Abstract
Fertility management techniques being promoted in sub-Saharan Africa (SSA) seek to grow indigenous vegetables economically and sustainably. This study was conducted in a phytotron chamber and compared yield, soil carbon (C) speciation and greenhouse gas (nitrous oxide (N2O) and carbon dioxide (CO2)) emissions from SSA soils of two ecoregions; the dry savanna (lna, Republic of Benin) and rainforest (Ife, Nigeria) cultivated with local amaranth (Amaranthus cruentus) under manure (5 t/ha) and/or urea (80 kg N/ha) fertilization. Vegetable yield ranged from 4331 kg/ha to 7900 kg/ha in the rainforest, RF, soils and 3165 kg/ha to 4821 kg/ha in the dry savanna, DS, soils. Yield in the urea treatment was slightly higher compared to the manure, and manure+urea treatment, but the difference was not statistically significant. Cumulative CO2 emissions over 21 days ranged from 497.06 to 579.47 g CO2-C/kg soil/day in the RF, and 322.96 to 624.97 g CO2-C/kg soil/day in the DS, while cumulative N2O emissions ranged from 60.53 to 220.86 mg N2O-N/kg soil/day in the RF, and 24.78 to 99.08 mg N2O-N/kg soil/day in the DS. In the RF samples, when compared to the use of urea alone, the combined use of manure and urea reduced N2O emissions but led to an increase in the DS samples. ATR-FTIR analysis showed that the combined use of manure and manure+urea increased the rate of microbial decomposition in the soils of the DS, but no such effect was observed in soils of the RF. We conclude that combining manure and urea fertilization has different effects on soils of the two ecoregions, and that RF farmers can reduce agricultural N2O emissions without compromising soil productivity and yield potential.
Highlights
Agriculture is a major contributor to global anthropogenic greenhouse gas (GHG) emissions, primarily from the use of mineral fertilizers and manures to crop and soil systems, as well as cultivation of peatlands [1,2]
The objective of this study is to investigate the effect of manure and fertilizer treatments on both GHG emissions and soil organic matter (SOM) speciation by determining and quantifying the impact of reduced mineral nitrogen fertilization and organic manure on vegetable yield, emission of CO2 and N2 O from sub-Saharan Africa (SSA) soils cultivated with an indigenous vegetable in a controlled environment
We found that the combined use of manure and urea increased the rate of decomposition in the dry savanna (DS) samples, increasing the proportion of the processed C species including aliphatic-C, aromatic-C and carboxylic-C forms in the DS samples, while no such effect on decomposition was observed in the RF samples
Summary
Agriculture is a major contributor to global anthropogenic greenhouse gas (GHG) emissions, primarily from the use of mineral fertilizers and manures to crop and soil systems, as well as cultivation of peatlands [1,2]. Many studies [9,12,13,14] have reported that combining organic and inorganic fertilizers led to a reduction in soil N2 O emissions and an increase in crop yields in Mali and Zimbabwe. These studies suggested that a combination of organic fertilization with low rates of inorganic N can be used as a mitigation option for reducing N2 O emissions while retaining similar crop yields. Organic materials have been shown to enhance the emissions of N2 O and CO2 when in combination with urea fertilizers [15,16], primarily due to the production of CO2 by the hydrolysis of urea to CO2 and ammonia, as well as stimulation of heterotrophic microbial activity [17]
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