The Effects of Different Agroforestry Practices on Glomalin Related Soil Protein, Soil Aggregate Stability and Organic Carbon-Association with Soil Aggregates in Southern Ethiopia.

Abstract

The conversion of natural ecosystems for agricultural production is changing the world's landscapes in pervasive ways. The severity of land degradation in southern Ethiopia has increased at an alarming rate due to high population density which has replaced the old agroforestry (AF) farming system with monocropping. One of the most significant consequences of these activities combined with climate change has been the reduction of biodiversity and land productivity (1). Among others, soil glomalin, soil aggregation and aggregate stability are parameters related to soil health that are affected by land use change . To curb such problems, AF is proposed as an adequate system, since it is an alternative cultivation system based on an ecological and economically sustainable strategy (2). This study was aimed to determine the effect of agroforestry practices (AFPs) on soil glomalin, soil aggregate stability (SAS) and aggregate association with soil organic carbon (SOC). Soil samples and woody species with plant height at breast height (DBH) were collected from homegarden based agroforestry practice (HAFP), cropland based agroforestry practice (ClAFP), woodlot based agroforestry practice (WlAFP) and trees on soil and water conservation based agroforestry practice (TSWAFP) using systematic sampling techniques. The data was analyzed by two way ANOVA and linear regression model by using R 4.2.1 software.  In this study, both easily extractable glomalin related soil protein (EEGRSP) and total glomalin related soil protein (TGRSP) were significantly (p < 0.05) higher in HAFP compared to AFPs, the EEGRSP and TGRSP which decreased in the order of HAFP>WlAFP>TSWAFP>ClAFP at upper surface . On the other hand, the macroaggregate fraction of all AFPs ranged from 22.6-36.5% (for 0-30cm) where the lowest was in ClAFP, while the highest was in HAFP. The micro-aggregate fraction ranged from 15.9–24.6%, where the lowest was in HAFP, but the highest was in ClAFP. The results also indicated that the comparison of SAS with SOC showed relatively higher SOC in macroaggregates than in micro-aggregates. Besides, both macro and micro-aggregate-associated with SOC was higher in HAFP than other three AFPs but SAS decreased with the increasing of soil depths. The results regarding the association of SOC with both macro and micro-aggregates was greatest in HAFP followed by WlAFP. The findings also elucidated that woody species diversity, richness and key soil parameters were strongly related with the EEGRSP, TGRSP, and SAS distribution. Thus, the management practices of AFP could influence the woody species diversity and richness, this, in turn, can influence glomalin and SAS. This implies that AFP can play an important role on the maintenance of soil biodiversity, enriching glomalin and other soil quality parameters with future implications for stable ecosystem.(1)Bhagwat et al, 2008. Trends in ecology & evolution, 23, 261-267; (2)Wall et, 2015. Nature,, 528, 69-76.The authors gratefully acknowledge the financial support of Comunidad de Madrid (Spain) and Structural Funds 2014–2020 (ERDF and ESF) project AGRISOST CM S2018/BAA‐4330