Quantifying inter-species nitrogen competition in the tomato-corn intercropping system with different spatial arrangements

Intercropping systems have been widely used worldwide due to their high economic benefits and land-use efficiency. While it is well known that inter-species nutrition competition in intercropping systems leads to high production efficiency, the effects of different spatial arrangements of intercropping species on these mechanisms remain unclear. The objectives of this study were to reveal differences in the soil nitrogen dynamics in the tomato-corn intercropping system with different spatial arrangements of crops and to determine suitable spatial arrangements. A two-year experiment was carried out during the 2018 and 2019 seasons to determine inter-species nitrogen competition in the tomato and corn systems with different spatial arrangements. The treatments included sole corn (SC), sole tomatoes (ST), two rows of tomatoes intercropping two rows of corn (IC₂–₂), and four rows of tomatoes intercropping two rows of corn (IC₄–₂) systems. Additionally, the modified HYDRUS (2D/3D) model was used to quantify soil nitrogen concentrations, solute fluxes, soil nitrogen distribution, and soil nitrogen balance in the crop root zone under the SC, ST, IC₂–₂, and IC₄–₂ systems. The modified HYDRUS (2D/3D) model could precisely capture the soil nitrogen dynamics with nRMSE ranging from 2.8% to 12.4%. In general, soil NH₄-N concentrations in the root zone of tomatoes of different systems decreased as follows: IC₂–₂ > IC₄–₂ > ST, while a reverse trend was observed in the root zone of corn. Compared with soil NH₄-N, differences in soil NO₃-N among different systems were more evident due to its higher mobility. IC₂–₂ had the highest nitrogen flux, cumulative N flux, N uptake (CNU), and the land equivalent ratio for nitrogen (LERN) among different systems. Among different intercropping systems, the corn's and tomato's highest crop yields occurred in IC₂–₂ and IC₄–₂, respectively, with an average of 13,406.0 and 98,732.3 kg ha⁻¹ in both years. Additionally, corn and tomato's highest nitrogen use efficiency (NUE) occurred in IC₂–₂ and ST, respectively. However, the land-equivalent ratio for nitrogen use efficiency (LERNUE) in IC₄–₂ was 5.4% higher than in IC₂–₂. Therefore, IC₄–₂ is the optimal intercropping system recommended for sustainable agriculture development. The findings of this study improve the understanding of the mechanisms of inter-species nitrogen competition between commercial and grain crops. The study also suggests to the farmers and government suitable spatial arrangements of an intercropping system that can be adopted to promote the development of sustainable agriculture.