Evaluation of Vermicompost-inorganic Fertilizer Combination on Growth, Yield and Quality of Strawberry

Abstract

Yield and quality of strawberry is constrained by sub-optimal management of the crop’s nutrient. Strawberry require large quantities of nitrogen (N), phosphorus (P) and potassium (K), and other nutrients for vigorous growth, as well as to maximize yield and quality. Synthetic fertilizers provide N, P and K in potentially higher concentrations compared with organic substrates. However, food safety and high production costs have seen a steady increase in the use of organic fertilizers such as vermicompost in strawberry production. Vermicompost is the product of the decomposition of organic matter that uses worms, and in particular red wigglers (Eisenia fetida). Vermicompost may not readily release nutrients thus necessitating the judicious combination with synthetic fertilizers. This study was carried out to (i) evaluate the effect of different combinations of inorganic fertilizer and vermicompost on growth and yield of strawberry, and (ii) to determine the effect of different combinations of inorganic fertilizer and vermicompost on quality of strawberry and soil properties. Treatments included a combination of different fractions of inorganic fertilizer and vermicompost, in addition to three controls of sole vermicompost, sole NPK fertilizer and control. Nutrient combinations were 100% NPK, 100% vermicompost , 50% NPK + 50% vermicompost, 75% NPK + 25% vermicompost, 25% NPK + 75% vermicompost, 100% NPK + 100% vermicompost, and unfertilized control. The treatments were applied in Chandler strawberry studied in field experiments for two seasons from October 2020- March 2021 and April 2021-September 2021 in Kabete farm, University of Nairobi. Experiments were set out in a randomized complete block design and replicated three times. Key data comprised plant growth parameters including number of crowns, runners and runner length, yield parameters including the number of fruiting plants, fruit growth rate, number of fruits, and fruit weight. Fruit quality parameters included fruit firmness, fruit color, total soluble sugars, vitamin C, and titratable acidity. Soil parameters consisting of bulk density, penetration resistance, porosity, infiltration rate, and soil microbiology were tested at the end of the second experimental season. Data were analyzed using the 12th edition of GenStat computer software. Treatment means were compared and separated using Fisher’s protected least significant difference. Application of vermicompost and inorganic NPK increased strawberry growth and yield compared with unfertilized control. In the first cycle of experimentation, addition of 100% NPK outperformed the other treatments with regards to crop developmental rates and number of crowns per plant. Under 100% NPK, crops produced crowns 13 days earlier compared with 100% VC treatment. However, significant shifts were observed during the second cycle where crops grown under 100% VC matured earlier and produced 9 crowns more compared with 100% NPK. Addition xiii of both inorganic NPK and vermicompost significantly increased the number of fruits and fruit weight compared with unfertilized control. Across the entire sampling period, vermicompost-NPK combination at a rate of 75% VC + 25% NPK surpassed the other treatments in regard to the number of fruits and fruit weight, having a mean of 27 fruits per square meter and a mean fruit weight of 22 grams. These results revealed that use of vermicompost alone or in combination with inorganic fertilizers is beneficial in field grown strawberry for improved growth and yield. In the second objective, there was a positive effect of vermicompost and inorganic NPK on strawberry fruit quality and soil properties. During the two experimental seasons, combination of vermicompost and inorganic NPK significantly influenced the quality of strawberry used compared with the three controls of sole NPK fertilizer, sole vermicompost and unfertilized control. Fruits that received 100% VC as well as 75% VC + 25% NPK outperformed their counterparts in selected fruit quality attributes. 100% VC fertilized plants produced fruits with the highest TSS (10.2). Fruits under 25% NPK + 75% VC as well as 100% VC had the lowest acidity (0.7%) and high vitamin C content of 36.7. Therefore, results from these selected quality attributes suggest that the use of vermicompost in combination with inorganic NPK led to an increase in quality of strawberry. Sole application of vermicompost outperformed its counterparts in regard to soil properties. Under 100% VC, soils had the lowest penetration resistance (3.22), highest infiltration rate (4.20) and highest porosity percentage (58.02%) compared to all other treatments. Soils that received 100% vermicompost had 160% more earthworms and 90% higher total biodiversity compared to soil that received 100% NPK. Soils in the control plots had 53% higher total biodiversity than soils with 100% NPK. In conclusion, addition of vermicompost in combination with inorganic NPK positively influences growth, yield, and quality of strawberry. Across the entire sampling period, sole vermicompost and 75% VC + 25% NPK had optimal results in most key parameters compared to other treatments. Nonetheless, economically optimal combinations of vermicompost and inorganic fertilizer deserve further investigation