An ancient soil amendment – biochar – could be a promising tool for future soil health enhancement and maintenance, according to a study by the Texas A&M Department of Horticultural Sciences.
Amit Dhingra, Ph.D., head of the department in the Texas A&M College of Agriculture and Life Sciences, Bryan-College Station, led the study “Metatranscriptomic analysis of tomato rhizospheres reveals insight into plant-microbiome molecular response to biochar-amended organic soil” published in Frontiers in Analytical Science. The research showed biochar improved the soil microbiome and plant root interactions with a spectrum of beneficial microorganisms found there.
“This is very relevant to horticulture production here in Texas because we have 1,300 soil types,” Dhingra said. “It is proof-of-principle that shows biochar could be a valuable amendment when it comes to enhancing and managing soil health.”
Biochar’s role in soil health enhancement
Variations of biochar have been used throughout history, Dhingra said. Ancient civilizations in Brazil used pyrolyzed organic biomass to enhance soil fertility in the Amazon.
Biochar used in this study looks like fine-grained charcoal. Its highly porous, carbon-rich characteristics facilitate enhanced water and nutrient exchange and may result in decreased soil acidification when amended to the soil. It can be made from any sort of biomass, from manure to crop residue like corn stalks. In this case, Dhingra’s team used biochar derived from wheat crop residue.
Research has shown that organic soil amendments improve microbiome health, and the addition of biochar is a promising strategy for enhancing soil fertility, beneficial microbe diversity and long-term sequestration of carbon, he said.
The team characterized the effects of biochar-derived crop residue on tomato growth, soil microbial diversity and rhizosphere-level gene expression responses in the organically grown fruit.
Dhingra’s research team was led by Washington State University postdoctoral scientist Seanna Hewitt, Ph.D., in collaboration with postdoctoral scientist Rishikesh Ghogare, Ph.D., at Texas A&M. The team also included graduate students from Texas A&M, Washington State University and an undergraduate student from the University of California, Riverside.
“Biochar is useful for reclamation and further evolution of a millennia-old strategy to improve soil fertility,” Dhingra said. “This study provides an effective methodology for further examination of the impact of biochar and any other soil amendments on soil and plant health, and potential uses across horticultural systems.”
Study shows enhanced beneficial microbial activity, numbers
Organic-certified wheat-based biochar amendments were applied and incorporated into sandy loam trial beds alongside control beds at a rate of 2 tons per acre. All trial beds were in certified organic soil.
Tomato transplants were placed in the biochar-amended and control beds and received organic 5-1-1 Alaska fish fertilizer once per week throughout the experiment. Rhizosphere samples were then taken at 25 days, or juvenile stage; 40 days, or vegetative growth stage; 55 days, or pre-flowering stage; and 70 days, with 75% of fruit at red ripe stage.
Dhingra said researchers concluded that the soil microbiome displayed heightened functional activity in several beneficial microbes while reducing the activity of pathogenic fungi throughout the study.
The conclusions were based on the responses of plant roots and the soil microbial community profiles. Active transcripts within the communities were quantified at four plant developmental stages between emergence and mature fruit being harvested.
Transcription in plants is the process of decoding plant gene’s DNA sequence resulting in the production of RNA, a molecule that represents the functional aspect of the DNA. The study revealed the microbiome can influence plant RNA and gene expression, Dhingra said, which makes biochar a potential enhancer to this symbiotic relationship when it comes to regulating critical plant development processes.
The study showed biochar treatments increased gene expression in tomatoes due to the presence and number of beneficial soil bacteria, or rhizobacteria, compared to control plots. Enrichment analyses revealed increased nitrogen cycling and breakdown of organic compounds in the soil microbiome throughout the experiment.
“There was evidence that the plant and microbiome were able to communicate better and modulate their function in the presence of biochar,” he said. “That modulation is important as the plant’s nutritional needs are known to change as the plant matures.”
Deeper look into biochar needed
Biochar protection of plant roots from pathogens, like fungal diseases, and enrichment of tomato root performance, such as metabolizing nitrogen, regulating other metabolic processes and production of organic compounds within the biochar-treated rhizosphere were all positive outcomes. Fruit yields and shoot fresh weights were not measurably improved by the biochar treatments, which was as expected in organic soils.
These early results provide a foundation for measuring biochar’s biological impacts in various crop and soil types under different management regimens. Further exploration could identify ways to optimize biochar’s application and potential role in production across the horticulture spectrum, Dhingra said. Experiments are underway to similarly test biochar in a pecan orchard and a vineyard.
“Not all biochar is created equally,” he said. “There are major structural and functional differences in biochar derived from different biomass sources, whether that is wheat cuttings, manure or hardwoods. Plants react differently to them, so we need to understand what works best for pecan growers or for wine grapes, in home gardens or organic to conventional commercial production settings.”
Dhingra said continued research is important because horticulture science continues to evolve beyond the aims of the Green Revolution, which primarily focused on yields. The goal now, he said, is to provide holistic approaches that bridge yield quantity and nutritional quality in ways that are economically and environmentally sustainable.
“The more we learn and understand about these natural relationships between soil and plants, the more it informs our development of sustainable strategies to enhance soil fertility and crop health across the spectrum of our production systems,” Dhingra said. “We need to produce 70% more food with 30% less land in the next two decades to meet the food demand, and we want to make sure that every inch of land remains highly productive.”
