Integration of agricultural systems for environmental sustainability: Vermicomposting organic resources for waste management and food production in a circular economy

Abstract

Food production creates organic waste. Dissolved air flotation (DAF) sludges from meat processing are problematic to dispose of; they are odorous, have high moisture contents and are rich in nutrients. Direct land application without stabilisation of nutrients is common. Paper wastes can often be recycled, but food-contaminated paper wastes are usually landfilled. Nutrients in these two organic resources are therefore usually wasted. This research demonstrated that the compost worm (Eisenia fetida Savigny) could produce vermicompost from novel mixtures of chicken DAF sludge and cardboard, meeting the New Zealand Standards for vermicasts and provided a beneficial effect on plant growth. This research investigated whether commercially produced vermicast applied to onions, potatoes and maize affected yield and/or quality over three consecutive years, with crop rotation on a market garden farm. While international field trials have shown vermicast to improve crop yields, this has not been investigated in rotational crop farming for maize, potatoes and onions. It also has not been conducted in New Zealand at the scale in this thesis. The treatments applied were annual applications of either chicken litter applied at 3 t fresh matter (FM)/ha, vermicast applied at 12.5 t FM/ha or 25 t FM/ha. The treatments were compared to a Control (normal farm management). All treatments, including the Control, received normal fertiliser rates. The trials showed that vermicast applied at 25 t fresh matter (FM)/ha increased onion density and yield (with estimated farmgate profit of >$800/ha), as well as maize grain kernel mass compared to the Control in the third season. This season was the driest, indicating the vermicast provided benefits to crops under abiotic stress. The chicken litter treatment reduced onion density in the second and third seasons. In the third season, this led to an increase in average onion bulb mass, but did not translate to an increase in yield above that of the Control. Additional glasshouse studies were conducted on the application of commercially produced vermicast to determine whether the method or timing of application impacted onion bulbs under glasshouse conditions. Another study investigated the potential for vermicast to supplement diammonium phosphate (DAP) fertiliser in a phosphorus (P) sparing trial in onions on a low Olsen P soil. Final soil Olsen P contents from treatments with 12.5 t FM/ha vermicast and 100% and 75% of recommended P were not significantly different to the Control (100% P and no vermicast). No effect of timing or supplementation of DAP was found on onion size or mass, though these trials were found to be underpowered. The effect of vermicast application timing in relation to crop production has not previously been investigated. Neither has the potential for vermicast to supplement imported phosphate fertiliser on low Olsen P soils. The outcome of this thesis is that beneficial vermicast can be produced from organic wastes and has potential to improve food production in New Zealand. It may also be possible to use vermicast to reduce reliance on conventional fertilisers such as DAP.