Dispersed trees on smallholder farms enhance soil fertility in semi-arid Ethiopia

Yikunoamlak Gebrewahid,Sara Tewolde-Berhan,Emiru Birhane,Esayas Meresa,Gebru Eyasu,Tewolde-Berhan Gebre-Egziabhier,Kassa Teka

doi:10.1186/s13717-019-0190-8

Abstract

IntroductionDispersed trees such as Oxytenanthera abyssinica (A. Rich.) and Dalbergia melanoxylon (Guill. & Perr.) which are objectively maintained or planted on farmland provide a significant contribution to soil fertility improvement. However, there was no quantitative information on the level of soil nutrient additions of these trees to the soil system.MethodsThis study was conducted on the farmers’ fields in Kafta Humera district, Tigray region (northern Ethiopia), where mature stands of O. abyssinica and D. melanoxylon trees exist. Radial distance-based soil sampling (under the canopy, near to canopy, and far from canopy) was adopted to quantify the role of these trees on soil fertility improvement. Soil parameters tested were soil reaction (pH), total nitrogen (TN), available phosphorus (AvP), electrical conductivity (EC), cation exchange capacity (CEC), and organic carbon (OC).ResultsThere was a negative linear relationship between the radial distance of the O. abyssinica tree trunk and soil TN, OC, CEC, and AvP contents but not for pH. Similarly, negative linear relationship between distance from D. melanoxylon and TN, OC, and AvP was obtained. The average total nitrogen (0.26% and 0.13%), available phosphorus (7.21 ppm and 6.37 ppm), and organic carbon (1.73% and 1.02%) contents were respectively higher under the tree canopies of O. abyssinica and D. melanoxylon compared with the adjacent open canopies. The amount of soil OC, TN, AvP, and CEC under O. abyssinica tree species was also significantly higher by 69%, 100%, 13%, and 42% compared to that of D. melanoxylon tree species. However, the amount of EC and soil pH was significantly lower by 57% and 19%, respectively.ConclusionIn general, O. abyssinica and D. melanoxylon added a significant amount of nutrients to the soil. Thus, retaining these important tree species on farmland played a positive role in replenishing soil fertility for resource-constrained households so as to reduce chemical fertilizer amendments.

Highlights

IntroductionDispersed trees such as Oxytenanthera abyssinica (A. Rich.) and Dalbergia melanoxylon (Guill. & Perr.) which are objectively maintained or planted on farmland provide a significant contribution to soil fertility improvement
Total nitrogen (TN) Total nitrogen significantly (P < 0.001) decreased with increasing distance from each tree trunk base. It decreased from 0.26% at the smaller distance to 0.12% at the far distance of O. abyssinica and from 0.13% at the smaller distance to 0.07% at the far distance of D. melanoxylon (Table 1)
Available phosphorus (AvP) The mean available phosphorus significantly decreased with increased distance from the tree base of both tree species

Summary

Introduction

Dispersed trees such as Oxytenanthera abyssinica (A. Rich.) and Dalbergia melanoxylon (Guill. & Perr.) which are objectively maintained or planted on farmland provide a significant contribution to soil fertility improvement. Integration of legume trees into agricultural systems, adds biologically fixed nitrogen and other agriculturally important nutrients to the soil (Rosenstock et al 2014) in a way that complements the crops grown in association with the trees (Akinnifesi et al 2010). These trees are known to bring about changes in edaphic, micro-climatic, and other components of the ecosystem through bio recycling of mineral elements, environmental modifications (including thermal and moisture regime), and changes in floral and faunal composition (Shukla 2009)

Methods

Results

Discussion

Conclusion