Microbial Enrichment of a Novel Growing Substrate and its Effect on Plant Growth

The quality of torrefied grass fibers (TGF) as a new potting soil ingredient was tested in a greenhouse experiment. TGF was colonized with previously selected microorganisms. Four colonization treatments were compared: (1) no inoculants, (2) the fungus Coniochaeta ligniaria F/TGF15 alone, (3) the fungus followed by inoculation with two selected bacteria, and (4) the fungus with seven selected bacteria. Cultivation-based and DNA-based methods, i.e., PCR-DGGE and BOX-PCR, were applied to assess the bacterial and fungal communities established in the TGF. Although colonization was not performed under sterile conditions, all inoculated strains were recovered from TGF up to 26 days incubation. Stable fungal and bacterial populations of 108 and 109 CFU/g TGF, respectively, were reached. As a side effect of the torrefaction process that aimed at the chemical stabilization of grass fibers, potentially phytotoxic compounds were generated. These phytotoxic compounds were cold-extracted from the fibers and analyzed by gas chromatography mass spectrometry. Four of 15 target compounds that had previously been found in the extract of TGF were encountered, namely phenol, 2-methoxyphenol, benzopyran-2-one, and tetrahydro-5,6,7,7a-benzofuranone. The concentration of these compounds decreased significantly during incubation. The colonized TGF was mixed with peat (P) in a range of 100%:0%, 50%:50%, 20%:80%, and 0%:100% TGF/P (w/w), respectively, to assess suitability for plant growth. Germination of tomato seeds was assessed three times, i.e., with inoculated TGF that had been incubated for 12, 21, and 26 days. In these tests, 90–100% of the seeds germinated in 50%:50% and 20%:80% TGF/P, whereas on average only 50% of the seeds germinated in pure TGF. Germination was not improved by the microbial inoculants. However, plant fresh weight as well as leaf area of 28-day-old tomato plants were significantly increased in all treatments where C. ligniaria F/TGF15 was inoculated compared to the control treatment without microbial inoculants. Colonization with C. ligniaria also protected the substrate from uncontrolled colonization by other fungi. The excellent colonization of TGF by the selected plant-health promoting bacteria in combination with the fungus C. ligniaria offers the possibility to create disease suppressive substrate, meanwhile replacing 20% to 50% of peat in potting soil by TGF

Growth of Chrysanthemum x grandiflorum in Different Peats and Change of Peat Properties during Cultivation

Marketable chrysanthemums were produced in several different peat types. Only the plants in one of the dredged frozen black peats and one of the milled white peats had a significant lower shoot dry weight than those in one of the sod and milled white peats, respectively. As the N-contents of the fertilized peats show neither deficiency nor excess in nutrient supply, possibly they are not the reason for the differences in shoot dry weight. The air capacity, which is extremely low in both dredged frozen black peats and dropped further during the cultivation period due to decomposition, also cannot explain the differences in shoot dry weight sufficiently (R-2=0.44*; n=12). A close linear negative correlation (R-2=0.77**; n=12) was found between the CAT (VDLUFA) soluble Fe and the shoot dry weight. Therefore, the Fe-contents might be a quality factor of peat to be used as a growing medium

Utilização de compostos orgânicos como substratos na produção de mudas de hortaliças Utilization of organic compost as substrate for vegetable seedling production

Visando determinar a viabilidade da utilização de compostos orgânicos obtidos com palhada de Crotalaria juncea L. e capim Napier (Pennisetum purpureum Schum.) como substratos na produção de mudas de hortaliças, realizaram-se experimentos com alface (folhosa), beterraba (raiz) e tomate (hortaliça de fruto). Estudou-se a eficiência de compostos produzidos a partir dos materiais: 100% de Crotalária Júncea; 66% de Crotalária Júncea + 33% de Napier; 33% de Crotalária Júncea + 66% de Napier; 100% de Napier; 33% de Crotalária Júncea + 66% de Napier, inoculado com 5% da massa com esterco bovino; 33% de Crotalária Júncea + 66% de Napier, inoculado com 100 L de Agrobio diluído a 5%; 100% de Napier, inoculado com 100 litros de Agrobio diluído a 5%. Como controle utilizou-se o substrato comercial Plantmax HT®. Avaliou-se altura da parte aérea, número de folhas, produção de massa fresca na parte aérea e produção de massa seca na parte aérea. O composto produzido com a mistura de 66% de Crotalária Júncea e 33% de Napier mostrou-se superior aos demais tratamentos para produção de mudas de alface, beterraba e tomate.<br>The viability of the organic compost utilization as a substrate for vegetable seedlings production, obtained from Crotalaria juncea L. and Napier grass (Pennisetum purpureum Schum.), was determined. The research was developed with lettuce (leaf vegetable), beetroot (root vegetable) and tomato (fruit vegetable). The organic composts were produced from: 100% Crotalaria Juncea; 66% Crotalaria Juncea + 33% Napier; 33% Crotalaria Juncea + 66% Napier; 100% Napier; 33% Crotalaria Juncea + 66% Napier, inoculated with 5% of the mass with cattle manure; 33% Crotalaria Juncea + 66% Napier, inoculated with 100 L of 5% diluted Agrobio; 100% Napier, inoculated with 100 L of 5% diluted Agrobio. We evaluated the height, leaf number, aerial green weight and aerial dry weight. A commercial substrate Plantmax HT® was used as control. The compost produced from the mixture of 66% Crotalaria Juncea and 33% Napier presented the best results, being adequate for the production of lettuce, beetroot and tomato seedlings