Evaluation of yield and yield components of green bean and bell pepper under replacement and additive intercropping systems

The use of intercropping as an effective component in sustainable agriculture, while increasing the ecological and economic diversity, cause increasing yield per unit area, yield stability under adverse environmental conditions, increasing the quantity and quality of the product, increasing water use efficiency, control of soil erosion, reducing pesticides use and increasing stability in agroecosystems. Plants from the family of legumes are among the plants that have a special place in intercropping because of their nitrogen fixation ability. Usefulness of intercropping cultivation of sweet corn and green bean has been reported to be better than monoculture. This study was designed and conducted with the aim of studying the effect of replacement and additive intercropping green bean with bell pepper on yield, yield components and land equivalent ratio in Mashhad weather conditions. 

The experiment was conducted in 2015-2016 growing season based on a randomized complete block design with three replications at the Research Farm of Agriculture Faculty, Ferdowsi University of Mashhad. Experimental treatments were 25% green bean+75% bell pepper, 50% green bean+50% bell pepper in replacement intercropping, 20% green bean+100% bell pepper and 40% green bean+100% bell pepper in additive intercropping and monoculture of green bean and bell pepper. Green beans have planted by seed and bell pepper transplants were sown at the same time in June 2016 in rows with a distance of 50 cm. In 4-leaf stage, green bean was thinned with an optimum density of 20 plants per square meter. In addition, the spacing on the row was considered 30 cm for transplants of bell pepper; in this case, its optimum density was 6.66 plant per square meter. At harvest time, green pod yield for green bean, fruit yield for bell pepper, other yield components and plant dry weight for two plants were measured, and land equivalent ratios were also calculated.

The highest green pod yield and plant dry weight for green bean with 57921.7 and 1051.03 kg ha-1, respectively, was observed in monoculture and the lowest values for 20% green bean+100% bell pepper with 11252.5 and 525.8 kg per ha, respectively. With the increase in the presence of green bean in replacement and additive intercropping, the green pod yield of green bean increased due to increasing of biological nitrogen fixation. For bell pepper, the highest fruit yield with 32766.7 kg ha-1 was observed in monoculture and the highest plant dry weight with 7816.6 kg ha-1 was observed for 75% bell pepper+25% green bean and the lowest fruit yield was obtained for 50% bell pepper+50% green bean and 100% bell pepper+20% green bean with 21183.3 and 21886 kg ha-1, respectively, and the lowest plant dry weight was obtained for 50% bell pepper+50% green bean with 3533.33 kg ha-1. Due to the fact that the highest number of fruits per plant was observed in monoculture of bell pepper, therefore, monoculture has higher fruit yield because it has more space for plants. The highest value of total land equivalent ratio (1.28 and 1.25) was obtained in ratios of 40% green bean+100% bell pepper and 50% green bean+50% bell pepper, respectively, indicating 28 and 25% yield advantage of intercropping compared to pure stands of species of these two plants. The lowest value of total land equivalent ratio (0.86) was observed in ratio of 20% green bean+100% bell pepper.

Comparison of different patterns of replacement and additive intercropping showed that cultivation pattern of 25% green bean+75% bell pepper was superior for most of the traits evaluated in green bean and bell pepper compared to other patterns. Additive intercropping pattern of 40% green bean+100% bell pepper had the highest total land equivalent ratio (1.28) which indicate the beneficial effect of mixed cropping pattern over pure cropping. Since green bean through biological nitrogen fixation, leads to reduction in the use of chemical fertilizers, intercropping of this plant with other plants such as bell pepper can increase the resources efficiency and improve yield quantity for bell pepper.