Changes of the humus status of Pellic Vertisol (FAO) soil type under long-term growing of field crops in a stationary trial without fertilization

V. Koteva1*, S. Kostadinova2
1Institute of Agriculture, 1 Indusrtialna, 8400 Karnobat, Bulgaria
2Department of Agrochemistry and Soil Science, Faculty of Agronomy, Agricultural University, 12 Mendeleev, 4000 Plovdiv, Bulgaria

Abstract. This investigation was aimed at determining the changes in the humus content of leached Pellic Vertisol under long-term growing of intensive field crops in crop rotation in a stationary field trial without fertilization. For this purpose agrochemical investigations were carried out in the 48-year-old stationary fertilizer trial maintained at the Institute of Agriculture, Karnobat, Bulgaria on Pellic Vertisol (FAO). The analyzed soil samples were taken from the 0-100 cm horizon of the stationary trial and from soil not subjected to anthropogenic influence (under forest vegetation and from virgin land). The total humus content was determined and the humus reserves and humus energy were calculated. It was found that the leached Pellic Vertisol subjected to long-term land use without introduction of fertilizers had humus content two times lower than the content in soil where natural soil formation processes occurred without anthropogenic influence (under forest vegetation and on virgin land). At 48-year growing of field crops without fertilization, humus content in the 40 cm soil horizon decreased with 5-7 relative percent. In the 40-100 cm horizon significant changes did not occur. High correlation was determined between the total humus reserves and the yield from the field crops (R from + 0.668 to + 0.724)