8Seed enhancement technologies i.e. priming, pelleting and coating have been extensively 9 used throughout the last century to improve crop yield and to reduce losses associated with 10 pest infestation. However, until recently, it has not been possible to non-destructively assess 11 the effect of seed enhancement technologies belowground due to the opacity of soil. Using X-12 ray Computed Tomography (X-ray CT) we undertook a 4D visualisation of the germination 13 process of four different sugar beet seed enhancement treatments (untreated / naked, coated, 14 pelleted and pelleted + coated) in soil. The aim of this study was to improve the understanding 15 of the germination process in the natural environment of the seed to inform future soil 16 management and seed enhancement processes. Using X-ray CT we were able to quantify the 17 germination and establishment process of different seed enhancement technologies in soil 18 non-destructively for the first time. We observed a delay in seedling growth posed by the 19 addition of a physical barrier, i.e. the seed coating. However, an enhanced radicle growth rate 20 was observed in pelleted, as well as pelleted and coated seeds, after overcoming the physical 21 barrier. The disadvantage posed by the addition of seed coating was overcome after four days 22 of seedling growth. Further work should focus on refinements to the type and composition of 23 the pelleting which we observed to have a retarded effect on seed germination. 24 Introduction 25

BackgroundSeed–soil contact is important to ensure successful germination, however, there is a paucity of reported studies that have quantified the microstructure at and around this critical interface, mainly due to the opacity of soil.ResultsHere we describe a novel methodology to non-destructively calculate the seed–soil contact area using X-ray Computed Tomography. Under controlled conditions, we observed that seed–soil contact was strongly influenced by the size and type of seed, with a seed–soil contact of ca. 15% for naked sugar beet seeds compared to ca. 32% for pelleted and coated seeds. Similar results were obtained for seeds sampled from the field albeit with a higher spatial variability.ConclusionsBy application of this new quantification method it is hoped seed enhancement technologies can be optimised and ultimately seedbed preparation improved to ensure better germination.

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Seed–soil contact plays an essential role in the process of germination as seeds absorb water through direct contact with the moist soil aggregates that surround them. Factors influencing seed–soil contact can be considered as those pertaining to soil physical properties (e.g. texture, bulk density, porosity, etc.) and those related to environmental conditions (e.g. temperature, rainfall, frost). Seed–soil contact is furthermore influenced by the specific field management processes that farmers apply, which have developed significantly over the last 30 years. However, the precise effect of cultivation on the actual contact area of the seed with the surrounding soil is based on a series of assumptions and is still largely unknown. This review considers the influence of soil management and its direct impact on seed–soil contact and establishment. We review the state of the art in methodology for measuring seed–soil contact and assess the potential for soil amendments such as plant residues and waste materials to improve seed–soil contact. Engineering the ‘optimal’ seed–soil contact remains a challenge due to the localized variation between the interaction with field management techniques and soil texture, climatic conditions and crop type. The latest imaging approaches show great promise to assess the impact of management on germination. Combining the techniques with the latest network models offers great potential to improve our ability to accurately predict germination, emergence and establishment.