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We studied the effects of Acacia albida on the growth and yield of wheat, maize, and teff with increasing distance from trees in Ethiopia in the 2014/2015 cropping season. The treatments comprised ...

Land use/land cover change drive changes in several ecosystem processes over short and long terms. In Ethiopia, the main land use/land cover change involves conversion of natural ecosystem into cultivated land. However, a recent change also involves conversion of cultivated and grazing land into Eucalyptus woodlots. This study was conducted to analyse the effects of such land use/land cover change on soil and nutrient losses. Three land use/ land cover types (cultivated land, grassland and Eucalyptus woodlot) were selected for a comparative assessment. A total of twelve runoff plots, each with 43.3 m2 area and with four replications, were installed. Rainfall depth, runoff volume and sediment samples (500 ml) were collected from each plots every morning and evening for 91 days (from 4th July to 2nd October, 2015) in the main rainy season. The sediment samples for ten consecutive days were stored in separate containers and composite sediment concentration samples were weighed after being filtered and oven dried for 24 hours at 105oc. From the samples taken at the end of the rainy season, separate composite a sample before filtration of one litre was analysed in the laboratory for nutrient losses. The effect of land use/land cover on soil and nutrients losses was statistically tested using analysis of variance. The study found that soil loss significantly differed between the land use/land cover types. Soil loss from cultivated land (16.8 ton/ha) was significantly higher than loss from grassland (7 ton/ha) and Eucalyptus stand (8.1 ton/ha). The soil and nutrient losses were positively correlated with runoff volume. There was higher nutrient (N and P) loss from cultivated land than grassland and Eucalyptus. From the results, it can be concluded that soil and nutrients losses are above tolerable limit, and perennial land covers including Eucalyptus stand reduce soil and nutrient losses significantly. This re-affirms the multi-purpose nature of Eucalyptus not only for socioeconomic benefit but also for soil erosion control when planted in appropriate locations. Key words: Cultivated land, grassland, runoff, sediment concentration, runoff plot.

Decline in farmland soil fertility due to nutrient depletion is a concern for smallholder farmers in the highlands of Ethiopia. In this study we tested if long-term addition of compost, either alone or in combination with nitrogen (N) and phosphorous (P) fertilizer, affected available soil nutrient status, grain/tuber harvests, agronomic N use efficiency, and plot level N and P nutrient balances. The on-farm experiments were conducted on four farm fields for up to 6 years in Beseku, Ethiopia. A randomized complete block design was used, with four treatments: full dose of compost applied alone at 2.4 t ha−1 DW organic matter (C); full dose of fertilizer (F); half compost and half fertilizer (CF); and, unfertilized control. In the upper 10 cm of the surface soil, several Mehlich-3 extractable nutrients (B, Ca, K, Mg, P, S, and Zn) had significantly higher concentrations in the C treatment (P

Soil fertility decline due to low nutrient input is a constraint for sustainable agriculture in smallholder farming systems in Ethiopia. In this study, crop productivity and soil organic matter buildup were compared in soils receiving locally made compost, applied either alone or in combination with NP fertilizer. The experiments had four treatments: full dose of compost (C), full dose of fertilizer (F), half compost and half fertilizer (CF), and unfertilized control (control). The full dose of compost was equivalent to 2.4 t ha −1 organic matter. The field study was conducted on four farm fields in the village Beseku, each representing different sub-villages. Participating farmers were selected based on their willingness and an assessment of dedication to carry out the experiment. The experiments, a randomized complete block design with three replications, were replicated across four farm fields. The treatments were repeated for six cropping seasons (years), and data on soil nutrient status and crop (maize, wheat, potato, and faba bean) harvests were collected. In the 0–10 cm soil layer, pH was ( P P −1 in C treatment, and by 4.74 and 0.45 t ha −1 in CF treatment. Treatment effects on crop harvests were significant ( P F > C > control in the initial season, CF > C > F > control in the next three consecutive seasons, and C > CF > F > control in the final year of the experiment. The overall combined yield was in the order of CF > C > F > control for maize and faba bean, CF > F > C > control for potato, and F > CF > C > control for wheat. The addition of either compost alone or in combination with NP fertilizer improved soil properties and crop productivity, compared with control and only fertilizer addition. Therefore, compost addition can serve as a complement to fertilizer use and reduce dependence on mineral fertilizer in low-input crop production system. The apparent synergy between compost and fertilizer addition needs further research in order to be explained.

Farmers' perceptions of soil fertility change were compared with observations on soil quality changes and crop performance in soils from a chronosequence representing a range of soil ages since conversion from forest to cropland (0 to 57 years). A majority of the farmers, 92 per cent, had observed a decline in soil fertility on their land. Farmers use crop yield, indicator plants, soil softness and soil colour to judge soil fertility. They identified 11 plants that they used to indicate high soil fertility and four plants that they used to indicate low soil fertility. There was a strong correlation (r = 0·96) between soil organic matter content (loss on ignition) and farmers' ranking of soil fertility based on colour and softness of soil samples from the chronosequence. The biotest experiment with maize showed an exponential decline in biomass production along the chronosequence, confirming the results of farmers' soil fertility ranking. In the biotest, total soil N predicted produced biomass well (r2 = 0·95), whereas the relationship with soil available P (Olsen) was less obvious. Among the eight analysed plant nutrients in the maize leaves, N content was found to correlate best with biomass production (r2 = 0·94). We conclude (i) that there is good agreement between farmers' knowledge and scientific indicators of soil fertility and (ii) that the major reason for declining soil fertility in Beseku is the decrease in N mineralization over time. Interventions should focus on supporting farmers to implement a diversified nutrient management strategy that can maintain or increase long-term productivity of the soil. Copyright © 2011 John Wiley & Sons, Ltd.

Exclusion of grazing animals and tree plantations are 2 methods that have been used for restoration of degraded lands in tropical semiarid areas. These 2 options can foster secondary forest succession by improving soil conditions, attracting seed-dispersal agents, and modifying microclimate for understory growth. We compared native woody plant diversity and soil chemical and physical attributes under exclosure and on Eucalyptus globulus (EGP) and Cupressus lusitanica (CLP) plantations. Vegetation data were collected by an inventory of stands with circular plots of 5.64 m radius, and soil samples were collected from the 4 corners and center of 20 3 20 m plots. As a result, 15 native woody plant species belonging to 13 families were recorded. Importance value index (IVI), Shannon-Wiener, Simpson’s diversity, and species richness were higher in the exclosure, followed by EGP and CLP. Contents of soil organic carbon and total nitrogen showed significance difference and were highest in the exclosure, followed by CLP, EGP, and grazing land. Although the difference was not significant, an increasing trend was observed for cation exchange capacity and K + . Bulk density was highest on the grazing land, followed by EGP, CLP, and exclosure. Our results suggest that degraded land reclamation can be achieved with plantation of rapidly growing tree species as well as exclosure. However, native woody species diversity and improved soil attributes are better achieved with exclosure. Exclosures can be established interspersed strategically with single- or mixed-species plantations to facilitate restoration of native vegetation. However, it is important to conduct further research on the comparative advantage of enrichment planting of exclosures with preferred tree species or exclosures interspersed within blocks of plantation.

Effect of prior land use on the recolonization of native woody species in plantation forests was investigated by assessing naturally regenerating flora (NRF) and soil seed banks (SSB) in plantation forests established on abandoned farmland and cleared natural forest sites in southern highlands of Ethiopia. Eucalyptus saligna and Cupressus lusitanica, two of the most widely planted tree species in the highlands of Ethiopia, were considered in the plantation treatments. About 66 plant species were recorded in the NRF and 55 plant species germinated from the soil samples collected for SSB analysis. Seedlings from the SSB were dominantly herbs, which accounted for 75% of the identified species germinated from the SSB, and native woody species accounted only for 10%. On the contrary, in the NRF native woody species were slightly more dominant (49%) than the herbs (45%). There was high species similarity between the NRF beneath the plantations and the standing vegetation in the adjacent natural forest. On the contrary there was very low similarity between the seedlings emerged from the SSB and the standing vegetation in the adjacent natural forest. Effect of prior land use was apparently stronger on the species composition of the SSB than the species richness of NRF under the plantations. The results also showed that overstory plantation species had stronger influence on the species richness of NRF rather than the pre-plantation land use history. As the SSB of the plantation sites lacked viable seed reserves for most of the naturally regenerating woody plants recorded underneath the plantations of both sites, it was assumed that seed dispersal from the adjacent natural forest has played major role in the recolonization process. From these results it could be shown that establishment of plantation forests either on abandoned farmland or directly on degraded natural forest sites can create comparable enabling environment for the recovery of the native forest flora, even if SSB are devoid of viable seeds of woody species, provided that there is a natural forest in the vicinity to donate seeds.

Depletion of soil organic matter (SOM) is a major component of soil degradation that threatens the sustainability of smallholder farming systems in Ethiopia. In this study, soil organic carbon (SOC) and total nitrogen (N) dynamics following deforestation and subsequent cultivation were evaluated using natural abundance of 13C and 15N along a farm field chronosequence cleared from tropical dry Afromontane forest in south central Ethiopia. Soil samples were collected from five closely located farm fields cultivated for 7, 10, 26, 34 and 53 years after clearance and from an adjacent natural forest soil. All the soils in the study were Mollic Andosols/Humic Haplustands. The δ13C values of the SOC of the farm fields in the 0–10 and 10–20 cm layers were significantly elevated compared to the natural forest soil. In the 0–10 cm layer, the lowest δ13C value of −23.17‰±0.36 was recorded from the natural forest soil and the highest value of −15.7‰±1.50 from the 53-year-old farm field. Fractionation of the SOC of the bulk soil based on the δ13C values showed that in the 0–10 cm layer the SOC of the forest origin declined by 74.6%, which is equivalent to 54.1 Mg C ha−1 or 740 kg ha−1 year−1, where as SOC input from the agricultural crops was low (240 kg ha−1 year−1). However, part of the SOC of the forest origin lost from the surface 0–10 cm soil layer was translocated to the 10–20 cm layer. The SOC derived natural forest approached steady state around 30 years after cultivation while the SOC derived from agricultural crops reached steady state already after 10 years. The results show that the remaining forest derived SOC is recalcitrant while the SOC derived from agricultural crops has a relatively short mean residence time. The soils of the farm fields also showed increasing δ15N values indicating a loss of N from the system. The increasing δ15N values were consistent with the loss of total N along the chronosequence. A continued loss of N combined with insufficient input of fertilizer will result in a decreased productivity of the studied farming systems.

To assess the effects of canopy characteristics and associated understory environmental factors of tree plantations on native woody species colonization, we measured canopy closure percent (CCP), leaf area index (LAI), understory air and soil temperatures as well as soil moisture in two broadleaved and two coniferous plantations in southern Ethiopia. The plantation species were Cordia africana (indigenous and broadleaved), Eucalyptus saligna (exotic and broadleaved), Cupressus lusitanica (exotic and coniferous) and Pinus patula (exotic and coniferous). The broadleaved species had significantly lower CCP (P

Soil attributes under two fast growing exotic plantations (Cupressus lusitanica and Eucalyptus saligna) established on abandoned farmlands were compared with soils of mechanized farming (MF), traditional farming (TF) and adjacent natural forest in Ethiopia. The plantations were established on an abandoned part of the MF site. All soils in the study were Humic Haplustands. Fifteen years after plantation establishment, the surface soil (0–10 cm) under C. lusitanica had lower bulk density, higher soil C, total N, cation exchange capacity (CEC), base saturation (BS), available K, exchangeable K, Ca, and Mg than the soils of MF and TF. On the contrary, the same soil layer under E. saligna had lower soil C, total N, BS, CEC, available P, available K, and exchangeable Ca than the soils of TF and MF. Except for some soil properties under C. lusitanica that showed consistently high concentrations, most soil properties in the sub-soil layers (10–20 and 20–40 cm) did not show clear differences between the sites as in the surface 0–10 cm soil layer. Comparison of the two farming situations showed higher soil compaction and poorer soil status under MF than TF. Computed deterioration index (DI) revealed a high positive index for the soil under C. lusitanica (DI=+337) suggesting a cumulative positive effect of the species on soil properties. Soil properties deteriorated under E. saligna (DI=−198) even compared to the soils subject to MF and TF (DI=−185 and −77, respectively). We concluded that forest plantations can be used to facilitate soil restoration on degraded farmlands, but that the degree, rate and direction of changes in soil attributes are species dependent. We suggest that long-term effects on soil properties should be considered as one of the criteria when selecting species for afforestation or reforestation of degraded farmlands.

Changes in soil C and total N stocks were investigated following reforestation of previously cultivated soil in comparison with soil subjected to continuous cultivation and soil under an adjacent natural forests in south central highlands of Ethiopia. Two of the most widely planted tree species in the highlands of Ethiopia, namely Eucalyptus saligna and Cupressus lusitanica , were considered in the plantation treatments. Soil C and total N contents in the upper 0–10 and 10–20 cm soil layers were significantly different in the order: Natural forest > C. lusitanica > E. saligna > Farmland. Differences in soil C and total N contents among the sites for soil depths greater than 20 cm were negligibly small and statistically not significant. Soil C and total N stocks in the upper 0.80 m mineral soil also varied significantly in the same order as above. Estimated average annual soil C accruals were 156 and 37 g C m -2 yr -1 for Cupressus lusitanica and Eucalyptus saligna , respectively. The results demonstrate that reforestation of former arable soils in the dry Afromontane region of Ethiopia could yield significant restoration of soil C and total N that are lost in the process of natural forest conversion into arable lands and subsequent cultivation. However, the two plantation species differed considerably with respect to the rate of soil C and total N accrual. This suggests that proper selection of tree species will considerably affect the magnitude and rate of soil C sequestration. Keywords : continuous farming, Cupressus lusitanica , Eucalyptus saligna , soil carbon sequestration, soil carbon loss SINET: Ethiopian Journal of Science Vol. 28(2) 2005: 99-108