Evaluating the Fertilising Potential of Blended Recovered Nutrients in Horticultural Growing Medium on Viola x wittrockiana L.

Viola x wittrockiana L. is an ornamental plant in high demand in horticulture. It is becoming more critical for greenhouse growers to focus on sustainable production to enhance plant quality while reducing negative environmental impacts. Therefore, assessing the effect of recycled phosphorous (P) and nitrogen (N) sources on the growth of viola could become very useful for producers in terms of sustainability. This experiment analysed the optimal fertiliser composition to grow viola using recovered fertilisers in a greenhouse trial under controlled conditions. Well-rooted viola plugs were grown in a standard peat-based growing medium. Using recycled sources of P and N as struvite and potassium struvite, ammonium sulphate, and ammonium nitrate, 14 fertiliser blends were prepared, tested, and compared with the slow-release commercial fertiliser Osmocote. Plants treated with ammonium nitrate showed healthy growth and optimal plant N concentrations. In contrast, most blends using the recovered ammonium sulphate resulted in an unacceptable increase of ammonium concentrations in the growing medium. The combination of ammonium sulphate and potassium sulphate caused an increase in the electrical conductivity in the growing medium, negatively affecting plant growth. However, blend 13 containing struvite, ammonium sulphate and potassium struvite expressed the best chemical composition with non-significant differences in the biomass from the positive controls, as it reduced the amount of potassium sulphate needed. Our results indicate that fertiliser blends containing P as struvite, N as ammonium nitrate or reduced amount of ammonium sulphate, and K as potassium struvite can substitute the use of mineral fertiliser blends to grow ornamental plant species as viola.

Wood Ash Based Treatment of Anaerobic Digestate: State-of-the-Art and Possibilities

The problem of current agricultural practices is not limited to land management but also to the unsustainable consumption of essential nutrients for plants, such as phosphorus. This article focuses on the valorization of wood ash and anaerobic digestate for the preparation of a slow-release fertilizer. The underlying chemistry of the blend of these two materials is elucidated by analyzing the applications of the mixture. First, the feasibility of employing low doses (≤1 g total solids (TS) ash/g TS digestate) of wood ash is explained as a way to improve the composition of the feedstock of anaerobic digestion and enhance biogas production. Secondly, a detailed description concerning high doses of wood ash and their uses in the downstream processing of the anaerobic digestate to further enhance its stability is offered. Among all the physico-chemical phenomena involved, sorption processes are meticulously depicted, since they are responsible for nutrient recovery, dewatering, and self-hardening in preparing a granular fertilizer. Simple activation procedures (e.g., carbonization, carbonation, calcination, acidification, wash, milling, and sieving) are proposed to promote immobilization of the nutrients. Due to the limited information on the combined processing of wood ash and the anaerobic digestate, transformations of similar residues are additionally considered. Considering all the possible synergies in the anaerobic digestion and the downstream stages, a dose of ash of 5 g TS ash/g TS digestate is proposed for future experiments.

Impacts of Slow-Release Nitrogen Fertilizer Rates on the Morpho-Physiological Traits, Yield, and Nitrogen Use Efficiency of Rice under Different Water Regimes

The efficient use of water and fertilizer is vital for optimizing plant growth and yield in rice production. To achieve sustainable rice production and resource management, the ways in which applied water and nitrogen affect the root and shoot morpho-physiology, as well as yield, must be understood. In this study, a pot experiment was conducted to investigate the effects of slow-release nitrogen fertilizer (sulfur-coated urea) application at three levels (light nitrogen (NL), medium nitrogen (NM), and heavy nitrogen (NH)) on the growth, yield, and nitrogen use efficiency (NUE) of rice grown under three water regimes (wetting and soil saturation (WSS), wetting and moderate drying (WMD) and wetting and severe drying (WSD)). The results revealed that differences in water regimes and fertilizer rates led to significant differences in the roots, shoots, yield, and NUE of rice. Increasing the N dosage by 5% enhanced the root and biomass production by 16% in comparison with that of the other groups. The NH×WSS treatment produced the greatest root length, weight, density, active absorption, and oxidation. However, the integration of WSS × NL generated the maximum value of nitrogen apparent recovery efficiency (63.1% to 67.6%) and the greatest value of nitrogen partial factor productivity (39.9 g g−1 to 41.13 g g−1). Transmission electron microscopy (TEM) images showed that plants grown under high and medium nitrogen fertilizer rates with WSS had improved leaf mesophyll structure with normal starch grains, clear cell walls, and well-developed chloroplasts with tidy and well-arranged thylakoids. These results show that TEM images are useful for characterizing the nitrogen and water status of leaves in the sub-micrometer range and providing specific information regarding the leaf microstructure. The findings of this study suggest that the application of NH×WSS can produce improvements in growth traits and increase rice yield; however, the NL×WSS treatment led to greater NUE, and the authors recommend its usage in rice agriculture.

USE OF AGROMINERAL AS SUBSTRATE FOR GROWTH OF EUCALYPTUS SEEDLINGS

Success in the production of eucalyptus seedlings directly affects the development of plants in the field. Several factors influence their initial growth, especially the substrate. This study aimed to evaluate the growth of Eucalyptus globulus seedlings and characteristics of the substrate using silicate agromineral (SA) in different proportions (substrate:SA; v/v): T0 – 100:00%, T1 – 90:10%, T2 – 80:20%, and T3 – 50:50%. The treatments were evaluated using a completely randomized design. Measurements of height (H), stem diameter (SD) and calculation of the H/SD ratio of the plants were performed every 3 weeks, totaling 4 measurements. At the end of the experiment (12 weeks), soil fertility analyses, granulometric analysis (sand, silt and clay) and total chemical analysis were carried out. Due to the chemical and mineralogical composition of SA, its use in substrate in a greater proportion (T3) promoted the increase of exchangeable K, Ca and Si contents, which influenced the increase in the sum of bases and cation exchange capacity. The levels of assimilable P and micronutrients Fe, Cu, Zn and Mn were also higher in this treatment. The increase in SA proportions in the substrate composition also favored increase in the sand fraction and reduction in the clay fraction. As for the growth of seedlings, the results were not significant for H and SD as a function of SA doses, leading to the conclusion that the solubilization and slow release of nutrients by SA did not influence the growth of the plants