The ability to substitute peat use in horticulture with potentially more sustainable alternatives hinges on the local availability of suitable biomass resources and whether these resources can be easily processed to achieve similar agronomic effectiveness to peat. This review estimates potential biomass availability in Ireland by reviewing production statistics and industry reports and identifying current uses and hypothetical processed biomass quantities. Annual estimates of the major biomass resources available in Ireland are 488,935 m³ of woody residues (mainly Sitka spruce pine) and 789,926 m³ of arable straws (from oats, wheat, barley, oil seed rape). The potential major processing pathways for the available biomass are mechanical (extruded, thinscrew, hammer milled, disc refined), carbonization (pyrolysis and hydrothermal carbonization) and composting. This review of the literature indicates that the major challenges to pyrolyzed alternatives in growth media include high alkalinity, high salinity and low water holding capacity. When biomass is processed into fibers, it requires additional processing to address nutrient immobilization (nitrogen and calcium) and the presence of phytotoxic compounds. We discuss possible solutions to these challenges in terms of agronomic management (altering fertigation, irrigation rates etc.), biomass conversion process optimization (changing conditions of processes and applying additives) and novel growth media formulations with various material inputs that complement each other. We conclude that while national alternative biomass resources are available in sufficient volumes to potentially meet growing media requirements, significant further research and demonstration are required to convert these materials to growth media acceptable to both commercial and retail sectors. Research needs to focus on transforming these materials into growth media, and how they will impact agronomic management of crops. Furthermore to this, the optimization of biomass conversion processes and novel formulations incorporating multiple types of biomass need to be the focus as we transition from peat products in professional horticulture.

Organic agriculture in smallholder sub-Saharan African farming areas faces a lot of challenges that are different from those experienced in other regions of the world. While local farmers use organic resources in some way, the adoption of organic agriculture as a means of commercial production is lagging. Peer-reviewed literature on organic agriculture in Zimbabwe and most of Africa is limited. This review identifies regional situational differences in the farming environment in sub-Sahara Africa and Zimbabwe and discusses the opportunities and challenges peculiar to smallholder organic agriculture farmers. Results show that organic agriculture in Zimbabwean smallholder farming areas is mainly promoted by non-governmental organisations and supporting public policy is lacking. Local markets for organic produce are not well developed and an opportunity exists to develop local markets through supportive public policies, private sector engagement and further training and farmer support. While most soils present challenges to crop production due to nutrient deficiencies, yield increases are possible with organic management and research on mixing/fortifying organic amendments is needed.

Hairy vetch (Vicia villosa Roth) is an introduced temperate forage legume in Zimbabwe that has no locally available commercial inoculant. In this study, Rhizobium leguminosarum bv. viceae strains MAR 1504, MAR 833 and MAR 346 available in Zimbabwe's strain bank were evaluated for nodulation and N₂-fixing effectiveness in a sandy soil (Typic Kandiustalf). There was no significant difference in hairy vetch biomass (range: 3.4–4.5 g pot⁻¹) and nitrogen (N) content between plants in acidic and limed soil, showing that soil acidity was not a major problem for hairy vetch productivity in the short term. Inoculation with R. leguminosarum significantly increased (p < 0.05) biomass production (range: 0.37–3.11 t ha⁻¹) and enhanced N₂ fixation of hairy vetch compared to the uninoculated control, which had no nodules and significantly less biomass. Hairy vetch fixed up to 66.5 kg N ha⁻¹ in the field, and this amount may be made available for cereal crops as green manure. From the strains tested, MAR 833 and MAR1504 were more effective than MAR 346 in increasing the amount of N₂ fixed per unit area and are thus recommended for further multilocation field testing in farmer's fields to allow conclusive identification of strains to use in commercial inoculant production.