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Biochar characteristics and application in the agriculture


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Recently biochar gained importance as a way to deal with global climate change, by sequestering C into soils, but also as a soil amendment and bioremediation tool. Many studies have demonstrated the positive influence of biochar on soil quality and subsequently, plant growth, although the results are not consistent and climate seems to be the main reason for this inconsistency. Number of studies has been conducted to find out how biochar affect soil characteristic, fertilizers efficiency as well as soil microbiota. The main focus of this review is to discuss biochar features and it application in agricultural practices that could improve soil productivity and in consequence plant growth and development.
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12. Biochar characteristics and application in the agriculture
Martyna Glodowska, Malgorzata Lyszcz
Institute of Soil Science and Plant Cultivation State Research Institute, Pulawy, Poland
Key words: biochar, soil amendment, carbon, plant growth, fertilizers, soil microbiology
Recently biochar gained importance as a way to deal with global climate change, by
sequestering C into soils, but also as a soil amendment and bioremediation tool. Many studies have
demonstrated the positive influence of biochar on soil quality and subsequently, plant growth,
although the results are not consistent and climate seems to be the main reason for this inconsistency.
Number of studies has been conducted to find out how biochar affect soil characteristic, fertilizers
efficiency as well as soil microbiota. The main focus of this review is to discuss biochar features and
it application in agricultural practices that could improve soil productivity and in consequence plant
growth and development.
Biochar, although not in the form we know today, has been used since centuries. The
incorporation of charcoal into the soil to enhance soil quality has been an agricultural practice for
thousands of years (Xu et al. 2012). Pre-Columbian people were combining charred residues of
organic and inorganic wastes with the soils that are known today as Terra Preta - rich in organic matter
and nutrients Amazonian soil. The oldest description of charcoal use in agriculture may be from the
17th century Encyclopedia of Agriculture by Yasusada Miyazaki, where he cited an even older
textbook from China. We know from there that rice husk charcoal has been used as a soil amendment
probably since the beginning of rice cultivation in Asia (Ogava and Okimori, 2010). Nowadays, the
term “biochar” refers to a product of biomass pyrolysis, wherein plant-based materials are heated
under anaerobic conditions to capture combustible gases. Originally, biochar production was
associated with slow pyrolysis, characterized by a long time (more than 10 h) under relatively low
temperature, typically around 400°C. More recently, there has been growing interest in biochar
production through fast pyrolysis, where the organic materials are rapidly heated to 450-600°C (Xu
et al. 2012). The reason why biochar gained public interest is mainly associated with its carbon
sequestration ability. Biochar is a promising tool to reduce the atmospheric CO2 concentration
because it slows the return of photosynthetically fixed carbon to the atmosphere (Xu et al., 2012). The
half-life of biochar in the soil is estimated to range from hundreds to thousands of years (Zimmerman
2010). Therefore, supplying the soil with biochar is a strategy for long-term carbon sequestration.
Moreover, there is increasing interest in biochar as a soil amendment. Number of studies has
demonstrated that biochar application can significantly improve crop productivity (Chan et al. 2007),
improve soil conditions (Xu et al., 2012), and increase the efficiency of fertilizers (Asai et al., 2009),
it can also be used in remediation processes (Chan et al., 2012). The main goal of this paper is to
review the effect of biochar on soil properties and discuss it use in the agricultural practices.
Effect of biochar on soil characteristics
Numerous studies have demonstrated that biochar have a positive effect on soil quality.
Biochar application can enhance organic matter content in soil what leads to increased soil fertility
(Xu et al., 2012). Depending on the feedstock and the pyrolysis features used in biochar production,
it can contain some nutrient but also due to its highly porous structure it can improve nutrient retention
in the soil. Also, biochar can reduce soil acidity and increases soil electrical conductivity and cation
exchange capacity (CEC), which results in higher nutrient availability (Laird et al. 2010). Some data
show that biochar can reduce the availability of trace elements to plants. Namgay and coworkers
(2010) found that concentrations of Cd, As and Cu in maize shoots significantly decreased after to
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the application of biochar, however; the uptake of heavy metals and their availability to the plant was
varying, depending on the metal and the rate of biochar application. Glaser et al. (2002) reported that
biochar application reduced aluminium toxicity to plant roots and soil microbiota. Considering the
environmental issues associated with the contamination of arable soils with heavy metals biochar
shows the potential to remediate cultivated soils. For example, Chan and coworkers (2012) provided
some evidences showing that pine needle based biochar can be efficiently used in bioremediation of
polycyclic aromatic hydrocarbons (PAHs) of contaminated soils. It was also shown that sewage-
sludge biochar decreased the plant-available Zn, Ni, Cu and Pb, the mobile forms of Cu, Ni, Zn, Cd
and Pb, as well as the risk of leaching of Cu, Zn, Ni and Cd. Freddo et al. (2012) reported that the
concentrations of metals, metalloids and PAH in four plant-based biochars (rice straw, bamboo,
redwood and maize) were lower than those reported as acceptable for sewage sludge and compost.
Biochar has high total porosity (Fig. 1) therefore it can retain water in small pores and increase soil
water holding capacity (Asai et al., 2009).
Figure 1. Biochar under a microscope, Brownsort, UK Biochar Research Centre.
From: http://www.nakanoassociates. com/biochar/
This may enhance water availability to crops and prevent form erosion. Some authors suggest
that it can be an important tool to manage water in agricultural production, particularly under water
stress conditions. For example, Artiola et al. (2012) report that biochar treatment significantly
influenced Bermuda grass growth in a 1-month water-stress experiment where 100% of the control
plants were killed. The survival rate of plant amended with 2 and 4% biochar were 50 and 100%,
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Dual effect of biochar and mineral fertilizers
Some studies investigated a combined effect of mineral fertilizers and biochar. For example,
Asai and coworkers (2009) reported that grain yield of rice was significantly higher after the
application of biochar at a rate of 4 and 8 t ha-1 in the presence of N fertilizer. Pot trials with romaine
lettuce showed that fresh weight was significantly higher after biochar application (at a rate of 2 and
4% w/w) compared to the control; similar effects were seen as a result of pre-treatment with
concentrated fertilizer solution. The authors speculated that this increase might be due to the storage
and release of fertilizer chemicals by biochar particles. Similarly, Hossain (2010) observed 20%
higher yields of cherry tomatoes after application of biochar with fertilizer, compared to the fertilizer
treatment alone. A pot trial was carried out to study the effect of biochar that had been produced from
green waste on the yield of radish (Chan et al. 2007). Three rates of biochar (10, 50 and 100 t ha1)
with and without additional N application (100 kg N ha1) were studied. In the absence of N fertilizer,
application of biochar to the soil did not increase radish yield, even at the highest rate of 100 t ha-1.
However, a significant biochar and N fertilizer interaction was observed. For example, an additional
increase in dry matter of radish, in the presence of N fertilizer, varied from 95% in the control to
266% in the 100 t ha1 biochar amended soils (Chan et al. 2007). Schulz and Glasern (2012)
investigated the effect of biochar on soil quality and plant growth under greenhouse conditions. They
showed that the addition of biochar to sand can increase plant growth. They observed a significant
synergy when the biochar was combined with a mineral fertilizer or compost. These combinations
have increased plant growth more than any increase due to pure biochar, compost or mineral fertilizer.
Igarashi (1996) conducted a cultivation experiment for crops amended with rice husk charcoal. He
applied charcoal with magnesium, phosphate, and lime, and rotated the soybean and maize crops. He
reported that a charcoal application significantly increased plant growth, root nodulation and yield.
The effect was sustained in the second crop of maize, and it continued up to the tenth crop rotation.
He also reported that the growth and yield of maize treated with charcoal were greater than those of
the control treatment, where only mineral fertilizers have been applied. All of the examples presented
above highlight the capacity of biochar to improve the fertilizers efficiency in a crop production.
Some authors (Asai et al. 2009) speculate that the fertilizer efficiency improvement might be
associated with the capacity of biochar particles to retain and slowly release fertilizer chemicals.
Others (Chan et al. 2007) attribute the fertilizer use efficiency to improved physical soil conditions or
reduced fertilizer run-off as a result of biochar application. Although there is some speculation
regarding the mechanism of this process, it is not completely understood, and there is still a need for
further study.
Response of crop to the biochar application
There are a number of investigations that reported the beneficial influence of biochar on plant
growth and development. Biochar can affect plant productivity in two ways: directly, as a result of its
nutrient content and release characteristics; and indirectly, due to improved retention of nutrients,
increase in soil pH, CEC, soil water retention and alteration of soil microbial populations and
functions (Graber et al. 2010). Biochar significantly improves soil fertility; it influences soil structure,
texture, particle size distribution, porosity, and density (Xu et al., 2012). Uzoma (2011) reported that
biochar application at a rate of 15 and 20 t ha -1 increased maize grain yield by 150 and 98%,
respectively, under sandy soil conditions. Graber (2010) found that number of nodes and canopy dry
weight of tomatoes treated with biochar amendment (0, 1, and 3 wt %) were significantly higher than
the control. In the same experiment, he showed that tomatoes treated with biochar had more buds and,
in the end, more fruit. Although, he showed that fruit weight, whole plant yield, and single fruit weight
were all significantly higher, he did not report differences between the two rates of biochar. Major et
al. (2010) conducted a long-term (4 year) experiment in a Colombian savanna oxisol. Following the
results, biochar application effect is most visible in the third and fourth years. Maize yield did not
significantly increase in the first year, but in the second, third and fourth years after application of
biochar at a rate of 20 t ha -1, maize grain yield increased over the control (28, 30 and 140%,
respectively). Likewise, in other long term study, Jones and coworkers (2012) reported no
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improvements in the growth of grass after first year from biochar application. However, in the second
and third years after application, at rates of 25 and 50 t ha -1, height and total dry biomass of grass, as
well as foliar N, were significantly higher than the control. Plant growth can be directly affected by
improved macro and micronutrient uptake. Chan et al. (2007) showed that the concentrations of P, K
and Ca in radish tissue increased significantly after applying biochar at a rate of 50 and 100 t ha -1.
They reported that the increase in P and K contents in the radishes that grew in biochar treated soil
was related to high concentrations of available P and exchangeable K present in the biochar. Also
some studies have been conducted to investigate the effect of biochar on the germination process.
Free at al. (2010) reported no significant effect of 5 different plant-based biochars on germination of
maize in a paper towel assay. However, Solaiman et al. (2012) showed that biochar generally
increased wheat seed germination at the lower application rates (1050 t ha-1) and decreased or had
no effect at higher rates of application.
Biochar affect microbial communities
Soil microbial function and structure are beneficially affected when favorable conditions
occur in the soil system. The soil microorganisms play a crucial role in soil structure and functioning.
They are responsible for soil formation, ecosystem biogeochemistry, cycling of nutrients and
degradation of plant residues and xenobiotics. The environmental factors which most significantly
influence bacterial abundance, diversity and activity are moisture, temperature and pH (Wardle 1998).
The pH of biochar depends on feedstock as well as type of pyrolysis applied in biochar production
but generally biochar application might be a good way to adjust the soil pH. Because of the high WHC
of biochar, it retains water and creates suitable and more stable habitats for bacteria. The biochar high
WHC can be considered as suitable protection for microorganisms against desiccation. Biochar may
retain moisture in the pore spaces that allow continued hydration of microorganisms in a drying soil.
A number of research efforts in Japan, as well as recent investigations from the US, have shown that
biochar supports the activity of many soil microorganisms important to agriculture. A recent review
of biochar and its effect on soil biota (Lehmann et al. 2011) provides considerable evidences that
application of biochar to the soil has significant effects on soil microbiota.
Biochar and its highly porous structure can provide a suitable habitat for many
microorganisms (Fig 2.) by protecting them from predation and desiccation, providing carbon (C),
energy and mineral nutrient.
Figure 2. Scanning electron micrograph of the biochar with a syntrophic co-culture of G. metallireducens and
G. sulfurreducens. From: Chen et al. 2014
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The increase in bacterial abundance might be associated with sorption to the biochar surface,
which prevents microorganisms from leaching and help to stabilize the population. Bacteria might be
attached to biochar particles in different ways such as flocculation, adsorption on the surface, covalent
bonding to carriers, cross-linking of cells or entrapment in a matrix (Lehmann et al., 2011). Biochar
is also considered to be suitable protection for microorganisms against desiccation. Seasonal drying
of soil leads to stress and, in effect, dormancy or mortality of some bacteria, with significant
differences between gram-negative and gram-positive bacteria.
A number of studies provide evidence that biochar influences the composition of soil
bacterial communities. It is commonly accepted that application of biochar leads to the changes of
soil physicochemical properties and provides metabolically available sources of carbon (C), which
may result in shifts in soil microbial community structure. Terminal restriction fragment length
polymorphism (TRFLP) studies conducted by Anderson and colleagues (2011) show that biochar
treatment enhanced the abundance of Bradyhrizobiaceae (~8%), Hyphomicrobiacea (~14%),
Streptosporangiaceae (~6%) and Thermomonosporaceae (~8%). Some negative effects of biochar on
the Streptomycataceae (~-11%) and Micromonosporaceae (~-8%) families were also observed.
Increases in N2-fixing rhizobia were reported in the rhizosphere whereas N2-fixing Frankiaceae
increased in both bulk and rhizosphere soil supplied with biochar. The authors suggest that biochar
treatment potentially enhances the growth of bacteria involved in N cycling in the soil, particularly of
those which may decrease the flux of N2O. A similar study conducted by Kolton et al. (2011) shows
that the genus most significantly affected by biochar application (3% wt/wt) was Flavobacterium.
The total relative abundance of this group was 4.2% of all operational taxonomic units (OTUs) in the
control treatment and 19.6% in biochar-amended soil. Simultaneously, there was a decrease in relative
abundance from 71 to 47% for the genus Proteobacteria. The authors suggested that biochar-enriched
soil led to important changes in the root-associated microbial community, characterized by induction
of several chitin- and aromatic compound-degrading genera. Ameloot et al. (2013) hypothesised that
the pyrolysis temperature in biochar production is a factor that might affect the microbial community.
They found a correlation between Gram-negative bacteria and low temperature pyrolysis biochar.
Furthermore, a high abundance of Gram-negative bacteria in a low 350°C biochar treatment and
increases in Gram-positive bacteria in all types of biochar except that produced at 700°C was reported.
Luo et al. (2013) provide the evidence that plant-based biochar pyrolyzed at low temperature (350°C)
increases microbial colonization at high soil pH compared to biochar pyrolyzed at 700°C. They
speculate that it might be because the availabilities of C, N and other nutrients were low in 700°C
biochar, as most were lost during pyrolysis. They also speculate that lower colonization of the 700°C
biochar might be because biochar produced at higher temperatures is characterized by fewer and finer
pores, which results in fewer physical niches for bacteria. Abit et al. (2012) showed that biochar
pyrolyzed at high temperature (700°C), and made out of pine chips, significantly reduced transport of
E. coli through a sandy soil under water-saturated conditions when compared to the control, in column
experiments. The authors explain that the difference between biochar types is due to differences in
pore size distribution for biochars produced from different feedstocks. They suggest that
incorporation of high temperature biochar made out of plant-based feedstocks to the soil might be a
potential method for reducing microbial movement through soils, and it might be considered as a
management practice for protecting shallow groundwater from pathogenic microorganisms.
Biochar became an important tool to mitigate the climate changes caused by anthropogenic
activities. But as it is presented above biochar can also be successfully used in agricultural sector. The
literature review presented above suggests that biochar is a material that significantly affects soil
quality by changing its structure as well as chemical composition. It can be used in the water stress
management and in the bioremediation processes, particularly in recovery of the soils contaminated
with PAHs and heave metals. There are a growing number of evidences showing positive effect of
biochar on plant growth and development; however this effect is strongly related to the climate and
soil type. Also, biochar when applied together with mineral or organic fertilizers seems to
significantly improve fertilizer efficiency and use by the plant. Finally, biochar was found to cause
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Full-text available
Biochar has gained importance due to its ability to increase the long-term soil carbon pool and improve crop productivity. However, little research has been done to evaluate the influence of biochar application to soil on the bioavailability of trace elements to plants. A pot experiment was conducted to investigate the influence of biochar on the availability of As, Cd, Cu, Pb, and Zn to maize (Zea mays L.). An activated wood biochar, pyrolysed at 550 degrees C, was applied at 3 rates (0, 5, and 15 g/kg) in factorial combinations with 3 rates (0, 10, and 50 mg/kg) each of As, Cd, Cu, Pb, and Zn separately to a sandy soil. After 10 weeks of growth, plants were harvested, shoot dry matter yield was measured, and concentration of trace elements in shoots was analysed. The soil in pots was analysed for extractable trace elements. The results showed that the addition of wood biochar to soil did not have any significant effect on the dry matter yield of maize plants, even at the highest rate of application. However, trace element application significantly reduced the dry matter yield from 10 to 93% depending on the type of trace element. Biochar application decreased the concentration of As, Cd, and Cu in maize shoots, especially at the highest rate of trace element application, whereas the effects were inconsistent on Pb and Zn concentrations in the shoots. The concentrations of extractable As and Zn in soil increased with biochar application, whereas extractable Cu did not change, Pb decreased, and Cd showed an inconsistent trend. Sorption of trace elements on biochar with initial loadings up to 200 mmol at pH 7 occurred in the order: Pb > Cu > Cd > Zn > As. The results show that biochar application can significantly reduce the availability of trace elements to plants and suggest that biochar application may have potential for the management of soils contaminated by trace elements.
Full-text available
Biochar, a charcoal-like product of the incomplete combustion of organic materials, is an increasingly popular soil amendment designed to improve soil fertility. We investigated the possibility that biochar could promote direct interspecies electron transfer (DIET) in a manner similar to that previously reported for granular activated carbon (GAC). Although the biochars investigated were 1000 times less conductive than GAC, they stimulated DIET in co-cultures of Geobacter metallireducens with Geobacter sulfurreducens or Methanosarcina barkeri in which ethanol was the electron donor. Cells were attached to the biochar, yet not in close contact, suggesting that electrons were likely conducted through the biochar, rather than biological electrical connections. The finding that biochar can stimulate DIET may be an important consideration when amending soils with biochar and can help explain why biochar may enhance methane production from organic wastes under anaerobic conditions.
Full-text available
Background and aims Biochar can be produced from a wide range of organic sources with varying nutrient and metal concentrations. Before making irreversible applications of biochar to soil, a preliminary ecotoxicological assessment is desirable. Methods First, we determined the effect of biochar type and rate on early growth of wheat in a soil-less Petri dish bioassay. Second, we investigated the effect of the same biochars on seed germination and early growth of wheat in ten soils with varying texture using a glasshouse bioassay. Finally, we investigated whether these biochars had similar effects on three plant species when grown in one soil. Results Biochar type and application rate influenced wheat seed germination and seedling growth in a similar manner in both the soil-less Petri dish and soil-based bioassay. Germination and early root growth of mung bean and subterranean clover differed from that of wheat in response to the five biochars. Conclusions We recommend use of the soil-less Petri dish bioassay as a rapid and simple preliminary test to identify potential toxicity of biochars on seed germination and early plant growth prior to biochar application to soil.
Full-text available
Biochar has been widely proposed as a soil amendment, with reports of benefits to soil physical, chemical and biological properties. To quantify the changes in soil microbial biomass and to understand the mechanisms involved, two biochars were prepared at 350 °C (BC350) and 700 °C (BC700) from Miscanthus giganteus, a C4 plant, naturally enriched with 13C. The biochars were added to soils of about pH 4 and 8, which were both sampled from a soil pH gradient of the same soil type. Isotopic (13C) techniques were used to investigate biochar C availability to the biomass. Scanning Electron Microscopy (SEM) was used to observe the microbial colonization, and Attenuated Total Reflectance (ATR) to highlight structural changes at the surface of the biochars. After 90 days incubation, BC350 significantly increased the biomass C concentration relative to the controls in both the low (p < 0.05) and high pH soil (p < 0.01). It declined between day 90 and 180. The same trend occurred with soil microbial ATP. Overall, biomass C and ATP concentrations were closely correlated over all treatments (R2 = 0.87). This indicates that neither the biomass C, nor ATP analyses were affected by the biochars, unless, of course, they were both affected in the same way, which is highly unlikely. About 20% of microbial biomass 13C was derived from BC350 after 90 days of incubation in both low and high pH soils. However, less than 2% of biomass 13C was derived from BC700 in the high pH soil, showing very low biological availability of BC700. After 90 days of incubation, microbial colonization in the charsphere (defined here as the interface between soil and biochar) was more pronounced with the BC350 in the low pH soil. This was consistent with the biomass C and ATP results. The microbial colonization following biochar addition in our study was mainly attributed to biochar C availability and its large surface area. There was a close linear relationship between 13CO2 evolved and biomass 13C, suggesting that biochar mineralization is essentially a biological process. The interactions between non-living and living organic C forms, which are vital in terms of soil fertility and the global C cycle, may be favoured in the charsphere, which has unique properties, distinct from both the internal biochar and the bulk soil.
Biochar from pine forest waste (PFW) was used in greenhouse pot experiments to evaluate plant growth using two levels (2% and 4% wt/wt) of biochar amendments applied to an alkaline, loamy sand soil. Biochar soil additions induced a large decrease in the soil bulk density (from 1.59 to 1.26 g cm−3) and large to moderate increases in gravimetric and volumetric soil-water contents, respectively, under pot and field moisture capacity conditions. The growth of romaine lettuce was initially adversely affected in the 4% biochar-amended soil. However, bermudagrass benefited from the biochar addition with increased biomass production and enhanced drought resistance. Both plant species showed statistically significant increases (compared with controls) in biomass yields at the 2% but not at the 4% biochar application rate. An incubation study indicated that soil microbial activity, as measured by evolved CO2, was significantly suppressed (−31% compared with the control) in the presence of biochar over a period of 4 months. The data indicated that addition of PFW biochar induced a species-dependent plant response and produced an overall decrease in microbial mineralization of organic materials. Vegetables such as lettuce may benefit from a period of excess irrigation, to leach any potentially toxic biochar-introduced salts or organic compounds, before seeding. Conversely, warm season grasses may adapt quickly to a soil amended with PFW biochar with increased biomass production and drought resistance.
Biochar, a by‐product of biomass pyrolysis, has been suggested as a mean to combat climate change, and at the same time to achieve agricultural and environmental benefits. As one possible source of the components with high aromatic structure in soil humus, biochar is of great importance in increasing soil carbon storage and improving soil nutrient retention and nutrient availability, and in maintaining the balance of soil ecosystem. This paper briefly reviewed and synthesized recent findings and discussions regarding the production and characteristics of biochar, its effects on global climate change and particularly in relation to the environmental effects of biochar in soils. Agronomic benefits of biochar application are critically highlighted because researches show that biochar had varied effects on crop productivity thorough the different bio‐physical interactions between the biochar and the soils, which are deserved for further investigations. Potential pitfalls and knowledge gaps were briefly discussed on the environmental behavior and the effects of biochar in agricultural ecosystem.
In Asian countries, people have a long history of using rice husk charcoal or wood ash as an agricultural soil amendment, but evidence of this has been long obscured. Since the 1980s, microbiological studies, mainly on symbiotic organisms, have been performed in Japan. Charcoal is a porous material with high water and air retention capacities and high alkalinity. Therefore, it stimulates root growth and enhances the infection of various symbiotic microbes to plant partners. The use of carbonised materials in agriculture, forestry, and construction will contribute to the sustainability of crop production, soil conservation, and carbon sequestration. Biochar-related research accumulated mainly in Japan is reviewed.
Our contemporary society is struggling with soil degradation due to overuse and climate change. Pre-Columbian people left behind sustainably fertile soils rich in organic matter and nutrients well known as terra preta (de Indio) by adding charred residues (biochar) together with organic and inorganic wastes such as excrements and household garbage being a model for sustainable agriculture today. This is the reason why new studies on biochar effects on ecosystem services rapidly emerge. Beneficial effects of biochar amendment on plant growth, soil nutrient content, and C storage were repeatedly observed although a number of negative effects were reported, too. In addition, there is no consensus on benefits of biochar when combined with fertilizers. Therefore, the objective of this study was to test whether biochar effects on soil quality and plant growth could be improved by addition of mineral and organic fertilizers. For this purpose, two growth periods of oat (Avena sativa L.) were studied under tropical conditions (26°C and 2600 mm annual rainfall) on an infertile sandy soil in the greenhouse in fivefold replication. Treatments comprised control (only water), mineral fertilizer (111.5 kg N ha–1, 111.5 kg P ha–1, and 82.9 kg K ha–1), compost (5% by weight), biochar (5% by weight), and combinations of biochar (5% by weight) plus mineral fertilizer (111.5 kg N ha–1, 111.5 kg P ha–1, and 82.9 kg K ha–1), and biochar (2.5% by weight) plus compost (2.5% by weight). Pure compost application showed highest yield during the two growth periods, followed by the biochar + compost mixture. biochar addition to mineral fertilizer significantly increased plant growth compared to mineral fertilizer alone. During the second growth period, plant yields were significantly smaller compared to the first growth period. biochar and compost additions significantly increased total organic C content during the two growth periods. Cation-exchange capacity (CEC) could not be increased upon biochar addition while base saturation (BS) was significantly increased due to ash addition with biochar. On the other hand, compost addition significantly increased CEC. Biochar addition significantly increased soil pH but pH value was generally lower during the second growth period probably due to leaching of base cations. Biochar addition did not reduce ammonium, nitrate, and phosphate leaching during the experiment but it reduced nitrification. The overall plant growth and soil fertility decreased in the order compost > biochar + compost > mineral fertilizer + biochar > mineral fertilizer > control. Further experiments should optimize biochar–organic fertilizer systems.
The objective of this study was to investigate the effect of biochar application (CA) on soil physical properties and grain yields of upland rice (Oryza sativa L.) in northern Laos. During the 2007 wet season, three different experiments were conducted under upland conditions at 10 sites, combining variations in CA amounts (0–16 t ha−1), fertilizer application rates (N and P) and rice cultivars (improved and traditional) in northern Laos.CA improved the saturated hydraulic conductivity of the top soil and the xylem sap flow of the rice plant. CA resulted in higher grain yields at sites with low P availability and improved the response to N and NP chemical fertilizer treatments. However, CA reduced leaf SPAD values, possibly through a reduction of the availability of soil nitrogen, indicating that CA without additional N fertilizer application could reduce grain yields in soils with a low indigenous N supply. These results suggest that CA has the potential to improve soil productivity of upland rice production in Laos, but that the effect of CA application is highly dependent on soil fertility and fertilizer management.