Biochar has been reported to have the potential to be used as an amendment in plant nurseries.

FIGURE 25.4 Nutrient-positive, nutrient-neutral, and nutrient-negative agricultural and silvicultural systems.

For example, when 25% biochar was mixed with 75% peat, enhanced hydraulic conductivity and water retention were observed (Dumroese et al., 2011). Addi­tionally, this study showed that the expansion of pelletized biochar (biochar that has been compressed with a binding agent in order to increase particle size), when wetted nearly offset the shrinkage typi­cally exhibited by peat over time. A coconut fiber and tuff growing medium was shown to induce improved resistance of tomatoes to the necrotrophic
fungus Botrytis cinerea when mixed with biochar at rates as low as 0.5% w/w (Elad et al., 2011). In another study, coconut fiber and tuff growing medium was shown to increase leaf size, plant height, flower devel­opment, and crop yield in pepper plants across all application rates from 1% to 5% w/w (Graber et al., 2010). In addition to container growth media, research is currently being conducted into the effects of plant containers constructed from molded biochar (Pulver,

2013) .

CONCLUSIONS, KNOWLEDGE GAPS,
AND RESEARCH NEEDS

It is critical to understand that biochar is not a single material, but rather an entire class of materials (Spokas et al., 2012a) with a broad spectrum of chemical,
physical, and biological properties that are drawn from both the diversity of feedstocks, production methods, and postproduction intermediary uses. It is also equally important to recognize the environmentally beneficial functions that biochar can perform after production and before application to soil and that there may be

desirable uses for biochars that are not suited to soil amelioration (Figure 25.9). Long-term field trial data related to biochar functions and properties as they change over time are extremely limited (Verheijen et al., 2010). Glasshouse projects that may display poten­tial field scale benefits of biochar should be conducted, and continually monitored in order to measure, rather than project, what may be achievable for agriculture and the environment using biochar. It will be essential moving forward to be able to predict the sorption longevity and saturation point of biochars for pesticides and other pollutants. It is unknown if over time biochar in soil will lose or retain its ability to deactivate herbicides (Kookana et al., 2011). Similar temporal uncertainties exist in relation to most other biochar char­acteristics, aside from C stability. The understanding of both the short — and long-term effects of biochar on soil microbial communities remains limited (Sohi et al.,

2008) , yet is of critical importance due to the important role of microbes in many nutrient cycles and pollutant degradation pathways. Biochar uses that precede its incorporation into soil remain largely uninvestigated. Research related to the potential suitability of biochar for intermediate uses before application to soil, such as surface water filtration, enteric mitigation of methane production in ruminants, container media, and landfill cover is almost nonexistent. However, biochar itself has only recently expanded to become the focus of scientific research worldwide, so perhaps research into indirect biochar uses will progress accordingly.

Acknowledgments

The authors would like to thank Christian Pulver at Cornell University for his comments on the chapter.