AHDB Horticulture funded Project TF 177 to assess the long-term effects of applied composted green waste mulch on the cropping of Braeburn and Cox apple orchards. Trees growing in a bare herbicide strip in a Braeburn and Cox orchard in Kent were compared with those mulched with composted green waste. The effects of the mulch were assessed on fruit size, weight, number per tree, maturity, mineral analysis, storage potential and soil moisture.
The mulch had a significant impact on fruit size particularly in Cox where, in every year of the project, fruit from trees that had been mulched were up to 6mm larger compared with fruit from untreated trees. For Braeburn, the effect was more variable.
In both Cox and Braeburn, the mulch led to an increase in fruit numbers resulting in significantly increased yields and equivalent returns per hectare. The mulch also led to more shoot growth in both varieties with young trees filling their space in the orchard earlier than untreated trees.
The compost treatment led to an increase in fruit nitrogen levels and a reduced level of calcium. This could have an adverse effect on the long-term storage potential of the fruit. Growers using such mulches must ensure that they analyse fruit mineral content every year before harvest and also analyse leaf and soil samples routinely and apply soil and foliar feeds accordingly.
Fruit on compost-treated trees matured around two weeks earlier than fruit on untreated trees, measured by an earlier drop in percentage starch and fruit firmness. There were also changes to fruit colour. Fruit from mulched trees did not show as much red colour and the background was a darker green although this was more a result of the fruit nitrogen content rather than any effect on maturity. Fruit from compost-treated orchards needs to be harvested separately and maturity tests conducted on farms to determine the optimum harvest date for individual orchards.