Effect of Relay Triple Intercropping Arrangements of Sugar Beet (Beta vulgaris), Chickpea (Cicer arietinum L.), and Mung Bean (Vigna radiate L.) on Yield and Yield Components

In conventional agriculture, crop production has gradually shifted from ecological production principles to economic approaches, which has led to the destruction of natural resources and land use change, as well as the reduction in resource consumption (Koocheki et al., 2016b). Satisfying the nutritional needs of a growing population whilst limiting environmental repercussions will require sustainable intensification of agriculture. The adverse effects of climate change are significantly decreasing yield and yield stability over time in current monocropping systems. We argue that intercropping, which is the production of multiple crops on the same area of land, could play an essential role in this intensification. Intercropping often increases resource use efficiency and agricultural productivity compared with growing the component crops solely and can enhance yield stability (Martin-Guay et al., 2018; Raseduzzaman & Jensen, 2017). In the case of an intercropping strategy, the growing period for the legume, as a cover crop, is longer to provide a high amount of fixed nitrogen and potential ground cover to compete with weeds (Vrignon-Brenas et al., 2018). The land equivalent ratio (LER) is often computed as an indicator to determine the efficacy of intercropping that measures land productivity. LER may be interpreted as the relative area required by sole crops to produce the same yields as achieved in a unit area of intercrop. The objective of the present study was to evaluate the effect of relay intercropping as replacement series of three plant species such as chickpea (Cicer arietinum L.), mung bean (Vigna radiate L.), and sugar beet (Beta vulgaris L.), on the yield, yield components, and land equivalent ratio under climatic conditions of Mashhad.

A field experiment was conducted at the Agricultural Research Station of Ferdowsi University of Mashhad, Iran, during the growing seasons of 2015-2016. For this purpose, a randomized complete block design with three replications was used. The treatments included sole cropping of chickpea (C), mung bean (M), and sugar beet (S), as well as intercropping with 25% L + 75% S, 50% L + 50% S, and 75% L + 25% S. The investigated traits of mung bean and chickpea were plant height, number of pods per plant, number of seeds per pod, number of branches per plant, seed weight per plant, and 100-seed weight, as well as the number of hollow pods per plant, number of seeds per plant, biological yield, seed yield, and harvest index. For sugar beet, the traits investigated were root height, fresh yield of root, dry yield of root, dry weight of shoot, sucrose content, and sucrose yield. The land equivalent ratio of chickpea, mung bean, and sugar beet was calculated (Sullivan, 2003) as follows: LER = Y1/I1 + Y2/I2 + Y3/I3, where Y1, Y2, and Y3 represent chickpea, mung bean, and sugar beet yield in intercropping, and I1, I2, and I3 represent chickpea, mung bean, and sugar beet yield in mono-culture, respectively. SAS 9.2 was used for analysis of variance. All the means were compared according to Duncan's test (p ≤ 0.05).

The results showed that the effect of relay triple intercropping arrangements of three species, such as mung bean and chickpea with sugar beet, was significant on yield components and seed yield, biological yield (p ≤ 0.05). The highest seed yield of chickpea and mung bean (2912 and 1247.83 kg/ha, respectively) and biological yield (6237.5 and 6816.7 kg/ha) were observed in sole culture, respectively. Also, the highest amount of fresh root yield was related to its sole cropping with 65242 kg/ha. The highest and lowest LER were calculated for 75% S + 25% L (with 1.53) and 25% S + 75% L (with 0.94), respectively.

Intercropping systems using ecological principles are one of the sustainable solutions to choosing plants suited to the needs, and competitiveness is very important. According to the results, relay triple intercropping of chickpea, and mung bean with sugar beet can be considered as ecological management and ecological intensification in the agroecosystems.