Identification of optimum seedbed preparation for establishment using soil structural visualisation (PhD)

Abstract

A key aspect of the condition of soil as a medium for growing plants is the soil physical environment under which germination, growth and establishment occur. Crucially this affects factors such as water content, oxygen availability and soil strength. The dynamics of soil physical properties, and in particular soil structure, of a range of soils and how they relate to plant establishment were considered during this project. By engineering a variety of seedbeds and contrasting soil structures using different cultivation techniques, from intensive (plough) to reduced (disc) strategies, significant differences in the physical properties of the soils and interactions with plant establishment were identified. Results showed significant reductions in plant populations were associated with increases in the soil porosity, with strong links to the pore size and roughness which influences soil-seed contact, water storage / flow and ease of plant / root movement within the soil. Preferred porosity conditions for establishment and yield occurred between 12 - 20 % soil porosity when measured by image analysis (i.e. mainly macropores). Recommendations for field cultivation for cereal crops are to perform minimal cultivation (discing) on light soils (sandy loam) as this produced the best structural requirements, with minimal to no reduction in establishment and yield. Heavier soils (clay loam) require greater soil loosening (disc & power harrow) to produce optimum structural conditions for seedbed drilling and crop establishment. Results show no advantage to rolling seedbeds, and in fact this resulted in poor seedbed soil structure in this study both as a result of compaction and of surface cracking, which are detrimental to the establishment and yield of the crop.