Composted Rabbit Manure as Organic Matrix for Manufacturing Horticultural Growing Media: Composting Process and Seedling Effects

Microwave-assisted hydrothermal carbonization of rabbit manure

Hydrothermal carbonization (HTC) is an efficient process capable of treating organic waste without the need for a pre-drying step. Animal manure is among the waste that can be treated using HTC. Manure is a nutrient-rich waste produced in large quantities and contains pathogens; therefore, proper management is required. The use of microwave irradiation in HTC process is considered as a fast and efficient method to treat manure. Rabbit manure (RM) represents the main waste stream generated by rabbit farming activities. In this study microwave-assisted HTC of RM was performed and the effect of operating conditions on the characteristic of the products was evaluated. Hydrochars are produced by varying temperature (180 °C and 230 °C), residence time (30, 60 and 120 min) and solid-to-liquid (S/L) ratio (1/10 and 1/20). Moreover, the potential application in agriculture was evaluated. Results indicate that varying operation conditions have different effect on process products. Specifically, increasing treatment temperature from 180 °C to 230 °C leads to hydrochar yield reduction, while increasing severity of the treatment increases fixed carbon and total phosphorus content in the hydrochar. Thus, by applying the microwave-assisted HTC process in RM at 230 °C for 120 min and with an S/L ratio of 1/10, a hydrochar with an increased content of fixed carbon (17.5 %) and phosphorus (16.4 g/kg) was obtained. Subsequently, germination assays performed using the abovementioned hydrochar confirm a phytostimulatory effect at low application rates (5 %), while applying the HTC process water induces phytotoxicity, at all concentrations examined.

Increasing silage maize yield and nitrogen use efficiency as a result of combined rabbit manure and mineral nitrogen fertilization

Combined application of organic and mineral fertilizers is crucial to obtaining high crop yields, increasing the utilization of nutrients by plants, and limiting their dispersion, thus protecting the environment, which underscores the importance of sustainable and minimally invasive agriculture. The aim of the field experiment was to determine the effect of application of rabbit manure (RM) and mineral nitrogen (Nmin) on the dry matter (DM) yield of maize and on nitrogen content, uptake, and use efficiency (NUE). RM application was tested at levels of 0, 20, 40 and 60 t·ha-1, and Nmin application at 0, 50, 100 and 150 kg·ha-1. Significant differences were noted in yield and in the content and uptake of nitrogen depending on both experimental factors. Increasing the application of RM and Nmin led to an increase in the yield of harvested maize and in the content and uptake of nitrogen. In terms of DM yield and nitrogen uptake (yield of crude protein), the most beneficial fertilizer variant was 60 t·ha-1 RM applied together with 100 kg·ha-1 Nmin. The highest NUE value was obtained following application of 20 t·ha-1 RM together with 150 kg·ha-1 Nmin.

Rabbit manure compost as a peat substitute for compound growing media: Proportioning optimization according to physiochemical characteristics and seedling effects

A large amount of rabbit manure is produced with the development of the rabbit industry, which will cause environmental pollution without proper treatment. Rabbit manure compost may be suitable for seedling cultivation, considering its low moisture, low heavy metal, high lignocellulose, and good fertilizer effect. In this study, a pre-proportioning test of growing media was conducted to optimize the ratio of perlite and vermiculite with peat/rabbit manure compost according to their physicochemical properties. Then, based on the results of the first proportioning optimization, the mixing ratio of rabbit manure compost and peat was further optimized using a bioassay. In this bioassay, salt-tolerant calendula (Calendula officinalis L.) and salt-intolerant cucumber (Cucumis sativus L.) were selected as test plants. The seedling effects (e.g., seedling emergence percentage, plant growth parameters, plant biomass, and nutrient effects) were evaluated. It was shown in the results that the rabbit manure compound growing media could be used for the seedlings, and suitable seedling performance was obtained with the increase of the total porosity (5.0%-61.2%), organic matter content (8.3%-39.9%), and nutrient elements from the rabbit manure compost. From the perspective of seedling emergence, there was no significant difference between rabbit manure compound media and peat treatment, in which the highest emergence percentages were >90%. At the same time, the nutrient performance of plant aboveground was significantly increased in rabbit manure compound growing media compared to peat treatment. In particular, the contents of P and Mg were increased by 31%-141.4% and 80.4%-107.8% for calendula and by 82.6%-117.4% and 35.1%-67.6% for cucumber, respectively. It was indicated in the two-step optimization that the rabbit manure compost proportion of 30%-50% (that is, 60%-100% instead of peat) was more suitable. Additionally, the greenhouse gas emission could be reduced by using rabbit manure compost replacing peat, and the greenhouse gas emission reduction potential would be 3.65 × 10⁵-4.06 × 10⁸ kg CO₂-equivalent/year in China, which has important ecological significance.

Effects of segmented aerobic and anaerobic fermentation assisted with chemical treatment on comprehensive properties and composition of wheat straw

Traditional aerobic composting used for straw treatment shows limited regulation effects and unstable properties, and it is necessary to introduce some co-processing methods to optimize its performance. Herein, segmented aerobic/anaerobic fermentation, combined with chemical treatment with wood vinegar/NaOH, was used to treat wheat straw. The results showed that anaerobic fermentation when used as the first stage could stabilize the wheat straw pH between 5.19 and 6.13 and improve nutrient contents. All treatments had greater effects on substrate aeration porosities (range of 14%) than on total porosity (range of 6%), and the water-holding porosities were improved to a greater extent by NaOH than by wood vinegar. The hemicellulose degradation rate of aerobic-anaerobic treatment was higher than that achieved with anaerobic-aerobic treatment, while the latter method was more effective at removing the neutral detergent-soluble as well as remaining organic matter, which was generated due to a higher KCl content in the ash.