Evaluation of Density, Dry Weight and Biodiversity of Weeds in Row Intercropping of Lettuce (Lactuca sativa var. capitata L.) and Alyssum (Lobularia maritima (L.) Desv.)

IntroductionDiversification through the use of intercropping systems is known to enhance stability. Intercropping is potentially able to reduce pests and weeds, increase the system production and increase the exploitation of available environmental resources, compared to monocultures. Ronald and Charles (2012), stated that weeds biomass decreased in the intercropping of maize and squash, due to squash ghosting on weeds. They also reported that the intercropping of pelargoniums (Pelargonium sp.) and mint (Mentha arvensis L.) decreased weed growth and biomass.Materials and Methods This experiment was conducted in 2014-2015 growing season based on a randomized complete block design with three replications at Agricultural Research Station, Faculty of Agriculture, Ferdowsi University of Mashhad. Experimental treatments were 1 row lettuce + 1 row alyssum (1:1), 2 row lettuce + 2 row alyssum (2:2), 3 row lettuce + 3 row alyssum (3:3), monocultures of lettuce and alyssum. Alyssum transplants were sown on 08/04/2015 and lettuce transplants were sown on 21/04/2015 in rows with a distance of 50 cm. During the growing season, composition of weed species together with weed density and dry matter were measure at 2 time in randomly sampled 0.6×0.6 m quadrates. Using the species frequency Margalef richness index and several diversity indices including Shannon- Weiner and Simpson’s index and species evenness were calculated for each treatment.Results and discussionAt first and second sampling, the highest density of weeds was observed in 2 row Lettuce + 2 row alyssum (2:2) with 282.4 and 122.03 plant per square meter, respectively. The lowest density of weeds was observed through the first and the second sampling, respectively, in Lettuce monoculture with 111.11 plant per square meter and in 1 row lettuce + 1 row alyssum (1:1) with 41.66 plant per square meter, respectively. In the first sampling, highest and lowest the Shannon-Wiener diversity index were observed in 2 row lettuce + 2 row alyssum (2:2) and 3 row lettuce + 3 row alyssum (3:3) with 0.53 and 0.35, respectively. In the second sampling, highest and lowest the Shannon-Wiener diversity index were observed, in 1 row lettuce + 1 row alyssum (1:1) and 2 row lettuce + 2 row alyssum (2:2) with 0.37 and 0.12, respectively. Also, in the first sampling, highest and lowest the Simpson’s diversity index were observed, in 2 row lettuce + 2 row alyssum (2:2) and 3 row lettuce + 3 row alyssum (3:3) with 0.66 and 0.44, respectively. In the second sampling, highest and lowest the Simpson’s diversity index were observed, in 2 row lettuce + 2 row alyssum (2:2) and alyssum monoculture with 0.46 and 0.05, respectively. In the first sampling, highest and lowest the Shannon-Wiener evenness index were observed, in 2 row lettuce + 2 row alyssum (2:2) and 3 row lettuce + 3 row alyssum (3:3) with 0.41 and 0.25, respectively. In the second sampling, highest and lowest the Shannon-Wiener evenness index were observed in lettuce monoculture and 2 row lettuce + 2 row alyssum (2:2) with 0.31 and 0.11, respectively. In the first sampling, highest and lowest the Margalef richness index were observed, in lettuce monoculture and 3 row lettuce + 3 row alyssum (3:3) with 1.48 and 0.98, respectively. In the second sampling, highest and lowest the Margalef richness index in 1 row lettuce + 1 row alyssum (1:1) and alyssum monoculture with 1.63 and 0.53, respectively.ConclusionThe results showed that the ecological characteristics of ecosystems such as diversity and density of weeds were affected by row intercropping patterns. In almost all cases except Margalef species richness index, intercropping 2 row lettuce + 2 row alyssum was better compared to other patterns of cropping. It can be concluded that the most important advantage of intercropping is stability of canopy structure in terms of weeds and crop population and therefore enhancing the competition ability of the crops.