Response of maize yield to nitrogen, phosphorus, potassium and sulphur rates on Andosols and Nitisols in Ethiopia

The use of fertilizers in balanced and adequate amounts is a prerequisite for increasing crop productivity and production. Unbalanced plant nutrient management continues to be a major factor contributing to low maize (Zea mays L.) yields due to lack of information on the dose–responses to macronutrients on different soil types in Ethiopia. This study was carried out to quantify maize yield response and agronomic efficiency of varying application rates of nitrogen (N), phosphorus (P), potassium (K) and sulphur (S) under balanced application of other nutrients across two soil types in Ethiopia. Field trials were set up on 29 farmers’ fields in four districts of Oromia and Southern Nations, Nationalities and Peoples Region (SNNPR) for three consecutive cropping seasons (2014–2017). The treatments consisted of six rates of N, P and S each and eight rates of K combined with balanced application of the remaining macronutrients, zinc (Zn) and boron (B). The treatments were laid out in randomised complete blocks design with three replicates per farm. Using nutrient dose–response modelling, the agronomic optimum rates of N, P, K and S were estimated at 46, 40, 17 and 10 kg ha−1 on Nitisols, with balanced application of the other nutrients. On Andosols, the optimum rates of N, P and S were estimated at 184, 20 and 30 kg ha−1, respectively, but the optimum K rate could not be estimated. The predicted maximum yields obtained with balanced nutrient application were lower on Andosols (3397–3640 kg ha−1) than on Nitisols (4630–6094 kg ha−1). Using the Mitscherlich dose–response model, the percentage deficiencies of N, P, K and S were estimated to be 1.3–3.3 times more on Nitisols than Andosols. Consequently, agronomic efficiencies of N, P, K and S were significantly lower on Andosols than on Nitisols. It is concluded that balanced application of 46 kg N ha−1 , 40 kg P ha−1 , 17 kg K ha−1 , 10 kg ha−1 S, 2 kg Zn ha−1 and 0.5 kg B ha−1 could be recommended for maize on Nitisols in the study area. Although this recommendation may also apply to Andosol, further research is needed as the productivity of Andosols appears to be limited by constrains other than N, P, K, S, Zn and B. We also recommend a shift from the blanket fertilizer recommendations to site-specific nutrient management based on good understanding of the variations in crop response with soil type and agroecology and appropriate soil and plant analyses

Balanced fertilization increases wheat yield response on different soils and agroecological zones in Ethiopia

The response of wheat to the application of different rates of nitrogen (N), phosphorus (P), potassium (K), and sulfur (S) under balanced fertilization on different soil types and agroecologies has not been well studied in Ethiopia. Therefore, the objectives of this study were to (1) determine soil-specific responses of wheat to N, P, K, and S under balanced fertilization; (2) quantify agroecology-specific N, P, K, and S response of wheat under balanced fertilization; and (3) determine nutrient use efficiency of wheat on different soil types under balanced fertilization. Trials were conducted on farmers’ fields across 24 locations covering 4 soil types and 5 agroecological zones (AEZs) from 2013 to 2017. The mean grain yields of wheat significantly varied with applied N and P fertilizer rates with soil types and AEZs. With balanced application of other nutrients, the optimum N rates for wheat were 138 kg N ha−1 on Cambisols and Luvisols, 92 kg N ha−1 on Vertisols, and 176 kg N ha−1 on Nitisols, while the optimum P rate was 20 kg P ha−1 on Cambisols and Vertisols. The nutrient dose–response curve did not reveal consistent pattern for K and S applications on all soil types. The agronomic efficiency of wheat decreased with increasing rates N and P on all soil types. The highest agronomic efficiency of N (15.8 kg grain kg−1 applied N) was recorded with application of 92 kg N ha−1 on Vertisols, while the highest agronomic efficiency of P (49 kg grain kg−1 applied P) was achieved with application of 10 kg P ha−1 on Cambisols. We conclude that applications of 92–138 kg N ha−1, 20 kg P ha−1, 18 kg K ha−1, and 10 kg S ha−1 under balanced application of zinc and boron could be recommended depending on soil type for wheat production in the study areas

Treatment of organic resources before soil incorporation in semi-arid regions improves resilience to El Niño, and increases crop production and economic returns

We are grateful for support from the DFID-NERC El Niño programme in project NE P004830, “Building Resilience in Ethiopia’s Awassa region to Drought (BREAD)”, the ESRC NEXUS programme in project IEAS/POO2501/1, “Improving organic resource use in rural Ethiopia (IPORE)”, and the NERC ESPA programme in project NEK0104251 “Alternative carbon investments in ecosystems for poverty alleviation (ALTER)”. We are also grateful to Anke Fischer (James Hutton Insitute) for her comments on the paper.Peer reviewedPublisher PD

A systems model describing the impact of organic resource use on farming households in low to middle income countries

We are grateful for support from the DFID-NERC El Niño programme in project NE P004830, “Building Resilience in Ethiopia’s Awassa region to Drought (BREAD)”, the ESRC NEXUS programme in project IEAS/POO2501/1, “Improving organic resource use in rural Ethiopia (IPORE)”, and the NERC ESPA programme in project NEK0104251 “Alternative carbon investments in ecosystems for poverty alleviation (ALTER)”. We are also grateful to Dr. V.U.M. Rao (Former Project Coordinator, AICRP on Agrometeorology, CRIDA, Hyderabad) and Dr. S.K. Chaudhari (DDG, NRM Division, KAB-II, ICAR, New Delhi) for their assistance in collecting meteorological data of Parbhani, Maharashtra.Peer reviewedPostprin

Soil Phosphorus Fractions as Influenced by Different Cropping Systems: Direct and Indirect Effects of Soil properties on Different P Pools of Nitisols of Wolayta, Ethiopia

Data from 12 surface soils (0 – 15 cm depth)of three cropping systems (enset, maize and grazing land) and path analysis was used to evaluate effects of soil properties: pH, texture (Clay, silt and sand) , organic carbon (OC) cation exchange capacity (CEC),citrate-dithionite-bicarbonate (CDB) extractable Fe and Al (Fed and Ald) on total phosphorous (Pt), organic phosphorous (Po), Olsen P (Available P) and Chang and Jackson (1957) inorganic phosphorous (Pi) fractions. Correlation analysis was performed to study the relationships between soil properties and different soil P pools while path analysis model was used to evaluate direct and indirect effect of these soil properties on the P pools. Only soil properties that significantly contribute to the fit of the model were used. High significant values of coefficient of determination (R2) and low values of uncorrelated residual (U) values indicate the path analysis model explains most of the variations in soil Pt, Po, Olsen-P, Saloid-P, Ca-P, Al-P, and Fe-P pools. Soil pH had significantly high and positive direct effect (D = 0.618*) on Pt, (D = 1.044***) on saloid P, and (D = 1.109***) on Fe-P with modest and negative indirect effect (D= -0.478 and -0.405) on saloid P and Fe-P, respectively, through OC. The direct effect of clay on Ca-P, Al-P and Fe-P (readily available P forms) was significant and negative with a relatively higher indirect effect on Fe-P through pH suggesting that clay is dominant soil property that influences readily available P pools in Nitisols of the study area. Fed had significant and negative direct effect (D = -0.430*) on Olsen available P with low negative indirect effect ( D = -0.154) through pH results in significant and negative correlation (r = -0.657*). The significant and negative direct effect of Fed on Olsen P indicates that crystalline iron is the sink for available P. Relative influence of the soil properties on the soil P pools was in the order: pH > clay > Fed > OC.  These results show that most of P pools of Nitisols of Wolayita are best predicted from pH, clay (texture), Fed and OC. On the other hand, our data also show that the inclusion of other soil variables is needed to fully predict Ca-P and stable P pools

Integrated soil fertility management for sustainable teff (Eragrostistef) production in Halaba, Southern Ethiopia

Low applications of inorganic fertilizer and decline in soil organic matter often contribute to loss of production in Sub-Saharan Africa. A trial was conducted on integrated soil fertility management of teff (Eragrostis tef) in Southern Ethiopia during the main cropping season of 2015. Treatments were based on recommended rates of inorganic fertilizer, applying organic fertilizer to provide the equivalent amount of N. Randomised treatments were replicated across six farms, including 100% as inorganic fertilizer, and inorganic and organic fertilizers in ratios 50:50, 67:33 and 33:67. All crop characteristics measured, except number of tillers and straw yield, showed statistically significant differences (p < 0.05). An inorganic-to-organic fertilizer ratio of 67:33 provided highest grain yield, while lowest total variable costs were obtained with the 33:67 ratio. Highest net benefit (520(±50) US$/ha) was obtained with the ratio 67:33, but the marginal rate of return over the 33:67 treatment was only 54(±8)%, and so did not provide sufficient return on the extra investment for inorganic fertilizer. Therefore, 33% inorganic fertilizer to 67% organic fertilizer is more economically viable. These trials demonstrate that, in addition to reducing long-term soil degradation, integrated soil fertility management can be an economically viable way of managing crops

The advantages and limitations of global datasets to assess carbon stocks as proxy for land degradation in an Ethiopian case study

Land degradation leads to ecosystem degradation, reducing ecosystem functioning and depleting ecosystems' resilience. The majority of factors linked to land degradation are closely related with the depletion of below- and above-ground stocks of organic carbon. Organic carbon stock is important for climate change mitigation and for restoring soil functions such as those crucial to support food security. In this study, we mapped carbon stocks to infer land degradation in a small area in the Ethiopian Great Rift Valley. The study aimed to assess carbon stock status and to identify limitations and advantages of using global data in mapping at local scale relative to using local data. Two different datasets were developed; i) a “global dataset” characterised by data from datasets with global coverage data, and ii) a “hybrid dataset” that coupled data from global datasets, soil data derived from a local survey, and land cover data derived from a supervised classification of satellite images. The results showed that i) global datasets introduced inaccuracy that must be taken into account for advocating interventions at a local scale, and ii) global datasets could be used at a small catchment level for decision-making, if a simple rank of values is sufficient, but they might provide an optimistic picture of land degradation because they overestimate stocks