Weed flora composition in a young olive orchard as affected by fertilizer types

Abstract

Manure is a useful source of nutrients in olive orchards, but its effect on weed growth in such an ecosystem has not been studied. A field experiment was conducted in a six-year old olive orchard (cv. Chondrelia Chalkidikis) in northern Greece to study the effects of two forms of fertilization (inorganic fertilizer and composted cow manure) on weeds abundance and weed flora composition (species diversity and dominance). A randomized complete block design with three treatments (inorganic fertilizer, 150 kg N ha−1 plus 205 kg P2O5 ha−1 plus 205 kg K2O; composted cow manure, 20 Mg dry weight ha−1; and control) replicated three times was used. Inorganic fertilizer and composted cow manure had no significant effect on the number of weed species (F = 0.288, P > 0.05), but improved olive fruit yield by 61.6% and 57.1%, respectively, compared with the non-fertilized control. Both inorganic fertilizer and composted cow manure increased the weeds dry biomass by 133.4% and 80.8%, respectively, compared with the non-fertilized control. There was a decrease in the biomass proportion (percentage of the total weed biomass) of annual species with composted cow manure (x2 = 6.72, P < 0.05), while no significant change in the biomass ratio of grasses and broadleaf weeds was observed. Fertilization increased the growth of Chenopodium album, mainly with the addition of inorganic fertilization; and Sonchus oleraceus, slightly more with the addition of composted cow manure. Centaurea solstitialis and Daucus carota had a high proportion only in the non-fertilized control plots. Composted cow manure can be used as an alternative fertilizer in olive orchards, without enriching weed flora in terms of species number. Long-term experiments would be useful to confirm the influence of composted cow manure on weed flora of olive orchards.