engleski

Nitrogen effects on weed populations in winter wheat

Field trials were carried out on humogley soil at Vrbanja site, in the growing seasons 1994-95 and 1995-96. Wheat (cv. Sana) was planted after soybean in both years. All experiments were designed as randomised block, in five replications with a plot size of 180 m2. Three rates of nitrogen as mineral fertiliser were applied (140, 170 and 200 kg N ha-1), whereby 50% was applied before the sowing time and 50% as a split dressing, in the end of March and in the middle of April. No herbicides have been applied. Samples of weeds (0.25 m2) in 20 replications per each plot were collected at the wheat stage of heading (Zadocs’scale 59-69). The samples were separated into species, counted and dried. Data were transformed logaritmically and analysed by ANOVA. Out of 45 discovered weed species, the most frequent were: Galium aparine, Papaver rhoeas, Thlaspi alliaceum, Chenopodium album, Sonchus arvensis, Ambrosia artemisiifolia, Anagallis arvensis and Polygonum spp. These species constituted about 73-87% of the total dry biomass of weeds. In the N fertilisation treatments the number of weed species was lower than in the zero nitrogen control, with non-significant differences. Weed density and weed biomass between four N treatments are considerably higher at 140 N and 170 N compared to zero nitrogen and 200 N treatments. When compared to the treatment with 70 kg N, the treatment with 200 kg N resulted in a considerable biomass decrease of the following populations: Galium aparine, Thlaspi alliaceum, Sonchus arvensis, Ambrosia artemisiifolia and Sinapis arvensis for 92%, 80%, 62%, 61% and 45%, respectively. This is due to an indirect effect of N, resulting in significantly higher crop density at nitrogen level of 200 kg and a stronger suppression by the crop. These results showed that increasing nitrogen can increase the ability of winter wheat to suppress weeds, i.e. the number of species, density and biomass decline.

winter wheat; nitrogen fertilizer; weed density; weed biomass

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