The effect of living mulch type and planting time on weed control and black seed yield

To evaluate the effect of living mulches on weed control and yield of Black cumin (Nigella sativa L.)  weeds by living mulch, a factorial split experiment has been conducted in the form of a randomized complete block design with four replications in the research farm of Aburaihan Campus, the University of Tehran in the 2017-2018 crop year. Factors of seedbed planting (stale seedbed and simple), type of living mulch (berseem clover (Trifolium alexandrinum L.), fenugreek (Trigonella foenum-graecum L.), and alfalfa (Medicago sativa L.), as well as planting time of living mulch (two weeks before and at the same time of black seed cultivation). The first factor is in the main plots and the combination of the second and third factors, in the subplots. Results show that fenugreek and alfalfa have been more successful in terms of weed control than clover with a 40% reduction in weed density and biomass, compared to the control without either live mulch or weeding. Also, in order to achieve the highest percentage of black cumin yield traits (83.02, 93.44, and 50.50), the number of capsules per plant, number of seeds per capsule, and 1000-seed weight are compared to the control. It is recommended to cultivate fenugreek at the same time as black cumin. In case of alfalfa, pre-sowing is also recommended. Stale seedbed planting system does not play a positive and significant role in weed control and increase in black seed yield traits. It is also better to grow fenugreek at the same time as black seed to get more seed yield in black cumin, but in case of alfalfa, it is better to plant earlier than black seed in the absence of any significant difference among planting times. It seems that alfalfa and fenugreek control weeds by accelerating canopy closure, increasing weed competition with black seed, not interfering negatively with black seed growth, and providing nitrogen to black seed have increased its yield.