Biochar affects essential elements of carrot taproots and lettuce leaves

Authors: OLSZYK, DAVID - Environmental Protection Agency (EPA); SHIROYAMA, TAMOTSU - Environmental Protection Agency (EPA); Novak, Jeffrey; CANTRELL, KERI - Former ARS Employee; Sigua, Gilbert; Watts, Donald - Don; JOHNSON, MARK - Environmental Protection Agency (EPA)

Submitted to: Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/19/2019
Publication Date: 1/21/2020
Citation: Olszyk, D., Shiroyama, T., Novak, J.M., Cantrell, K., Sigua, G.C., Watts, D.W., Johnson, M.G. 2020. Biochar affects essential elements of carrot taproots and lettuce leaves. Horticultural Science. 55(2):261-271. https://doi.org/10.21273/HORTSCI14421-19.
DOI: https://doi.org/10.21273/HORTSCI14421-19

Interpretive Summary: Access to healthy (nutritionally adequate and safe) food is essential for individual welfare and economic development. Global United Nations reports estimate that 821 million of the worlds people were undernourished. An important component of healthy food is the concentration of trace elements such as potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), zinc (Zn) and copper (Cu). Soil types supply elements which are essential to plant growth. Thus, maintaining soil fertility is key to the concentrations of elements present in plants especially vegetables used for human consumption. Biochar is used as a soil amendment to improve soil fertility especially delivering multiple elements to soils. Thus, biochar could be an important tool to increase the availability of soil elements necessary to improve plant mineral nutrition. Despite the commercial support for use of biochar as a soil amendment, there has been relatively little research on both the potential positive or negative effects on vegetable crops. We conducted a greenhouse study to determine the impact of biochar additions to soil on the elemental composition of carrots and lettuce. In this study, biochar increased K concentrations in both lettuce leaves and carrot taproots with addition of high-K concentration poultry litter biochar. Biochar had unintended consequences by causing decreases in essential elements in edible parts of plants. Decreases in Ca, Mg, Zn, Fe and Mn in lettuce leaves; and to a lesser extent, carrot taproots with some biochars, were observed in this study. These decreases occurred despite higher concentrations of these elements in the biochar, such as poultry litter, compared with the soil, and may be related to the ability of biochar to sequester metals. Our results indicate that a potential drawback of using biochar as a soil amendment is that some elemental concentrations in vegetable crops are reduced.

Technical Abstract: Essential element concentrations in crops can affect human health. While biochar has the potential as a soil amendment to improve crop yields, it may also affect the concentrations of elements such as potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn) and zinc (Zn) in edible portions of crops. We evaluated the effects of biochar on lettuce (Lactuca sativa L. cv. Black-Seeded Simpson) leaves and carrot [Daucus carota subsp. sativus (Hoffm.) Schübl. cv. Tendersweet] taproot elements to better characterize effects of biochar on important human nutrients in food crops. Plants were grown in a greenhouse using sandy loam (Coxville, Fine, kaolinitic, thermic Typic Paleaquults) and loamy sand (Norfolk, fine-loamy, kaolinitic, thermic Typic Kandiudults,) series soils, amended with biochar produced from four feedstocks: pine chips (PC), poultry litter (PL), swine solids (SS), switchgrass (SG); and two blends of PC plus PL (PC/PL, 50/50% and 80/20% weight/weight). Biochar was produced at 350, 500 and 700°Celcius from each feedstock. Lettuce leaf and carrot taproot total elemental concentrations were determined by inductively coupled plasma analysis. Biochar (especially manure-based) decreased nutrient concentrations in lettuce leaves, with Ca, Mg and Zn affected most. Carrot taproot nutrient concentrations also deceased, but to a lesser extent. Some biochars increased leaf or taproot elemental concentrations, especially K. This study indicated that biochar can both decrease and increase leaf and taproot nutrient concentrations important for human health. Thus, the biochar characteristics should be carefully considered when used as a soil amendment on vegetable crops.