INFLUENCE OF SOME AGRONOMY FACTORS ON SPIKE COMPONENTS AFTER A RARE INCIDENCE OF FUSARIUM HEAD BLIGHT EPIPHYTOTY OF WINTER WHEAT I. EFFECT OF LONG-TERM CROP ROTATION, MINERAL FERTILIZATION AND SOWING TERM

摘要

The investigation was performed in two field experiments during the spring of 2005 in the region of north-east Bulgaria. The year was characterized with fusarium epiphytoty on common winter wheat rare for this region. In the first trial a long-term rotation of wheat as a continuous crop and two-course rotation with maize were studied and the following rates of mineral fertilization were investigated: N_OP_OK_O, N_(60)P_(50)K_(30), N_(120) P_(100)K_(60), N_(180)P_(150)K_(60) The second trial investigated wheat grown after spring peas in an ecological agriculture system. Four sowing terms (earlier than optimal, two sowing dates within the optimal term, and later than optimal) and four sowing rates (400, 500, 600 and 700 germinating seeds per m2) wereanalyzed. Variety Enola was sown in both trials. The number of visibly fusarium-infected spikes was established per unit area. The main spike components were determined at stage full maturity in both visibly healthy and visibly infected spikes: number ofgrains and grain weight per spike, as well as 1000 grain weight. In the first trial the number of spikes infected with fusarium varied within 1.0-12.7 items per m~2. The highest degree of visible infection was registered after predecessor maize fertilized with the maximum fertilization rate. The number of spikes infected with fusarium after previous crop spring peas in the second trial varied from 0.1 to 6.6, being limited by the sowing term and increasing with the higher crop density. Fusarium infection had a strong negative effect on spike components. In the first trial highest reduction was registered in grain weight per spike, which in the infected spikes accounted for 40-45 % of the mean grain weight in the visibly healthy spike. The relative damage caused by the infection increased with the higher fertilization rates. Wheat grown after predecessor peas had higher values of the visibly healthy spike components. At the sowing date most favorable for fusarium infection (5th October), the mean number of grains per infected spike constituted 59.3 % from the visibly healthy one. Thousand grain weights were reduced twice and grain weight per spike - 3.4 times. The increase of the sowing rate had a slight negative effect on the values of the fusariuminfected spike components.