COMPARISON OF MODEL SIMULATION RESULTS WITH THE IRRIGATION SCHEDULES BY ZAHARIEV ET AL.1986 | СРАВНЕНИЕ НА РЕЗУЛТАТИТЕ ОТ МОДЕЛНИ СИМУЛАЦИИ С ПОЛИВНИТЕ РЕЖИМИ НА ЗАХАРИЕВ И КОЛЕКТИВ 1986

The study compares several irrigation scheduling alternatives for precise irrigation relative to Pustren site, Stara Zagora, with currently adopted scheduling in the region Zahariev et al.1986. Simulations are performed by the validated WINISAREG model Pereita et al, 2003. The model is used to generate the following irrigation scheduling alternatives: refilling the soil reservoir and adopting a MAD of 0.47 1; refilling the soil reservoir and adopting MAD = 0.32 2; and partially refilling the soil reservoir and adopting MAD = 0.47 3. These alternatives are built in agreement with past studies to develop improved furrow irrigation practices applied to vertisol cracking soil which prove that high deep percolation occurs for low soil moisture at time of irrigation due to preferential flow when cracks are formed; contrarily, percolation is controlled when irrigating at higher soil moisture before soil cracking about 80-82% of field capacity. Results of inflow-outflow measurements under such conditions show that the average infiltrated depth in a furrow set is within the range of 80-100 mm for continuous furrow irrigation. Results for surge irrigation have shown that further improvements on the distribution uniformity could be achieved while the application depth could be reduced by 18-25%. Thus Alternative 1 relates to furrow irrigation with continuous flow performed at soil moisture above the cracking level with application depths of 90 mm. Alternatives 2 and 3 refer to furrow surge irrigation with application depths of 60 mm. Simulated probability curves of net irrigation requirements NIRs and net irrigation demands IDs relative to the developed alternatives are compared with results from previous studies Zahariev et al., 1986. It is found that the irrigation schedules presently advised in the region do not fully cover crop requirements in average and dry seasons, when some yield decrease and deep percolation may occur. Simulations show that all three alternatives for precise irrigation scheduling can easily adapt to climate variability mainly by adequately selecting the irrigation dates. Results of simulations do not allow selecting one among the three alternatives as the best irrigation scheduling strategy but are useful to later building an information system for farmers using actual weather data.