Improving fertilizer recommendations for farmers is essential to increase food security in smallholder landscapes. Currently, blanket recommendations are provided across agro-ecological zones, although fertilizer response and nutrient use efficiency by maize crop are spatially variable. We aimed to identify factors that could help to refine fertilizer recommendation by analyzing the variability in fertilizer response (FR) and the agronomic nitrogen use efficiency (N-AE). A literature search for on-farm studies across Kenya and Sub-Sahara Africa (SSA), excluding Kenya, yielded 71 publications. The variability in FR was studied using a meta-analysis whereas key factors that influence FR and N-AE were studied with linear regression models. On average, the FR was 2, but it varied considerably from 1 to 28.5 (excluding outliers). In SSA, 18% of the plots were non-responsive plots with an FR < 1. The main factors affecting N-AE for Kenya were P-Olsen, silt content, soil pH, clay and rainfall, whereas only soil pH, exchangeable K and texture were important for SSA. However, our study indicates that available data on soil, climate and management factors could explain only a small part (< 33%) of the variation in FR and N-AE. Soil pH, P-Olsen, silt content, and rainfall had significant but low levels of power in explaining variation in FR and N-AE. Our findings indicate that strategies to refine fertilizer recommendation should include information on soil types and soil properties.
Tag: greenhouse gas emissions
CongoFlux: Measuring greenhouse gas exchange to better understand the contribution of the Congo Basin’s forests to fight climate change
Yangambi, in the Democratic Republic of Congo, is now home to the Congo Basin’s first eddy covariance station: the CongoFlux tower. Reaching high above the canopy, this structure delivers continuous and accurate data on greenhouse gas exchange between the atmosphere and the forest, which is critical to better understand the role that tropical forests play sequestrating carbon and mitigating climate change.
Spatial and temporal variability of soil N2O and CH4 fluxes along a degradation gradient in a palm swamp peat forest in the Peruvian Amazon
Mauritia flexuosa palm swamp, the prevailing Peruvian Amazon peatland ecosystem, is extensively threatened by degradation. The unsustainable practice of cutting whole palms for fruit extraction modifies forest’s structure and composition and eventually alters peat‐derived greenhouse gas (GHG) emissions. We evaluated the spatiotemporal variability of soil N2O and CH4 fluxes and environmental controls along a palm swamp degradation gradient formed by one undegraded site (Intact), one moderately degraded site (mDeg) and one heavily degraded site (hDeg). Microscale variability differentiated hummocks supporting live or cut palms from surrounding hollows. Macroscale analysis considered structural changes in vegetation and soil microtopography as impacted by degradation. Variables were monitored monthly over 3 years to evaluate intra‐ and inter‐annual variability. Degradation induced microscale changes in N2O and CH4 emission trends and controls. Site‐scale average annual CH4 emissions were similar along the degradation gradient (225.6 ± 50.7, 160.5 ± 65.9 and 169.4 ± 20.7 kg C ha−1 year−1 at the Intact, mDeg and hDeg sites, respectively). Site‐scale average annual N2O emissions (kg N ha−1 year−1) were lower at the mDeg site (0.5 ± 0.1) than at the Intact (1.3 ± 0.6) and hDeg sites (1.1 ± 0.4), but the difference seemed linked to heterogeneous fluctuations in soil water‐filled pore space (WFPS) along the forest complex rather than to degradation. Monthly and annual emissions were mainly controlled by variations in WFPS, water table level (WT) and net nitrification for N2O; WT, air temperature and net nitrification for CH4. Site‐scale N2O emissions remained steady over years, whereas CH4 emissions rose exponentially with increased precipitation. While the minor impact of degradation on palm swamp peatland N2O and CH4 fluxes should be tested elsewhere, the evidenced large and variable CH4 emissions and significant N2O emissions call for improved modeling of GHG dynamics in tropical peatlands to test their response to climate changes.
Land-use change and Biogeochemical controls of soil CO2, N2O and CH4 fluxes in Cameroonian forest landscapes
Deforestation and land-use change are accelerating in the Congo Basin and elsewhere in the tropics affecting the soil-atmosphere exchange of greenhouse gases (GHG). There is a lack of data from Central Africa. We quantified fluxes of CO2, CH4, and N2O at the soil-atmosphere interface in a secondary forest, a cocoa agroforest, and an unfertilized cropland. Soil respiration was highest in the secondary forest (15.37 ± 3.42 Mg C ha−1 y−1), intermediate in the cacao agroforest (12.26 ± 2.91 Mg C ha−1 y−1) and the lowest in the unfertilized cropland (8.74 ± 2.62 Mg C ha−1 y−1). Likewise, N2O fluxes were highest in the secondary forest (2.17 ± 0.20 kg N ha−1 y−1), intermediate in the cacao agroforest (1.40 ± 0.08 kg N ha−1 y−1) and lowest in the unfertilized cropland (1.04 ± 0.15 kg N ha−1 y−1). Soils were a sink for atmospheric CH4 and sink strength was high in the secondary forest (−3.60 ± 1.83 kg CH4 ha−1 y−1) and cacao agroforest (−3.61 ± 2.09 kg CH4 ha−1 y−1) and low in the unfertilized cropland (−1.9 ± 1.59 kg CH4 ha−1 y−1). Variation in soil water content rather than temperature was the dominant driver of seasonal variations of the fluxes at all study sites and N availability affected both N2O and CH4 fluxes. Our results suggest that tropical land-use change is decreasing soil respiration, decreasing the strength of the soil CH4 sink and decreasing N2O emissions, in landscapes that do not practice agriculture with chemical fertilization.