Mr Roshan Babu Ojha1, Mr. Sushil Lamichhane1, Dr. Kabindra Adhikari2
1University of New England, Armidale, Australia, 2University of Arkansas, Fayetteville, USA
Southern Terai plains of Nepal, most productive land, represents 4% area (0.5 million ha) of the Indo-gangetic plains and 21% area of Nepal is at the threat of Soil Organic Carbon (SOC) decline. SOC accrual primarily depends upon temperature and precipitation which are the key drivers of SOC spatial variation. So, we aimed to study the degree of relationship between SOC and bioclimatic factors in the region. Soil organic matter (%) of 0-30 cm depth from 13,287 observations was retrieved from national land use planning project. Nineteen bioclimatic variables (eight precipitation and eleven temperatures variables) were taken from worldclim dataset version 2.0. Primary components of the variables were identified by principal component analysis (PCA) and the contribution of variables in the PCs using factor analysis along with covariance of OC (Cov.(OC,y)) with other variables was calculated. The minimum, maximum, average, and coefficient of variation of SOC content of the region was 0.005, 6.88, 1.04, and 61.7% respectively. There is significant (p-value = 0.013) reduction in SOC values from Western to Eastern (negatively correlated with longitude, r = -0.021) region. Among the 19 bioclimatic factors 70% of variation is explained in PC1 and PC2 with the most factor loading on precipitation of the wettest month, precipitation of the wettest quarter, annual precipitation, precipitation of the warmest quarter, longitude. Covariance analysis suggested SOC change primarily depend upon the precipitation related bioclimatic factors like precipitation of the wettest month (Cov.=0.21), precipitation of the wettest quarter (Cov.=0.20) and annual precipitation (Cov.=0.19), and precipitation of warmest quarter (Cov.=0.18) rather temperature related bioclimatic factors such as Isothermality (Cov.=0.009), temperature seasonality (Cov.=-0.01), mean temperature of wettest quarter (Cov.=0.01), and mean temperature of warmest quarter (Cov.=0.02) So, the longitudinal gradient, seasonality and distribution of precipitation pattern greatly affected the SOC accrual in the southern IG plains of Nepal.
Roshan Babu Ojha (M.Sc.Ag, 2014; B.Sc.Ag, 2012 Tribhuwan University), currently a PhD Scholar in the University of New England, is a soil scientist to the Soil Science Division, Nepal Agricultural Research Council (NARC) since 2015. He served as a national focal point for the Global soil partnership program of UNFAO, Rome, Italy from 2016-2018. Before joining NARC, he worked as an assistant professor in Himalayan College of Agricultural Science and Technology, Purwanchal University and teaches several courses of soil science. Soil organic carbon management, Soil fertility, and Integrated Plant Nutrient Management are his field of expertise. He is awardee of ‘Young Scientist’ award (2017) hosted by Society of Agriculture Innovation and Development, India and ‘Outstanding Contribution Scientist in Soil Conservation’ award (2018) jointly hosted by the Global Soil Partnership, UNFAO and the organizing committee of soil health and sustainable development international symposium, Beijing, China.