What was it all about?

From 2019 to 2024, this investment has conducted research into optimising the rate and timing of nitrogen additions, to help growers achieve maximum yield and nutritional value.

Mushrooms are an important source of protein in the human diet. They are increasingly viewed as a sustainable meat replacement, with button mushrooms (Agaricus bisporus) the most popular and economically important mushroom in Australia, Europe and North America. Button mushrooms are cultivated on a defined, straw-derived compost, and in Australia the nitrogen (N) required to grow these high-protein foods is provided mainly by the addition of poultry manure. The conversion of straw and poultry manure to productive compost is carried out by a huge range of bacteria and fungi in the compost, but little is known about which microbes in the compost are essential for incorporation of the necessary N, and how reproducible this microbial process is.

Using the correct balance of carbon (C) and N sources to produce mushroom compost is critically important in achieving maximum mushroom yields. This project has examined how changes in the amount and form of N added, the rate and timing of N addition, and the other compost components used can affect the proportion of added N recovered in the mushroom caps, the yield and quality of the mushrooms, and the loss of N as ammonia and nitrogen oxide gases during composting. Over 80 per cent of the added N is recovered in the composting /cropping process, but only about 15 per cent of this N is found as protein in the mushrooms that go to market, while most of the rest remains in the spent compost.

Mushroom composters have relied on chicken manure as their N source for many years, but changes in chicken husbandry have led to a reduction in the availability and the N content of manure, so alternative N sources are urgently required. This project has reviewed alternative N sources for use in Australian composting, evaluating such diverse materials as fish wastes, wool, and vegetable digestate. Recommendations are made to supplement or replace the current use of poultry manure as a sole N source.

The composting process relies on bacteria and fungi to break down the raw materials and incorporate added N into the compost. This project has compared the microbial populations present at different stages of composting in facilities from different Australian states in detail. This has revealed the presence of thousands of different microbial species in the compost, and described how their populations change during composting, and how they affect the incorporation of N into the compost. Although feedstock formulations and composting process differ between producers, the microbial populations in different composts are remarkably similar at the end of the compost conditioning process. This knowledge has been used by isolating samples of the major bacteria in compost and designing mixtures of microbes that can potentially be applied to low-productivity composts in order to produce better yields for the farmer.