Effects of plant arrangement on some agronomic traits of various common bean (Phaseolus vulgaris L.) cultivars under drip tape irrigation conditions in Shahrekord region

Introduction:
The findings of previous investigations show that the best density to achieve high yields with most of the beans (Phaseolus vulgaris L.), including the local Khomein cultivar, stands roughly at 40 plants m2 (Mehrpooyan et al., 2010). There is no comprehensive information available on bean yield performance under drip tape irrigation. Common bean is widely cultivated in Chaharmahal and Bakhtiari province, however, given its high water consumption and due to drought spells in the region in recent years, its production has sharply declined. While common bean requires 7000 to 8000 m3 of water per hectare during the growing season (Alizadeh, 2003), farmers use more than 15000 m3 of water per hectare for beans throughout the growing season. The use of drip tape irrigation can reduce water consumption in beans. The use of this irrigation method requires changing the planting method and proper arrangement of cropping systems. The objective of the present study was to determine optimum plant arrangement in common bean varieties under drip tape irrigation conditions.

Materials and methods:
In this study, a factorial experiment was conducted in a randomized complete block design with three replications in spring and summer of 2016 and 2017 at Chahartakhte Research Station in Shahrekord region. The first factor was cultivar (Koosha chitti bean, Yaghut red bean and Dorsa white bean), and the second factor was the planting arrangement (row spacing of 75 cm with 2, 3 and 4 planting lines per row, and the row spacing of 60 cm with 2 planting lines on each row). Different traits at vegetative and reproductive stages of bean plants were recorded and at the end of the growing season, yield and yield components of the cultivars and water productivity were determined. The experimental data were analyzed by using SAS statistical program and the means were compared by Tukey test (p < 0.05).

Results and Discussion:
The combined analysis of variance showed that plant height, number of seeds per pod, number of pods per plant, 100 seed weight, grain yield and water productivity were affected by bean cultivars and planting arrangement. The interaction effect of cultivar and planting arrangement was significant on 100 seed weight, grain yield and water productivity. The grain yield components were significantly difference among different cultivars. The highest number of pods, seeds per pod, 100-seed weight and grain yield were respectively recorded with Yaghut red bean, Koosha chitti bean, Koosha chitti bean, and Koosha chitti bean. The traits such as number of pods and weight of 100 seeds are controlled and affected by genetic and non-genetic factors such as environment. The number of seeds per pod is the most stable trait of beans and is mostly influenced by genotype (Salehi, 2015). The cultivars studied in this experiment exhibited differences in plant height, grain yield components, grain yield, and water use efficiency. Among crops, bean has the highest diversity in growth habit, seed size and maturity. There are a wide variety of genetic variations in bean pool genus. Therefore, due to genetic differences, under the same climatic conditions, the occurrence of different phenotypes (grain yield, number of pods per plant, 100 seed weight, etc.) is inevitable, and the difference between them is the result of genetic differences and their different response to the environment. Drip tape irrigation produced the highest water use efficiency when three or four lines of beans were planted on a 75 cm row, while plant density was constant for all treatments. The highest water use efficiency was obtained from Koosha chitti bean, which can be explained by the highest grain yield.

Conclusion:
The highest grain yield and water productivity were obtained from Koosha chitti bean cultivar. Although the four lines per row arrangement on the 75 cm row gave the highest seed yield and water productivity, it did not differ significantly with the three lines per row on the 75 cm row. Therefore, if the goal is to reduce water consumption and increase water productivity, planting three or four lines per row can be considered on 75 cm row, but because of the ease of planting three lines per row on 75 cm row, it can be recommended to farmers.