This paper presents the standardized precipitation evapotranspiration index (SPEI)-based approach to agricultural drought monitoring (ADM-SPEI approach) combining well-known methods, expert’ critical opinions, and local agro-climatic specificities. The proposed approach has been described in detail in three phases. This allows its application in any region and modification according to different agro-climatic conditions. The application of the ADM-SPEI approach has resulted in obtaining a modified SPEI for different crops (agricultural drought SPEI (AD-SPEI_crop)) in the Vojvodina region. In the first phase of the proposed approach, analytical hierarchy process (AHP) was used to obtain an experts’ group decision regarding the most suitable method for calculating evapotranspiration for a particular analyzed region. In the second phase, SPEI was modified and adjusted to the conditions in Vojvodina, where ET₀ was replaced by ET_c. In the validation phase, the results of the application of AD-SPEI_crop were compared to crop yields and well-known indices and evaluated by the experts’ feedback. The statistically significant correlations were achieved between AD-SPEI_crop and crop yields. The highest correlations were achieved in the months when the analyzed crops were in the developmental stages when they are most sensitive to drought. The AD-SPEI_crop better correlates to the crop yields compared to SPEI. The comparison of AD-SPEI_crop to the standardized precipitation index (SPI), SPEI, and self-calibrated Palmer drought severity index (SC-PDSI) shows that it can successfully detect dry and wet periods. The results have indicated that the proposed approach can be successfully applied, and AD-SPEI_crop has shown a good performance for agricultural drought monitoring.

In order to study the effect of different irrigation schedules on yield and water use of onion (Allium cepa L., cv. Alek and Kupusinski jabučar), a field experiment was conducted on the calcareous chernozem soil in the Institute of Field and Vegetable Crops, Novi Sad in Serbia during 2005, 2006 and 2007 growing seasons. The experiment was arranged in a randomized complete block design and adapted to conditions of sprinkling irrigation. Three irrigation treatments according to available soil water depletion (Т1 30, Т2 50 and Т3 70%) and a rainfed treatment (Т0) were included. Results showed that onion yield was significantly affected by irrigation. The highest onion bulb yields of 30.22 and 34.99 t ha-1 were obtained from treatment T1 and Т3, respectively, in 2005. However, the highest onion bulb yields of 38.46 and 40.07 t ha-1 were obtained from T2 and Т3 treatment in 2006 and 40.96 t ha-1 from T1 treatment in 2007, respectively. The lowest yield of 10.10 t ha-1 was obtained from T0 treatment in 2007 with limited precipitation and higher than average seasonal temperatures. The seasonal evapotranspiration values of irrigated (ETirr) and non irrigated (ETO) onions ranged from 435.6 to 542.9 mm and 290.2 to 393.9 mm, respectively. The highest and lowest water use efficiency (WUE) of 91.35 kg and 34.80 kg ha-1 mm-1 was obtained in irrigation and rainfed conditions in 2007, respectively. The highest irrigation water use efficiency (IWUE) of 280.54 kg ha-1 mm-1 was obtained from Т1 treatment in 2007, while the lowest value of 45.83 kg ha-1 mm-1 was obtained from T1 treatment during the rainy period of 2005. High yields of bulbs produced from treatments Т1, Т2 and Т3 in different years indicated that amount and distribution of precipitation seriously affected the soil water regime and irrigation schedule of onion in the region. Therefore, irrigation schedule of onion has to be adjusted to climatic conditions of each year, mostly to amount and distribution of precipitation. Key words: Onion yield, irrigation scheduling, evapotranspiration, water use efficiency.

Drip irrigation is gaining importance in mitigating the consequences of water scarcity even in regions with abundant rainfall. The transition from surface to subsurface drip irrigation is accompanied by numerous problems. To overcome these issues, shallow subsurface drip irrigation can be potentially used as an effective drought control tool that brings additional benefits compared to conventional surface drip irrigation techniques. This research investigated the effects of different calculations of daily crop water requirements, reference evapotranspiration (ETo), and pan evaporation (Eo) on the yield and water use efficiency of pepper irrigated with a surface and shallow subsurface drip irrigation system. The experiment was conducted in field conditions in the Vojvodina region, the northern part of Serbia. The irrigation scheduling was based on the water balance approach. The calculated evapotranspiration rate was about 400 mm for the pepper growing period, regardless of the calculation method. The highest yield of pepper and evapotranspiration water use efficiency was obtained on the Eo variant with surface drip irrigation. However, irrigation water use efficiency showed no statistical significance concerning the calculation of evapotranspiration and irrigation type. The results indicated that both calculation methods and irrigation types can be used in pepper production, but priority should be given to pan-evaporation-based calculation.

Research was carried out at Rimski Šančevi experiment field of Institute of Field and Vegetable Crops in Novi Sad in the period 1993-2004. The experiment included an irrigated and non-irrigated control treatment. Irrigation water use efficiency (Iwue) and evapotranspiration water use efficiency (ETwue) were determined in order to assess the effectiveness of irrigation on soybean yield. The average yield increases of soybean due to irrigation practice was 0.82 t ha-1, ranging from 2.465 t ha-1 in years with limited precipitation and higher than average seasonal temperatures (2000) to 0 t ha-1 in rainy years (1996, 1997, 1999). Evapotranspiration water use efficiency (ETwue) of soybean ranged from 0.11 kg m-3 to 1.36 kg m-3 with an average value of 0.66 kg m-3, while irrigation water use efficiency (Iwue) varied from 0.11 kg m-3 to 1.04 kg m-3 with an average value of 0.56 kg m-3. Effect of irrigation on yield of soybean and results of both ETwue and Iwue which were similar to those obtained from the literature indicate that irrigation schedule of soybean in the study period was properly adapted to plant water requirements and water-physical soil properties. Determined values of ETwue and Iwue could be used for the planning, design and operation of irrigation systems, as well as for improving the production technology of soybean in the region.

The study was aimed at determining the most suitable irrigation schedule program for hemp grown for fibers by using evaporation from the free water surface (E_o), measured by a Class A pan and related crop plant coefficient (K_c). The experiment, carried out in Vojvodina, a northern part of the Republic of Serbia, included three irrigation regimes: I₁, I₂, and I₃ corresponding, respectively, to daily evaporation from an open water surface (E_o), two interrow spacings: RS₁ (12.5 cm) and RS₂ (25 cm), and topped (T) and not topped (NT) variants. The K_c values used for the calculation of daily evapotranspiration (ET_d) were 0.42 for April and May and 1.00 (I₁), 0.80 (I₂), and 0.60 (I₃) from June to the harvest. In addition, the nonirrigated (I_o) control variant was also included in the trial. The dioecious fiber hemp variety Marina was used for the trials. Irrigation was carried out by a drip irrigation system and was scheduled based on the water budget method. It started when readily available water (RAW) in the soil layer of 0.4 m was completely depleted by the plants. In the first year of the study, irrigation did not influence the yield of hemp fiber, but in the second one, the best result was achieved for the irrigation variant I₁. Interrow spacing did not have a statistically significant effect on both the hemp fiber yield and the quality. The topping of plants significantly decreased the yield of hemp, and it is not recommended when the hemp is cultivated for fibers. The quality of the hemp fibers was not influenced by irrigation, inter-row spacing, and topping. The rate of hemp evapotranspiration was in an interval of 312 mm (ET_a) to 520 mm (ET_m). The highest values of IWUE and ETWUE in both years and the bark yield in the first year were detected for the I₃ irrigation variant, which suggested that the crop plant coefficient (K_c) of 0.6 could be recommended for the correction of E_o values in the calculation of the daily evapotranspiration of hemp (ET_d) from June to August. The yield response factor (K_y) with values of 0.22 and 0.60 for the total growing season reveals that, in rainy years, hemp for fiber production could be grown without irrigation in the temperate climate of the Vojvodina region. However, such years are rare. Without doubt, irrigation of fiber hemp is recommended in the mentioned region in order to obtain high yields of good quality product.