Design of the hydroponic experiment

The hydroponic experiment was conducted from September to December 2017 in the glasshouse of Yunnan Agricultural University. The illumination was 14 h a day/10 h of night, and the temperature was 26 °C/22 °C. A two-factor randomized block design was used in the experiment. Factor A was the N application level, and three treatments with four replicates were established: no nitrogen (N0), conventional nitrogen (N 1:2 mmol/L Ca[NO₃]₂) and high nitrogen (N 2:5 mmol/L Ca[NO₃]₂). Factor B was the planting pattern: faba bean monocropping, which included six faba bean seedlings grown alone in pot culture; wheat/faba bean, which included three faba bean seedlings grown, and nine wheat seedlings grown on the other side; the distance between the faba bean seedlings and the wheat seedlings was 10 cm with four replicates per treatment (Fig. 4). The nutrient solution formulation used was (mmol/L): K₂SO₄ 0.75, MgSO₄ 0.65, KCl 0.1, KH₂PO₄ 0.25, H₃BO₄ 0.001, MnSO₄ 0.001, CuSO₄ 0.0001, ZnSO₄ 0.001, (NH₄)₆Mo₇O₂₄ 0.000005, Fe-EDTA 0.2³². Calcium ions in the form of CaCl₂ (2 mmol/L) were added to the no-N treatment.

Diagram of the planting patterns in the greenhouse.

Seeds of the same size and plumpness with a complete seed coat were selected, soaked in 10% (v/v) H₂O₂ for 30 min, cleaned with deionized water, and then soaked in saturated CaSO₄ for 12 h until the seeds were full and bloated. The seeds were then wrapped with wet filter paper, immersed in a saturated CaSO₄ solution, germinated in a culture chamber at 25 °C, and the cotyledons were expanded and cultured in 1/2 nutrient solution for 24 h before being cultured in a total nutrient solution. The nutrient solution was circulated throughout the whole cultivation process using a ventilation pump. The volume of nutrient solution was 4 L, and it was stored in a plastic pot (28 cm in the upper diameter, 20 in the lower diameter and 17 cm high), and the nutrient solution was changed every three days. The pH of the nutrient solution was maintained between 6.20 and 6.30. A completely random arrangement was used in this experiment.