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Item The potential of biochar in improving drainage, aeration and maize yields in heavy clay soils(PLOS, 2018-05-11) Obia, Alfred; Mulder, Jan; Hale, Sarah Elizabeth; Nurida, Neneng Laela; 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 experi ment, 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 incu bated 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. Both Ksat and air capacity followed a significant quadratic relation (p<0.05) upon BC addi tion, decreasing at low BC doses, reaching a minimum at 3–5% BC and increasing at higher doses. Results allowed a partial attribution of the yield increases to changes in soil physical properties such as changes in bulk density and not clearly to Ksat and air capacity.Item Biochar Application to Soil for Increased Resilience of Agroecosystems to Climate Change in Eastern and Southern Africa(Springer Nature Switzerland, 2019) Obia, Alfred; Martinsen, Vegard; Cornelissen, Gerard; Børresen, Trond; Smebye, Andreas Botnen; Munera-Echeverri, Jose Luis; 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 biochars produced from woody materials or those produced at high temperature. Such soils with low pH and carbon contents are common in tropical areas. Another effect of biochar at field-relevant doses of ≤5% is the improvement of physical properties such as increased aggregate stability by up to 7%, increased aggregate mean weight diameter by 8–13%, increased soil water contents and reduced soil temperature fluctuations. Similar changes to soil properties have been found to increase yield by 10% based on global dataset, but up to fourfold increases have also been reported for acidic low CEC soils. One key challenge to implementation of biochar technology for increased yields is probably the unavailability of large quantity of biochar often in tens of Mg ha−1 that is required for field application. Conservation agriculture (CA) with its three principles of minimum tillage, residue retention and crop diversification may partly address this key challenge of biochar implementation. This can be achieved by applying biochar only in the tilled part of land in a minimum tillage operation, which can be only 10% of the land surface. In this way, biochar may increase the positive attributes of CA such as increased rainwater harvesting and crop yields. Further solution to the quantity of biochar material for field application is the application of limited quantity of biochar in combination with traditional amendment such as manures either in mixtures or after co-composting. In this way, biochar is expected to deliver its benefits to manure resulting in improved soil properties and increased yields. Overall, incorporation of biochar in CA-based farming system alone or in combination with manures might contribute to building of climate- resilient agroecosystem.Item Effect of biochar on crust formation,penetration resistance and hydraulic properties of two coarse-textured tropical soils(Soil & 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 Conservation tillage and biochar improve soil water content and moderate soil temperature in a tropical Acrisol(Soil & Tillage Research, 2020-03) Obia, Alfred; Cornelissen, Gerard; Martinsenb, Vegard; Smebyea, Andreas Botnen; Martinsenb, Jan Mulder; Smebyea, Andreas Botnen; 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 com pared 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 con ductivity. 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 Biochar Applied with Inorganic Nitrogen Improves Soil Carbon, Nitrate and Ammonium Content of a Sandy Loam Temperate Soil(MDPI, Basel, Switzerland, 2022-02-23) Omara, Peter; Aula, Lawrence; Otim, Fred; Obia, Alfred; Souza, Joao Luis Bigatao; Arnall, Daryl BrainBiochar 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 ha−1) and three biochar rates (5, 10, and 15 t ha−1). 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.