Optimizing the Planting Time and Stand Density of Sunn Hemp Intercropping for Biomass Productivity and Competitiveness in a Maize-Based System

Context: Optimizing cover crop intercropping should aim to be sustainable, economically feasible and environmentally benign. Significant consideration must be given to cover crop plant timing and stand density adjustments to complement the resource demands of the dominant crop, while ensuring optimal biomass yields. Objective: The study assessed a range of intercropping indices to evaluate the influence of different planting times and stand densities of sunn hemp (Crotalaria juncea L.) when intercropped with maize (Zea mays L.). The evaluation focused on interspecies interactions in relation to aboveground biomass production. Methods: A split-plot experiment was conducted using the in-field rainwater harvesting (IRWH) technique. The main plot factors included three intercropping times: simultaneous with maize planting, at the V15 and the R1 maize growth stages. The subplot factors consisted of three stand densities (16, 32 and 48 plants m-2), with three replicates for both the 2019/20 and 2020/21 seasons. Intercropping indices, including land equivalent ratio and coefficient, area time equivalent ratio, land use efficiency, system productivity index, percentage yield difference, relative crowding coefficient, aggressivity, competitive ratio and actual yield loss were employed to assess interspecific interactions and their impact on biomass productivity. Results: Results show that intercropping sunn hemp at maize planting or the V15 maize growth stage can reduce stand density to 32 plants m- 2 without reducing sunn hemp biomass yield. The land equivalent ratio was highest (2.20), with intercropping at the V15 maize growth stage and lowest (2.09) with simultaneous intercropping at maize planting. The relative crowding coefficient was highest (34.4) at the V15 maize growth stage at 32 plants m- 2 stand density and lowest (-45.9) with simultaneous intercropping at planting at the same stand density. Intercropping during the R1 maize growth stage influenced competition on sunn hemp with the highest actual yield loss of -0.07. Competitive ratios were significantly higher for maize (26.19) and sunn hemp (0.16) with R1 and V15 maize growth stage intercropping, respectively. However, sunn hemp's actual yield loss was higher (0.25) with intercropping during the V15 maize growth stage than in sole cropping. Conclusions: Intercropping sunn hemp both simultaneously with maize planting and during the V15 maize growth stage with a stand density of 32 plants m- 2 demonstrated enhanced biomass productivity, thereby offering viable intensification choices. The utilization of multiple intercropping indices can contribute to a more comprehensive and precise evaluation of interspecies interactions, consequently leading to improved decision-making.