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Use of irrigation requirements and scheduling as drought indicator

Milena Kercheva, Zornitsa Popova Institute of Soil Science “Nikola Poushkarov Sofia, BULGARIA. Use of irrigation requirements and scheduling as drought indicator. BALWOIS 2010 CONFERENCE 25-29 May 2010, Ohrid, Republic of Macedonia.

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Use of irrigation requirements and scheduling as drought indicator

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  1. Milena Kercheva, Zornitsa Popova Institute of Soil Science “Nikola Poushkarov Sofia, BULGARIA Use of irrigation requirements and scheduling as drought indicator BALWOIS 2010 CONFERENCE 25-29 May 2010, Ohrid, Republic of Macedonia

  2. The study compares the identification of summer drought by some wide-spread drought indices, namely seasonal net precipitation, SPI, PDSI and simplified water balance, on one hand and net irrigation requirements and scheduling of maize grown in soils with contrastive hydraulic properties in Sofia region. Aim

  3. long-term (1961-1990) records of climate data for Sofia region; 10-days average values of reference evapotranspiration ETo (FAO56) and the daily precipitation summer drought indicators: precipitation sums for vegetation period and for the maize critical period July-August, standardized precipitation index - SPI (McKee et al., 1993), Palmer Drought severity index - PDSI (Alley W.M. 1984 ), ranked water balance (Sabeva et al., 1968). simulation of irrigation scheduling of maize was performed using CROPWAT program (Smith, 1992). Constant application depth of 60 mm that partially refills the soil reservoir was adopted. soils with contrastive properties: low water permeable Vertisol of high water holding capacity (180 mm.m-1) and medium permeable Chromic Luvisol of 140 and 106 mm.m-1 total available water. The case study is conducted using

  4. Input parameters of the maize development stages data for CROPWAT program Temperature characteristics of maize (FAO group 400) development stages, Sofia plain. Maize parameters used as input of CROPWAT program

  5. Frequency and mean first irrigation date (± std, days) for years with different number of irrigations of maize. (TAW – total available soil water capacity). Results abMaximum rain infiltration rate: a –15 mm/day; b - 40 mm/day

  6. Climate characteristics of years differentiated by the number irrigations of maize, grown in soil with medium TAW (140 mm m-1)

  7. Net irrigation demands of maize grown in soil of TAW=140 mm.m-1 and SPI(3) for July and August, Sofia field. (The years are sorted according to the net irrigation demands in the soil of TAW=140 mm.m-1) Comparison of the results related to net irrigation demands of maize for soils of medium (TAW=140 mm.m-1) and low (TAW=106 mm.m-1) water holding capacity with SPI(3) for July and August, calculated on 3 months base. The higher is the net irrigation demands of maize in medium soils the lower (less than -0.85) is the SPI(3)August.

  8. Net irrigation demands of maize grown in soil of TAW=106 mm.m-1 and SPI(3) for July and August, Sofia field. (The years are sorted according to the net irrigation demands in the soil of TAW=140 mm.m-1) For soils with low water holding capacity the drought in the May-June period should also be considered

  9. The identification of 8 drought years (1961, 1962, 1964, 1965, 1985, 1987, 1988, 1990) by net irrigation demands of maize in medium soil (TAW=140 mm.m-1) and SPI(3) August is confirmed by the PDSI and SPI(12), which account for the long lasting drought Drought indices: PDSI – for Vertisol (TAW=180 mm.m-1)and Chromic Luvisol (TAW=140mm.m-1); SPI(12), Sofia region.

  10. The percent of years of high irrigation demands when more than two irrigation events are required is 26%, 13% and 42%, respectively for soils with medium, high and low water holding capacity. The predicted high net irrigation demands of 180-300 mm under maize in medium soils is well related to the values of SPI(3)August < -0.85. For soils of low water holding capacity the drought in the May-June period should be also considered. The statistical analyses relative to the studied period indicate some deviations of the estimates given by climate indices and those of the net irrigation demands. Taking into account the practical use of the results it is recommended to use probability of exceedance of net irrigation requirements and demands as additional indicator for summer drought and as a basis for assessment of the other indices Conclusions

  11. The present study was supported by the project DMCSEE (SEE/A/091/2.2/X) “Drought Management Centre for South East Europe” financed by the SEE Transnational Cooperation Program of the European Regional Development Fund (ERDF). Acknowledgements

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