Contents lists available at ScienceDirect Soil & Tillage Research journal homepage: www.elsevier.com/locate/still The strategic use of minimum tillage within conservation agriculture in southern New South Wales, Australia Mark Conyers a, ⁎ , Vince van der Rijt a , Albert Oates a , Graeme Poile a , John Kirkegaard b , Clive Kirkby b a NSW DPI, Agricultural Institute, Pine Gully Road, Wagga Wagga, 2650, Australia b CSIRO Agriculture and Food, PO Box 1700, Canberra, ACT, 2610, Australia ARTICLE INFO Keywords: Wet aggregate stability Hydraulic conductivity ABSTRACT Occasional, strategically applied tillage within an otherwise no-till system conflicts with the philosophical ideal of zero disturbance of soil, yet is often needed to manage soil constraints, pests and weeds. This study reports the impacts of a single strategic tillage applied to long term no-till soils (10–16 years) with a scarifier or offset discs, compared with ongoing no-till, on soil conditions and crop growth over four seasons at three locations in southern New South Wales, Australia. The tillage occurred just prior to sowing in autumn and under different management conditions at each site. The effect of a single tillage on wet aggregate stability (WAS) ranged from 0 to 14% loss of macro-aggregates, and the recovery time was generally one or two years with the exception of one site-year. The effect of a single tillage on saturated hydraulic conductivity was not statistically significant. Crop establishment was decreased by tillage in some site-years but effects on crop dry matter and grain yield tended to be neutral or minor. In most cases, seasonal effects and crop sequence had a much larger effect on crop pro- ductivity than tillage. The results demonstrated that strategic use of tillage within an otherwise no-till system generated minor and short term impacts on soil conditions. Strategic tillage therefore provides a tool for more flexible management of soil, pest and weed constraints to ensure long term productivity and sustainability of dryland mixed farming systems in southern New South Wales, Australia. 1. Introduction Conservation agriculture involves three key principles of reduced tillage, soil cover by crop residue retention and diverse rotations (Giller et al., 2015; Kirkegaard et al., 2014). The concept of reduced tillage is sometimes extended to complete zero tillage or “no-till”. However in many farming systems where soil, weed and disease constraints can limit production, tillage remains a useful management tool. In many situations difficulties can arise when reduced tillage is extended to complete no-till: (1) Acidic soil: the effectiveness of limestone in ameliorating soil acidity in a semi-arid climate is improved by incorporation (Conyers et al., 2003; Scott and Coombes, 2006). (2) Nutrient stratification: nutrient pools such as organic nitrogen, phosphorus and alkalinity from plant residues can accumulate in a relatively shallow surface layer under no-till (Franzluebbers, 2002; Garcia et al., 2007; Paul et al., 2003) where they are less accessible to plant roots due to extremes of temperature (sub zero to > 50 °C) and because of frequently dry soil. (3) Diseases: no tillage can favour diseases such as Rhizoctonia solani (Rovira, 1986) and also inhibitory Pseudomonads (Simpfendorfer et al., 2001) around the roots of some species and cultivars. Ad- ditionally, conventional tillage has been found to suppress plant parasitic nematode populations compared with direct drilling (Rahman et al., 2007). (4) Invertebrate pests: reduced tillage is associated with increased abundance of slugs (Voss et al., 1998; Glen and Symondson, 2003) while tillage is associated with lower numbers of snails (Pomeroy, 1969). A decreased number and activity of slugs and snails after a pasture phase and prior to canola (Brassica napus) crops is highly desirable. (5) Vertebrate pests such as mice and other rodents appear to have more stable habitat under conservation tillage (Johnson, 1986) and so tillage could be used as part of integrated pest management. (6) Integrated weed management: certain weeds might require the use https://doi.org/10.1016/j.still.2019.05.021 Received 12 November 2018; Received in revised form 7 March 2019; Accepted 23 May 2019 ⁎ Corresponding author. Present address: 11 Finch Place, Wagga Wagga, NSW, 2650, Australia. E-mail address: mconyers@bigpond.net.au (M. Conyers). Soil & Tillage Research 193 (2019) 17–26 0167-1987/ © 2019 Elsevier B.V. All rights reserved. T