Yield and Nutritive Value of Mung Bean Forage (Vigna radiata L.) Affected by Potassium Fertilizer in Drought Conditions

Mung bean (Vigna radiata L.) is native to India and its seeds are rich in phosphorus and protein. Drought is one of the most important limiting agents of plant production. Carbohydrate metabolism and the process of dry matter distribution is disrupted by limitation of carbon stabilization due to stomata closure and reduction of photosynthesis under drought stress. Potassium is an essential nutrient and the most abundant cation that it has a major role in plant growth and almost all related activities. The presence of potassium enhanced the synthesis of hydrocarbons and proteins, which results in amplification of plant tolerance to drought stress.

Experiment was performed at Agricultural Research Institute, in 2017-2018 to study the yield and nutritive value of mung bean. This research was conducted as split plot based on a randomized complete block design with three replications. Main plot was drought stress consist of 60, 90 and 120 mm evaporation from the A class pan and sub plot was including 0, 85, 170 and 255 kg.ha-1 potassium sulfate fertilizer. The characteristics plant height, biological yield, seed yield, insoluble fiber in neutral detergent, insoluble fiber in acid detergent, water soluble carbohydrate, crude protein and dry matter digestibility were measured. The samples nitrogen content was estimated by Kjeldahl set and it was multiplied by the protein coefficient 6.25 and the crude protein percentage was calculated. Van Soest method was used for measuring of insoluble fiber in neutral detergent and insoluble fiber in acid detergent. Ethanol was utilized to measure soluble sugars by sulfuric acid method. The percentage of digestible dry matter was estimated according to Equation (1).DMD= 88.9 - (0.779×ADF%) (1) Variance analysis of data was carried out by MSTAT-C software and the comparison of the means was done with Duncan's multiple range test at the 5% probability level.

The results showed that drought stress treatment on all mung bean plant characteristics was significance at 1% level. The effect of sulfate potassium fertilizer on plant height, biological yield, seed yield, insoluble fiber in acid detergent, water soluble carbohydrate, crude protein and dry matter digestibility at 1% significance level and on insoluble fiber in neutral detergent were significant at 5% level. The interaction effect of drought stress and potassium sulfate fertilizer on Plant height, biological yield, insoluble fiber in neutral detergent, insoluble fiber in acid detergent, water soluble carbohydrate, crude protein and dry matter digestibility at 1% significance level and on seed yield were significant at 5% level. The results showed that in the control irrigation + application of potassium sulfate fertilizer (170 kg.ha-1) compared to the control potassium treatment, plant height and biological yield increased by 37.9% and 89.6%, respectively. In the control irrigation + application of potassium sulfate fertilizer (170 kg.ha-1) compared to the control potassium treatment, dry matter digestibility increased by 30.12% and insoluble fiber in neutral detergent and insoluble fiber in acid detergent decreased by 44.3% and 43.8%, respectively. The most amount of water soluble carbohydrate (18.3%) in 120 mm evaporation from A class pan and the highest value of crude protein (22.8%) in 90 mm evaporation from A class pan and in both characteristic application were effective 170 kg.ha-1 of potassium sulfate.

The result showed that interaction of drought stress and potassium sulfate fertilizer on quantitative and qualitative of mung bean traits was significant. Plant height and biological yield increased 37.9% and 89.6% by addition of sulfate potassium consumption from 0 to 170 kg.ha-1, respectively. Seed yield enhanced compared to control treatment (33.8%) by using of 255 kg.ha-1 potassium sulfate. Drought stress decreased dry matter digestibility and it increased crude protein, water soluble carbohydrate, insoluble fiber in neutral detergent and insoluble fiber in acid detergent. Potassium sulfate fertilizer amount 170 and 255 kg.ha-1 recommend for maintaining of yield and qualitative of mung bean in Sistan region in non-stress and drought stress conditions.