Interspecific interaction and productivity in a dryland wheat/alfalfa strip intercropping

Intercropping pasture with grain crops provides a strategy for diversifying cropping systems and establishing a foundation for mixed crop-livestock farming systems. Investigating the effects of strip design and nitrogen (N) application on interspecific interaction, crop yield, N use efficiency (NUE), and land equivalent ratio (LER) in dryland wheat/alfalfa intercropping. We conducted a four-year field experiment, which tested three intercrops, namely, 2-row wheat with 1-row alfalfa (I21), 4-row wheat with 2-row alfalfa (I42), and 8-row wheat with 4-row alfalfa (I84), as well as sole wheat (SW) and alfalfa (SA). N rates of 150 (HN) and 75 kg ha−1 (LN) were applied for wheat. Winter wheat exhibited earlier spring green-up than alfalfa and maintained dominance during co-growth. Over the four seasons, I21, I42, and I84 resulted in wheat yield (based on the wheat strip area) increases of 19.0%, 16.7%, and 24.0%, respectively, under HN, and 34.1%, 31.9%, and 43.4% under LN. Alfalfa growth was constrained during co-growth but recovered after the wheat harvest. Alfalfa in I42 and I84 maintained forage yield (based on the alfalfa strip area) as high as SA. Intercropping increased wheat NUE under both N conditions but did not significantly affect alfalfa NUE. I84 attained the highest LER of 1.01–1.14 and 1.11–1.25 under HN and LN respectively. Net revenue of I84 was lower than SA but three times higher than SW. Wide-strip wheat/alfalfa intercrop with low-N showed the best performance, which is promising in diversifying farming system and improving agricultural sustainability.