تاثیر خاک ورزی مداوم بر تولید محصولات کشاورزی در حاشیه مناطق گرمسیر به سمت آب هوای خشک The Influence of Tillage Frequency on Crop Productivity in Sub-Tropical to Semi-Arid Climates

Introduction Adoption of conservation agricultural (CA) practices including no-tillage (NT) has been widely embraced in grain growing regions of Queensland (Thomas et al. 2007) and across Australian agriculture (Llewelyn et al. 2012). However, within CA farming systems, strategic or occasional tillage (ST) is being utilized for a number of reasons by landholders in the Northern Grains Region (NGR) of Australia (Argent et al. 2013). These can include but are not limited to the control of herbicide resistant weed populations and soil- and stubble-borne diseases, and to address stratification of nutrients and organic carbon near the soil surface (Dang et al. 2015a). It can be misconstrued as to what the ST process consists of, or if there is even a place for it within CA. Strategic tillage can be best described as an opportunistic use of tillage operation/s (adequate tillage implement for desired outcome at adequate soil water level) in an otherwise NT system (Crawford et al. 2015, Dang et al. 2015a). A potential benefit is that it can provide a circuit breaker in herbicide use, addressing the build-up of resistant weed populations. However, the risk is, that poor timing or too many tillage application can lead to detrimental soil health impacts. Palm et al. (2014), states that CA is a system of agronomic practices that includes reduced tillage (RT) and NT. Reduced tillage occurs during seed bed preparation and hence a more regular tillage application, therefore strategic tillage should be a natural inclusion, as it involves far less tillage frequency than RT. Reviews such as Dang et al. 2015a, Dang et al. 2015b, and Busari et al. 2015, depicted a good representation of the process involved within the CA management system and the risk/benefit of including strategic tillage in these systems. These reviews also discussed the potential for productivity decline with time if a strategic tillage process is not included within CA systems. This sentiment is supported in Kirkegaard et al. (2014) which stated ‘the avoidance or exclusion of ST within the CA process makes little sense if considerable overall benefits are put at risk’. Nationally, increasing herbicide resistant weed populations have been reported as threatening crop-production profitability and sustainability across 20 million ha (Walsh and Powles 2007). Werth et al. (2011), stated that within the sub-tropical cropping region of north-east Australia, up to five weed species have evolved glyphosate resistance; namely annual ryegrass (Lolium rigidum), awnless barnyard grass (Echinochloa colona), liverseed grass (Urochloa panicoides), flaxleaf fleabane (Conyza bonariensis), and windmill grass (Chloris truncate). While efficient and effective herbicide use is still the preferred management style within the NGR, utilizing tillage as stated previously has re-entered CA potential management options. Other methods such as increased seeding rates and decreasing row spacing (Bajwa et al. 2016; Lemerle et al. 2004) have demonstrated positive results for productivity while addressing weed competition. While there are large amounts of literature on the benefits of CA (inclusive of NT, RT, and minimal tillage (MT) compared to aggressive tillage), very little has been published on the impacts of ST in NT systems, especially within Australia. The purpose of undertaking this tillage frequency study was to address literature gaps on the impacts of strategic tillage on productivity of CA systems.