The effects of waste derived fertilisers and composts on crop production

The waste from olive oil production is a valuable source of nutrients that has the potential, when used well, to be a useful organic amendment to aid crop growth. It does have some drawbacks with potential phytotoxicity due to being likely to have a high amount of phenols present and a high conductivity. The waste from olive oil production used in these trials was composted with different animal manures to produce a number of products with different characteristics. In some of the trials a replacement form of organic amendment in the form of chicken manure was used instead. In addition to these amendments, some of the trials included biochar as an additional organic amendment to see if the properties of the biochar had any effect on plant development and yield.
The trials discussed in this thesis take place over a 3 year period on 3 different crops: winter wheat, oilseed rape and strawberries. The wheat was grown at both field and pot scale in the trials.
The field scale trials with oilseed rape and winter wheat showed no significant differences between yields when comparing a mineral fertiliser to a substitute chicken manure fertiliser. In the first harvest year the oilseed rape showed significantly higher yields on the plots that received biochar as an amendment, however this result was not replicated by the winter wheat in that or the subsequent harvest year.
When the olive mill waste compost was used as a substrate replacement for strawberries, the strawberry crop showed no significant patterns or changes in development due to the amendment applied in the first year. In the subsequent when used again as a growth media and more graduated inclusion amounts (% v/v) the OMW caused plant mortality in plants receiving more than 20% inclusion of compost. The compost used in this year had a high conductivity to which the high plant mortality was attributed. The plants that received more than15% OMW compost also produced significantly less marketable fruit, and the fruits produced were more poorly pollinated. In the same year, the OMW was applied to wheat at pot trial scale, but used as a fertiliser and applied at the same nitrogen loading rate as the mineral nitrogen applied. In this trial there was no plant mortality of the wheat, and no discernible difference in the plant development.

These trials have shown that compost of olive mill waste and animal manures can be used as an alternative to traditional mineral fertilisers on both arable and horticultural crops in the UK and as a soilless media replacement, however it is important to consider the characteristics of the OMW before applying it.