**6. References**


**1. Introduction** 

Chernozems WRBSS, 2006).

productivity.

Takahashi&Anwar, 2007; Kunzova&Hejcman, 2009).

Panayotova, 2005; Nankova et al., 1994 & 2005; Nankova, 2010).

combination between nitrogen, phosphorus and potassium.

**6** 

**Soil Fertility** 

Margarita Nankova

*Bulgaria* 

**Long-Term Mineral Fertilization and** 

Long-term experiments are very important in studying the changes of soil fertility and environmental conditions as well as in analyzing the stability and quality of crop production. Such experiments give us more information how to use the good agronomic practices and how to protect the nature. Probably the oldest still-running arable crop fertilizer experiment is the Broadbalk Experiment established by John B. Lawes in Rothamsted (UK) in 1843 (Goulding et al., 2000). Thanks to this experiment many other long-term fertilizer experiments were established worldwide (Sims, 2006; Khan et al., 2007;

In Bulgaria also have investigations on such long-term fertilizer trails (Koteva, 2010;

Dobrudzha Agricultural Institute-General Toshevo is situated in North-Eastern part of Bulgaria on black earth zone (Picture 1). The main soil type is chernozem (Haplic

The aim of this investigation was to follow the effect of the long-term agronomy practices and especially fertilization on the nutrition regime of slightly leached chernozem soil in the region of South Dobrudzha after 40 years mineral fertilization with different norm and

A long-term fertilizer experiment , which was established in 1967 is still running. In two field crop rotation (wheat-maize) four nitrogen and phosphorus and three potassium norms were tested – 0, 60, 120, 180 and 0, 60, 120 kg/ha respectively. The experiment was designed according to the method of the "net square", applying the full version of the design in four replications. The experiment was designed by the method of the "net square", applying the full version of the design (4 x 4 x 3 = 48) in four replications. On the 40th year from the beginning of the trial (2007) after wheat harvest, soil samples were taken every 20 cm down the soil profile till depth 400 cm. A motor-driven portable soil sampler was used (Iliev&Nankova, 1994; Iliev, 2000). The changes of some agrochemical characteristics were determined in selected variants with high average 40th year

*Dobrudzha Agricultural Institute – General Toshevo* 

