Intercropping maize and soybean increases efficiency of land and fertilizer nitrogen use; A meta-analysis

Intercropping exploits species complementarities to achieve sustainable intensification by increasing crop outputs per unit land with reduced anthropogenic inputs. Cereal/legume intercropping is a classical case. We carried out a global meta-analysis to assess land and fertilizer N use efficiency in intercropping of maize and soybean as compared to sole crops, based on 47 studies reported in English and 43 studies reported in Chinese. The data were extracted and analyzed with mixed effects models to assess land equivalent ratio (LER) of intercropping and factors affecting LER. The worldwide average LER of maize/soybean intercropping was 1.32 ± 0.02, indicating a substantial land sparing potential of intercropping over sole crops. This advantage increased as the temporal niche differentiation between the two species was increased by sowing or harvesting one crop earlier than the other as in relay intercropping, i.e. with only partial overlap of the growing periods of the two species The mean fertilizer N equivalent ratio (FNER) was 1.44 ± 0.03, indicating that intercrops received substantially less fertilizer N than sole crops for the same product output. These fertilizer savings are mainly due to the high relative maize yield and the lower N input in the intercrop compared to the input in sole maize. This meta-analysis thus shows that exploiting species complementarities by intercropping maize and soybean enables major increases in land productivity with less fertilizer N use. Both LER and FNER increased as the difference in growth duration increased for maize and soybean, but were not affected by fertilizer N rate. LER increased when soil organic matter increased but FNER did not change with soil organic matter.