Nitrogen competition and recovery effects of maize in different maize/legumes intercropping systems

Objectives Interspecific competition and compensation are important mechanisms to showcase the advantage of intercropping systems. The objective of the present study was to explore the N competitive ability of maize relative to legumes during intercropping. We also examined the maize N uptake recovery effect under sole cropping and when intercropped with different legumes.

Methods A field experiment was conducted at the experimental site of the Gansu Academy of Agricultural Sciences in Zhangye, Gansu Province, China, from 2018 to 2019. The experiment included three intercropping systems: maize and pea (M/P), maize and faba bean (M/F), maize and soybean (M/S), and four sole cropping systems, including sole pea (SP), faba bean (SF), soybean (SS), and maize (SM). The crop dry matter weight and N concentration at the maturity stage were investigated, the N uptake equivalent ratio (NER) of the intercropping system and partial N uptake equivalent ratio (pNER) of the crops were calculate. Maize competitive ratio relative to legume (CR_ml), the relationship between CR_ml and NER, the partial nitrogen uptake equivalent ratio of legume (pNER_l), the partial N uptake equivalent ratio of maize (pNER_m), and the N uptake of intercropped maize were assessed.

Results Over the two years average, NER values of M/P, M/F, and M/S were 1.33, 1.26, and 1.38, respectively. The pNER_l value among intercropping systems was not (P>0.05) different. The pNER_m value in M/S was (P<0.05) greater than that in M/P and M/F; N uptake of intercropped legumes was (P<0.05) lower than sole legumes, but legume N concentration was not (P>0.05) different between intercrop and sole legumes. Maize N concentration among the intercropping systems was not (P>0.05) different. Maize N uptake in M/P, M/F, and M/S was 62.2%, 51.0%, and 79.9% of the value recorded for sole maize. Maize N uptake in M/S was 33.4% and 62.6% higher than in M/P and M/F, respectively. CR_ml value in M/S was higher than 1 and (P<0.05) higher than in M/P and M/F, but the CR_ml value in M/P and M/F were lower than 1. The recorded values for the maize recovery effect in intercropping systems were less than 1. A significant positive correlation was found between CR_ml and NER, pNER_m, and a significant negative correlation between CR_ml and pNER_l.

Conclusions Based on the two years of study, the maize/pea, maize/faba bean, and maize/soybean intercropping system showed higher N uptake equivalent ratio than the sole maize system in Hexi Corridor. Maize and legumes compete for N during intercropping, with pea and faba bean stronger than soybean in competing for N during the intercropping. After harvesting the legumes, maize did not show any apparent N uptake recovery effect.