Агрохимична оценка на различни подтипове Черноземи и оптимизиране на торенето при основни селскостопански култури

English. The study is based on the data obtained from a three-year crop rotation in a field trial on Lleached Chernozem and Calcareous Chernozem carried out respectively at Field Trial Stations in Gramada, Vidin district and Alvanovo, Targovishte district. The experiments are designed according to the block method in four replications. Three main soil tillage practices were studied within each crop out of irrigation: a1 – ploughing (25 - 27 cm) – disking (10 - 12 cm) – ploughing (25 - 27 cm)

a2 – loosening (25 - 27 cm)

loosening + disking (10 - 12 cm) and a3 – ploughing (20 - 22 cm)

ploughing 10 - 15 cm + disking

direct sowing. The three levels of nitrogen fertilization were studied: N0, N12, N18 kg/da in sunflower

N0, N10, N20 kg/da in wheat

N0, N24, N30 kg/da in corn maize – b1, b2 and b3. The phosphorous and potassium fertilizers were applied as a background in different manners of application and amounts – P12K12 kg/da annually and P36K36 kg/da in a single application for the whole crop rotation c1 and c2. The following amounts seem to be efficient for the terms of the trial: sunflower – N12 kg/da, wheat – N10 kg/da, corn maize – N0 kg/da. The single application of P36K36 kg/da registered a similar influence, compared to the annual amount applied – P12K12 kg/da. Regarding the studied cultivations, the disking at 10 - 12 cm + 6 - 8 cm or loosening at 25 - 27 cm appears to be the most proper cultivation in sunflower, direct sowing in wheat and corn maize.