# On-Farm Composting of Hop Plant Green Waste--Chemical and Biological Value of Compost
## 2 Materials and Methods  
### Experiment Setting--Compost Pile Formation, Temperature Monitoring and Weather Conditions  
The experiments were set on three hop producing farms in the Lower Savinja Valley, Slovenia, where different composting practices were tested. The composting process was carried out between September 2020 and April 2021 (Figure 1). After the hop cone harvest in September, three trapezoidal composting piles with the height of 2 m were built from hop biomass after harvest (stems and leaves) from 1 ha of hop field (approx. 15 tonnes each). Piles varied in the size of the particles the biomass was cut to by the harvest machine (Table 1). Aside from that, two piles were left uncovered throughout the season, and one--EM--was hermetically covered with black foil one month after it had been built, as it simulated fermentation. There were no additives in compost pile CON, which presented the control. Pile BC was mixed with biochar (activated carbon obtained from different types of softwood, particle size less than 1 mm, stabilized with water) during the pile construction at the rate of 4% dry weight. The addition rate of biochar for composting was modified by [PERSON] et al. 's (2016) [25] study, where they studied chicken manure composting with the addition of biochar at the rate of 5% of dry weight. In pile EM effective microorganisms (EMTM; a mixture of bran mixed with molasses (sugar and water), enriched with beneficial microorganisms (lactic acid bacteria, yeasts, photosynthetic organisms, enzymatically active fungi--over 80 different species of aerobic and anaerobic microorganisms) were sprayed on the hop waste after being cut by the harvest machine in concentration 2 L/tonne, as suggested by the producer. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Compost Nr.** & **Turning** & **Cover** & \begin{tabular}{c} **Particle Size of Hop** \\ **Biomass (cm)** \\ \end{tabular} & \begin{tabular}{c} **Additive at Compost Pile** \\ **Preparation** \\ \end{tabular} \\ \hline CON & 7-times & / & 2–10 & / \\ \hline BC & 11-times & / & 2–5 & Biochar (11 kg/tonne) \\ \hline EM & \begin{tabular}{c} 2-times (both before covering the pile) \\ \end{tabular} & \
\begin{tabular}{c} Black foil cover after \\ 1 month \\ \end{tabular} & 1–5 &
\begin{tabular}{c} Effective microorganisms \\ (2 L/tonne) \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Treatment-related composting procedures. Figure 1: Experimental setup: (**A**) hop biomass waste; (**B**) particle size of hop stems; (**C**) temperature measurements in compost piles during composting; (**D**) compost turning; (**E**) form of a compost pile at hop farm. TinyTag(r) temperature data loggers with a range from \(-40\)\({}^{\circ}\)C to \(+85\)\({}^{\circ}\)C [26] were put in the core of the piles to monitor the temperature. A customized TFA(r) thermometer probe was used to measure the temperature at depths of 50 and 100 cm in all four cardinal directions on a regular basis. The piles were turned when the temperature reached 65 \({}^{\circ}\)C; the number of turnings required is listed in Table 1. All three composets were compared with each other to figure out which of investigated compost treatment is optimal for composting hop biomass on hop farms. There were a lot of rainy days in the last week of September and in the first half of October. In contrast, there was almost no rain from 17 October to 15 November. The winter was above average in warmth and rain; there was no snow. The average daily temperature in January ranged from \(-2.5\)\({}^{\circ}\)C to \(+3.5\)\({}^{\circ}\)C; in February from \(1.2\)\({}^{\circ}\)C to \(8.3\)\({}^{\circ}\)C; in March from \(4.2\)\({}^{\circ}\)C to \(8.7\)\({}^{\circ}\)C; and in April from \(7.2\)\({}^{\circ}\)C to \(11.2\)\({}^{\circ}\)C. The amount of precipitation was 75 mm in January, 154 mm in February, 33 mm in March and 63 mm in April. There was nearly the same amount of precipitation (1.5 mm less) than the long-term average, but the distribution was uneven.