Effect of Green Bean (Phaseolus vulgaris L.) Additive iIntercropping on Growth, Potato (Solanum tuberosum L.) Equivalent Yield and Land Use Efficiency under Different Levels of N Fertilizer

IntroductionOne of the ways to move towards sustainable agriculture is to create diversity and using intercropping of crops, cultivars and / or different isolines in agriculture. In order to increase productivity in the agricultural system, resource management and inputs also play a key role. In addition, to preserve ecological balance and stability of the system, the main goals in the intercropping systems are maximum exploitation of environmental resources such as water, soil, food, the quantitative as well as qualitative increase of yield, and reduction of damage from pests, diseases, and weeds. In addition, improvement social conditions, such as greater economic stability and adequate nutrition for humans are pursued. Therefore, the present study aimed to exploit the agro-ecological benefits of additive intercropping of green bean in reduction of nitrogen consumption in potato cultivation and improving the land use efficiency and potato equivalent yield. Materials and MethodsIn order to evaluate the effects of additive intercropping of green bean on potato growth, tuber yield, nitrogen use efficiency, land use efficiency, and potato equivalent yield as well as green bean yield, an experiment was conducted at the Farm Research of Faculty Agriculture (latitude 35◦1'N, longitude 48◦31'E and 1690 m altitude), Bu-Ali Sina University, Hamedan, Iran, in the growing season of 2016. Experiment was laid out as a factorial based on randomized complete block design with three replications. Four planting patterns including sole cropping of potato (M1), green bean intercrops between potato rows (M2), green bean intercrops within potato rows (M3) and green bean intercrops between and within potato rows (M4) were applied in combination with three levels of nitrogen fertilizer (N0, N80 and N160: 0, 80 and 160 kg N ha-1, respectively). Intercropping system was done using additive design. So that, the potato density was kept constant and in all cropping patterns, 50% sole green bean planting density was added to potato plots. Traits of plant height (PH), tuber yield (TY), number of tuber per plant (NTP), tuber dry matter (TDW), harvest index (HI), and potato equivalent yield (PEY) for potato, and green bean pod yield (GPY), number of pods per plant (NPP), and biological yield (BY) for  green bean were evaluated. Land equivalent ratio (LER), relative value total (RVT) indices were also studied.Results and DiscussionResults demonstrate that planting pattern and N had the strongest influence on tuber equivalent yield as well as tuber yield of winter wheat followed by interactions between these treatment factors. Accordingly, when normal and high N levels were applied, potato equivalent yield values were comparable to, or higher than, those obtained without consumption of N. The highest potato tuber yield (42.50 t.ha-1) was revealed at the treatment of green bean intercrops between potato rows with consumption of 160 kg N ha-1. This treatment did not show significant difference with the treatment of green bean intercrops between potato rows with consumption of 80 kg N ha-1, which had a yield of 41.51 t.ha-1. Also, the highest values for yield of green beans (515 g.m-2), the land equivalent ratio (1.50), total relative value (1.45) and the highest potato equivalent yield (54.38 t.ha-1) were obtained at M2 × N80 (green bean cultivation between potato rows with consumption of 80 kg N ha-1) treatment. Legumes have the ability to nitrogen fixation and using of them in intercropped systems can be suitable for reduce nitrogen use as well as environmental problems. Therefore, in terms of growth, tuber yield, land use efficiency and nitrogen utilization efficiency, treatment of green bean intercrops between potato rows with consumption of 80 kg N ha-1 was the best treatment for potato production.ConclusionIn general, the cultivation of green beans between potato rows due to ecological, morphological and nutritional differences has cooperation aspects in intercropping. This will increase the productivity of the land, the light and food in the unit area and the diversity in agricultural ecosystems.  Materials and methods: In order to evaluate the effects of additive intercropping of green bean on potato growth, tuber yield, nitrogen use efficiency, land use efficiency, and potato equivalent yield as well as green bean yield, an experiment was conducted at the Farm Research of Faculty Agriculture (latitude 35◦1'N, longitude 48◦31'E and 1690 m altitude), Bu-Ali Sina University, Hamedan, Iran, in the growing season of 2016. Experiment was laid out as a factorial based on randomized complete block design with three replications. Four planting patterns including sole cropping of potato (M1), green bean intercrops between potato rows (M2), green bean intercrops within potato rows (M3) and green bean intercrops between and within potato rows (M4) were applied in combination with three levels of nitrogen fertilizer (N0, N80 and N160: 0, 80 and 160 kg N ha-1, respectively). Intercropping system was done using additive design. So that, the potato density was kept constant and in all cropping patterns, 50% sole green bean planting density was added to potato plots. Traits of plant height (PH), tuber yield (TY), number of tuber per plant (NTP), tuber dry matter (TDW), harvest index (HI), and potato equivalent yield (PEY) for potato, and green bean pod yield (GPY), number of pods per plant (NPP), and biological yield (BY) for  green bean were evaluated. Land equivalent ratio (LER), relative value total (RVT) indices were also studied. Results and discussion: Results demonstrate that planting pattern and N had the strongest influence on tuber equivalent yield as well as tuber yield of winter wheat followed by interactions between these treatment factors. Accordingly, when normal and high N levels were applied, potato equivalent yield values were comparable to, or higher than, those obtained without consumption of N. The highest potato tuber yield (42.50 t ha-1) was revealed at the treatment of green bean intercrops between potato rows with consumption of 160 kg N ha-1. This treatment did not show significant difference with the treatment of green bean intercrops between potato rows with consumption of 80 kg N ha-1, which had a yield of 41.51 t ha-1. Also, the highest values for yield of green beans (515 g m-2), the land equivalent ratio (1.50), total relative value (1.45) and the highest potato equivalent yield (54.38 t ha-1) were obtained at M2 × N80 (green bean cultivation between potato rows with consumption of 80 kg N ha-1) treatment. Legumes have the ability to nitrogen fixation and using of them in intercropped systems can be suitable for reduce nitrogen use  as well as environmental problems. Therefore, in terms of growth, tuber yield, land use efficiency and nitrogen utilization efficiency, treatment of green bean intercrops between potato rows with consumption of 80 kg N ha-1 was the best treatment for potato production.Conclusion: In general, the cultivation of green beans between potato rows due to ecological, morphological and nutritional differences has cooperation aspects in intercropping. This will increase the productivity of the land, the light and food in the unit area and the diversity in agricultural ecosystems.