Effects of Fagopyrum esculentum (Buckwheat) and Vigna radiata (Mung Bean) Cover Crops (Monoculture and Mixture) on Soil Organic Matter, Total Nitrogen, and Available Phosphorus

Abstract

Cover crops play a vital role in enhancing soil health and agroecosystem sustainability. This study evaluated the effects of monoculture and mixed cover crops on soil nutrient dynamics under dry subtropical conditions in Bhutan. The experiment followed a randomized complete block design with four treatments: buckwheat (Fagopyrum esculentum) monoculture, mung bean (Vigna radiata) monoculture, buckwheat-mung bean mixture, and control (no cover crops). The biomass of the cover crops was sampled destructively 45 days after sowing and then incorporated into the soil. Five composite soil samples were collected at intervals of 15 days to determine the changes in soil nutrients after the incorporation of cover crop residue. By 60 days after residue incorporation, soil organic matter levels were significantly higher in the mung bean (7.64 ± 0.66%) and mixture plots (6.85 ± 0.62%) compared to the control plots (5.41 ± 0.28%). Total nitrogen was also significantly higher in the mung bean (0.38 ± 0.03%), and mixture plots (0.34 ± 0.03%), compared to the control plots (0.27 ± 0.01%). Buckwheat (monoculture) consistently enhanced available phosphorus levels (0.23 ± 0.01 ppm), followed by the mixture (0.14 ± 0.01 ppm), both significantly higher than mung bean (0.06 ± 0.01 ppm) and the control plots (0.09 ± 0.01 ppm). These findings emphasize the potential use of buckwheat and mung bean as cover crop mixtures to enhance soil health through complementary nutrient contributions. This study provides valuable insights for promoting cover cropping practices to address soil fertility challenges in Bhutan.