive chambers. On the Sodosol and Dermosol there was 30% and 70% more runoff, respectively, from ST plots than from NT plots, however, volumes were similar between tillage treatments on the Vertosol. Erosion was highest after ST on the Sodosol (8.3tha–1 suspended sediment) and there were no treatment differences on the other soils. Total nitrogen (N) loads in runoff followed a similar pattern, with 10.2kgha–1 in runoff from the ST treatment on the Sodosol. Total phosphorus loads were higher after ST than NT on both the Sodosol (3.1 and 0.9kgha–1, respectively) and the Dermosol (1.0 and 0.3kgha–1, respectively). Dissolved nutrient forms comprised less than 13% of total losses. Nitrous oxide emissions were low from both NT and ST in these low-input systems. However, ST decreased CH4 absorption from both soils and almost doubled CO2 emissions from the Sodosol. Strategic tillage may increase the susceptibility of Sodosols and Dermosols to water, sediment and nutrient losses in runoff after heavy rainfall. The trade-offs between weed control, erosion and GHG emissions should be considered as part of any tillage strategy.

Strategic tillage increased the relative abundance of Acidobacteria but did not impact on overall soil microbial properties of a 19-year no-till Solonetz

Continuous no-till (NT) farming is widely practiced in Australia, but it is prone to weed infestation. Strategic tillage (ST) can be used to effectively control weeds; however, it is unclear whether ST influences soil microbial properties. We investigated whether one- or two-time tillage events using a chisel plough influence the soil microbial properties of an acidic Solonetz with 19-year NT management. Soil samples were collected from 0–10 and 10–20 cm soil depths, 1 year post-ST after a chickpea crop. Microbial biomass C (MBC) and N (MBN), community-level physiological profiling (CLPP, MicroResp™) and fluorescein diacetate as an indicator of total microbial activity (TMA) were determined in soil. The composition of soil microbial communities was profiled using terminal reaction fragment length polymorphism (T-RFLP) and 16S rRNA sequencing. Detection and DNA-based quantitation of ChitinaseA, nifH, amoA, narG, nirK and nosZ genes were used to assess ST effects on soil C and N cycling. Our results show that one- and two-time chisel did not change soil MBC/MBN, TMA or CLPP. Likewise, ST did not change the composition of soil microbial communities and the abundance of genes encoding enzymes involved in key steps of C and N reactions at either soil depth. However, one-time chisel increased relative abundance of Acidobacteria RB41 and Acidobacteria iii1-15, and two-time chisel slightly increased the average C utilisation, both at 10–20 cm soil depth. This suggests that even after a cropping season of chickpea, ST effects on soil microbial properties of the NT Solonetz were negligible. One- and two-time chisel could potentially address the issues associated with long-term NT without impacting overall soil microbial properties.

Short-term impact of an occasional tillage on microbial communities in a Vertosol after 43 years of no-tillage or conventional tillage

Occasional strategic tillage (ST) has been suggested as a possible solution to manage herbicide-resistant weeds and control crop diseases in Australia's northern grain-growing regions. We evaluated the impact of ST on microbial communities as indicators of soil quality for two distinct tillage systems that have been applied to a Vertosol for 43 years (no-tillage – NT or conventional tillage – CT) and two stubble management practices (retention – SR or burning – SB). Soil samples were collected 15 weeks after ST and analysed for total enzymatic activity (fluorescein diacetate assay), metabolic diversity (Ecoplates Biolog®) and bacterial community structure (terminal restriction fragment length polymorphism). There was no significant effect of ST on the measured biological attributes. However, total enzymatic activity for treatments under CTSR and CTSR-ST were significantly higher compared with NTSR-ST (+0.8 fluorescein μg ml−1 g−1 soil h−1, P < 0.01). Differences may be attributed to a significant increase in bulk density for CTSR treatment (P < 0.05) and an increment in bulk density on CTSR-ST plots. The lack of changes may be attributed to a high resistance and/or resilience of soil microbial communities after 15 weeks of tillage. More studies on the long-term effect of ST are required to assess the impact on soil biological properties.

Strategic tillage on a Grey Vertosol after fifteen years of no-till management had no short-term impact on soil properties and agronomic productivity

Over half of the arable land in the northern grains region of Australia is managed using no-till (NT), a farming method which has improved crop yields and soil quality while reducing the input and labour costs. However, concerns have arisen among farmers over the control of weeds in continuous NT systems. An occasional targeted tillage operation (termed strategic tillage — ST) has been proposed as a management tool to reduce problem weed populations but may adversely influence soil properties and those of associated microbial communities. To assess the potential impacts of a ST operation on soil properties, a Grey Vertosol with fifteen years of NT in Northern New South Wales, Australia was tilled using either a chisel cultivator or disc chain on March 15th 2013 or on April 5th 2013. We hypothesised that ST using these minimal or low soil inversion implements at either timing would not adversely influence soil properties in the short-term (4–7weeks). The measured soil properties were soil volumetric moisture content (VMC), pH, bulk density (BD), electrical conductivity (EC), available phosphorus (P), soil organic carbon (SOC), microbial biomass carbon (MBC), metabolic activity (MA), genetic structures of bacterial communities and wheat yield (tha−1). We found that ST with either a chisel cultivator or a disc chain has great potential to assist in weed management as it did not statistically influence crop productivity or the physical, chemical and biological properties of the soil, regardless of the tillage timing.

High-residue cover crops alone or with strategic tillage to manage glyphosate-resistant Palmer amaranth (Amaranthus palmeri) in southeastern cotton (Gossypium hirsutum)

Glyphosate-resistant (GR) Palmer amaranth (Amaranthus palmeri S. Wats) is redefining row crop weed management in the southeast United States due to its widespread distribution, high competitive ability, copious seed production, and resilience against standard weed management programs. Herbicides alone are failing to provide adequate control of GR Palmer amaranth; thus, use of conventional tillage is increasing in the Southeast in order to control GR Palmer amaranth. Cultural practices consistent with maintenance of conservation tillage were evaluated to determine if they could suppress weeds in cotton (Gossypium hirsutum L.). An on-farm research and demonstration project was initiated in the fall of 2009 in Alabama, Georgia, South Carolina, and Tennessee to address well-founded concerns that conservation tillage systems were at risk because of GR Palmer amaranth. The research continued in certain states for two additional years. Cultural practices contrasted in the conservation tillage system were a no-till planted high-residue cover crop, one-time fall inversion tillage followed by the planting of a high-residue cover crop, and winter fallow only without a cover crop. Cover crop biomass yields varied from 570 to 6,790 kg ha−1 (509 to 6,063 lb ac−1) depending on location, type of cover crop, planting date, and environment. Fall inversion tillage increased cover crop biomass at all locations, likely due to preparation of a favorable seed bed for seedling establishment or alleviation of soil compaction or both. One-time fall inversion tillage reduced the number of GR Palmer amaranth escapes compared with the other treatments. Where GR Palmer amaranth densities were relatively low (approximately 1,000 plants ha−1 [405 plants ac−1] or fewer), there were few differences in the number of GR Palmer amaranth escapes among treatments. Where GR Palmer amaranth densities were relatively high (18,000 plants ha−1 [7,284 plants ac−1] or greater), winter fallow systems had higher Palmer amaranth densities escaping weed management programs compared to either cover crop system. The number of Palmer amaranth escapes declined exponentially as a function of cover crop biomass regardless of tillage. For sites with two years of data, no year by treatment interaction was detected, indicating that relative GR Palmer amaranth escape densities were sustained in each treatment for two seasons. Trends in cotton yields were the opposite of those for Palmer amaranth escapes. High-residue cover crops tended to suppress Palmer amaranth and increase cotton lint yields. However, no cultural management system consistently netted greater returns than other systems across locations and years.

One-time strategic tillage does not cause major impacts on soil microbial properties in a no-till Calcisol

Strategic tillage (or occasional tillage) has been touted as a potential solution for the severe weed infestations of long-term no-till (NT). Nevertheless, there is little information on the influence of strategic tillage on microbial properties of Australian NT soils. In the present study, we assessed the influence of strategic tillage on the microbial properties of a seven years’ NT Calcisol in Moonie, Queensland, Australia. We tested the hypothesis that the application of one-time strategic tillage with chisel or offset disc does not cause major impacts on soil biological health in a NT system. Strategic tillage was applied once and soil samples were collected 13 months after tillage from the depths 0–10 and 10–20cm. The measured biological indicators included soil microbial biomass carbon, catabolic activity (MicroResp™ assay) and total microbial activity (fluorescein diacetate method). The structure of bacterial communities was profiled by quantitative polymerase chain reaction (qPCR) and terminal reaction fragment length polymorphism (T-RFLP). Principal components analyses based on qPCR and T-RFLP data did not show tillage effects on soil bacterial communities. However, relative to the NT, chisel tillage led to significant increases in microbial biomass carbon (+34.4%), abundances of Alphaproteobacteria (+74.6%), Bacteroidetes (+113.7%) and Firmicutes (+36.5%), and the utilisation of D+ cellubiose (+178.4%) as well as mannitol (+167.2%) at 0–10cm depth. In contrast, the influence of offset disc tillage was restricted to an increased abundance of Alphaproteobacteria (+64.6%) at 0–10cm depth. Our study suggests that, overall, one-time strategic tillage using either chisel or offset disc had a minor positive influence on soil biological attributes of the NT Calcisol 13 months after tillage.

Occasional tillage has no effect on soil microbial biomass, activity and composition in Vertisols under long-term no-till

Heavy rains in recent years have triggered an increase in herbicide-resistant weeds and crop diseases in long-term no-till (NT) farming systems in Queensland, Australia. As a possible solution, occasional or strategic tillage (ST) has been applied during summer fallow in two farms located near Jimbour and Biloela, Queensland, Australia. We investigated the impact of different frequencies (one to three passes) and timings (December, January and March) of tillage imposition on microbial indicators of soil health. Tillage implements included chisel plow sweeps at the Biloela site and narrow chisel point and offset disc at the Jimbour site. Seven soil samples were collected from each plot in April 2013 at 17, 10 and 2 weeks post-ST from 0 to 0.1 and 0.1 to 0.2 m depths and composited separately for each soil depth. Samples were analysed for microbial biomass C, enzyme activity, community-level physiological profiling (CLPP) via microrespirometry method and bacterial genetic fingerprinting. Overall, there were no significant differences for any of these parameters between NT and ST at both sites. However, irrespective of tillage treatments, significant differences between soil depths were found for enzyme activity (Biloela), substrate utilisation (Jimbour and Biloela) and bacterial genetic fingerprinting (Jimbour). There were no major effects of ST on the microbial indicators used either under different timings, frequencies or type of tillage implement. Therefore, ST with chisel plow sweeps, narrow chisel point and offset disc may be undertaken with minimal impact on soil microbial communities to combat problems associated with long-term NT Vertisols, such as weed and soil-borne disease outbreak in Queensland, Australia.

Changes in the soil quality attributes of continuous no-till farming systems following a strategic tillage

The adoption of no-till farming systems has greatly reduced energy and machinery inputs while significantly improving soil health and productivity. However, the control of crop weeds and diseases in no-till (NT) systems has become increasingly difficult for landholders in Australia’s northern grains regions, with occasional strategic tillage (ST) being considered as a potential management option. This study investigated the effects of occasional ST on physical, chemical and biological soil properties, productivity, and weed control on five long-term (7–44 years) NT-managed soils. The study area extended from Biloela (Vertosol, 666 mm annual rainfall), Condamine (Sodosol, 624 mm annual rainfall), Moonie (Dermosol, 636 mm annual rainfall) and Warwick (Vertosol, 675 mm annual rainfall) in Queensland to Wee Waa (Vertosol, 582 mm annual rainfall) in New South Wales. Tillage treatments included chisel, offset disc and prickle–disc chain with various timings and frequencies. Soil samples (0–0.3 m) obtained 3 and 12 months after occasional ST were analysed for total and particulate organic carbon (TOC, POC), available phosphorus (P), bulk density, soil water, and microbial enzymatic activity. In-crop weed density was also recorded. One-time tillage, with chisel tines, offset disc or chain harrows, in long-term NT helped to control winter weeds in the first year, with variable results in the second year. Grain yield overall showed no significant impact in either year, except on the Brown Sodosol (P = 0.08) in the first year. The initial impacts of strategic tillage on soil water were largely restricted to the 0–0.1 m depth range, with slight, non-significant decreases occurring. Available P, TOC, POC and total microbial enzymatic activity were not significantly impacted by either cultivation frequency or implement type. The use of an occasional ST for the purpose of weed control could be utilised as a viable management option for NT systems in the region without impacting on long-term productivity.

Sense and nonsense in conservation agriculture: Principles, pragmatism and productivity in Australian mixed farming systems

Adoption of conservation agriculture (CA) principles in Australia increased rapidly during the 1990s and it now boasts the highest adoption rates worldwide. These principles of (1) diverse rotations (2) reduced (or no-) till systems and (3) the maintenance of surface cover make good sense in extensive, mechanised, rain-fed cropping systems on erosion-prone, structurally-unstable soils. Indeed reduced fuel and labour costs, soil conservation and moisture retention are the most commonly stated reasons for adoption of CA principles by farmers in Australia. Yet even in Australia, while broadly applicable, the adaptation and application of CA principles within specific farming systems remains pragmatic due to the diverse biophysical and socio-economic factors encountered. Most “no-till” adopters continue some strategic tillage (∼30% cropped area) for a range of sound agronomic reasons, intensive cereal systems dominate, and partial removal of crop residues as hay or by grazing livestock is commonplace within the largely mixed-farming systems. Although this challenges the notion of “ideal” CA principles (zero-till with no soil disturbance, full stubble retention and >3 species in rotations) this high degree of flexibility in CA principles as practiced in southern Australian mixed farming systems makes sense to optimize both economic and environmental outcomes. In addition, some proposed ecosystem service benefits of CA such as soil carbon sequestration and energy efficiency have been recently questioned. Though the socio-economic factors of small-holder farming systems in Africa and south Asia are more diverse and clearly different to Australian farms, some of the biophysical challenges and economic realities are shared (infertile soils, variable and extreme climates, relatively low input levels, integrated crop–livestock systems, small profit margins, highly variable income). It is therefore useful to consider from a biophysical standpoint why a pragmatic approach to CA principles has been necessary, even in a relatively high-adopting country like Australia, and why we should expect similarly ‘imperfect’ adoption of CA (if at all) in the diverse smallholder systems of Sub-Saharan Africa and South Asia. We review aspects of CA adoption in Australia in an effort to draw out important lessons as CA principles are adapted elsewhere, including the smallholder farming systems of Sub-Saharan Africa and South Asia.

Managing glyphosate resistance in Australian cotton farming: modelling shows how to delay evolution and maintain long-term population control

Glyphosate resistance is a rapidly developing threat to profitability in Australian cotton farming. Resistance causes an immediate reduction in the effectiveness of in-crop weed control in glyphosate-resistant transgenic cotton and summer fallows. Although strategies for delaying glyphosate resistance and those for managing resistant populations are qualitatively similar, the longer resistance can be delayed, the longer cotton growers will have choice over which tactics to apply and when to apply them. Effective strategies to avoid, delay, and manage resistance are thus of substantial value. We used a model of glyphosate resistance dynamics to perform simulations of resistance evolution in Sonchus oleraceus (common sowthistle) and Echinochloa colona (awnless barnyard grass) under a range of resistance prevention, delaying, and management strategies. From these simulations, we identified several elements that could contribute to effective glyphosate resistance prevention and management strategies. (i) Controlling glyphosate survivors is the most robust approach to delaying or preventing resistance. High-efficacy, high-frequency survivor control almost doubled the useful lifespan of glyphosate from 13 to 25 years even with glyphosate alone used in summer fallows. (ii) Two non-glyphosate tactics in-crop plus two in-summer fallows is the minimum intervention required for long-term delays in resistance evolution. (iii) Pre-emergence herbicides are important, but should be backed up with non-glyphosate knockdowns and strategic tillage; replacing a late-season, pre-emergence herbicide with inter-row tillage was predicted to delay glyphosate resistance by 4 years in awnless barnyard grass. (iv) Weed species’ ecological characteristics, particularly seed bank dynamics, have an impact on the effectiveness of resistance strategies; S. oleraceus, because of its propensity to emerge year-round, was less exposed to selection with glyphosate than E. colona, resulting in an extra 5 years of glyphosate usefulness (18 v. 13 years) even in the most rapid cases of resistance evolution. Delaying tactics are thus available that can provide some or many years of continued glyphosate efficacy. If glyphosate-resistant cotton cropping is to remain profitable in Australian farming systems in the long-term, however, growers must adapt to the probability that they will have to deal with summer weeds that are no longer susceptible to glyphosate. Robust resistance management systems will need to include a diversity of weed control options, used appropriately.