Improving Carbon Sequestration and Yield of Barley (Hordeum vulgare) through Combined Application of Green Manure and Mineral Fertilizers under Cambisols in Ethiopian Highlands

ABSTRACT

Nowadays, due to high population pressure more fragile lands are put into farming which then leads to low crop yield, loss of biodiversity and above all contributing to increased greenhouse gas emissions. This two year study (2020-2021) evaluated the potential of legume green manure (GM) species in improving soil fertility and barley yield, and their ability to effectively sequester soil organic carbon (SOC) towards reducing greenhouse gas emissions. The GM crops; lupine and vetch were planted during the main rainy season on the land that previous barley crop was harvested and left bare and fallow. The green manures crops were chopped and ploughed under at their 50% flowering stage and the main test crop, barley was introduced during the next cropping season. The treatments included (i) vetch GM, (ii) vetch GM + 23N + 20P, (iii) lupine GM, (iv) lupine GM + 23N + 20P, (v) fallow, (vi) fallow + 46N + 20P laid down in RCBD design with three replications. The N rate used was half when integrated with the GM species but full dose with the fallow system, whereas P was full dose. Results showed that barley grain & biomass yields were increased by 3.7 to 39.8% and 10.66 to 38.58%, respectively due to the application of the GM crops. The highest grain yield (4.1 t ha^-1) and biomass yield (10.1 t ha^-1) were recorded from vetch + NP application while the least grain yield (2.94 t ha^-1) & biomass yield (7.24 t ha^-1) were registered from the traditional fallow system. Green manure addition has brought 25 to 95.41% SOC relative change in the top 0-20cm soil depth compared with the traditional fallow system. Since both GM species are legumes, they added more N to the soil alongside with storing more C in the soil so that C: N ratio was also not affected. The highest carbon sequestered was from sole application of vetch GM (26.18 t C ha^-1 yr^-1) followed by vetch + NP applications (22.82 t C ha^-1 yr^-1). Lupine GM alone sequestered 9.24 t C ha^-1 yr^-1 and lupine + NP sequestered 6.86 t C ha^-1 yr^-1. The carbon balance in the fallow and fallow + NP combinations were negative (-0.98 and -1.40 t C ha^-1 yr^-1, respectively) indicating that there was C loss to the atmosphere. Therefore, application of vetch and lupine GMs with and/or without inorganic fertilizer integration had positively contributed towards improving the yield of barley and sequestering more C as compared to the local fallow practice.