The influence of irrigation regime and plant protection on productivity and quality of onions using the drip irrigation method

Abstract

Onion is one of the main vegetable crops used in fresh, cooked, and roasted; it is indispensable for the preparation and flavoring of a wide variety of dishes. Practical experience of specialized farms of different sizes and forms of ownership against the background of a steady increase in purchasing prices for onions, causes an increase in the production in different countries of the world, including Ukraine. Therefore, studies on optimizing irrigation regimes and the development of an integrated plant protection system for growing onions in the southern Ukraine are relevant.

Onion is one of the most valuable and common vegetable plants. The largest areas of food crops are located in the steppe of Ukraine. However, mostly varieties of foreign origin of onion are introduced, which are often unable to fully reveal their potential in the complex natural and ecological conditions of the Steppe. The analysis of the actual state of agricultural production in Ukraine shows that the provision of the population with environmentally safe vegetables, including onions, is insufficient and amounts to 80-85% of the scientifically grounded need. The key to increasing the yield of onions without increasing the area of sowing is the application of modern technologies that ensure the formation of high and qualitative yield, as well as being justified from an economic point of view and maximize profits.

The purpose of the research was to determine the effect of the irrigation regime and plant protection on the productivity and quality of onion in conditions of drip irrigation in southern Ukraine. The objective of the study was to determine the effect of the factors under study on yield, water consumption, quality of onion, the proportion of factors influencing the total sugar content, the content of vitamin C, the content of dry matter.

Field and laboratory studies were conducted during 2014-2016 on the territory of the experimental farm "Plodove" of the Rice Institute of the National Academy of Sciences of Ukraine. The agrotechnics in the experiment were generally accepted for conditions, with the exception of the studied factors. The predecessor was winter wheat. Watering was carried out in accordance with the experimental scheme.

The difference in weather conditions, which was recorded in some years of research, has had a significant effect on the yield of onion. The lowest indexes of average factor productivity of the investigated crop 55.0 t/ha were recorded in 2015 without plant protection, which can be explained both by the effects of drought and the high level of humidity in the second half of the growing season. This caused damage to the leaf surface, caused premature drying of plants and had a very negative impact on yields.

On average, over the years of research, the tendency of the growth of the yield of onion in the use of chemical protection of plants and the growth of soil moisture from 70 to 90% of LMC (lowest moisture content) is observed. The lowest index of yield 54.2 t/ha was with irrigation regime of 70% of LMC and without plant protection.

The maximum productivity is indicated in variants with irrigation 80-90% of LMC and in the application of chemical protection of plants, where it was 83.5-84.2 t/ha. The largest marketability within the range of 85.3-90.7% is indicated in the variant with irrigation 90% of LMC and in variants with an irrigation regime of 70-80% of LMC this indicator has decreased to 74.5-76.8%. The highest average diameter of the bulb of 64.8 mm was in the variant with irrigation regime of 90% of LMC and in the chemical system of plant protection.

On average, factor A (irrigation regime) indicated an increase in onion yield from 67.9 to 70.8-72.4 t/ha or 4.1-6.3% when the level of moisture provision of plants was improved in variants with irrigation 80 and 90% of LMC. Regarding the protection of plants, it has been proved that the average yield factor of the investigated crop increased from 57.5 t/ha in the control variant without protection to 70.9-82.7 t/ha or 18.9-30.5%.

The lowest consumption of irrigation water for the formation of 1 ton of onions was recorded in the variant with chemical protection of plants and irrigation at 70 and 80% of LMC, on which the water consumption coefficient decreased to 45.1-47.3 m3/t.

Marketability and average diameter of the bulbs also reached the highest level in variants with irrigation 80-90% of LMC and application of chemical protection of plants.

The conducted dispersion analysis of the field data obtained in the field experiment was able to establish significant differences in the effects of irrigation regimes and plant protection on plant productivity. The maximum impact on the yield of onion was provided by the protection of plants (factor B), whose impact increased to 63.5%. Irrigation regime (factor A) also significantly influenced the studied indicator – 12.9%. Practically at the same level – 12.8% was the share of influence of the interaction of the investigated factors, and the influence of other unrecorded factors (residual index) accounted for 10.8% of the total volume of the harvest. 

Indices of quality of onions changed under the influence of factors that were put into study. Total sugar was in the range of 6.2-8.4%. On average, by factor A, this figure decreased by 4.4-6.2%, with an increase of pre-watering threshold from 70 to 80-90% of LMC. Application of plant protection caused an increase in the content of total sugars on average to 7.7-7.9% or 19.1-21.8%. Analysis of the content of vitamin C and dry matter also allowed revealing a tendency to reduce these indicators in variants with irrigation scheme 80-90% of LMC by 2.7-4.4%, and vice versa, increase by 2.0-9.1% - with application of biological and chemical protection of plants. The content of dry matter in the bulbs fluctuated to a lesser extent –  from 10.2 to 12.9%, with a tendency to decrease this index with an increase of pre-watering threshold of soil from 70 to 90% of LMC.