Влияние на променливото минерално торене С, N и P върху биопродуктивните показатели на естествен тревостой от типа Chrysopogon gryllus L.

anglais. During the period of 2011-2013, in the region of the Central Balkan Mountain, at altitude of 460 m, on light gray pseudopodsolic soil, was studied the influence of annual rotation of N, P and NP-mineral fertilization on the yield and botanical composition of a natural sward of the type Chrysopogon Gryllus. The following variants were studied: 1. Not fertilized (Control 1)

2. Annual fertilization by N6Р6 (Control 2)

3. 1-st year fertilization by N6, 2-nd and 3-rd - by Р6

4. 1-st year fertilization by P6, 2-nd and 3-rd - by N6

5. 1-st and 2-nd year fertilization by N6, and 3-rd - by Р6

6. 1-st and 2-nd year fertilization by P6, and 3-rd - by N6

7. 1-st year fertilization by N6, 2-nd year - by P6, 3-rd year - by N6

8. 1-st year fertilization by P6, 2-nd year - by N6, 3-rd year - by P6. We found out a positive influence over the dry matter yield as a result of the rotation of individual fertilization by N6 and P6. The highest effect, from the variable mineral fertilization, was found in fertilizing by N6 during the 1-st and 2-nd year, and in the 3-rd by P6 (var. 5), as the average increase for the period in the dry matter yield, in relation to the not fertilized variant and the variant with annual combined fertilization N6 P6 (Control 2), was within the limits from 14.02% to 66.49%. The slightest was the effect from the variable mineral fertilization by N6 and P6 in variants 8 (P6

N6

P6)

4 (P6

N6

N6)

6 (P6

P6

N6) as average for the three-year period, the increase in yield was within the limits from 13.37% to 24.53% in relation to not fertilized control. All variants of variable fertilization had as a result both increased species diversity, and increased participation of valuable grasses for fodders in the sward. As a result of fertilization and depending on climate conditions during the third year from the experimental period was found an evident tendency for transformation of the sward from type Chrysopogon gryllus in type Аgrostis capilaris- Festuca fallax.