Science-based decision support for formulating crop fertilizer recommendations in sub-Saharan Africa

Open Access Article; Published online: 31 Jan 2020In sub-Saharan Africa, there is considerable spatial and temporal variability in relations between nutrient application and crop yield, due to varying inherent soil nutrients supply, soil moisture, crop management and germplasm. This variability affects fertilizer use efficiency and crop productivity. Therefore, development of decision systems that support formulation and delivery of site-specific fertilizer recommendations is important for increased crop yield and environmental protection. Nutrient Expert (NE) is a computer-based decision support system, which enables extension advisers to generate field- or area-specific fertilizer recommendations based on yield response to fertilizer and nutrient use efficiency. We calibrated NE for major maize agroecological zones in Nigeria, Ethiopia and Tanzania, with data generated from 735 on-farm nutrient omission trials conducted between 2015 and 2017. Between 2016 and 2018, 368 NE performance trials were conducted across the three countries in which recommendations generated with NE were evaluated relative to soil-test based recommendations, the current blanket fertilizer recommendations and a control with no fertilizer applied. Although maize yield response to fertilizer differed with geographic location; on average, maize yield response to nitrogen (N), phosphorus (P) and potassium (K) were respectively 2.4, 1.6 and 0.2 t ha−1 in Nigeria, 2.3, 0.9 and 0.2 t ha−1 in Ethiopia, and 1.5, 0.8 and 0.2 t ha−1 in Tanzania. Secondary and micronutrients increased maize yield only in specific areas in each country. Agronomic use efficiencies of N were 18, 22 and 13 kg grain kg−1 N, on average, in Nigeria, Ethiopia and Tanzania, respectively. In Nigeria, NE recommended lower amounts of P by 9 and 11 kg ha−1 and K by 24 and 38 kg ha−1 than soil-test based and regional fertilizer recommendations, respectively. Yet maize yield (4 t ha−1) was similar among the three methods. Agronomic use efficiencies of P and K (300 and 250 kg kg−1, respectively) were higher with NE than with the blanket recommendation (150 and 70 kg kg−1). In Ethiopia, NE and soil-test based respectively recommended lower amounts of P by 8 and 19 kg ha−1 than the blanket recommendations, but maize yield (6 t ha−1) was similar among the three methods. Overall, fertilizer recommendations generated with NE maintained high maize yield, but at a lower fertilizer input cost than conventional methods. NE was effective as a simple and cost-effective decision support tool for fine-tuning fertilizer recommendations to farm-specific conditions and offers an alternative to soil testing, which is hardly available to most smallholder farmers

Closing yield gaps in maize production in Southeast Asia through site-specific nutrient management

Rising incomes and changing dietary requirements are swiftly transforming maize (Zea mays L) in Southeast Asia from a food staple into an important industrial commodity. Increased maize production is required to meet rising demands, but additional production should come from the sustainable intensification of existing farmlands to minimize the undesirable effects of agriculture on the environment. We hypothesize that maize yields, profit, and N use efficiencies can be significantly increased through site-specific nutrient management (SSNM), thereby reducing yield gaps in the region. Through a combined approach of simulation modeling and on-farm research in at least 65 sites in 13 major maize-producing domains across Indonesia, Vietnam and the Philippines from 2004 to 2008, we were able to (a) quantify maize yield gaps and yield responses to fertilizer application, (b) evaluate the agronomic and economic performance of SSNM, and (c) evaluate the incremental profitability of SSNM in various production and grain and fertilizer price scenarios. The average exploitable yield gap between the attainable yield and current farmers’ yield in Southeast Asia was about 0.9 t ha−1. Yield responses to fertilizer application across the region followed the order N > >P > K. Yield response to N was higher in irrigated sites than in rainfed sites (6 t ha−1 versus 2 t ha−1), while P and K fertilizer responses were similar across production systems (<2 t ha−1). Yield with SSNM was 1.0 t ha−1 (+13%) higher than the current farmers’ fertilizer practice (FFP) measured in the same cropping seasons. Yield increases were associated with a 10% decrease in the average N rate, but with increased application of K at sites where the previous K rates were low. Average N use efficiency increased by 42%, mainly by adjusting the rates and timing of N application to the stages of crop development. Across all sites and seasons, profitability increased by US$167 ha−1 per crop, which was equivalent to15$100 ha−1 season) were greatest in highly favorable rainfed environments; less favorable rainfed areas were vulnerable to unfavorable market prices. We conclude that SSNM has the potential to close existing yield gaps in the maize production systems of Southeast Asia by improving yield, nutrient use efficiency, and profitability

Precision nutrient management in conservation agriculture based wheat production of Northwest India: Profitability, nutrient use efficiency and environmental footprint

In the high-yielding wheat production systems in Northwest (NW) Indo-Gangetic Plains of India, intensive tillage operations and blanket fertilizer recommendations have led to high production costs, decreased nutrient use efficiency, lower profits and significant environmental externalities. No-tillage (NT) has been increasingly adopted in this region to reduce costs and increase input use efficiency. But, optimal nutrient management practices for NT based wheat production are still poorly understood. Opportunities exist to further enhance the yield, profitability, and resource use efficiency of NT wheat through site-specific nutrient management (SSNM). On-farm trials were conducted in seven districts of Haryana, India for two consecutive years (2010–11 and 2011–12) to evaluate three different approaches to SSNM based on recommendations from the Nutrient Expert® (NE) decision support system in NT and conventional tillage (CT) based wheat production systems. Performance of NE based recommendations was evaluated against current state recommendations and farmers’ practices for nutrient management. Three SSNM treatments based on NE based recommendation were (1) ‘NE80:20’ with 80% N applied at planting and 20% at second irrigation (2) ‘NE33:33:33’ with N split as 33% basal, 33% at Crown Root Initiation (CRI) and 33% at second irrigation; and (3) ‘NE80:GS’ with N split as 80% basal and further application of N based on optical sensor (Green Seeker™)-guided recommendations. Yield, nutrient use efficiency and economic profitability were determined following standard agronomic and economic measurements and calculations. Cool Farm Tool (CFT), an empirical model to estimate greenhouse gases (GHGs) from agriculture production, was used to estimate GHG emissions under different treatments. Wheat grain and biomass yield were higher under NT in 2010–11 but no difference was observed in 2011–12. The three NE-based nutrient management strategies increased yield, nutrient use efficiency as well as net return as compared to state recommendation and farmers’ fertilization practice. Global warming potential (GWP) of wheat production was also lower with NT system as compared to CT system and NE-based nutrient managements as compared to farmers’ fertilization practice. State recommended nutrient management had similar GWP as NE-based nutrient managements except NE80:GS in which GWP was the lowest. Results suggest that no-tillage system along with site-specific approaches for nutrient management can increase yield, nutrient use efficiency and profitability while decreasing GHG from wheat production in NW India