evaluation of growth and species composition of weeds in maize-cowpea intercropping based on additive series under organic farming condition

introduction weeds are main factors reducing crops yield, especially under organic farming conditions (). it has been reported that weed populations are more in organic farming compared to conventional cropping systems, resulting in more reduction of growth and yield. although the chemical control is a fast and effective way for controlling weed populations, some negative impacts of the recent weed management on public health and the natural environment, increased the concerns of using weed chemical compositions. thus, non-chemical weed control is in high importance. intercropping, an agronomical operation in which two or more crops are grown simultaneously in the same field, is one of the most important methods for increasing biodiversity in agricultural ecosystems (amosse et al., 2013; rostami et al., 2009; yuan-quan et al., 2012). therefore, the current research was aimed to evaluate the possible non chemical controlling of weeds in a maize-cowpea intercropping system. materials and methods a field experiment was conducted in the north of khuzestan during the growing season 2013-2014. the experiment was based on a randomized complete block design with three replications. maize and cowpea were planted in two sole crop systems and four intercropping systems based on an additive series, including t1:100 percent maize+25 percent cowpea, t2: 100 percent maize+50 percent cowpea, t3: 100 percent maize+75 percent cowpea and t4: 100 percent maize+100 percent cowpea. no chemical materials (fertilizer and pesticide) were used during growing season. environmental usage by intercropping patterns was evaluated by measuring photosynthetically active radiations (par) (mean of five points in each plot, selected randomly) and soil moisture content at three stages. at harvest time, all plants of each plot were harvested and grouped and weighed according to their species type. complementary effect of intercropping in using environmental resources was calculated using relative yield total (ryt) index. weed smothering efficiency (wse) was used to evaluate the effect of intercropping on reducing weeds the dry weight. results and discussion results indicated that soil moisture content, par interception and soil temperature were affected by cropping patterns. the lowest and highest values of soil temperatures were observed in intercropping and sole crop systems, respectively. intercropping systems exploited soil water more than sole crops. par interception was higher in intercropping compared to sole cropping. however, sole cowpea showed lower par interception compared to maize sole crop. relative yield total (ryt) index was more than unity in all intercropping systems. weed smothering efficiency (wse) showed that dry weight of weeds was reduced by 21-26 and 28-42 percentages in intercropping systems compared to sole maize and sole cowpea cropping systems, respectively. the growth of weeds (in terms of total dry weight) in intercropping systems were reduced in which from five recorded weed species, the dry weight of them, including amaranth (amaranthus retondus l.), pigweed (echinocloa cruss-gali l.), purslane (portulaca oleraceae l.) and halikakabon (solanum nigrum l.) decreased in intercropping compared to sole cropping systems. intercropping components showed a complementary relation in consuming environmental resources including soil moisture and par. since the soil temperature was lower in intercropping compared to sole cropping, lower soil moisture in intercropping cannot be resulted from higher evaporation in intercropping, but also the widespread root system in intercropping resulted in higher efficiency in soil moisture consuming. relative yield total more than unity, showing the advantages of intercropping in environmental resources consumption. soil covering and higher biodiversity are two main factors reducing weeds growth in intercropping because the two recent factors lower par availability for weeds which can reduce weed. the current research, taller maize absorbed incoming par and shorter cowpea intercepted par at ground surface, resulting in lower par for weeds. higher plant populations in intercropping have been reported as a main factor for reducing environmental resources availability for weeds reducing their growth. conclusion the relative yield total was more than unity, indicating the complementarity of maize and cowpea in intercropping systems for environmental resources consumption which was resulted in lower weeds growth. thus, intercropping can be used as a non-chemical method for weeds control.