This paper based on the researches carried out during 2006-2008 in Agricultural Research and Development Station Oradea on a preluvosoil. All the soil profile are low acid (6.11 – 6.8), humus content (1.44  – 1.75%) is small and total nitrogen is low median (0.127 – 0.157). After 30 years of good soil management, good practices the soil phosphorus content became very good (from 22.0 ppm to 150.8 ppm) on ploughing depth, potassium content (124.5 ppm) is median.The source of irrigation water was a drill of 15 m depth. Irrigation water quality was very good: pH = 7.2; Na + = 12.9; mineral residue = 0.5 g/l; CSR = -1.7; SAR = 0.52.Ten to ten days determination of the soil moisture on 0-75 cm depth emphasized the presence of the pedological drought every year: 39 days in 2006; 104 days in 2007 and 81 days in 2008; soil moisture decreased below wilting point every year too: 5 days in 2006 and 2008 and 6 days in 2007.Irrigation use – 1100 m 3 /ha in 2006, 2900 m 3 /ha in 2007, 3350 m 3 /ha in 2008 – for maintaining the soil water reserve between easily available water content and field capacity determined the improve of the soybean microclimate. The values of de Mrtonne aridity index (IdM) fpor optimum irrigated soybean characterized the microclimate like „wet” in 2006 (IdM = 45.2) and 2007 (IdM = 44.2) and like „wet I” in 2008 (IdM = 53.4). Irrigation suspending in the different months of the soybean irrigation season determined a smaller values of IdM and a worse microclimate, too.The biggest soybean yield were obtained in the irrigated variant without irrigation suspending in the soybean irrigation season: 3510 kg/ha in 2006, 3170 kg/ha in 2007 and 4050 kg/ha in 2008. In comparison with this variant the yield losses from unirrigated variant were of 25.4% in 2006; of 81.7% in 2007 and of 66.6.% in 2008; the yield losses are very significant statistically. Very significant statistically are the yield losses from the variants with irrigation suspending in the months of soybean irrigation season, too.The inverse link between pedological drought and yield and the direct link between de Martonne and yield sustain, too the need of the irrigation for pedological drought control and for microclimate improve in soybean from Crişurilor Plain.

soybean, yield; pedological drought; irrigation suspending; de Martonne aridity index

Presentation: oral