Morphophysiological and biochemical characteristics of bean (Phaseolus vulgaris L.) in response to tea waste mulch and weed control

Legumes are the most important source of vegetable protein supply. Seed bean contains 25-22 percent protein, and it has a high nutritional value for human which is a major source of protein supply in most modern societies. Today protein deficiency is one of the acute nutritional problems in the diet of millions of people in developing countries. Bean ranks third after pea and lentil in Iran as one of the developing countries with dry and semi-arid climate. Moreover, as to the weeds management of the cropping systems, weeds are controlled by hand as an earliest means, and by airplanes, chemical pesticides, hormones, and viruses as the most complete tools. Various studies show that weed control treatments especially hand weeding treatments caused higher yield than control treatment, indicating the importance and priority of hoeing in the cultivation of beans. Mulch as a new phenomenon in agriculture has caused a fundamental change in the use of chemical pesticides, controlling weeds in fields, preventing soil erosion, and increasing water penetration in soil layers. Also, the use of plant mulch can compensate soil nutrients and increase the organic nitrogen content of the soil. The advantages of using plants mulch could be increasing soil nitrogen for the main plant, protecting soil erosion, increasing soil quality, reducing evaporation, and increasing water penetration in the soil, improving water use efficiency, maintaining good soil temperature and suppressing weeds. Considering the growing need for weed control in bean fields through non-chemical and mulch applications as an ecological alternative for sustainable agriculture, an experiment was conducted to investigate the effect of tea waste mulch and weed control on morphophysiological and biochemical characteristics of bean. 

This study was conducted at the Research Farm of Tarbiat Modares University, with a factorial experiment using a RCBD with three replications. Five time of weed control including no weed control, and weed control every 1, 2, 4 and 6 weeks and three rates of tea waste mulch at 0, 5 and 10 ton.ha-1 were used. Common bed preparation techniques such as plowing, disc and leveling was done in a land area of 1000 m-2. The dimensions of each plot were 4 m by 3 m. The planting was carried out on March 20, with a density of 25 plants m-2, with a spacing of 50 cm between the planting rows and eight centimeters on the planting row. The first irrigation was carried out immediately after planting using T-tape. The next irrigation intervals were every 5 days.

The results showed that the combined effects of weed control and tea waste mulch on all measured traits were significant. Also, the two-way interaction of these factors was significant for soluble carbohydrate, starch, number of pods per plant of bean and dry weight of weed. The highest yield and yield components of bean were observed in weed control once per week and 10 tons tea waste mulch per hectare. The highest photosynthesis rate and water-soluble carbohydrate content was observed in the same treatment. Weed control reduced the competition of weeds with bean and could provide more resources to the crop. Thus, the application of tea waste mulch affects the absorption of nutrients by the roots. Other studies reported that dandruff mulch, such as mulch, was more effective in control of weeds than light cleared mulches due to the lack of light on the surface of the soil and produces good grain yield. The researchers reported that the highest grain yield was obtained from mulch clichés treatment, which were categorized by black and white plasterboard treatments in a statistical group.

The results of this study suggest that weed control and application of 10 tons tea waste mulch per hectare could improve photosynthesis rate, reduce protein content and increase starch and water-soluble carbohydrate contents of bean seed. Weed control once per week after bean emergence and application of five and 10 ton ha-1 mulch reduced weed dry weight by 45.48% and 74.12%, respectively. Finally, application of 10 tons tea waste mulch per hectare and weed control every 2 weeks is recommended for bean fields. Overall, it appears that application of tea waste mulch and weed control at the beginning of emergence was superior for seed production comparing to the late weed control and without mulching.