Quantifying the effect of compost mulches on the nutrient uptake and fruit quality

The higher soil C levels observed at the mulch treatments (3 to 8) compared to the unmulched control treatments (1 and 2) in 2010 was also observed in both 2005 and 2008 (data not shown).

No clear trends were observed between the soil mineral concentrations and the rate of plant mineral uptake. However, highest soil Ca levels were observed with treatments 5 and 6, and even though not significant, leaf Ca was the highest at treatment 6 in 2009 and at treatments 5 in 2010. Similarly, with Mg the highest soil levels where observed at treatments 6, even though not significant, this resulted in the highest leaf Mg levels in both 2009 and 2010 together with treatment 5, and the highest fruit Mg levels in 2009.

Furthermore, the soil pH was significantly lower at the control treatments (treatment 1(average pH 4.42) and treatment 2 (average pH 4.63)) at all depths. The 2007 analyses indicated that the percentage of mycorrhizal colonized roots were significantly higher at the mulched treatments compared to the unmulched (except for treatment 3). Only in 2010 all the mulched treatments resulted in significantly lower fruit N levels, however this was the general trend from 2007, especially with treatments 3, 6, 7 and 8. This however did not correspond with leaf N as no clear trends could be identified in 2009 and 2010. Analysis in 2007 indicated that the unmulched treatments contained a significantly higher number of microbes during spring time (data not shown).

In contrast to the spring analyses, bait lamina analysis during summer resulted in microbial activity being the lowest at the unmulched control treatments (data not shown). Despite the lower yields produced by all the mulched treatments in this trial, fruits size and quality remained unaffected in 2009 and 2010 due to treatments. At treatments 6 and 8, where compost tea was added in addition to the compost/ mulch, no clear trends were found in terms of mineral uptake to the leaves or fruit. Furthermore, no distinguishable trends were evident in terms of soil biota, tree growth, yield or fruit quality throughout this trial period.