As the Global Landscapes Forum – the world’s largest science-led platform on sustainable land use – begins on December 19 in Bonn, Germany, ICRISAT research in Ethiopia shows how crop yields can be doubled in degraded soils while reducing fertilizer wastage through precision soil fertilization.
Ethiopia, a land of farming contrasts, exports high quality coffee beans from its highlands but has millions of small drylands farmers in regions like Afar or Tigray with meagre crop harvests as they suffer recurrent droughts and widespread soil degradation. In Sub-Saharan Africa, agronomists blame poor soil fertility as one if not the first limiting factor of farming. Yet, the use of fertilizer is sparse with less than 10kg fertilizer per hectare compared to 200 to 300kg in Europe. This decline of soil fertility costs Ethiopia 3% of its GDP (Bojo & Cossells, 1995). For years, crop scientists have been underlining the need to replenish soils to improve Ethiopian food potential.
Low crop response to fertilizers prompts the studies
Since the 1970s, the Ethiopian government has invested in fighting against soil erosion through community-based watershed programs and restoring soil health. Recently, they undertook a very ambitious soil fertility program, with nation-wide soil testing and mapping, producing district-level soil maps showing essential soil nutrient deficiencies. With this soil fertility atlas, Ethiopian agricultural services produced district-level soil fertility recommendations while five fertilizer blending factories across the country could supply specific fertilization packages according to the recommendations. Despite this massive public support, crop yield gains have been modest. As landscape and farming systems could vary a lot across each district, the need for fine tuning recommendations was identified following feedback from farmers and regional governments. Research organizations and development NGOs were consulted. In this context ICRISAT conducted two studies in two wheat-based farming systems in the highlands of Lemo and Endamohoni districts with the support of the Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ), the German development agency, USAID Feed the Future through and Africa Rising programme.
Based on the results of more than 600 farmers’ field experiments, ICRISAT scientist Dr Tilahun Amede says that there is potential for doubling crop yields if location-specific nutrient management is practiced depending on the landscape position of farms and the cropping system.
Fine tuning fertilization recommendations
Studies show that precision fertilization improves on-farm productivity and resilience. Crop yields increased by 45-200% with targeted fertilizer use and the right agronomic practices while fertilizer wastage was reduced by 20-80%. Soil health was improved through water conservation efforts, organic amendments and the right dosage of fertilizer. Research shows also that grain quality improved with the application of micronutrients like Sulfur and Zinc.
These results were obtained in regions where centuries of nutrient mining had resulted in severe and eroded soils that produce 40% less than the global average. Yields in farmers’ fields in Lemo and Endamohoni are three times less than what is recorded in research fields.
Approach adopted to fine tune recommendations for farmers
More than 600 on-farm and on-station field experiments, testing on different landscapes various fertilizer combinations of Nitrogen (N), Phosphorus (P), Potassium (K), Sulfur (S) and Zinc (Zn) with different ratios were conducted in six wheat belts. ICRISAT capitalized on earlier attempts by Agricultural Transformation Agency (ATA-Ethiosis) and other stakeholders.
Homogeneous cropping management zones were identified and categorized as hillslopes, midslopes and footslopes based on the degree of slope, soil fertility, water-holding capacity and other parameters.
Development of ‘Decision Support Tools’
GIS-based analysis was used to interpolate potential niches of the respective response level.
Agronomic practices recommended for both sites included:
Soil and water conservation structures: Building soil bund/terrace to ensure that the soil, seed and fertilizer are not washed away.
Integrated soil fertility management: Application of chemical fertilizers with organic amendments and other technologies.
Split application of urea: To minimize nitrogen loss and increase fertilizer use efficiency, about one third of urea should be applied at planting; the remaining two-third should be applied at 40-45 days after planting.
Weeding: At least twice per cropping season. It could be done first at the time of split application of urea at 40-45 days after sowing and second a week before flowering.
Sowing in a row: For proper input placement and weeding.
Use of high-yielding and adapting wheat varieties: To facilitate increased yields.
Soil amendment to decrease acidity: Application of lime was advised.
The above recommendations are also suitable for barley, sorghum and millets.
Decision guide for fertilizer application
In general, fertilizer response was higher in the footslopes and midslopes hence greater fertilizer requirement. Expected yields were in the range of 8.0-4.5 t/ha and 4.5-2.5t/ha for footslopes and midslopes respectively. The hillslopes had an expected yield of 2.5-1.5 t/ha and were advised lesser fertilizer. In areas that had yields less the 1.5 t/ha fertilizer application was not recommended and application of organic amendments was encouraged. Legumes as precursor crops were recommended for better yield of succeeding crops.
The above recommendations of right fertilizer dosage combined with good agronomic practices gave farmers a yield increment that was more than double.
For further information:
Jemima Mandapati, Senior Communication Officer Strategic Marketing and Communication ICRISAT.