RESUMEN

Combined application of biochar and nitrogen (N) fertilizer could offer opportunities to increase rice yield and reduce methane emissions from paddy fields. However, this strategy may increase nitrous oxide (N2O) emissions, hence its interactive effects on GHG emissions, global warming potential (GWP) and GHG intensity (GHGI) remained poorly understood. We conducted a systematic review to i) evaluate the overall effects of combined application of biochar and N fertilizer rates on GHGs emissions, GWP, rice yield, and GHGI, ii) determine the quantities of biochar and N-fertilizer application that increase rice yield and reduce GHGs emissions and GHGI, and iii) examine the effects of biochar and different types of nitrogen fertilizers on rice yield, GHGs, GWP, and GHGI using data from 45 research articles and 183 paired observations. The extracted data were grouped based on biochar and N rates used by researchers as well as N fertiliser types. Accordingly, biochar rates were grouped into low (≤9 tons/ha), medium (>9 and ≤ 20 ton/ha) and high (>20 tons/ha), while N rates were grouped into three categories: low (≤140 kg N/ha), medium (>140 and ≤ 240 kg N/ha), and high (>240 kg N/ha). For fertiliser types, N rates were grouped as: low (≤150 kg N/ha), medium (>150 and ≤250 kg N/ha), and high (>250 kg N/ha) and N types into: urea, NPK, NPK plus urea (NPK_urea) and NPK plus (NH4)2SO4 (NPK_(NH4)2SO4). Results showed that biochar and N fertiliser significantly affected GHGs emissions, GWP, GHGI and rice yield. Compared to control (i.e., sole N application), co-application of high biochar and medium N rates significantly decreased CH4 emission (82 %) while low biochar with low N rates enhanced CH4 emission (114 %). In contrast, high biochar combined with low N decreased N2O emission by 91 % whereas medium biochar and high N rates resulted in 82 % increase in N2O emission relative to control. The highest GWP and GHGI were observed under co-application of medium biochar and low N rates. Highest rice yield was observed under low biochar rate and high N rate. Regardless of N fertiliser type and biochar rates, increasing N rates increased rice yield and N2O emissions. The highest GWP and GHGI were recorded under sole NPK application. Combination of low biochar and medium N produced low GHGs emissions, high grain yield, and the lowest GHGI, and could be recommended to smallholder farmers to increase rice yield and reduce greenhouse gas emissions from paddy rice field. Further studies should be conducted to evaluate the effects of biochar properties on soil characteristics and greenhouse gas emissions.

RESUMEN

Floodplains represent a huge but poorly understood and hence underutilised agricultural resource in the tropics. Insight into the pedogenesis of the soils could guide their exploitation. This study assessed the physicochemical and mineralogical properties of floodplain soils and explored the interrelationships among these properties for informed inferences on contemporary pedogenic processes. Surface (0-20 cm) and subsurface (69-200 cm) horizons of four pedons of River Benue floodplains (central Nigeria) on shale/alluvium were sampled and analysed. The physicochemical and mineralogical properties were examined for relationships whose pedological significance was discussed. Silt and clay contents were in the ranges of 117-614 and 50-500 g kg-1, respectively, being generally higher in the surface and sub-surface horizons, respectively. The soils are young with one surface horizon being silt loam. The surface horizons had higher soil pH (5.9) but lower soil organic carbon (12.63 g kg-1), total nitrogen (1.05 g kg-1), effective cation exchange capacity (18.58 cmol kg-1), and available phosphorus (5.50 mg kg-1) than the sub-surface horizons. The minerals followed the order quartz < illite < kaolinite. Quartz related inversely to the clay minerals (kaolinite and illite), but none of these minerals influenced the physicochemical properties. Instead, soil textural/acidity indices influenced those defining colloidal activity and fertility status, implying greater dependence on their mixed parent material than overall pedogenesis. It is inferred from the mineralogical relations that illitization prevails in these fast-weathering soils. The lesser influence of pedogenesis on their inherent fertility calls for effective management using the multifunctional sawah ecotechnology. The illitization may not cause environmental problems due to clay activity. Alluvial deposit-mediated increases in silt could promote carbon sequestration; however, off-site detrimental effects of nutrients associated with this erosion-susceptible silt would be expected.

Asunto(s)

RESUMEN

The study of trace and major elements in the biosphere has traditionally focused on the transition and basic metals; the rare earth (REMs), alkaline earth (AEMs) and alkali metals (AMs) that equally constitute environmental contaminants are rarely considered especially in the tropics. The levels and spatial variation of some REMs, AEMs and AMs in the 0-50-cm layer of agricultural soils of Ikwo in southeastern Nigeria typing a humid tropical environment were studied. Soil sampling was undertaken at five zones namely north, south, east, west and centre (covering over 60% of the land area) in the 2017 dry season. Four soil samples were collected from each of the four cardinal points (with evidence of mining and agricultural activities), and two from the centre (serving as reference zone), totalling 18. Metal concentrations were determined using inductively coupled plasma atomic emission spectroscopy. The metals were grouped into REMs (Ce, La, Sm), AEMs (Ba, Ca, Mg, Sr) and AMs (Cs, K, Na, Rb). All metals increased in concentration from the north, or the south (for Ce and Sm only), towards the centre. Overall, they were reasonably similar in distribution pattern among the five zones. Cationic ratios did not vary markedly, reflecting the greater role of pedogenesis than anthropogenic activities in the area. Nevertheless, their variations showed more K, Ca, Sr and La enrichments over the other metals. Enrichment factor and pollution index of the REMs showed healthy levels of these elements in the soils. The data from this preliminary study may add to the data pool on levels and occurrence of REMs, AEMs and AMs in largely disturbed ecosystems of the humid tropics.

Asunto(s)

RESUMEN

Crude oil spillage effects on the environment often wane with time, making late remediation of affected soils look irrelevant. Physicochemical quality of a sandy soil under 9-year-old spillage was compared with that of adjacent unaffected site in southern Nigeria. Soil bulk density and equilibrated water content were higher in affected than unaffected site, but permeability did not change. The spillage increased soil pH, organic carbon, total nitrogen and available phosphorus by about 7%, 1700%, 133% and - 16%, respectively. It lowered divalent exchangeable bases/acidity but raised base saturation. It increased total petroleum hydrocarbon (PHCt) and micronutrients/heavy metals (Fe, Mn, Zn, Cd and Pb), all of which were below their critical limits in soils by regulatory bodies. Soil pH, organic carbon and PHCt correlated positively with all five micronutrients/heavy metals; total nitrogen did so with Zn and Pb. Nine-year period may be insufficient for spillage effects in sandy soils to cease to be evident. Such effects for PHCt and heavy metals, however, are deemed tolerable for ecological safety.

Asunto(s)