Nitrogen Use Efficiency (NUE) is one of the established metrics for benchmarking management of Nitrogen (N) in various systems. Numerous approaches to calculate NUE exist, making it difficult to compare the performances of systems depending on the methodology used. This study adopted the conceptualized framework by European Union Nitrogen Expert Panel (EUNEP) to calculate NUE values for cereal crops to determine future trends for the first time in the Lake Victoria region. Data were collected through in-person interviews among maize and rice smallholder farmers within the Lake Victoria region. A total of 295 observations were recorded. Collected data on yield and N fertilizer were used to make projections on the changes of NUE based on scientific and policy recommendations for Sub-Saharan Africa for 2020 (base year), 2025, 2030, and 2050. Significant differences in maize grain yield for both fertilized and unfertilized farms were observed with very low yields of 2.4 t ha-1 (fertilized) and 1.4 tha-1 (unfertilized). The graphical representation of NUE of both maize and rice showed that most farmers were in the zone of soil N mining. Projected results showed that most maize farmers within Lake Victoria region will continue to experience NUE values >90%, low N inputs <50 kg N ha-1) and less than 5 t ha-1 maize crop yield over the years. For rice farmers, Nyando and Nzoia catchments had surpassed the set target of both yield (6 t ha-1) and N input (50 kg N ha-1). However, NUE values remain higher than the optimal ranges of 50-90% (127.14% -267.57%), indicating risks of depleting soil N status. The unbalanced N fertilization also showed a trend below the linear neutrality option and the average N output for good N management for both crops. Therefore, farmers need to explore various crop management options that could increase N use efficiencies. This should be coupled with policies that promote farmers to access more N input and advocate for optimal management of N and improved quality of the cereals
Apart from nitrogen (N) rates, N use efficiency (NUE) (yield N/total input N) is affected by seasons, crop developmental stages, and varieties. Knowledge of how these factors affect NUE in rice production in Kenya is limited. Therefore, field experiments were conducted with ‘low rates’ of N (simulating farmers’ practices) of 0, 26, 52 and 78 kg N ha−1 with five varieties (MWUR1, MWUR4, IRAT109, NERICA4 and NERICA10) and higher rates of N (125, 175, and 225 kg N ha−1) simulating researchers’ doses with two lowland varieties (Basmati 370 and BW 196) and IR 72. Another experiment on NUE responses to sites, N rates and dose (split or full dose) was undertaken with the IR97 variety. With the ‘low rate’, yields increased with incremental N rates up to 52 Kg N ha−1 and declined (during cold periods, for some varieties). In this scenario, the N agronomic efficiencies (AEN) declined with increasing N but depended on sites and seasons. However, most AEN values were above 100, implying nutrient mining. In most cases (except at the Mwea site), the N utilization efficiency (NUtE) ranged from 16 to 22kg kg−1 and were not significantly affected by sources and methods of N application. In all cases, an increase in N elicited declining trends in NUtE. Moreover, N uptake efficiency ranged between 22 and 90kg kg−1 without significant variation among varieties. For the ‘high N rates’, high biomass yield resulted in higher grain yields in BW 196 and IR 72 but yield declined beyond 75 kg ha−1 N rates due to poor grain filling, particularly when a cold period coincided with booting and grain filling. We conclude that N rates, doses and rice varieties are key determinants of AEN and NUtE in contrasting rice growing seasons in Kenya. Cropping seasons and rice varieties are therefore potential key determinants of sustainable rice productivity and improved NUE in rice-based systems in the studied regions of Kenya.
The Abuja Fertilizer Declaration in 2006 recommended the increase of fertilizer use from the current practice for Sub-Saharan Africa (SSA) to achieve food sufficiency and improve soil fertility status. However, the current recommended rates of fertilizer have not been evaluated for specific crops on their potential to reduce the yield gap and optimize nitrogen use efficiency (NUE). In this study, with nitrogen (N) being a significant yield-determinant nutrient, four N use scenarios were drawn from existing recommendations and were evaluated under field conditions for maize crops in two catchments of the Lake Victoria basin. The scenarios included Business as Usual (BAU, 0 kg N ha−1), 25% of the Abuja declaration (ADS 12.5 kg N ha−1), 50% of the Abuja declaration (ADS 25 kg N ha−1), and Abuja declaration–Abuja scenario (ADS, 50 kg N ha−1). The results revealed that increasing N input levels significantly influenced the growth and yield of maize crops. The ADS scenario recorded the highest grain yield increase (167.39%) in Nyando and 103.25% in Rangwe catchments compared to the BAU scenario. N deficits were observed in all the N use scenarios with a range of −66.6 to −125.7 kg N ha−1 in Nyando and −62.5 to −105.4 kg N ha−1 in Rangwe catchments with the 50% ADS scenario having the highest deficits. The deficits imply that the added N input is insufficient to create an N balance for optimal NUE with consequent high risks of soil N mining. In both catchments, all N use scenarios were within the recommended agro-physiological N efficiency (APEN) level of between 40 and 60 kg kg−1 N. The partial N balance obtained at Nyando (1.56–3.11) and Rangwe (1.10–4.64) was higher than the optimal values, a sign of insufficiency of N inputs and possible risk of soil N depletion in all the scenarios. Our findings conclude that the proposed N rates in the region are still very low for food sufficiency and optimized NUE. Therefore, there is a need to explore other sources of N such as biological N fixation and organic manure and inform policy- and decision-makers to recommend higher rates beyond the “Abuja declaration” with the prospect of reaching target yield and optimizing NUE values based on specific crop recommendations.
Climate change has been viewed to result from anthropogenic human activities that have significantly altered the Nitrogen (N) cycle and carbon cycles, increasing the risks of global warming and pollution. A key cause of global warming is the increase in greenhouse gas emissions including methane, nitrous oxide, and carbon among others. The context of this chapter is based on a comprehensive desktop review on published scientific papers on climate change, greenhouse emissions, agricultural fertilizer use, modeling and projections of greenhouse gases emissions. Interestingly, sub-Saharan Africa (SSA) has the least emissions of the greenhouses gases accounting for only 7% of the total world’s emissions, implying that there is overall very little contribution yet it has the highest regional burden concerning climate change impacts. However, the values could be extremely higher than this due to lack of proper estimation and measurement tools in the region and therefore, caution needs to be taken early enough to avoid taking the trend currently experienced in developed nations. In SSA, agricultural production is the leading sector in emissions of N compound to the atmosphere followed by energy and transportation. The greatest challenge lies in the management of the two systems to ensure sufficiency in food production using more bioenergy hence less pollution. Integrating livestock and cropping systems is one strategy that can reduce methane emissions. Additionally, developing fertilizer use policy to improve management of fertilizer and organic manure have been potentially considered as effective in reducing the effects of agriculture activities on climate change and hence the main focus of the current chapter.
Climate change has been viewed to result from anthropogenic human activities that have significantly altered the Nitrogen (N) cycle and carbon cycles, increasing the risks of global warming and pollution. A key cause of global warming is the increase in greenhouse gas emissions including methane, nitrous oxide, and carbon among others. The context of this chapter is based on a comprehensive desktop review on published scientific papers on climate change, greenhouse emissions, agricultural fertilizer use, modeling and projections of greenhouse gases emissions. Interestingly, sub-Saharan Africa (SSA) has the least emissions of the greenhouses gases accounting for only 7% of the total world’s emissions, implying that there is overall very little contribution yet it has the highest regional burden concerning climate change impacts. However, the values could be extremely higher than this due to lack of proper estimation and measurement tools in the region and therefore, caution needs to be taken early enough to avoid taking the trend currently experienced in developed nations. In SSA, agricultural production is the leading sector in emissions of N compound to the atmosphere followed by energy and transportation. The greatest challenge lies in the management of the two systems to ensure sufficiency in food production using more bioenergy hence less pollution. Integrating livestock and cropping systems is one strategy that can reduce methane emissions. Additionally, developing fertilizer use policy to improve management of fertilizer and organic manure have been potentially considered as effective in reducing the effects of agriculture activities on climate change and hence the main focus of the current chapter.
Blossom end rot (BER) is one of the physiological disorders of economic importance in tomato farming since it significantly reduces yield and thus affects profit margins. Most tomato disorders are due to mineral deficiencies and unbalanced nutrition. Improving the supply of specific nutrients and uniform soil moisture can reduce their occurrences. This study was conducted to evaluate the influence of watering regimes, Calcium (Ca) and Potassium (K) on blossom end rot occurrence in two tomato varieties in Maslah and Guul sites. The trials were laid out in a randomized complete block design (RCBD) in split-split plot arrangement with watering regimes (daily, thrice and twice a week) as main plots, tomato varieties (Riograde and Rionex) as sub plots, and 3 levels of Ca and K (0 Kg/ha, 25 Kg/ha, 50 kg/ha) as the sub-sub plots and replicated three times. Calcium treatments had the lowest score of blossom end rot compared to control. In Guul, the highest BER score (2.83) was observed under the control treatment while the lowest score (1.06) was recorded on the 50 kg/ha, Ca rate. Similar results were observed in Maslah with the control having the highest score of BER (3.22) while Ca 50 kg/ha scored lowest (1.11). No statistical differences were observed in the K treatments in the two study sites, however it was notable that lower rates of K reduced the blossom end rot incidences. Water stress led to increase in severity of the BER in the two study sites. In Guul, the highest score was in minimal watering regime (twice a week) of 2.36 score and lowest was at optimal watering regime (daily) of 1.08 score whereas in Maslah the highest blossom end rot score was in minimal watering regime (twice a week) of 3.19 and the lowest score of 1.19 on medium watering regime (Thrice a week).Therefore, optimal application of Ca, K, at 50 kg/ha with adequate and uniform soil moisture can improve management of blossom end rot in tomatoes thus raising farmer’s returns.
The application of nitrogen (N) fertilizers and liming (CaCO3) to improve soil quality and crop productivity are regarded as effective and important agricultural practices. However, they may increase greenhouse gas (GHG) emissions. There is limited information on the GHG emissions of tropical soils, specifically when liming is combined with N fertilization. We therefore conducted a full factorial laboratory incubation experiment to investigate how N fertilizer (0 kg N ha−1, 12.5 kg N ha−1 and 50 kg N ha−1) and liming (target pH = 6.5) affect GHG emissions and soil N availability. We focussed on three common acidic soils (two ferralsols and one vertisol) from Lake Victoria (Kenya). After 8 weeks, the most significant increase in cumulative carbon dioxide (CO2) and nitrous oxide (N2O) fluxes compared with the unfertilized control was found for the two ferralsols in the N + lime treatment, with five to six times higher CO2 fluxes than the control. The δ13C signature of soil‐emitted CO2 revealed that for the ferralsols, liming (i.e. the addition of CaCO3) was the dominant source of CO2, followed by urea (N fertilization), whereas no significant effect of liming or of N fertilization on CO2 flux was found for the vertisol. In addition, the N2O fluxes were most significantly increased by the high N + lime treatment in the two ferralsols, with four times and 13 times greater N2O flux than that of the control. No treatment effects on N2O fluxes were observed for the vertisol. Liming in combination with N fertilization significantly increased the final nitrate content by 14.5%–39% compared with N fertilization alone in all treatment combinations and soils. We conclude that consideration should be given to the GHG budgets of agricultural ferralsols since liming is associated with high liming‐induced CO2 and N2O emissions. Therefore, nature‐based and sustainable sources should be explored as an alternative to liming in order to manage the pH and the associated fertility of acidic tropical soils.
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