The effects of crop establishment system and field traffic on soil physical properties, root system architecture and crop yield of winter wheat (Triticum aestivum L.) under a range of soil textures

Soil management and the agricultural methods used to establish crops is regarded as one of the most important applications governing crop productivity. Soil compaction is created by conventional agricultural systems. Coupled with a cool, wet Atlantic climate such as Ireland and the UK, machinery trafficking can have a negative impact on soil structure and crop performance. To date, there is a dearth of studies which examine the impact of tillage depth and machinery traffic on root system architecture, growth and yield. As roots provide water, nutrients and anchorage to the growing plant, their role for crop improvement and resilience to climate change cannot be overstated. However, root knowledge remains limited because soil is opaque , making root and soil studies complex. This research uses X-ray computed tomography to unravel the in-situ root and soil interactions in field soils for the first time. The core objectives of this research were to use a novel method based on a combination of traditional two-dimensional (2D) and more advanced three-dimensional (3D) image analysis technologies. The study assessed the impact and interaction between four crop establishment systems and three trafficking regimes on crop performance and root growth of winter wheat (Triticum aestivum L.) at three different stages of the crop growth cycle (Tillering, flag leaf and anthesis). The study was conducted over two growing seasons (2018/19 & 2019/20) and included three soil textures (loamy sand, clay loam and clay). Four tillage systems were used in the Irish site: Plough, till and sow (300 mm), deep tillage (250 mm), shallow tillage (100 mm) and zero tillage while ploughing was omitted from the two UK sites. Each establishment method was applied using three different trafficking regimes: conventional tyre pressure (1.5 bar), low tyre pressure (0.8 bar) and no traffic. The effect of crop growth, yield and corresponding effect on soil and root physical properties were studied. Further knowledge and insights into root behaviour and architecture has been achieved using X-ray CT. This study showed that field traffic significantly affects rooting properties resulting in reduced root surface area, volume, root length and root length density (RLD) (P < 0.001) in long term tillage trials. It causes an increase in root thickness (root diameter) which results in shorter root systems with limited soil exploration for water and nutrients. Trafficking increases soil penetration resistance (P < 0.000) and bulk density (P < 0.05) compared to untrafficked soil which significantly affects soil porosity (P < 0.05). The compaction effects of trafficking are more pronounced in zero and shallow tillage systems when soil moisture is at field capacity during drilling, resulting in yield loss of + 30% in comparison to conventionally managed systems (plough, till & sow). Tyre pressure did not have a significant impact on rooting and soil properties but it generally slightly mitigated the effects of compaction on yield, rooting and soil physical properties. Overall, trafficking had a significant impact on crop yield (P < 0.001). Tillage practice had a significant effect on soil physical properties, crop yield and root growth. The results suggest that loamy sand sites benefit from zero tillage systems through increased rooting length, RLD and moderate compaction benefits which possibly increased water and nutrient retention. The results suggest that deep tillage systems create a porous structure increases rooting properties but reduces moisture retention. Moreover, this work has shown that soil texture has a significant influence on root growth. Moderate compaction benefits of root growth in clay soils reduced rooting but increased crop yield significantly compared to sandy loam soils which caused plants to partition more carbon to root growth, leading to less crop yield. This work has shown that root system architecture can be measured in field soils.