Cereal–legume intercropping increases the nitrogen (N) input from biological nitrogen fixation (BNF) and improves the exploitation of fertilizer and soil N, often leading to higher grain N content and higher productivity per unit land area compared to monocrops. Previous studies have found that these effects are more tangible under low soil and fertilizer N conditions compared to high N availability, and there is a need to assess the N uptake at critical crop development stages in order to time the N application for maximum uptake and use efficiency. The objective of this study was to assess the productivity of pea–barley intercropping compared to monocropping under 0 kg N ha⁻¹ (0 N) and 100 kg N ha⁻¹ (100 N). In 2017, a split plot experimental design was implemented with pea (Pisum sativum) sole crop (SC pea), barley (Hordeum vulgare) sole crop (SC barley), and pea–barley intercrop (IC total) as the main plots and 100 N applications in two 50 kg N ha⁻¹ splits at 30 and 60 days after emergence as subplots within the main plots. The Land Equivalent Ratio (LER), based on grain dry matter (GDM) yields in the pea–barley intercrop (IC total), was higher (1.14 at 0 N and 1.10 at 100 N), indicating 10–14% greater radiation, nutrient, and water use efficiency compared to the sole crops and 4% greater resource use efficiency at 0 N compared to the 100 N; this illustrated greater total intercrop productivity compared to sole crops. The 100 N treatment decreased the SC pea and pea in intercrop (IC pea) GDM and grain dry matter N (GDMN) and increased the GDM and GDMN in SC barley and barley in the intercrop (IC barley). Intercropping increased the grain N content and therefore the protein content of the grains in 0 N and 100 N treatments. The highest fertilizer N yield, % nitrogen derived from fertilizer (%NDFF), and % nitrogen use efficiency (%NUE) were achieved in SC barley followed by IC total, indicating that intercropping improved the soil and fertilizer N use compared to SC pea. The IC pea increased the % nitrogen derived from atmosphere (%NDFA) from 67.9% in SC pea to 70.1% in IC pea. IC total increased the share of %NDFF, %NDFS, and %NDFA compared to the SC pea, which indicated a significant advantage of intercropping due to the complementarity of the component species under limited N supply in the field.

Intercropping (IC) can reduce nitrogen fertilizer requirements, supress weeds, and improve crop yields and yield stability. Three field trials were conducted in Denmark in 2018 with intercropping and sole crops (SC) using spring wheat, barley, faba bean and field pea to compare productivity under five fertilizer levels. The trials were carried out using in a split-plot design with four. Anomalous weather during the 2018 cropping season created drought conditions and high temperatures above 31°C. No effect of fertilizer treatment was found, and total dry matter and grain yields were supressed in all systems. Wheat grain yields averaged 2.14 t ha⁻¹ across systems, ranging from 1.58 t ha⁻¹ as a component of the IC to 2.44 t ha⁻¹ as SC, and barley grain yields averaged 2.35 t ha⁻¹. Faba bean yielded 1.78 t ha⁻¹ as SC, but failed in the IC. Pea failed in both systems. Intercropping barley with cover crops had no effect on grain yield or total dry matter. These results suggest that intercropping provided no production advantage during a drought and illuminate the need to continue conducting research and breeding on drought-resistant cultivars.

Intensive use of mineral N fertilizers and organic amendments has resulted in higher N2O emissions. A growing worldwide concern for these problems has motivated researchers, environmentalists, and policy makers to find alternatives to overcome such losses. Biological nitrogen fixation is one of many natural biological approaches to minimize the use of fertilizers and to possibly reduce N2O emissions. A greenhouse study was performed by growing inoculated and noninoculated soybean seeds (Glycine max (L.) Merr.) in PVC columns. The objective was to measure the contribution of Bradyrhizobium Japonicum and mineral-N fertilizer to promoting N2O emission. A closed chamber technique was used for gas sampling. N2O measurements were carried out shortly after nodulation. Bradyrhizobium Jopanicum induced N2O cumulative (121.8 μg kg−1) fluxes of inoculated seeds was significantly (α = 0.05) higher than those of mineral N fertilized treatment (NIS) and the control (bare soil). Total nitrogen content of the roots and seeds was not affected by inoculation. Total carbon ( 42.1 ± 0.1%), total nitrogen (3.1 ± 0.1%), and crude protein (19.9 ± 0.7%) contents of leaves of the inoculated seeds were significantly higher than those of noninoculated seed treatments. N2O fluxes significantly increased with high dissolved organic carbon content (70.77 ± 3.99 mg L−1) at R3 and at R8 stages when (39.60 ± 0.94 mg L−1) concentrations were high.