The repeatability of reusing peat as horticultural substrate and the role of fertigation for optimal reuse.

Direct reuse of horticultural substrates may facilitate the transition from linear to circular greenhouse cultivation. Characteristics of spent growing media from strawberry cultivation were compared to substrates from ornamentals, mushrooms, microgreens, and greenhouse vegetables. Direct reuse of spent peat as a stand-alone material was tested in three trials under commercial conditions. In the first trial strawberry cultivation on reused growing media with included crop residues resulted in similar yield as for virgin blends in a spring cultivation. In the second trial repeated reuse of spent growing media was tested in an autumn cultivation, either with direct reuse or with reuse after shredding and steam treatment for sanitation. Nutrient retention did not increase further during repeated reuse. Yield was similar to virgin peat for the direct reuse and steam sanitation treatments. Under reuse deterioration in terms of physical properties was not observed. Biological stability remained high for all media during reuse. Reusing peat for strawberry 3 times did not lead to any problems for yield or substrate. In the third trial the effects of fertigation regimes with reduced P and K input on nutrient retention during direct reuse in a spring cultivation were limited. In contrast, significantly lower N, P, K, Mg and Ca contents in the substrate were measured when fertigation was replaced by water in the last two weeks of the cultivation. Cation exchange capacity in the spent peat in all trials remained high during reuse. Ca was the dominant cation on the exchange complex.

Physiological and Morphological Implications of Using Composts with Different Compositions in the Production of Cucumber Seedlings.

Compost has a broad application in terms of the improvement of the soil properties. This research work was conducted to present the molecular implications of using compost obtained from different substrates to improve soil parameters for cucumber seedlings cultivation. In the experiment, the following compost mixtures were used: sewage sludge (80%) + sawdust (20%); sewage sludge (40%) + sawdust (10%) + biodegradable garden and park waste (50%); biodegradable garden and park waste (90%) + sawdust (10%); sewage sludge (80%) + sawdust (20%) + Eisenia fetida; sewage sludge (40%) + sawdust (10%) + biodegradable garden and park waste (50%) + Eisenia fetida; biodegradable garden and park waste (90%) + sawdust (10%) + Eisenia fetida. The final substrate compositions consisted of compost mixtures and deacidified peat(O) (pH 6.97; Corg content-55%, N content-2.3%), serving as a structural additive, in different mass ratios (mass %). The produced plants underwent biometric and physiological measurements as well as enzymatic analyses of stress markers. Based on the conducted studies, it has been found that the substrate productivity depends not only on the content of nutrient components but also on their structure, which is moderated by the proportion of peat in the substrate. The most effective and promising substrate for cucumber seedling production was variant 2 (I), which consisted of 25% compost from sewage sludge (40%) + sawdust (10%) + biodegradable garden and park waste (50%) and 75% deacidified peat. Despite the richness of the other substrates, inferior parameters of the produced seedlings were observed. The analysis of the enzymatic activity of stress markers showed that these substrates caused stress in the plants produced. The study's results showed that this stress was caused by the presence of Eisenia fetida, which damaged the developing root system of plants in the limited volume of substrate (production containers). The adverse influence of Eisenia fetida on the plants produced could possibly be eliminated by thermal treatment of the compost, although this could lead to significant changes in composition.

Elucidating the microbiome of the sustainable peat replacers composts and nature management residues.

Sustainable peat alternatives, such as composts and management residues, are considered to have beneficial microbiological characteristics compared to peat-based substrates. Studies comparing microbiological characteristics of these three types of biomass are, however, lacking. This study examined if and how microbiological characteristics of subtypes of composts and management residues differ from peat-based substrates, and how feedstock and (bio)chemical characteristics drive these characteristics. In addition, microbiome characteristics were evaluated that may contribute to plant growth and health. These characteristics include: genera associated with known beneficial or harmful microorganisms, microbial diversity, functional diversity/activity, microbial biomass, fungal to bacterial ratio and inoculation efficiency with the biocontrol fungus Trichoderma harzianum. Bacterial and fungal communities were studied using 16S rRNA and ITS2 gene metabarcoding, community-level physiological profiling (Biolog EcoPlates) and PLFA analysis. Inoculation with T. harzianum was assessed using qPCR. Samples of feedstock-based subtypes of composts and peat-based substrates showed similar microbial community compositions, while subtypes based on management residues were more variable in their microbial community composition. For management residues, a classification based on pH and hemicellulose content may be relevant for bacterial and fungal communities, respectively. Green composts, vegetable, fruit and garden composts and woody composts show the most potential to enhance plant growth or to suppress pathogens for non-acidophilic plants, while grass clippings, chopped heath and woody fractions of compost show the most potential for blends for calcifuge plants. Fungal biomass was a suitable predictor for inoculation efficiency of composts and management residues.

Enxofre elementar no manejo do pH de substrato orgânico alcalino / Elemental sulfur for pH management of alkaline organic substrates

Embora existam recomendações agronômicas consolidadas para a elevação do pH de substratos orgânicos, poucas são as informações disponíveis para a redução. Porém, a crescente utilização de matérias-primas alternativas às tradicionais torna necessário o emprego de métodos para diminuição do pH, já que alguns materiais com boas características físicas e biológicas são alcalinos e incompatíveis com o cultivo da maioria das espécies. Os objetivos do presente trabalho foram verificar a eficiência do enxofre elementar (S0) na diminuição do pH de um substrato orgânico alcalino e avaliar um critério para determinação da dose a ser adicionada. Para tanto, testou-se a mistura de cinco doses de S0 a um substrato comercial composto por casca de eucalipto compostada (0, 4, 8, 12 e 16g S0 dm-3 de substrato), com base no valor do seu poder de neutralização (PN). Avaliou-se o pH e a condutividade elétrica (CE) dos substratos. Observou-se que o S0 é eficiente na redução do pH de substratos orgânicos, mas acarreta aumento da CE. O PN do substrato é um critério confiável para balizar a determinação da dose de S0 a ser utilizada.

Although agronomic recommendations for raising the pH of organic substrates are consolidated, little information is available for its reduction. The increasing use of alternative raw materials, however, makes it necessary to develop methods for decreasing pH, since some materials with good physical and biological properties are alkaline and are not recommended for the majority of species. The objective of this research was to determine the efficiency of elemental sulfur (S0) in decreasing the pH of an alkaline substrate, and evaluate a method to calculate the dose to be added. It was evaluated the mixture of five doses of S0 to a commercial substrate compound of composted eucalyptus bark (0, 4, 8, 12 and 16g S0 dm-3 substrate), based on its neutralizing value (NV). The pH and electrical conductivity (EC) of the substrates were assessed. The S0 is effective in reducing the pH of organic substrates, but it causes increases in EC. The NV of the substrate is a reliable criterion for guiding the determination of the S0 dose to be added.