Does Compost Use Affect Post-Harvest Quality of Vegetables?

In prior research, we have often observed increased uptake of nutrients into leaves of peppers when we added compost to the soil. Since some of those nutrients may help to improve postharvest quality, we wanted to study the effects of compost on postharvest quality. The objectives of this study were:
To determine nutrient uptake into tomato, pepper, and cucumber fruit and lettuce leaves grown with or without compost;
To measure quality parameters of those vegetables before and after storage.

The experiment was done on a commercial farm with sandy soil in southeast Florida. The growing system used was raised beds with drip irrigation, fertigation, and polyethylene mulch. Treatments were no-compost (NC), single-year compost (SYC), and multi-year compost (MYC) (which had a yard trimming compost applied to them the year before). In the second year, new plots were used for the SYC and NC treatments. Horse manure compost was used at 10 Tƒ³A-1 the first year and 25 Tƒ³A-1 the second year.

In each year, tomatoes and peppers were planted in the first season (Sept.-Dec.), followed by cucumbers and lettuce in the same plots in Jan.-April. After harvest, samples of the vegetables were taken for testing for nutrients and two or more boxes of each vegetable were stored for varying periods of time at the recommended storage temperatures. There were few differences in firmness of fruit or percent of decayed vegetables after controlled temperature storage.

In all cases where there were differences in tomato nutrient contents, nutrients were higher in fruit from compost plots-especially the MYC treatments. While calcium in tomatoes was different only in the first season, phosphorus was different in both seasons, and potassium in the second season. In the first season, calcium in the pepper fruit was higher in peppers from NC compost plots, manganese was lower in MYC and copper was lower in fruit from SYC than the other two treatments. In the second season, manganese and zinc were lower in compost plots.
There were no differences in cucumber fruit nutrients during the first season, and, in the second season, only phosphorus was higher in the MYC treatment. During the first season, lettuce leaf calcium was higher in MYC than in SYC or NC, but there were no differences during the second season.

Despite the differences in nutrient contents, there were no clear trends in storage life differences. Based on previous compost research in our area, higher rates of compost application may have given us more results. But, we tried to use realistic rates of compost that growers are more likely to use. There is a need for many more studies on the effects of organic soil amendments (composts and/or cover crops) on storage characteristics of vegetables and fruit. Improvement in produce storage quality could be an additional marketing tool for those growers who use organic soil amendments, and an incentive for others to include them to their production systems.