M. Nankova*, I. Iliev, N. Nankov, G. Milev

Dobrudzha Agricultural Institute, 9520 General Toshevo, Bulgaria

Abstract. The agricultural area of South Dobrudzha is about 81% of its territory. The main reason for this are the favorable physical and geographical factors: even relief and soils of high fertility potential. The total arable area is 345452.3 ha, 344015.1 ha of which are arable land and only 1437.2 ha are forests. This imposes the necessity of constant monitoring on the current status of the nutrition regime in the production areas. The current status of soil fertility as expressed through the content of nitrogen, phosphorus and potassium available to plants in the respective agro-ecological regions of chernozem soils in Bulgaria, show that the soil reaction according to the soil sub-type varied from acid and slightly acid to slightly alkali and alkali. The values measured in water and salt suspension did not imply occurrence of harmful acidity and the need of liming. The reserve of available nitrogen forms was comparatively low (from 20 to 80 kg N/ha for the entire 0 – 40 cm layer). The status of phosphorus nutrition was unfavorable. The amount of available phosphorus can be considered moderate to good only at 6.5% of the investigated geographic locations. At all other locations the content in the two investigated layers (0 – 20 cm and 20 – 40 cm) was low. Critical low level of available phosphorus was determined in 30.4% of the geographical locations. These results are due to the fact that for more than two decades now annual phosphorus fertilization has not been applied because of various reasons and therefore the considerable reserves of available phosphorus accumulated until the 1990s in the arable land were exhausted fast, thus causing an alarmingly negative balance of phosphorus. The content of exchangeable potassium in the two investigated soil layers defines the soils in South Dobrudzha as having good to very good reserves of this macro element. The main reason for this is the fact that the soil-formative materials have high potassium content.