Greenhouse Gas Emissions Response to Fertilizer Application and Soil Moisture in Dry Agricultural Uplands of Central Kenya

Peter Semba Mosongo,Suying Chen,Xiaoxin Li,Gokul Gaudel,Yuying Wang,Chunsheng Hu,Wenyan Li,David Mburu,David E Pelster

doi:10.3390/atmos13030463

Abstract

In sub-Saharan Africa, agriculture can account for up to 66% of anthropogenic greenhouse gas (GHG) emissions. Unfortunately, due to the low number of studies in the region there is still much uncertainty on how management activities can affect these emissions. To help reduce this uncertainty, we measured GHG emissions from three maize (Zea mays) growing seasons in central Kenya. Treatments included: (1) a no N application control (C); (2) split (30% at planting and 70% 1 month after planting) mineral nitrogen (N) applications (Min—100 kg N ha−1); (3) split mineral N + irrigation (equivalent to 10 mm precipitation every three days—MI); (4) split mineral N + 40 kg N ha−1 added as manure (MM—total N = 140 kg ha−1); and (5) split mineral + intercropping with faba beans (Phaseolus vulgaris—MB). Soil CO2 fluxes were lower in season 1 compared to seasons 2 and 3 with fluxes highest in Min (p = 0.02) in season 2 and lowest in C (p = 0.02) in season 3. There was uptake of CH4 in these soils that decreased from season 1 to 3 as the mean soil moisture content increased. Cumulative N2O fluxes ranged from 0.25 to 2.45 kg N2O-N ha−1, with the highest fluxes from MI during season 3 (p = 0.01) and the lowest from C during season 1 (p = 0.03). The average fertilizer induced emission factor (0.36 ± 0.03%) was roughly one-third the default value of 1%. Soil moisture was a critical factor controlling GHG emissions in these central Kenya highlands. Under low soil moisture, the soils were CH4 sinks and minimal N2O sources.

Highlights

In Africa, agriculture accounts for up to 66% of anthropogenic greenhouse gas (GHG) emissions, and much of these emissions come from livestock, croplands are still responsible for approximately 15% of agricultural GHG emissions [2]
This study shows that agricultural soils from the dry uplands of central Kenya were
Cumulative soil nitrous oxide (N2 O) fluxes were correlated in two out of the three growing seasons with mean soil moisture content where emissions increased with N input

Summary

Introduction

In Africa, agriculture accounts for up to 66% of anthropogenic GHG emissions, and much of these emissions come from livestock, croplands are still responsible for approximately 15% of agricultural GHG emissions [2]. Face acute food shortages annually [3], is home to one of the fastest growing populations in the world. According to the Food and Agricultural Organization (FAO) (2017), there are 4 million Kenyans facing acute food shortages. In response to these shortages, the Kenyan government, hoping to emulate successful projects in Malawi and the Millennium Villages, has increased incentives for smallholder farmers to purchase and apply synthetic fertilizers through the National Accelerated Agricultural Input Access Program (NAAIAP) [4] to staple crops (e.g., maize (Zea mays)), with the aim of improving yields [3]. Kenya experienced a 4.7% annual increase in fertilizer use between 2015 and 2018 [5]

Methods

Results

Conclusion