Abstract

A study was conducted to determine the irrigation regime and its impact on the yield of three genotypes of greenhouse tomatoes in 2022 at the experimental field of MVCRI – Plovdiv in an unheated steel-glass greenhouse of the Venlo type. The experiment was conducted in three irrigation regimes:
Optimal 100%M, reduced by 25% and increased by 25%, using water-saving technology.
The size of the irrigation norms, the number of irrigations for the growing season and their distribution by development phases for the soil and climatic conditions of the Plovdiv region were determined.
The obtained results for irrigation of greenhouse tomatoes show that 18 irrigations were implemented during the growing season in order to maintain soil moisture between 85-100% of the maximum field moisture capacity for the conditions of Plovdiv from the beginning of May to the end of July.
The size of the irrigation rates by regimes varies from 14.9 to 24.7 mm, and the irrigation rates – from 268 to 447 mm. The maximum irrigation rates during the period with the most significant water consumption can be applied after 3-4 days and satisfy the needs of the plants. The analyzed results of the yields obtained from the three tomato genotypes at different irrigation rates show that the highest total yield of greenhouse tomatoes is formed in the variant with 125% implementation of the irrigation rate, followed by the variant with 100% irrigation rate, and the lowest, in the variant with 25% reduction in the irrigation rate.
Obtaining a good effect from irrigation and the most productive use of irrigation water is possible only when applying an optimal irrigation regime, consistent with the requirements of the crops grown.
A number of studies have been conducted in our country on the limiting factor – water. Their main goal is to establish the best efficiency of applying different irrigation regimes for irrigation under optimal and insufficient water supply. (Kireva et al 2020)
The best results in terms of water use in this crop are obtained when the soil moisture is above 85% of the WHC and is applied to water-saving irrigation techniques. This method fully meets the requirements for sustainable agriculture and ecological fruit production, including ensuring high yields and quality of production, reducing unwanted side effects. (Bucks et al.,1982; Kireva ,2020.)
The results obtained by (Mukherjee, S., et al. 2023) show that physiological characteristics, yield and water productivity are significantly influenced by the irrigation system and soil moisture regime, with drip irrigation improving the average yield of tomatoes by 25%.
It was found that reducing the optimal rate (100% M) with a water stress of 50% (50%M), a significant decrease in yield (13.16%) was observed in greenhouse tomatoes (Wu et al. 2022 ; Lu et al. 2019 ). Alternatively, Wu et al. ( 2022 ) stated that under optimal irrigation conditions, tomato plants produced more fruits than those grown under deficit irrigation.
With the studies of the mutual influence of different irrigation regimes on the yield of tomatoes grown in a polyethylene unheated greenhouse, it was found that the impact of irrigation on yield has a greater effect at higher levels of irrigation rate, (Stoyanova A. et al.,2020; Stoyanova A. et al. 2019).
Studies of the irrigation regime and its influence on the yields of tomatoes grown in plastic greenhouses using drip irrigation are quite scarce, and the studies carried out in our country are for the conditions of the Sofia Field (Aboamera M. 1992; Kireva,; Kireva R.,2020) and for St. Zagora (Stoyanova An. et al. , 2020), which cannot be indicative of other agro-climatic regions of the country, which are characterized by different soil and meteorological conditions. Given the above, it is evident that research is needed to establish the complex influence of the irrigation regime on the quantity and quality of the yield of tomatoes grown in glass unheated greenhouses for the soil and climatic conditions of a region with developed vegetable production, such as Plovdiv. This will be achieved by using principal component analysis to assess the effects of tomato quality and the efficiency of water use and fertilization.
Study objective – determining the irrigation regime and its influence on the yields of greenhouse tomatoes for the region of the city of Plovdiv