Biochar has been gaining popularity as a potentially sustainable management method to increase soil health while sequestering carbon and increasing the global soil carbon pool. Research on biochar’s influence on soil health has been increasing, yet there is still a significant lack of published studies focused on the effects of biochar on the diversity of soil biota. Moreover, the majority of documented research was conducted in controlled conditions. As biological activity is a key component of soil quality, it is vital to understand the influences of biochar on soil biota at the field level. The objectives of this study were threefold. The first objective was to characterize changes in physiochemical properties of soils amended with biochar. Results showed that application rates of approximately 2 percent yielded an increase in desirable soil properties that were long lasting. The second objective was to analyze nematode community indices and the bacteriovores to fungivores ratio in biochar amended field plots. Nematode community assemblages were identified and compared in both the control and highest biochar treatments. Nematode communities were significantly different with maturity indices indicating greater temporal stability in the biochar-amended soils. The third and final objective was to evaluate changes in native soil bacteria as a result of biochar application. The bacterial diversity of the control, two percent and four percent biochar-amended field soils were assessed using high-throughput sequencing of 16S rRNA and taxonomic assessment. While overall community diversity was not significantly affected, the abundance of specific bacterial taxa were significantly affected, indicating the potential for shifts in biogeochemical cycling in biochar-amended soils.
The sustainability of small farms in the Northeastern U.S. has been continually threatened by both the rising costs to operate and the degradation of soil quality. The number of small farms (sales less than $250,000 per year) in operation fell 7.7% from 2002-2007 (USDA-NASS, 2009) and has been declining for several decades. Small farms compete with large farms for economic viability and without the large land area to increase profitability, they must find alternate ways to increase yield and/or decrease operating costs to stay profitable. One large factor involved in the sustainability and yield is the quality and health of the soils. Soil quality must be maintained to ensure high crop yield, yet often, conventional farming practices cause continual soil quality degradation from intensive cultivation and inorganic fertilizer application. Counteracting this inverse relationship is a major challenge and often requires significant shifts in agricultural management practices.
Soil degradation in agricultural soils causes loss of soil fertility, crop yield reduction, decreased biological activity, and increased acidification (Laird et al., 2010). Recently, biochar has been touted as having many potential uses as a soil amendment for improving soil quality, specifically improving cation exchange capacity, pH and nutrient availability. However, soil biology also plays a significant role in biogeochemical processes that influence soil health and quality and should be included in a more comprehensive study of soil health. significant improvements in soil fertility have been reported with biochar application as low as 2% (w/w) (Novak et al., 2009). Even negatively charged nutrients (i.e. nitrate) have shown reduced leaching in biochar-amended soils (Ventura et al., 2012), leading to theories including microbial immobilization or inhibition of nitrification. Recent data also showed reduced nitrate leaching (Zheng et al., 2013), but soil fauna and microbial communities were not determined.
Soil microbial communities are complex and the interaction of these communities with nutrient cycling is even more so. The addition of biochar to soils can affect this community and its role(s) in the soil significantly. When the physical and chemical properties of a soil amended with biochar change abruptly, microbes respond differently and thus, rapid environmental changes may cause shifts in the microbial community composition. Applying biochar to soils can significantly affect the microbial community and its role(s) in the soil significantly. One theory is that biochar ameliorates the presence of specific compounds, such as VOCs that can inhibit/enhance microbial processes such as mineralization (Spokas et al., 2011; Wang et al., 2013). Microbial community shifts are more accurately assessed using molecular analysis of 16S-rRNA, as culture-based identification underestimates population diversity (Leff et al., 1995).
Complementary to microbial community analysis, community structure of soil fauna like nematodes can also be a viable bio-indicator of environmental health (Bongers et al., 1999). Nematodes vary in their responses to pollutants and disturbances in their environment as the analysis of these responses in community structure can be a powerful tool for in situ assessment of soil health, as lower maturity and diversity can be signs of environmentally unfavorable (Bongers et al., 1999). They are stable temporally and play significant roles in nutrient processing yet nematode response to biochar has been largely overlooked (Lehmann et al., 2011). Community indices, used to measure nematode status based on the varying sensitivities of different taxa (Neher et al., 2004), together with physiochemical and bacterial community changes can be a powerful analysis of soil quality changes in response to biochar. Nematode response to biochar amendment has been largely overlooked and under-reported in literature (Lehmann et al., 2011). Together, identifying the nematode and bacterial community changes as well as the physical changes that result from the addition of biochar to agricultural soils can be a powerful analysis of soil quality.
The purpose of this project was to evaluate biochar amendment as a sustainable method for sustainably improving soil heath and quality in the northeast. Soil was evaluated through identifying shifts in the physiochemical properties and biological communities caused by the addition of biochar to a fine sandy loam soil. Changes in bacterial families that are essential to natural nutrient cycling in the soil were characterized, nematode community indices which are great bio-indicators of soil health were calculated and lastly, changes to the physiochemical properties of soil due to the amended low-temperature biochar were analyzed.
The experiment will be conducted at the Crops and Animal Research and Education Farm of the University of Massachusetts in South Deerfield. The soil is a Winooski silt loam. Mean annual precipitation at this site is 1143 mm and the mean annual temperature is 7°C.
In July 2012, biochar was applied to the research plots in a randomized block design at the field site. The research plots are 3 m wide by 6 m long and were created as the groundwork for a long-term study on the effects of biochar on agricultural soils in the Northeast (ongoing). A low temperature (350°C), slow pyrolysis biochar (sourced off site) was applied to 5 replicates at the rates of (0, 2, 4, 6, and 8% w/w) and incorporated into the top 15 cm of the soil (see Tables 1 and 2).The sourced biochar was a by-product of lump hardwood charcoal production, allowing for a more sustainable and inexpensive source. Sweet corn (Spring Treat, Johnny’s Selected Seeds, Winslow, ME) was planted on the research plots. Physical properties and nutrient content of the plots have been continually monitored since biochar application. Sweet corn yield and quality have also been assessed each summer. Sweet corn has been used to best elucidate the effects of biochar on nitrogen retention and uptake, as sweet corn is a high nitrogen-demanding crop. Plants were 20 cm apart within rows and 76 cm between rows. No other crops (or cover crops) were planted on the biochar plots; weeds were removed and prevented with periodic mechanical weeding and herbicide application.
- Soil Property Analysis
Soil samples were taken during early spring, time of planting, in season and after harvest of sweet corn. Three soil sub-samples were taken from 0-20 and 20-40cm in each sub-plot, combined and dried overnight. From each master sample, 8g of soil was measured and shaken in 40mL of 1.0 mM CaCl2 for 15 minutes and then filtered. Filtrate was then analyzed for nitrate by colorimetric determination using flow injection analysis (QuickChem 8000, Lachat Method Number 13-107-06-2-D. Zellweger Analytical, Milwaukee, WI, USA). All extracted samples were stored at 4oC until processing. Soil samples were analyzed for other nutrient analysis as well using microwave plasma atomic emission spectrophotometry (MP-AES Agilent 4100 Agilent Technologies, Santa Clara, CA). Soil samples were extracted in Modified Morgans solution, as recommended in the Northeastern States Soil Testing handbook. Soils were analyzed for P, K, Ca, Mg, Mn, Cu, Zn, Fe and B using the MP-AES Agilent 4100 (Agilent Technologies, Santa Clara, CA). Sweet corn was harvested at maturity and weighed for fresh yield. Post-harvest, corn plant tissue was analyzed using the Corn Stalk Nitrate Test (CSNT) to assess in-season nitrogen sufficiency.
- Nematode Analysis
Soil samples were taken at 3 different times from the biochar field plots: early May, before herbicide application and soil preparation, mid-June at PSNT timing and late-August post crop harvest. Five sub-samples (0-20cm)were taken from each plot within the rows of corn and combined. Soil for nematode sampleswere stored at 4°C until processing. Three technical replicates for each plot were used. Nematodes were extracted from the soil using the modified Cobbs sifting and gravity method followed by centrifugation and sugar flotation (Neher et al., 1999; Neher et al., 2010). Nematode samples were added to a counting dish, identified and counted under an inverted compound microscope. Nematodes were identified to family level using published identification keys (Goodey, 1963; Mai and Lyon, 1975; Tarjan et al., 2014). Nematodes were assigned to their appropriate trophic groups and colonizer-persister values (Neher et al., 2004; Okada et al., 2005; Yeates et al., 1993). The maturity index (MI), Shannon Diversity index, and ratio of bacteriovores to fungivores were calculated for each technical replicate for each plot (Ferris et al., 2001; Neher et al., 2004).
- Bacteria DNA Analysis
Five soil sub-samples (0-20cm)were taken from each field plot and combined for bacterial DNA sequencing. Soil sampleswere stored at -20 oC until extraction. For DNA extraction, MoBio’s PowerSoil DNA Isolation kit was used accorind to the manufactuer’s protocol. Samples will be analyzed using 16S ribosomal RNA gene. Samples were sent to the SeqMatic Laboratory, LLC. in Fremont, CA, and sequenced (150bp paired-end) using the Illumina MiSeq (Illumina, Inc. San Diego, CA). An RNA-based phylogeny of bacteria was constructed for each biochar treatment.
Biota populations and soil quality properties were analyzed statistically using Univariate Analysis of Variance (ANOVA) as appropriate followed by Tukey’s Test.
It was hypothesized that the soil health and quality of these field soils would be impacted by the addition of harwood biochar. Physical qualities were affected; soil density was lowered with the addition of biochar, and discreet increases in soil moisture content were observed (although not statistically significant). Chemical properties such as pH did significantly increase improving the growing condition of the soil by raising the pH into an optimal range for not only sweet corn but also many other agricultural crops as shown in Figure 1. The overall soil CEC improved slightly with increased biochar application rates, however the percent base saturation was improved drastically due to the retention of important plant nutrients such as calcium, magnesium and potassium. Soil phosphate availability was increased likely due to the release of phosphate salts from the biochar itself and greater retention of phosphate due to cation bridging. Nutrient availablility in the biochar amended soils is presented in Table 3. This area of focus is still not fully understood and requires greater research into the interaction of biochar surface functional groups and phosphate retention. Soil nitrate availability was not significantly impacted, other than in an increase in immobilization due to the increase in soil carbon content which resulted in significantly lower available nitrate at PSNT in higher biochar treatment levels.In the 2012 growing season, the addition of biochar to the prime agricultural lands used in this study showed minor yield improvement at an application rate of 2% (w/w) but decline with further increase of application rate to 4% or higher. The biochar treatment level of 2% corresponds to a rate of 40.5 t ha-1of biochar.
Management practices have a significant effect on the nematode population in agricultural soils. The addition of biochar to soils that are annually prepared by disk-harrow and planted under sweet corn has allowed for greater succession into a more temporally stable assemblage as indicated by the larger maturity index, and lower population od colonizer nematodes. However, an application rate of 8% biochar by weight (160 t ha-1) is not recommended for most agricultural soils. A smaller application rate of 2% is recommended, but may not impact the nematode community significantly at that low rate. Further investigation of nematode populations at lower biochar application rates is necessary to investigate this further.
Overall, the changes in the microbial communities with the addition of biochar were modest, potentially indicating an overall temporal-stability of diverse microbial communities in soil after biochar amendment. While individual taxa were significantly affected, there was no overall significant difference in total abundance, observed OTUs or alpha diversity indices. It is suggested, however, that a 4% (w/w) biochar amendment may have limited benefits, as alpha diversity, whole tree phylogenetic diversity and observed OTUs all declined when compared to a 2% (w/w) biochar amendment. An application rate of 2% (81 t ha-1) biochar to the temperate agricultural soils studied here had a priming effect on species diversity as compared to untreated soil. Coupled with the small agronomic benefit reported earlier at this treatment level, this study recommends an application rate of no more than 2% using the biochar and soil presented here.
Soil health degragation and the loss of agricultural productivity is a signfiicant challenge that farmers face in today’s world of intensified agricutlure. Constant soil cultivation and inorganic inputs are significant causes of soil health decline accross the globe. The potential for reduction in the widespread overuse of chemical fertilizers and other soil inputs can mean increases in the soil’s overall health, productivity and the economic sustainability of small farms. Biochar has the potential to aid in the retention of soil nutrients, increase the soil pH and lessen the need for damaging soil cultivation. The results fromt his current work showcase the soil health supporting properties of biochar when used in agricultural settings and have recived great interest from local farmers wishing to learn more about biochar use, as was evident by the questions raised and
Education & Outreach Activities and Participation Summary
As mentioned, results were being shared with other researchres and growers at the UMASS field day in July 2015. This was an interactive farm tour of the UMass Research Farm and included short oral presentations of the research and currnet findings of each project. Attached is a schedule of presentations. Results will also be presented at the Northeastern Plant, Pest, and Soils Conference in January, 2016.
Manuscripts are currently in preparation for submission to Geoderma and Soil Biology and Biochemistry for publication. The first on the soil physiochemical response of soil to the addition of hardwood biochar and the second paper in preparation focuses on the soil nematode and bacterial community changes as a result of biochar soil amendment.
The results of this work show that charcoal production can generate an otherwise waste product that is suitable for use as a biochar amendment. This may allow a shift in the economics of biochar production which is currently expensive and often completed at a very small scale. Beyond the cost savings in using a by-product as a legitimate biochar source, the potential savings for farmers who amend their soils with biochar is substantial. According to the results in this study, biochar can replace other pH amending soil condiditoners such as lime. While lime aids in raising soil pH temporarily requiring yearly or biannual applciaitons, biochar has a long lasting effect on the pH and can limit or altogether replace lime with a one-time application.
Biochar has also shown to increase the cation exchange capacity, and retention of cationic nutrients such as Mg, Ca, and K. This also will lessen the qualitity of applied nutrients required to maintain healthy concentrations of these nutrients in the soil.
Areas needing additional study
In order to better understand the change in the soil biota, a study on the soil myccorhizae is neccesary. The soil ecosystem is a complex network of relationshis and fungi are integral to this ecosystem.
In addition, repeated nematode studies are neccesary to beter identify changes in hte community structure.