Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2014
Publication Date: 11/24/2014
Citation: Sigua, G.C., Hunt, P.G., Stone, K.C., Cantrell, K.B., Novak, J.M. 2014. Contrasting effects of sorghum biochars and sorghum residues on soil chemical changes of coastal plains ultisols with winter wheat. Soil Science. 179(8):382-392.
Interpretive Summary: The fertility of highly weathered Ultisols in the southeastern Coastal Plain of United States is low. In this region, intensive crop production depletes soil nutrients and reduces soil organic carbon. In the soil, the use of more stable compounds such as carbonized materials from incomplete combustion of organic materials could provide a long-term stability for maintaining high levels of organic matter and available nutrients. Incorporation of pyrolyzed organic residues could be an important factor in sustaining soil fertility and improving soil physical conditions. A greenhouse study was conducted to evaluate the effects of uncharred and pyrolysed sorghum residues, with or without supplemental inorganic phosphorus (P) fertilizer on 1) aboveground and belowground biomass of winter wheat; 2) nutrient composition and uptake of winter wheat; and 3) changes of soil chemical properties of two Ultisols. In highly weathered Coastal Plains Ultisols, addition of sorghum biochars has provided agronomic benefits and has no negative consequences in terms of wheat growth, uptake, or soil quality. Our results have shown that addition of sorghum biochars increased total biomass of winter wheat by about 31% over the control plants. The effect of sorghum allelopathy is somewhat noticeable in our study because of the decrease in the total biomass of winter wheat with sorghum residues of about 19% and 56% when compared with the control plants and winter wheat treated with sorghum biochars, respectively. Addition of supplemental inorganic P to both the pyrolyzed and uncharred sorghum residues did not increase the total biomass of winter wheat. The conversion of sorghum residue into sorghum biochar is potentially a win-win strategy for both environmental and crop productivity improvement. However, before rushing to any conclusion about the economic and ecological benefits of sorghum residue-to-sorghum biochar transformation, we may need to consider that we have insufficient evidences to show that pyrolyzed sorghum residues has a better performance than the original uncharred sorghum residues. The contrasting effects of uncharred and pyrolyzed sorghum residues as reported in our study could be important in terms of satisfying the long term environmental risk assessment and better understanding for the use of sorghum residues and/or sorghum biochars.
Technical Abstract: Although most soil properties were improved following applications of various crop residues, there is still a need to pursue additional research that will improve understanding on the impact of soil fertility enhancement because the effect could vary greatly between sorghum residues and sorghum biochars. We investigated the effects of sorghum (Sorghum bicolor, L) residues (SR) and sorghum biochars (SB) with or without supplemental inorganic phosphorus (P) on biomass and nutrient uptake of winter wheat (Triticum aestivum, L) and soil chemical changes of two Coastal Plains Ultisols (Norfolk and Dunbar soils) in two similar greenhouse experiments. The rates for SR and SB were 13,000 and 5,200 kilogram (kg) per hectare (ha), respectively. Inorganic P was added at the rate of 40 kg P/ha. Wheat biomass and nutrient uptake in both experiments varied significantly with sorghum treatments and differed widely between soil types. Most of the chemical properties of soils in both experiments were significantly affected by sorghum treatments and also varied significantly between soil types. In highly weathered Coastal Plains Ultisols, addition of SB has provided agronomic benefits and has no negative consequences (allelopathy) in terms of wheat growth, nutrient uptake, or soil quality. However, the effect of sorghum allelopathy is somewhat noticeable because of the decrease (19%) in the total biomass for winter wheat treated with SR. Biomass and uptake responses of winter wheat and changes in soil properties have demonstrated widely differing agronomic effects between SB and SR. Our results may seem to indicate that the conversion of sorghum residue into sorghum biochar is a win-win strategy for both environmental and crop productivity improvement.