Evaluation of intercropping buckwheat and cowpea in improving yield and weed control under deficit irrigation conditions

Modern intensive agriculture has boosted crop yields through chemical inputs. However, this approach has caused decreased biodiversity, harm to human health, and environmental degradation. Developing sustainable agricultural practices that increase productivity while minimizing negative effects, especially in arid and semi-arid regions, requires strategies like deficit irrigation and environmentally compatible weed control methods such as intercropping. This study aims to assess the performance of an intercropping system comprising buckwheat and cowpea under deficit irrigation and minimal weeding. The research seeks to provide insights into the viability of this approach for sustainable agriculture in water-limited environments.

A field experiment was conducted in 2022 at the Agriculture and Natural Resources campus of the University of Tehran research farm in a randomized complete block design with split-split plot arrangements. The main plot factor included three levels of irrigation: 100% of the plant's water requirement (control), 85% of the water requirement and 70% of the water requirement compared to the control. The subplot factor consisted of five planting patterns: sole cultivation of buckwheat, sole cultivation of cowpea, and three intercropping patterns of buckwheat and cowpea with different row ratios (1:1, 3:1, and 1:3). Timing of weed removal, as the sub-subplot factor, was implemented at five levels: no weeding (control), weeding until the second, fourth, sixth, and eighth weeks after cultivation.

The highest grain yield of buckwheat (2436.9 kg ha-1) and cowpea (2495.5 kg ha-1) was observed in the sole cultivation plot with eight weeks of post-planting weeding under full irrigation. These results are attributed to higher planting densities in sole cultivation compared to intercropping. The 1:1 intercropping pattern with eight weeks of post-planting, exhibited the best cowpea leaf area index (3.36), and buckwheat (4.1) and similarly, this intercropping pattern with six weeks of post-planting resulted in the highest number of branches per plant (16). Sole cowpea plot under 85% deficit irrigation exhibited the highest weed dry weight (145.7 g m-2). The highest Land Equivalent Ratio (1.08), was observed in the 1:1 intercropping pattern with two weeks of post-planting weeding under full irrigation. Interestingly, the 1:1 intercropping pattern also showed the lowest weed biomass (12.1 g m-2) without specific weed management under 70% irrigation.

Most intercropping treatments achieved a land equivalent ratio greater than one, highlighting the superior efficiency of this planting method compared to sole cultivation. Specifically, the 1:1 intercropping pattern successfully controlled weed biomass, increased grain yields under deficit irrigation, and some for both crops. Therefore, intercropping offers a promising strategy to reduce reliance on herbicides and improve overall land use efficiency.