Browsing by Author "Obia, Alfred"
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Item Biochar Application to Soil for Increased Resilience of Agroecosystems to Climate Change in Eastern and Southern Africa(Springer, Cham, 2019) Obia, Alfred; Martinsen, Vegard; Cornelissen, Gerard; Børresen, Trond; Botnen Smebye, Andreas; Munera-Echeverri, Jose L.; Mulder, JanWith the current unreliable rainfall pattern, which is expected to worsen due to climate change, agricultural production might become more challenging especially among resource-poor farmers in Eastern and Southern Africa. This calls for adaptation of farming systems to overcome this emerging challenge. Biochar, a product of biomass pyrolysis, with long-term evidence from Amazonia, might contribute to a climate-resilient farming system. This is due to its positive effects on soil chemical and physical properties resulting in increased crop yields, which has been experimentally demonstrated largely within the last two decades. In acidic low cation exchange capacity (CEC) soils, biochar derived from corncob at 5% application rate, for example, increased pH by ≥1 unit and CEC by ≥2 cmolc kg−1 in addition to direct nutrient supply. Increased CEC may be linked to the observed increase in soil organic carbon content (biochar carbon/sequestered carbon) due to biochar addition. Sequestration of carbon due to biochar has been reported to be stronger in soils that have low pH and low carbon contents, with greater effects from biocharsItem Biochar Applied with Inorganic Nitrogen Improves Soil Carbon, Nitrate and Ammonium Content of a Sandy Loam Temperate Soil(Nitrogen, 2022) Omara, Peter; Aula, Lawrence; Otim, Fred; Obia, Alfred; Bigatao Souza, Joao L.Biochar is suggested to improve soil properties. However, its combination with inorganic nitrogen (N) fertilizer in temperate soils is not well understood. This study compared the effect of fertilizer N-biochar-combinations (NBC) and fertilizer-N (FN) on total soil N (TSN), soil organic carbon (SOC), soil nitrate (NO3 –N), and ammonium (NH4 +–N). Soil samples were taken from experiments at Efaw and Lake Carl Blackwell (LCB), Oklahoma, USA with ten treatments consisting of three N rates (50, 100, and 150 kg N ha1) and three biochar rates (5, 10, and 15 t ha1). Results at Efaw showed greater TSN and SOC under NBC compared to FN by 3 and 21%, respectively. No percentage difference was observed for NH4 +–N while NO3 –N was lower by 7%. At LCB, TSN, SOC, NO3 –N, and NH4 +–N were higher under NBC by 5, 18, 24, and 10%, respectively, compared to FN. Whereas application of biochar improved SOC at both sites, NO3 –N and NH4 +–N were only significant at LCB site with a sandy loam soil but not at Efaw with silty clay loam. Therefore, biochar applied in combination with inorganic N can improve N availability with potential to increase crop N uptake on coarse textured soils.Item Biochar dispersion in a tropical soil and its effects on native soil organic carbon(Public Library of Science, 2024-04) Obia, Alfred; Lyu, Jing; Mulder, Jan; Martinsen, Vegard; Cornelissen, Gerard; Smebye, Andreas Botnen; Zimmerman, Andrew RAlthough biochar application to soils has been found to increase soil quality and crop yield, the biochar dispersion extent and its impacts on native soil organic carbon (SOC) has received relatively little attention. Here, the vertical and lateral migration of fine, intermediate and coarse-sized biochar (<0.5, 0.5–1 and 1–5 mm, respectively), applied at low and high doses (1.5–2 and 3–4% w/w, respectively), was tracked using stable isotope methods, along with its impact on native SOC stocks. Biochar was homogeneously mixed into the surface layer (0–7 cm depth) of a loamy sandy Acrisol in Zambia. After 4.5 y, 38–75% of the biochar carbon (BC) was lost from the applied layer and 4–25% was detected in lower soil layers (7–30 cm). Estimating BC mineralization to be no more than 8%, 25–60% was likely transported laterally out of the experimental plots. This conclusion was supported by observations of BC in the control plot and in soils up to 2 m outside of the experimental plots. These processes were likely progressive as recovery of BC in similar plots 1 year after application was greater in both surface and lower soil layers than after 4.5 y. Fine and intermediate-sized BC displayed the greatest downward migration (25.3 and 17.9%, respectively), particularly when applied at lower doses, suggesting its movement through soil inter-particle spaces. At higher dosages, fine and intermediate-sized particles may have clogged pore, so coarse biochar displayed the greatest downward migration when biochar was applied at higher doses. In the BC treatment plot soil profiles, native SOC stocks were reduced by 2.8 to 24.5% (18.4% on average), i.e. positive priming. However, some evidence suggested that the soils may switch to negative priming over time. The dispersion of biochar in soil should be considered when evaluating biochar’s agronomic benefits and environmental effects.Item Biochar Effect on Maize Yield and Soil Characteristics in Five Conservation Farming Sites in Zambia(Agronomy, 2013) Cornelissen, Gerard; Martinsen, Vegard; Shitumbanuma, Victor; Alling, Vanja; Breedveld, Gijs D.; Rutherford, David W.; Sparrevik, Magnus; Hale, Sarah E.; Obia, Alfred; Mulder, JanBiochar addition to agricultural soils can improve soil fertility, with the added bonus of climate change mitigation through carbon sequestration. Conservation farming (CF) is precision farming, often combining minimum tillage, crop rotation and residue retention. In the present farmer-led field trials carried out in Zambia, the use of a low dosage biochar combined with CF minimum tillage was tested as a way to increase crop yields. Using CF minimum tillage allows the biochar to be applied to the area where most of the plant roots are present and mirrors the fertilizer application in CF practices. The CF practice used comprised manually hoe-dug planting 10-L sized basins, where 10%–12% of the land was tilled. Pilot trials were performed with maize cob biochar and wood biocharItem Conservation tillage and biochar improve soil water content and moderate soil temperature in a tropical Acrisol(Soil and Tillage Research, 2020) Obia, Alfred; Cornelissen, Gerard; Martinsen, Vegard; Smebye, Andreas B.; Mulder, JanProjected climate change in Sub-Saharan Africa involves increased drought and elevated soil temperature. Conservation farming (CF), including minimum tillage, crop rotation and crop residue retention, is proposed as a climate smart soil management option to adapt to climate change through enhanced climate resilience. Here, we determine the effect on soil moisture and temperature of CF planting basins in a Zambian Acrisol. Construction of CF planting basins (40 cm x 15 cm, while 20 cm deep), using hand-hoes, is a commonly used minimum tillage practice among small holders in southern Africa, effectively requiring tillage of only 10 % of a field. The study included basins under regular CF and under CF with 4 t ha−1 pigeon pea biochar (CF+BC). Effects are compared with those in an adjacent soil under conventional tillage, where the entire land surface is ploughed. Soil moisture and temperature sensors were installed in the root zone, 10–12 cm deep, for continuous monitoring during two growing seasons. Soil moisture decreased in the order CF+BC > CF > conventional farming. Due to rainwater harvesting in the basins, maximum soil water retention under CF+BC and CF was greater than under conventional farming (+59 % to +107 % and +15 % to +65 %, respectively). Soil drying after free drainage until permanent wilting point lasted longer under CF+BC (18.4–22.3 days) than under both CF and conventional farming (13.3–18.4 days and 14.9–17.8 days, respectively). In situ soil maximum temperature and diurnal temperature range in the growing season increased in the order CF+BC < CF < conventional farming due to decreases in soil moisture. However, additional laboratory tests, with soil-BC mixtures at field capacity, revealed that BC addition to soil, which caused a decrease in bulk density, also resulted in a significant decline in soil thermal conductivity (p < 0.001). Thus, we hypothesize that BC-enhanced soil moisture in basins helped to reduce soil temperature and its fluctuations, due to both increased heat capacity and decreased thermal conductivity. This study shows that CF in combination with BC in an Acrisol, through enhancing plant-available water and moderating soil temperature, is important for crop productivity and has potential as an element of climate smart agriculture.Item Effect of biochar on crust formation, penetration resistance and hydraulic properties of two coarse-textured tropical soils(Soil and Tillage Research, 2017) Obia, Alfred; Børresen, Trond; Martinsen, Vegard; Cornelissen, Gerard; Mulder, JanBiochar (BC) has been reported to improve a number of soil structural and hydraulic properties but detailed studies are scant on how BC affects crust formation, penetration resistance, water repellency and saturated hydraulic conductivity (Ksat). The objective of this study was to quantify the effect of maize cob BC of three different particle sizes on soil crusting (penetration resistance), water repellency, and Ksat of loamy fine sand and sandy loam in Zambia. The BC particle sizes were<0.5 and 1–5 mm applied at 17.5 and 35 t ha−1 in the two soils and intermediate size of 0.5–1 mm applied at lower rates (17.5 and 28 t ha−1 in the loamy fine sand and 13.3 and 26.7 t ha−1 in the sandy loam). Water repellency included both water drop penetration time (WDPT) and minimum molarity of the ethanol droplet at which rapid infiltration into the soil occurs. The BC was produced by slow pyrolysis of corn cobs at a temperature of 350 °C. Biochar, added homogeneously to the upper 7 cm of the soil, reduced the penetration resistance of surface soil of sandy loam with both the crust intact (−2.1 ± 0.6 N cm−2 per percent BC added; p =0.001 in March 2015 and slightly smaller in October 2014) and the crust removed (−2.9 ± 0.6 N cm−2 per percent BC added; p=0.0001). This effect occurred irrespective of particle size of BC (p > 0.05). No effect of BC on penetration resistance was found in the loamy fine sand (p > 0.05). In dry sandy loam with moisture content<1% v/v, the proportion of wettable crusted surface was significantly smaller (25%) than in moist soil (98%) with moisture content of ∼ 10% v/v. Only fine BC of<0.5 mm increased WDPT of the crusted surface of sandy loam (p < 0.05), reducing the proportion of wettable surface from 98 to 80% in moist soil and from 25 to 18% in dry soil. Coarser BCs, instead, increased the proportion of wettable crusted surface from 25% to 45% and 90% for 3% 0.5–1 mm BC and 4% 1–5 mm BC addition, respectively, in dry soil. Biochar significantly reduced Ksat (p < 0.05) in sandy loam below the crust by 0.17 ± 0.07 cm h−1 per percent BC added. However, no effect was found in loamy fine sand. Since BC amended sandy loam below the crust showed no water repellency, reduction in Ksat cannot be explained by water-repellent nature of BC. Instead, this may be due to clogging of soil pores by BC or to collapse of soil structure near water saturation.Item Effect of Soil pH Increase by Biochar on NO, N2O and N2 Production during Denitrification in Acid Soils(PloS one, 2015) Obia, Alfred; Cornelissen, Gerard; Mulder, Jan; Dörsch, PeterBiochar (BC) application to soil suppresses emission of nitrous- (N2O) and nitric oxide (NO), but the mechanisms are unclear. One of the most prominent features of BC is its alkalizing effect in soils, which may affect denitrification and its product stoichiometry directly or indirectly. We conducted laboratory experiments with anoxic slurries of acid Acrisols from Indonesia and Zambia and two contrasting BCs produced locally from rice husk and cacao shell. Dose-dependent responses of denitrification and gaseous products (NO, N2O andN2) were assessed by high-resolution gas kinetics and related to the alkalizing effect of the BCs. To delineate the pH effect from other BC effects, we removed part of the alkalinity by leaching the BCs with water and acid prior to incubation. Uncharred cacao shell and sodium hydroxide (NaOH) were also included in the study. The untreated BCs suppressed N2O and NO and increased N2 production during denitrification, irrespective of the effect on denitrification rate. The extent of N2O and NO suppression was dose-dependent and increased with the alkalizing effect of the two BC types, which was strongest for cacao shell BC. Acid leaching of BC, which decreased its alkalizing effect, reduced or eliminated the ability of BC to suppress N2O and NO net production. Just like untreated BCs, NaOH reduced net production of N2O and NO while increasing that of N2. This confirms the importance of altered soil pH for denitrification product stoichiometry. Addition of uncharred cacao shell stimulated denitrification strongly due to availability of labile carbon but only minor effects on the product stoichiometry of denitrification were found, in accordance with its modest effect on soil pH. Our study indicates that stimulation of denitrification was mainly due to increases in labile carbon whereas change in product stoichiometry was mainly due to a change in soil pH.Item Effect of Two Years of Conservation Agricultural Practices on Weed Seed Banks Evaluated Using Three Techniques(East African Nature and Science Organization, 2024-07-06) Otim, Godfrey Anyoni; Ocan, David; Kumakech, Alfred; Tumwebaze, Susan; Obia, AlfredUnderstanding the soil seed bank is very important when developing integrated weed management technologies and detecting the influence of crop management practices on weeds. In conventional weed control, farmers tend to focus on the above-ground, yet the above-ground vegetation is related to the below-ground soil seed bank. Several soil seed bank estimation methods have been used to estimate the soil seed bank, but varying results have been obtained under different field management practices and soil depths. In this study, we compared three methods for estimating the soil seed bank: seedling emergence method and two direct seed extraction methods (floatation and cloth bag) for determining weed seed density and diversity from different soil depths under conservation farming practices. The three methods had significant differences in estimating weed densities from the soil seed bank (p<0.001). The greenhouse seedling emergence method had a mean number of 5.06, cloth bag had 4.07 while floatation method had the lowest number of 3.38 per 300g of soil. The mean highest weed density was obtained from soil depth of 0-15 cm (5 weeds/300g vs 1.6 weeds/300g of soil from 15-30 cm depth). For soil seed bank diversity, cloth bag method had the highest mean value followed by greenhouse emergence and lastly floatation method with Simpsons diversity index of 2.72, 1.79 and 1.31, respectively. Shannon Weiner diversity index followed the same pattern for the three methods. The methods had different sensitivity to density and diversity and therefore greenhouse emergence method should always be combined with cloth bag method. The greenhouse emergency method detected a total of 26 weed species, cloth bag detected 22 weed species and Floatation method detected 18 weed species. Despite, the greenhouse emergence method detecting more species than the cloth bag at 26 and 22 weed species, respectively, it had a lower Simpson’s diversity index than the cloth bag method due to lower species evenness. Sampling of the entire soil plough layer of 0-30 cm depth for disturbed agricultural soils may produce the best results. Seasons significantly influenced soil seed bank diversity and not soil seed bank density where second season (B) significantly increased soil seed bank diversity. Soil cover practice through intercropping maize with soybean significantly reduced soil seed bank density and not diversity in both minimum and conventional tilled plots. This positive influence on weed density and diversity is a good indicator for integration into a weed management programItem In situ effects of biochar on aggregation, water retention and porosity in light-textured tropical soils(Soil and Tillage Research, 2016) Obia, Alfred; Mulder, Jan; Martinsen, Vegard; Cornelissen, Gerard; Børresen, TrondBiochar (BC) has been reported to improve soil physical properties mainly in laboratory and greenhouse pot experiments. Here we study, under field conditions, the effect of BC and its particle sizes on soil aggregate stability, bulk density (BD), water retention, and pore size distribution in two experiments in Zambia. A) Farmer practice experiment in sandy loam with maize cob BC in conservation farming planting basins under maize and soybeans crops. B) Maize cob and rice husk BC particle size experiments ( 0.5, 0.5–1 and 1–5 mm particle sizes) in loamy sand and sand. In the farmer practice experiment, BC increased aggregate stability by 7–9% and 17–20% per percent BC added under maize and soybeans crops respectively (p < 0.05) after two growing seasons. Total porosity and available water capacity (AWC) increased by 2 and 3% respectively per percent BC added (p < 0.05) under both crops, whereas BD decreased by 3–5% per percent BC added (p 0.01). In the maize cob BC particle size experiment after one growing season, dose was a more important factor than particle size across the soils tested. Particle size of BC was more important in loamy sand than in sand, with 0.5 and 1–5 mm sizes producing the strongest effects on the measured properties. For example, BD decreased while total porosity increased (p < 0.01) for all BC particle sizes in sand whereas only 1–5 mm BC significantly decreased BD and increased total porosity in loamy sand (p < 0.05). However, AWC was significantly increased by only 0.5 and 1–5 mm BCs by 7–9% per percent BC added in both loamy sand and sand. Rice husk BC effect after one year followed similar pattern as maize cob BC but less effective in affecting soil physical properties. Overall, reduced density of soil due to BC-induced soil aggregation may aid root growth and with more water available, can increase crop growth and yields.Item Minimum Tillage and Soil Surface Cover Reduced Weed Density but Not Diversity Over Four Growing Cycles(East African Nature and Science Organization, 2024-10-01) Otim, Godfrey Anyoni; Ekwangu, Joseph; Tumwebaze, Susan; Obia, AlfredThis study investigated use of cultural practices to address weed challenges that present one of the highest costs to farmers. The parameters explored included the effects of tillage and soil cover practices on weed density and diversity, evaluated in a split plot experimental design. Increasing rainfall amounts significantly increased weed density and weed diversity. Minimum tillage significantly suppressed weeds with a density of 80/m2 compared to conventional tillage density of 124/m2. Soil cover practices similarly suppressed weed density (p<0.05) compared to sole crops without soil cover intervention. Maize with mulch had the lowest density (64/m2) followed by maize intercropped with one line of soybean between maize being more effective in weed suppression (92/m2 vs 113/m2). Sole maize and sole soybeans treatment both had a density of ~121/m2. Weed diversity, as measured by Shannon-Weiner index and Simpsons index were not statistically different across treatment (p>0.05). However, weed species count was higher in minimum tillage by 05% compared to conventional tillage, hence it calls for investment in minimum tillage and intercropping practices to allow a more diverse weed community that will be less competitive, less prone to dominance by highly adapted weeds, hence promoting ecological sustainabilityItem The potential of biochar in improving drainage, aeration and maize yields in heavy clay soils(PLoS One, 2018) Obia, Alfred; Mulder, Jan; Hale, Sarah E.; Laela Nurida, Neneng; Cornelissen, GerardHeavy clay soils are globally widespread but their poor drainage and poor aeration limit their use for agriculture. This study was designed to test the effect of the amendment of biochar (BC) from woody shrubs on drainage/saturated hydraulic conductivity (Ksat), soil aeration/air capacity, available water capacity and biomass and grain yields of maize. In a field experiment, BC from Gliricidia sepium was applied in planting basins or rip lines at 2.5% and 5% w/w in addition to a control without BC. The maize biomass and grain yields were higher in BC treated plots compared to control (p<0.05) during the 2012 and 2013 seasons. There was no significant difference in the yields between 2.5% and 5% BC treatments (e.g. grain yield were 6.6 and 8.1 t ha-1 in 2012 and 9.3 and 10.3 t ha-1 in 2013 compared to control with 4.2 and 6.7 t ha-1 in 2012 and 2013, respectively). Soil from the same field site was also mixed with a similar woody shrub BC from Eupatorium adenophorum in the laboratory at rates of 2.5%, 5% and 10% BC w/w and a control without BC. The mixtures were then incubated and subjected to two wet-dry cycles for two weeks. Core samples were taken from the incubated soil and tested for bulk density, Ksat and pF measurements. Total porosity and moisture at field capacity and wilting point were 72.3%, 43.7% and 23.7%, respectively, and not affected by BC amendment (p>0.05). In contrast, bulk density decreased linearly by 0.011±0.002 g cm-3 per percent BC added (p<0.001). Ksat and air capacity of the soil were 288 cm day-1 and 30.9%, respectively falling within the generally accepted optimal range.Item Significant build-up of soil organic carbon under climate-smart conservation farming in Sub-Saharan Acrisols(Science of The Total Environment, 2019) Martinsen, Vegard; Munera-Echeverri, Jose L.; Obia, Alfred; Cornelissen, Gerard; Mulder, JanConservation farming (CF) involving minimum tillage, mulching and crop rotation may offer climate change adaptation and mitigation benefits. However, reported effects of CF, as applied by smallholders, on storage of soil organic carbon (SOC) and soil fertility in Sub-Saharan Africa differ considerably between studies. This is partly due to differences in management practice, soil type and adoption level between individual farmers. Where CF involves planting basins, year-to-year changes in position of basins make SOC stock estimates more uncertain. Here we assess the difference in SOC build-up and soil quality between inside planting basins (receiving inputs of lime and fertilizer; basins opened each year) and outside planting basins (no soil disturbance or inputs other than residues) under hand-hoe tilled CF in an Acrisol at Mkushi, Zambia. Seven years of strict CF husbandry significantly improved soil quality inside planting basins as compared with outside basins. Significant effects were found for SOC concentration (0.74 ± 0.06% vs. 0.57 ± 0.08%), SOC stock (20.1 ± 2.0 vs. 16.4 ± 2.6 t ha−1, 0–20 cm), soil pH (6.3 ± 0.2 vs. 4.95± 0.4) and cation exchange capacity (3.8 ± 0.7 vs. 1.6 ± 0.4 cmolc kg−1). As planting basins only occupy 9.3% of the field, the absolute rate of increase in SOC, compared with outside basins, was 0.05 t C ha−1 yr−1 This corresponds to an overall relative increase of 2.95‰SOC yr−1 in the upper 20 cm of the soil. Also, hot water extractable carbon (HWEC), a proxy for labile organic matter, andItem Vertical and lateral transport of biochar in light-textured tropical soils(Soil and Tillage Research, 2017) Obia, Alfred; Børresen, Trond; Martinsen, Vegard; Cornelissen, Gerard; Mulder, JanField experiments were conducted in Arenosols (loamy fine sand) and Acrisols (sandy loam) in Zambia to quantify vertical and lateral transport of biochar (BC) using the BC and soil 13C isotope signatures and total organic carbon contents. There were three experimental treatments composing of no BC, 0.5 and 0.5–1 mm BCs each with three replicates arranged in completely randomized design. The applied BCs were made from rice husk, except 0.5–1 mm BC in sandy loam, which was from maize cob. One year after mixing BC homogeneously in the 0–5 cm surface layer, soil down to 20 cm depth was sampled. The downward migration of BC was significant down to 8 cm depth in sandy loam and down to 6 cm in loamy fine sand. Below these depths, there was no significant difference in BC amounts between the BC amended and the reference plots. There was a general tendency for greater downward migration for the 0.5 mm than for 0.5–1 mm BC. Total BC recovery at 0–5 cm depth in the BC-treated soils amounted to 45–66% of the total applied amount of BC. As only 10–20% was recovered in the deeper soil layers, 24–45% of the applied BC could not be accounted for in the soil profile. Although, decomposition and downward migration to below 20 cm depth may contribute to the loss of BC from the surface soil, much can be attributed to lateral transfer through erosion. This is the first study that explicitly focuses on the theme of BC dispersion and shows that in Arenosols and Acrisols of the tropics, the downward migration of BC is limited.