Abstract
AbstractIntercropping can improve yield and nitrogen use efficiency in organic vegetable production by pairing crops with complementary resource use. An intercrop field experiment was conducted to determine yield, root growth and nitrogen (N) dynamics using faba bean (Vicia faba L.) grown as a vegetable and pointed cabbage (Brassica oleracea var. capitata cv. conica). Both crops were grown in monocropping (MC) and intercropping systems (IC). Minirhizotrons were used to measure root growth. Yield of pointed cabbage per metre row was 28% higher under the IC system than under MC, whereas faba bean yield as fresh seeds did not differ. The land equivalent ratio was 1.06, showing that improved yield under IC resulted from efficient land resource use. Even though MC cabbage had the highest aboveground biomass, total N accumulation was higher under IC and MC faba bean systems. Both root frequency and intensity were greater under IC faba bean rows compared with MC faba bean because of the presence of cabbage roots in faba bean rows. Monocropped cabbage had the highest root intensity and the lowest amount of soil mineral N in the 0–1.5 m depth after harvest. Monocropped cabbage was efficient in assimilating N, whereas MC faba bean was efficient in exporting N as harvestable yield. The nitrogen use efficiency using the IC system (75%) was higher than growing faba bean (44%) and cabbage (65%) alone. Thus, faba bean as an intercrop in organic cabbage production systems improves land and N use efficiency by complementary root growth.
Highlights
Vegetable production systems require high amounts of nitrogen (N)
We hypothesized that intercropping faba bean with pointed cabbage will result in more efficient use of N in both species than would occur in the respective monocrop systems because: (1) intercropping improves the land equivalent ratio (LER) of the intercropping systems (IC) system (LER > 1) as faba bean is less competitive than cabbage for mineral N, (2) intercropping increases N use efficiency (NUE) because of complementary N use, and (3) intercropping increases root intensity and root depth compared with monocropped faba bean
The N uptake efficiency (NUpE) was higher in IC and MC cabbage systems than in the MC faba bean system, and N utilization efficiency (NUtE) was highest in the MC faba bean system, followed sequentially by the IC and MC cabbage systems (Table 2)
Summary
Vegetable production systems require high amounts of nitrogen (N). Excess fertilizer application and poor timing of mineral N availability relative to crop N demand may result in leaching of nitrate and reduction in N use efficiency (NUE). Intercropping, that is, cultivating two crop species simultaneously, has the potential to reduce nitrate leaching and increase NUE by improving N utilization and increasing root exploitation of N (Xie & Kristensen, 2017; Zhang et al, 2016). To avoid yield reductions because of interspecific competition for N, crops chosen for intercropping should be species that are unlikely to compete with one another for N, that is, use resources in complementary ways Legumes such as faba bean (Vicia faba L.) are effective in intercropping systems because they are less competitive for soil mineral N because of their ability to fix atmospheric N. We intercropped faba bean grown as a vegetable crop and pointed cabbage to quantify root growth, plant and soil mineral N concentrations, and yield parameters relative to their respective monocrop (MC) and intercrop (IC) systems. We hypothesized that intercropping faba bean with pointed cabbage will result in more efficient use of N in both species than would occur in the respective monocrop systems because: (1) intercropping improves the LER of the IC system (LER > 1) as faba bean is less competitive than cabbage for mineral N, (2) intercropping increases NUE because of complementary N use, and (3) intercropping increases root intensity and root depth compared with monocropped faba bean
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