Conventional surface-application of agricultural lime takes many years to increase pH deeper in the soil profile, which is a barrier to increased adoption of liming. We conducted a series of experiments to measure the rate of vertical movement of alkali and identify the factors that determine this movement into the subsurface, to evaluate the feasibility of ameliorating acidic subsurface soil using residual (undissolved) lime (CaCO 3) at Wongan Hills (30.858S, 116.748E) and Merredin (31.488S, 118.218E) and to test whether deep tillage and lime incorporation can significantly speed up the amelioration of subsurface soil acidity at Kalannie (30.428S, 117.298E). Multiple applications of lime to the surface of the soil at higher rates (total 6-8.5 Mg ha-1) significantly increased subsurface soil pH but only in the 0.10-0.20 m depth by 0.049 pH units per year over 10-24 years. A large proportion of the surface-applied lime was stratified in the top few centimetres of the soil and incorporation of this undissolved lime with a rotary hoe to a depth of 0.25 m significantly increased soil pH (by 0.63 units) within a year in the Wongan Hills field experiment. Deep incorporation of 6 Mg ha-1 lime to a depth of 0.45 m through excavation and spading with a small rotary hoe also increased soil pH by more than a unit and decreased Al concentration to below the toxic level within two months in the Kalannie experiment, allowing wheat (Triticum aestivum L.) plants to produce root systems up to 0.59 m deep compared with 0.26 m for the control. Our soil column leaching experiment indicated that surface incorporation of lime in higher rainfall regions can be useful to treat subsurface soil acidity but that the rate of improvement in subsurface pH was slow. Therefore, deeper incorporation of lime using cost-effective strategic deep tillage is likely to be necessary.

In the conservation agricultural systems practised in Australia, cultivation is not commonly utilised for the purpose of weed control. However, occasional use of tillage (strategic tillage) is implemented every few years for soil amelioration, to address constraints such as acidity, water repellence or soil compaction. Depending on the tillage method, the soil amelioration process buries or disturbs the topsoil. The act of amelioration also changes the soil physical and chemical properties and affects crop growth. While these strategic tillage practices are not usually applied for weed control, they are likely to have an impact on weed seedbank burial, which will in turn affect seed dormancy and seedbank depletion. Strategic tillage impacts on seed burial and soil characteristics will also affect weed emergence, plant survival, competitive ability of weeds against the crop and efficiency of soil applied pre‐emergent herbicides. If growers understand the impacts of soil amelioration on weed demography, they can more effectively plan management strategies to apply following the strategic tillage practice. Weed seed burial resulting from a full soil inversion is understood, but for many soil tillage implements, more data is needed on the extent of soil mixing, burial of topsoil and the weed seedbank, physical control of existing weeds and stimulation of emergence following the tillage event. Within the agronomic system, there is no research on optimal timing for a tillage event within the year. There are multiple studies to indicate that strategic tillage can reduce weed density, but in most studies, the weed density increases in subsequent years. This indicates that more research is required on the interaction of amelioration and weed ecology, and optimal weed management strategies following a strategic tillage event to maintain weeds at low densities. However, this review also highlights that, where the impacts of soil amelioration are understood, existing data on weed ecology can be applied to potentially determine impacts of amelioration on weed growth.

Estimates indicate that 30% of land surface globally is affected by soil acidity, influencing agricultural production. Application of lime increases soil pH and improves crop growth. We tested the hypothesis that liming will reduce rigid ryegrass (Lolium rigidum Gaudin) growth by improving the competitive ability of the crop. Experiments at Merredin and Wongan Hills in Western Australia indicated that application of lime in previous years reduced L. rigidum density, biomass, and seed production in wheat (Triticum aestivum L.) crops in 2018. At Merredin, L. rigidum seed production in 2018 was reduced from 9,390 to 2,820 seeds m−2, and wheat tiller number and yield was increased, following lime application of 0 to 6,000 kg ha−1 in 2016. At Wongan Hills, lime application of 4,000 kg ha−1 in 1994 reduced seed production in the 2018 wheat crop from 4,708 to 1,610 seeds m−2, and application of 3,000 kg ha−1 of lime in 2014 reduced seed production from 3,959 to 921 seeds m−2 in 2018. Again, lime increased wheat tiller number, but not yield. A screen house experiment (in controlled conditions) indicated that lime application increased the initial growth of both L. rigidum and wheat seedlings. This supports the conclusion that reduced L. rigidum growth and seed production in the field resulted from increased competitive ability of the crop, rather than any direct and detrimental impact of lime on L. rigidum growth. Incorporation of lime reduced initial emergence of L. rigidum in controlled conditions, with L. rigidum seeds at a uniform depth, and in the field experiments in situations of high weed density, with seeds buried by the incorporation process. Nationally, the revenue loss from residual L. rigidum in crop is A$93 million per year. The current research confirms that application of lime will increase the competitive ability of crops growing in regions with acidic soils.

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Existing technologies for lime (CaCO 3 ) incorporation into acidic field soils result in the heterogeneous distribution of limed and acidic soil sections. In a study characterising the response of wheat ( Triticum aestivum L.) to the amendment of an acidic soil profile with vertically limed slots [1] , elucidation of the dynamics of root proliferation within the acidic and limed soil sections was a prerequisite to understanding the mechanisms driving the above-ground responses. Rubidium (Rb) has been used widely as a non-radioactive tracer for root activity [2] in soil. However, the contrasting pH in a heterogeneously limed soil profile and related aluminium toxicity effects to roots can influence the availability and uptake of Rb, and quantitative data relating Rb uptake to root phenology in this scenario are lacking. To validate the use of Rb as a tracer for root activity within vertically limed slots in an acidic soil profile, its uptake by wheat roots from acidic or limed sections of subsoil, and its relation to root architecture was assessed. Wheat plants were grown in a glasshouse in 29 cm deep, vertically split soil columns with acidic (pH 3.9), Al-toxic subsoil on one side and the same soil amended with lime on the other side. Rubidium chloride was applied at 5, 10 or 20 mg Rb kg −1 to either limed or acidic soil sections. Wheat plants were grown for 28 days, after which the Rb content in shoots and the root length and diameter in each of the discrete soil sections was measured. Foremost, the Rb amendments (5, 10 or 20 mg Rb kg −1 soil) did not induce any toxic effects; shoot dry weight and root length in the limed and acidic sections of the subsoil were not statistically different among the rubidium-amended and non-amended treatments, regardless of its placement (limed vs. acidic sections). Average root lengths in the limed sections of the subsoil (69.5 m section −1 ) were approximately 10-fold greater than in the acidic sections (6.3 m section −1 ). Likewise, the concentration of Rb in shoots was, on average, 7-fold greater where Rb was applied to the limed (vs. acidic) subsoil section and was positively influenced by the rate of Rb amendment in the limed ( p ≤ 0.05), but not the acidic section of the subsoil. Rubidium uptake into shoots was significantly correlated ( p ≤ 0.05) with the length of roots within the Rb-amended subsoil section. The uptake of Rb from acidic or limed subsoil sections was determined by the root length in the Rb-amended subsoil section, regardless of the rate of Rb amendment. The uptake of Rb per unit of root length from acidic or limed sections of subsoil was not significantly different. The data validate the use of Rb as a tracer for the dynamics of root length proliferation in limed subsoil sections in a hetero...