Dynamics of N acquisition and accumulation and its interspecific N competition in a wheat-faba bean intercropping system

Objectives We studied the nitrogen (N) content and N uptake of intercropping wheat and faba bean to clarify the relationship in nitrogen competition and accumulation between wheat and faba bean under different N application levels, so to propose a scientific nitrogen management for the intercropping system.

Methods A field experiment of two factors with randomized block design was conducted under wheat monocropped, faba bean monocropped and wheat and faba bean intercropping conditions, and the four N levels were 0, 90, 180 and 270 kg/hm² for wheat and 0, 45, 90, 135 kg/hm² for faba bean. Both grain yield and above-ground N accumulation of wheat and faba bean were measured, and Logistic model was used to simulate the key N uptake parameters and N uptake dynamics. The N competition capacity between intercropping wheat and fababean was analyzed.

Results The yield of wheat was increased by 33.4%, but faba bean yield was decreased by 20.7% in the intercropping system, as compared to corresponding mono-cropping. However, the intercropped wheat and faba bean had a yield advantage under N0 and N1 levels (LER > 1). Through Logistic model analysis, the peak N uptake of wheat was 12–19 days later than that of faba bean. Intercropping increased the maximum N accumulation (A), the maximum N uptake rate (R_max) and the initial N uptake rate (r) of wheat, but decreased the A, the time needed to reach the maximum N uptake rate (T_max) and R_max of faba bean under the four N levels. During the vegetative growth stage, intercropping tended to decrease N uptake and accumulation of wheat, and the N competitiveness of wheat was lower than that of faba bean in intercropping, but N application could improve the N competitiveness of wheat. Intercropping increased R_max of wheat by 34.1%, 44.6%, 21.0% under N0, N1 and N2 levels due to the interaction between N level and planting pattern, respectively. Thus, when wheat reached its N uptake peak, intercropping increased the N uptake rate and N accumulation of wheat by 15.1%–48.4% and 9.2%–28.9%, but decreased those values of faba bean by 7.3%–28.4% and 7.9%–14.0%, respectively. During reproductive growth stage, the N competitiveness of wheat was greater than that of faba bean, and the strongest N competitiveness of wheat was under N1 level.

Conclusions The yield advantage of intercropping is due to the increased initial and maximum N uptake rate of wheat (r and R_max), and the increased wheat N uptake rate and N accumulation in the reproductive stage. Reasonable N input could relieve the competition and increase the synergistic role for the N nutrition of wheat and faba bean, to achieve high yield and high nitrogen efficiency.