The effect of animal manure extracts as a source of nutrients on growth, yield, and quality of hydroponically grown tomatoes (Solanum lycopersicum L.).

Abstract

Tomatoes rank as the second most vital vegetable crop in the world, they are grown globally except Antarctica. They are highly nutritional as they contain vitamins and antioxidants that benefit human health. The cultivation of these fruits is however costly due to the overuse of chemical fertilizers since their nutrient formulations are very expensive. Thus, this study assessed the potential of animal manure extracts on the growth of tomatoes under hydroponic production system. The first experiment evaluated the nutrient concentrations of fresh manure and vermicompost from three different sources (chicken, cow and goat) and to further optimize nutrient extraction by passive and active extraction methods. The second experiment investigated how extracts from animal manure influenced growth, leaf gas exchange and chlorophyll fluorescence of tomatoes (cv. CLX 532) grown in the soilless hydroponic system. The third experiment assessed the impact of animal manure extracts on yield, physiochemical and nutritional quality of tomatoes grown in soilless hydroponic cultivation. The findings showed that, over the composting period, cow manure increased all nutrients, goat manure increased N, P, Ca, Mg, Zn, Cu and Mn; while chicken manure enhanced P, Ca, Mg, Zn, Cu and Mn. Aerated compost tea had a higher nutrient content than non-aerated compost tea, chicken-based compost tea (N, P, K, Ca, Mg, Zn, Mn, Cu and EC), cow-based compost tea (P, Mg, Cu and Zn) and goat-based compost tea (P, K, Ca and Mg). Therefore, pre-composting before vermicomposting is highly recommended. Furthermore, using the active extraction method (aerated) increased the nutrient availability in the animal-based compost tea. The findings for the second experiment showed that applying goat manure extract (GME) and chicken manure extract (CHME) boosts plant height, stem diameter, fruit number, intercellular CO2 rate (Ci), intrinsic water use efficiency (WUEi), maximum fluorescence (Fm) and nonphotochemical quenching (qN) while cow manure extract (CME) increased stomatal conductance (gs), maximum quantum efficiency of photosystem II (Fv/Fm) and electron transport rate (ETR). The findings for the third experiment showed that the application of CHME enhanced the number of fruits, shoot mass, TSS, TA, TSS/TA, BrimA, colour index and firmness, CME affected shoot mass, while GME affected TSS/TA, BrimA, firmness and phenolics concentration. Furthermore, fruits fertigated with the commercial fertilizer were rich in macronutrients, whereas those fertigated with animal manure extract (AME) had elevated levels of micronutrients. Based on these findings, animal manure extracts could serve as an alternative source of nutrients in the soilless production of tomatoes, especially CHME and GME. They improved growth, yield, leaf gas exchange, chlorophyll fluorescence and overall fruit quality.