Effect of Spent Mushroom (Agaricus bisporus Imbach.) Compost on Growth, Yield and Water Use Efficiency of Mungbean (Vigna radiata L.) in Conditions of Cut Irrigation in Pod Formation Stage

Plants are exposed to several environmental stresses, all affecting plant growth, and development, which hampers crop plants' productivity. The mungbean (Vigna radiata L.) is a plant species from the legume family. This plant is an enriched source of protein, fiber, antioxidants, and phytonutrients. It plays an important role in the human diet and improves soil fertility by fixing atmospheric nitrogen. The average yield of mungbean is quite low. One way to improve crop yield and production is the management of fertilizers such as spent mushroom compost that greatly affect mungbean growth, development, and yield. Spent mushroom compost (SMC) is the residual compost waste generated by the mushroom production industry. It is readily available, and its formulation generally consists of wheat straw, dried blood, horse manure, and ground chalk composted together. This research was carried out to study the effects of different levels of spent mushroom compost on mungbean's quantitative yield and water use efficiency under drought stress. 

This research was conducted in 2016-17 as a split plot based on a completely randomized block design with three replications at the Research Farm of the University of Gonabad. Main factor levels concluded of full irrigation (300 m3 in each irrigation) and irrigation disruption at the pod formation stage, and subfactor consisted of 0 (control), 20, 40, 60, and 80 t.ha-1 spent mushroom compost. 

The results showed that under drought stress, the highest seed yield (1660 kg.ha-1) obtained in the treatment of 60 t.ha-1 spent mushroom compost and 40 t.ha-1 spent mushroom compost decreased the effects of drought stress. In full irrigation, the highest biological yield observed in treatments of 80 (7377 kg.ha-1) and 60 t.ha-1 (6132 kg.ha-1) spent mushroom compost and drought stress and no application of fertilizer decreased biological yield (46%). In drought stress conditions, application of 40, 60, and 80 t.ha-1 spent mushroom compost increased water use efficiency compared to control, and the highest water use efficiency was observed in the treatment of 60 t.ha-1 spent mushroom compost. Application of 80 t.ha-1 spent mushroom compost increased the lateral branch number by 44% compared to control. The highest and the lowest pod number per plant were obtained in treatments of 80 to.ha-1 spent mushroom compost (27 pods per plant) and control (17.3 pods per plant), respectively. Less irrigation increased water use efficiency, so each level of SMC in full irrigation conditions did not significantly differ from similar levels under drought stress. The main consequences of drought in crop plants are reduced cell division and expansion rate, leaf size, stem elongation and root proliferation, disturbed stomatal oscillations, plant water and nutrient relations with diminished crop productivity, and water use efficiency. Spent mushroom compost is an excellent source of humus. SMC does not contain any pests or weed seeds because of the high temperatures associated with the composting and pasteurization processes. SMC also contains very low levels of pesticides and heavy metals. The negative effects of drought stress on plants of the legume family have been proven in other studies. Research on wheat reported that spent mushroom compost increased seed number per spike. 

The results showed that drought stress reduced most of the studied traits. Application of 20 t.ha-1 spent mushroom compost did not significantly affect most studied traits. The highest effect on plant height, lateral branch number, and pod number per plant were observed in the treatment of 80 t.ha-1 spent mushroom compost. In general, according to the results of this research, applying optimum amounts of spent mushroom compost as an eco-friendly input in drought stress can improve growth characteristics and yield.