Compost, rich in plant nutrients, is a readily available fertilizer with beneficial effects on physical, chemical, biochemical and biological properties of the soils. Moreover compost-based treatments can exert protective effects against plant diseases occurrence and/or stimulate an enhanced plant physiological status with improvements in quantity and quality of crop productions. In this study the effects of three different compost-based cropping managements on the productive response and main quality parameters of watermelon fruits were investigated. Treatments, in comparison with the conventional cultivation method, were: soil amendment with an agricultural waste compost (AWC), a municipal waste compost (MWC) and a foliar treatment with a compost tea blend (CTB). The productive responses and colour parameters related to compost treatments did not show significant differences compared to control ones, which reached a total yield of about 10.22 kg·m -2 with a mean weight of 2.74 kg. AWC caused a higher ascorbic acid content with an increase of 50% than conventional treatment, while fruits obtained by CTB showed higher values in firmness and Quality Index than control samples. The analysis of main sugars highlighted that the application of compost as biofertilizer influenced the ratio among fructose, glucose and sucrose with respect to those observed for control fruits.
Among summer fruits, watermelons have a very high favour by consumers because to their high satiety index, low caloric intake and thirst-quenching and refreshing capability. In recent years, mini and seedless watermelons (Citrullus lanatus, Thunb.) have been developed to respond to the needs of small families, singles and consumers that have limited refrigerator space. The appeal to the mini watermelons can be further strengthened by the introduction of sustainable crop production, which gives an added value to the fruit. Increasing interest to food safety and environmental pollution has stimulated the attention for compost as valid alternative to the use of chemical fertilizers, beside the recovery of by-products from the refusals. Compost is the final product of the composting process, a solid state controlled microbial fermentation of organic and no degraded matters, which can include crop residues, animal wastes, food garbage, organic municipal and industrial wastes. Pane et al. [
Agronomic trials were carried out in 2012, under a greenhouse system in a loamy soil, at organic farm “IdeaNatura” located in Eboli (Salerno, Italy). The experimental design was a randomized complete block with plot areas of about 100 m2 each, replicated three times. Mini watermelon plants (cv Chicago) were transplanted on April 12th, on single raw, at distances of 0.50 × 1.80 m, in order to have a density of 1.10 plants∙m−2. Two different experiments based on the comparison among two compost and control amendments and between compost tea aerial spry treatments and not-treated plots were carried out. The compost treatments were:
・ On-farm Agricultural Waste Compost (AWC), prepared from residues of corn, cabbage, fennel and salads mixed to wood chips [
・ Municipal organic Waste Compost (MWC) purchased at Gesenu (Perugia, Italy);
・ Compost Tea Blend (CTB) prepared by mixing (50% vol.) two 1-week aerated teas produced by water extraction of artichoke and artichoke + fennel green composts (20% vol.) [
Composts were applied at a dose necessary to supply 170 kg∙ha−1 of nitrogen, thus 6 ton∙ha−1 of AWC (N = 2.8%) and 8.5 ton∙ha−1 of MWC (N = 2.8%) in dry weight, and were incorporated into the soil at a depth of 15 cm. CTB, water diluted 10% vol., was weekly applied by spraying aerial parts of the plants. Total yield was determined in an assay area of about 11 m2 for each plot. For each compost treatment five fruits were analyzed for the evaluation of the main agronomical, chemical, physical and sensory parameters.
Moisture and pH were determined in accordance with the Association of Official Analytical Chemists (AOAC) official methods [
Ascorbic acid was determined by ion exchange chromatography according to Cinquanta et al. [
Firmness was measured by compression tests using a texturometer (Ametek Lloyd Instruments LRX plus, United Kingdom), with specific software (Nexygen batch 4.1). The size of watermelon samples analyzed was standardized with a cylinder cutter into pieces 2 cm in diameter and 1 cm in height. Firmness of watermelon samples was obtained from load and strain curves recorded during the compression of cylindrical samples to 50% of initial height, using two horizontal parallel plates, with the sample placed on the middle of the lower plate [
A comprehensive survey of the sensory characteristics of colour of the pulp, crispness, sweetness, juiciness, mealinins and global odours of mini watermelons, was carried out. The intensity of the sensory terms was scored on nine-point structured scale (1 = none; 9 = extreme). Random samples of different treatments were presented in three-digit coded plates and were separately evaluated by 12 untrained consumer panelists. The mean scores for each attribute were finally summed to give an overall sensory score known as the Quality Index (QI). For the calculation of QI, mealiness attribute was considered as negative value.
All analyses were performed in triplicates. The average and standard deviation of each chemical, physical and sensory parameters results were subjected to a mono-factorial variance analysis (ANOVA), and the significance of differences (P < 0.05) among means was determined with Fisher’s Least Significant Difference (LSD) test. Statistical analysis was performed using an SPSS version 13.0 for Windows (SPSS, Inc., Chicago, IL, USA).
The productive responses to AWC, MWC and CTB treatments, compared to their control plots, were reported in
The force corresponding to breakdown of the fruit tissue during compression test of flesh fruits was used as firmness of the mini watermelon samples. Fruit firmness and texture are most closely associated with cell wall
Sample | Total yield (kg∙m−2) | Fruits | ||||
---|---|---|---|---|---|---|
Weight (kg) | N˚ m−2 | Major diameter (cm) | Minor diameter (cm) | Pericarp thickness (cm) | ||
CTRL | 9.82 ± 0.27a | 3.12 ± 1.12a | 4.44 ± 0.64a | 16.73 ± 0.50a | 15.20 ± 1.11a | 1.24 ± 0.14a |
MWC | 8.70 ± 0.98a | 3.10 ± 1.38a | 4.04 ± 0.89a | 16.67 ± 0.11a | 15.65 ± 0.60a | 1.14 ± 0.11a |
AWC | 9.64 ± 0.39a | 3.12 ± 1.10a | 4.29 ± 0.54a | 16.73 ± 0.42a | 15.66 ± 0.95a | 1.23 ± 0.17a |
Sample | Total yield (kg∙m−2) | Fruits | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
Weight (kg) | N˚ m−2 | Major diameter (cm) | Minor diameter (cm) | Pericarp thickness (cm) | ||||||
CTRL | 10.62 ± 1.13a | 2.36 ± 0.07a | 4.66 ± 0.43a | 16.60 ± 0.53a | 15.80 ± 0.20a | 1.21 ± 0.06a | ||||
CT | 9.42 ± 1.27a | 2.90 ± 0.59a | 4.02 ± 0.51a | 16.53 ± 1.28a | 15.62 ± 1.22a | 1.18 ± 0.11a | ||||
Different letters mean significant difference (P < 0.05).
structure and composition. Firmness is determined largely by the physical anatomy of the tissue, particularly cell size, shape and packing, cell wall thickness and strength, and the extent of cell-to-cell adhesion, together with turgor status [
The comparison of firmness parameter detected on mini watermelon samples grown with and without different types of compost was shown in
Brittle properties of flesh fruits were recorded through rigidity value (
The amount of the principal sugars (glucose, fructose and sucrose) detected in mini watermelon flesh cultivated by different treatments, was reported in
Colour parameters detected on the middle of the different watermelon samples were reported in
The use of different types of compost, compared to conventionally cultivation, showed significant differences in vitamin C content (
The quality assessment of mini watermelons was reported in
Sample | L* | a* | b* | C* | H˚ | Ascorbic acid (mg/100g fw) | Flesh firmness (N) | Flesh rigidity (KN/m) |
---|---|---|---|---|---|---|---|---|
CTRL | 40.08 ± 3.70a | 20.11 ± 3.01a | 19.15 ± 2.22a | 27.88 ± 2.79a | 43.80 ± 5.19a | 8.62 ± 0.20c | 5.20 ± 0.26a | 3.47 ± 0.17b |
MWC | 39.40 ± 2.42a | 22.27 ± 1.13a | 18.74 ± 1.70a | 29.13 ± 1.69a | 40.04 ± 2.38a | 5.84 ± 0. 15b | 4.27 ± 0.21b | 3.29 ± 0.16b |
AWC | 39.59 ± 1.87a | 22.78 ± 1.07a | 16.65 ± 2.65a | 28.26 ± 2.40a | 35.91 ± 3.55a | 12.93 ± 0.18a | 4.91 ± 0.24a | 4.43 ± 0.22a |
Sample | L* | a* | b* | C* | H˚ | Ascorbic acid (mg/100g fw) | Flesh firmness (N) | Flesh rigidity (KN/m) |
---|---|---|---|---|---|---|---|---|
CTRL | 36.42 ± 3.01a | 21.49 ± 3.58a | 15.08 ± 4.29a | 27.64 ± 4.31a | 34.38 ± 4.10a | 8.23 ± 0.15a | 4.12 ± 0.21b | 4.02 ± 0.20a |
CTB | 35.85 ± 1.86a | 18.37 ± 1.25 a | 15.19 ± 2.66a | 23.87 ± 2.52a | 39.29 ± 3.72a | 5.98 ± 0.09b | 5.89 ± 0.29a | 4.27 ± 0.21a |
Different letters (a, b, c) mean significant difference (P < 0.05).
Sample | Flesh colour | Global odours | Crispness | Juiciness | Sweetness | Mealiness | Quality Index |
---|---|---|---|---|---|---|---|
Control | 7.00 ± 0.35a | 6.71 ± 0.38ab | 6.57 ± 0.40a | 7.71 ± 0.20ab | 7.43 ± 0.38a | 1.57 ± 0.20a | 33.86 ± 1.8a |
MWC | 7.33 ± 0.63a | 6.33 ± 0.30b | 5.17 ± 0.28b | 6.15 ± 0.35b | 7.17 ± 0.28a | 3.17 ± 0.40b | 30.3 ± 1.4b |
AWC | 7.83 ± 0.35a | 7.33 ± 0.40a | 7.50 ± 0.35c | 8.00 ± 0.30a | 7.67 ± 0.42a | 2.17 ± 0.30a | 36.2 ± 2.0a |
Sample | Flesh colour | Global odour | Crispness | Juiciness | Sweetness | Mealiness | Quality Index |
---|---|---|---|---|---|---|---|
CTRL | 8.00 ± 0.26b | 6.83 ± 0.99a | 6.33 ± 0.32b | 7.50 ± 0.35b | 8.33 ± 0.32b | 4.50 ± 0.38b | 32.50 ± 3.2b |
CTB | 9.00 ± 0.63a | 8.00 ± 0.53a | 7.83 ± 0.41a | 8.67 ± 0.52a | 8.83 ± 0.41a | 2.33 ± 0.30a | 40.00 ± 1.3a |
Different letters (a, b, c) mean significant difference (P < 0.05).
as crispness, juiciness and sweetness, and negative ones like mealiness. In fact, it is worth noting that crispness of mini watermelons grown with AWC was significantly higher than control and MWC samples, which presented the lowest score. About juiciness, mini watermelons treated with AWC and MWC were different (P < 0.05) between them but not with respect to the control samples.
Mini watermelons grown with MWC had the highest score of mealiness with respect to AWC and control samples, which were perceived similarly. This tasting attributor affects negatively the Quality Index. The assessment of mini watermelons grown with CTB revealed significant differences (P < 0.05) when compared with its control, as regard crispness, juiciness and mealiness. In fact, CTB mini watermelons were crispier and juicier but less mealy than control samples. Lastly, CTB samples were preferred to the control ones, whereas AWC mini watermelons were preferred to MWC and control samples.
Compost and compost teas are largely reported to be complementary to conventional methods of crop management for the enhancement of the quality associated to the agricultural products [
Sugars content together with colour of the flesh are the most important parameters that influence the consumer acceptability of mini watermelon fruits. As reported elsewhere [
The kind and amount of various carbohydrates directly influence fruit flavour components, such as sweetness [
Carbohydrate accumulation is closely related to stachyose metabolism [
Ascorbic acid (AA) has long been considered an important nutritional component of the fruits. The concentration of vitamin C in watermelon’s flesh depends on several factors such as cultivar, environmental conditions and cultural practices. In fact, it ranges from 38.2 - 69.8 mg/kg fw, as reported by Leskovar et al. [
The differences found for vitamin C, but also for the other quality parameter investigated, among fruit samples treated by compost with respect to their control, may be attributed to a different concentration and/or release of potassium salt to the plant. Lester et al. [
The efficacy of AWC soil amendment and CTB foliar spray were particularly evident on the qualitative intrinsic parameters of the fruits rather than on agronomic traits while, MWC decreased overall parametric set. Few previous studies concerning the use of the compost to grow plants of this species highlighted a low sensitive yield response to compost amendment [
The results of this study highlighted that two compost amendments and a compost tea aerial spry treatments did not change growth and yield factor of the crop. Compost-based treatments seemed to influence the quantitative profile of sugars of the fruits even if the sweetness, judged by the panelists did not show significant differences among the samples. Compost tea, specifically, provided improvement for Quality Index which represented the overall sensory score of the watermelons and thus higher preferences by the consumers. The data obtained in this study allowed presuming that the compost and compost tea should be used as a valid and promising alternative to the use of chemical stimulants in mini watermelon cropping systems.
Greenhouse trial of this research was supported by the “BioCompost” Project, funded by the PSR 2007/2013 European funding programme (F.E.A.S.R., Measure 124).