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To achieve efficient weed control through cover cropping, the plant species chosen is very important. Growing different legume cover crop (CC) species single and in mixtures with grass may increase the number of provided ecosystem services, including reliable suppression of weeds. We conducted an experiment using randomized complete block design with four replications in 2014/15 - 2015/16 growing seasons, at the Experimental Field of Maize Research Institute in Zemun Polje (Serbia). Single cover crops were considered as the main factor (common vetch and field pea), mixtures common vetch and field pea with winter oats and traditional variant, without coverage on biomass. Green biomass of the cover crops was incorporated in the soil, and treatments with favorable establishment and above-average biomass yields tended to suppress weeds by showing lower weed dry matter and weed numbers. The weediness of sweet maize was much higher in the second year of investigation. The number of weed species, fresh and dry biomass of weeds were the least in the variants with mixtures, while the number of plants per specieswas the lowest in the single cover crops. So, mixtures were not as effective as legume single sown CCs, species combinations increased resilience against adverse weather conditions, an advantage to achieving efficient weed control over a long-term period. The statistically significant difference in the fresh biomass of weeds obtained in the control variant (540.46 and 385.88 g) was especially pronounced compared to the variants with single cover crops (391.63 and 486.53 g) and their mixtures (260.00 and 250.78 g), indicating a higher proportion of perennial weed species.

Increasing the soybean cultivated area is closely related to the intensification of crop rotation. The introduction of soybean as a legume crop has a positive effect on the weediness and yield of other crops, primarily maize and winter wheat. In order to prove the advantages of crop rotation in relation to the continuous cropping, a longer period of testing is required, i.e a certain number of rotations in each of the crops is required. This paper presents results of the effects of crop rotation on a weed community in soybean. A trial was settled on the experimental field of the Faculty of Agriculture, Radmilovac in 1992. The following cultivation systems have been observed: soybean continuous cropping, maize-soybean-winter wheat rotation (three crop rotation), and winter wheat-maize-soybean-spring barley+red clover-red clover-sunflower (six-crop rotation). The conventional cropping practices for cultivation of soybean were applied in continuous cropping and crop rotations. Crops are grown in non-irrigation regime, on chernozem luvic soil type. Long-term effects of various cropping systems on weed infestation were observed by the one square meter area method in 2015. The dominant species in continuous cropping and crop rotations were similar: Datura stramonium L., Solanum nigrum L., Amaranthus retroflexus L., Chenopodium album L., Sorghum halepense (L.) Pers and Convolvulus arvensis L. Scop. However, the number of weed species, the number of plants per weed species, fresh and air dry biomass was the highest in soybean continuous cropping and the smallest in three- and six crop rotation. In particular, there are large differences in the number of plants per weed species (in continuous cropping 43.8 and in crop rotation 12.6 and 12.8 per square meter) and in fresh weight (233.1 versus 96.9 and 108.2 g m-2 ). The 23-year continuous cropping was obviously a respectable period for making unambiguous and precise conclusions. Crop rotations, are more effective in suppressing the number of plants per weed species and decreasing biomass of weeds.

Weed seeds in and on the soil are the primary cause of weed infestations in maize. Cropping system diversification through the use of longer rotations of dissimilar species can increase the range of stress and mortality factors that regulate weed population dynamics, and thus can be useful for maintaining effective weed control while reducing the burden of crop protection placed on herbicides. This paper deals with effect of continuous cropping, two-, three- and six crop rotation on the weediness of maize. A trial was settled on the experimental field of the Faculty of Agriculture, in 1992. The following cultivation systems have been observed: maize continuous cropping, maize-winter wheat rotation (two-), maize-soybean-winter wheat rotation (three-) and winter wheat-maize-soybean-spring barley+red clover-red clover-sunflower (sixcrop rotation). The common conventional cropping practices specific for maize were applied in systems. Crops are grown in non-irrigation regime, on leached chernozem. Long-term effects of various cropping systems on weed infestation were observed by the one square meter area method in 2015. The 23-year continuous cropping was obviously a respectable period for making unambiguous and precise conclusions. Namely, the number of weed species, and especially the number of plants per weed species, has been increasing in maize continuous cropping over years, but the increasing tendency certainly depended on meteorological conditions in particular years. Maize continuous cropping was characterised by the highest number of weed species and plants per weed species with the dominance of perennial species, due to, first of all, great abundance of plants per species Sorghum halepense (L.) Pers and Convolvulus arvensis L. The highest number of plants per annual weed species in maize continuous cropping was recorded in species Solanum nigrum L., Chenopodium album L. and Amaranthus retroflexus L. Dominant species in crop rotations were the same as in maize continuous cropping, only the increased distribution of perennial species Cirsium arvense (L.) Scop. and Agropyrum repens (L.) Beauv. was observed in the six-crop rotation. Crop rotations, especially the three crop rotation, are more effective in suppressing the number of plants per weed species and decreasing fresh biomass of weeds than continuous cropping and the two and six crop rotation are.