Executive Summary: Developing a dependable organic fertilizer for the horticultural industry

Summary of Project and Key Findings:
Composted chicken manure contains valuable nutrients for agricultural and horticultural production, but contains a lot of water, which increases transport costs. Osflo Fertiliser Limited (Osflo) saw that there was an opportunity to improve their product by pelletising the manure, which would make it cheaper to transport and easier to spread. The purpose of this research was to determine how pelletising the manure affected the release of plant-available nitrogen (mineral N) from the manure.

Osflo provided the Bioeconomy Science Institute with a sample of pelleted composted chicken manure and a sample of standard composted chicken manure to test for nutrient release rate. These samples were tested for nutrient content and incubated with soil for a 98-day period to determine the pattern of nutrient release. Periodic measurements were taken to determine mineral nitrogen concentrations. The treatments, replicated four times, were as follows:

1. Unfertilised soil (control)
2. Unfertilised soil + pelleted chicken manure (2.0 g of pelleted composted manure)
3. Unfertilised soil + standard chicken manure (2.2 g of standard composted manure)

The laboratory tests showed that pelletising removed a considerable amount of water from the compost and increased the bulk density, which consequently increased the nutrient density. The incubation study showed that approximately 60% of the total N in the compost (either pelleted or not) is likely to be released as plant-available (mineral N) over a 98-day period, assuming a typical total N concentration for standard chicken manure. This agrees with data from other studies on composted poultry manure. The remaining 40% of the nitrogen will be released over a period of several months to years. The maximum concentration of mineral N released from the manures was observed at 56 days of incubation at 10°C and at 28 days of incubation at 20°C. Per unit of total N contained, both pelleted and standard manure release very similar amounts of mineral N, indicating that pelleting did not significantly affect the plant-availability of the nitrogen in the compost. The increase in nutrient density (including N) of the manure by pelletising meant that pelleted manure showed a higher release of plant-available N per unit weight or per unit volume than standard manure. This will be a great benefit to growers because pelletising will reduce transport costs.

There were also other benefits from pelletisation, which will require further confirmation. These included a lower pH, which may lower volatilisation losses if surface-applied, and delayed nitrification, which may reduce nitrate leaching compared with standard chicken manure.