Irrigation regimes for drip irrigation of watermelon in mulched and non-mulched fields

. In most regions of Uzbekistan, the biological productivity of the climate will decrease by 10-20%, and in some regions by 30-40%, the steppe and semi-desert zones will expand further. Therefore, it is impossible to effectively develop irrigated agriculture without the development and implementation of resource and water-saving technologies aimed at increasing the efficiency of irrigated water use. We carried out our experiments based on the development of optimal irrigation norms for the cultivation of watermelon plants in mulched fields by drip irrigation, keeping the differentiated soil moisture (60...70...60%, 65...75...65%, 70…80...70% and 75…85...75% SAM) in the defined norm. In this case, the soil moisture limit before irrigation is 60...65...70...75% SAM according to the experimental options of 0-20 cm layer in the "planting - shatrik" period and 0-40 cm layer in the "shatrik - bloom" period; The 0-50 cm layer was maintained at 70...75...80...85% SAM during the "bloom - fruit formation" period and the 0-50 cm layer at 60...65...70...75% SAM during the " fruit formation - ripening" period.


Introduction
According to many leading experts, the importance of factors influencing the increase in plant productivity is distributed as follows: reclamation, including water -49%, weather conditions -15%, seed -8%, other factors -31%. In this regard, weather conditions and irrigation are one of the main factors of crop production and yield increase [1,2].
The rational use of water requires the regulation of the water regime of the soil in such a way as to minimize infiltration and water losses, to isolate the water balance to the maximum and to maintain the mode of automorphic soil formation, allows to get economically useful crop [3].
The need for soil improvement will increase with expected global climate change. In most regions of Uzbekistan, the biological productivity of the climate will decrease by 10-20%, and in some regions by 30-40%, the steppe and semi-desert zones will expand further [4]. Therefore, it is impossible to effectively develop irrigated agriculture without the development and implementation of resource and water-saving technologies aimed at increasing the efficiency of irrigated water use [5][6][7][8][9].
Soil moisture is one of the important indicators of soil fertility -the main factor in the development and growth of plants [10]. Watermelon soil moisture dynamics is formed depending on meteorological conditions and drip irrigation regimes. That 's why, we conducted research to study watering parameters when growing watermelon plants by drip irrigation.

Materials and methods
Experiments were carried out in 2021-2022 at the "Center for Innovative Developments and Consultancy in Agriculture" DUK pilot farm at the Tashkent State Agrarian University.
Experiments were conducted in four replications in a randomized block (reversible) method. Watermelon seeds were sown in pairs (2.50+0.70): 2x0.50 cm. We used white and black polyethylene films with a width of 140 cm and a thickness of 0.02 cm for mulching the watermelon fields. Polyethylene films of this size are the optimal size for mulching (2.50+0.70):2x0.50 cm beds. This experiment was conducted on the "Shirin" variety of the watermelon plant.
Soil temperature (soil thermometer), seed germination, number of seedlings, phenological observations and biometric measurements, irrigation method, duration and number of irrigations (by V.YE. Kabayev's zuldar method) [4][5][6], yield amount, leaves surface area, number of leaves, stem and root weight, chemical composition of watermelon fruit, economic efficiency were studied from the day after planting watermelon seeds.

Results and discussion
The analysis of the experimental indicators obtained on the dynamics of moisture in the active layer of the soil when we carried out our experiments based on the development of optimal irrigation norms for the cultivation of watermelon plants in mulched fields by the method of drip irrigation, based on the preservation of differentiated soil moisture (60...70...60%, 65...75...65%, 70…80...70% and 75…85...75% SAM), showed that during the studies on all options of the experiments, the calculated rates of watering were maintained and no decrease was observed. Before watering, soil moisture was 2-4% lower than the permissible limit.
In our experiments, the time and speed of watering were determined taking into account the developmental stages of the watermelon plant, moisture reserves in the soil, atmospheric precipitation and meteorological conditions. Characteristics of watering parameters of watermelon plants in different regimes of drip irrigation in mulched fields are presented in Table 1.
Field studies have shown that in the initial period of plant development "planting -shatrik", the moisture limit before irrigation was maintained at 60...65...70...75% SAM. It was found that the norm of soil moisture falling below 60% can have a negative effect on the watermelon plant.
In the same period "planting -shatrik", the moisture limit before irrigation was 65...75...65% SAM, and the irrigation rate was 23 m 3 /ha. The water regime parameters of the watermelon plantation are similar to the option with a preirrigation limit of 60...70...60% SAM.
During this phase, "planting -shatrik", of plant development, in the option with the pre-irrigation limit of 75-85-75% SAM, depending on the meteorological conditions, irrigation was carried out 3-5 times, the norm is the same as in the option of 70-80-70% SAM. In the second "shatrik -bloom" period, according to the experimental options, the moisture before irrigation in the 0-40 cm layer was maintained at 60...65...70...75% SAM. According to the experimental options, irrigation was carried out 5-9 times. Due to the fact that the soil moisture had not fallen below the specified amount, we carried out irrigation at the rate of 46-92 m 3 during the period of "shatrik -bloom".
During the period of "bloom -fruit formation" of watermelon, the depth of maintaining the moisture level in the soil la yer before irrigation was 0-50 cm, according to its options, the marginal field moisture capacity was maintained at the level of 70...75...80...85% SAM.
During this period, in the 60-70-60% SAM option of the irrigation regime, irrigation in the non-mulched area corresponded to 138-161 m 3 /ha, the total irrigation was respectively 2415-2195 m 3 /ha. In this phase, in the 70-80-70% SAM option of the irrigation regime, the total irrigation rate was 805-1242 m 3 /ha in mulched and non-mulched fields, and the number of irrigations was 7-9 pcs. In the 75-85-75% SAM option of the irrigation regime in mulched and non-mulched fields of watermelon, the total irrigation rate was 920-1380 m 3 /ha, and the number of irrigations was 8-10.
During the period of "fruit formation -ripening", moisture in the 0-50 cm layer, according to the experimental options, soil moisture before irrigation was maintained at the level of 60...65...70...75% SAM. In this period, in the 60-70-60% option of the irrigation regime, the irrigation rate in mulched and non-mulched fields was 115 -161 m 3 /ha, and the total irrigation rate was 460 -805 m 3 /ha in this period. During the period of "fruit formation -ripening", in the 70-80-70% option of the irrigation regime, the total irrigation rate was 609 -966 m 3 /ha, and the number of irrigations was 6-8 pcs. In the 75-85-75% SAM option of the irrigation regime, the irrigation rate was 115-138 m 3 /ha, and the number of irrigations was 7-9 pcs.
In addition, it should be noted that 7-10 days before the start of harvesting watermelons, irrigation was stopped for all options of drip irrigation regimes ( Figure  1).
The results of our research showed that among the 4 different irrigation regimes, the yield of watermelon was higher in the option, where soil moisture was maintained at the level of 70-80-70% SAM, than in other options. At the same time, it was distinguished from the rest by the high quality of watermelon fruits. In the cultivation of the "Shirin" variety of watermelon in mulched and non -mulched fields, 23 -30 times the specified rate of irrigation was carried out to maintain the average regime of this option.
Watermelon yield and fruit quality increased in the 70-80-70% option, and a significant difference was observed in the number of irrigations and the total irrigation rate compared to the 75-85-75% option. These indicators make it possible to get a high yield and ecologically clean product from the watermelon plant while using less water for our farmers at a time when the climate is changing sharply and the water shortage is increasing.  As a result of the analysis and research of the moisture dynamics of the active soil layer according to the researched experimental options, the following was determined: the drip irrigation regime, first of all, the weather conditions during the active vegetation period of watermelon plants and the phenophases of the plant is determined taking into account the demand for water. It is also necessary to take into account the agrotechnical measures (such as mulching) used in the cultivation of the plant when determining the watering regimes of the watermelon plant. Because these agrotechnical measures directly affect the water consumption and transpiration coefficient of the watermelon plant. Another factor that affects the irrigation regime is that the soil moisture before irrigation is below the permissible level during the growing season.

Conclusions
Watermelon cultivation technology by drip irrigation gave good results in the territory of the Republic of Uzbekistan, and this cultivation technology allowed to get a high yield of watermelon based on the regulation of parameters of nutrients and water regimes. In addition, this cultivation technology has significantly reduced water consumption compared to conventional irrigation, while increasing productivity. This makes it possible to grow watermelon even in regions where there is no possibility of direct irrigation.
Also, among the options of our research, the option with soil moisture limit before irrigation of 70-80-70% has a positive effect on the formation of vegetative and generative organs of the watermelon plant, as well as the increase in overall productivity compared to other rest options.