1a. Objectives (from AD-416):
1. Develop specifically designed biochar or biochar mixtures that amend sandy SE coastal soils to increase aggregation, improve nutrient retention, sequester organic carbon, improve microbial characteristics, and decrease overall soil strength. 1a. Evaluate designer biochars and biochar blends impact on soil quality in laboratory incubations. 2. Determine relationships between cover crop selection, crop residue addition/removal, C loss pathways, and C sequestration to develop management practices that increase profile soil organic C (SOC) contents and maintain/improve soil microbial populations related to plant productivity. 2a. Determine the effects of sandy coastal soils and their management such as harvest frequency and N fertilizer rates on the following: a) switchgrass yields, b) improvements of in-profile SOC, c) C sequestration, d) switchgrass thermal bioenergy value, and e) nutrient removal with harvested biomass. 2b. Determine amount of residue that can be removed from a Coastal Plain soil while still maintaining crop productivity. 2c. Assess management practices that increase SOC contents in long-term tillage experiments.
1b. Approach (from AD-416):
The current method to improve degraded soils would be incorporation of crop residues which do not persist. To improve soils and their productive potential, there is a need to develop better management systems and more recalcitrant forms of soil organic C (SOC), such as biochar (a charcoal-like byproduct made during pyrolysis of organic feedstocks). First, biochars that have been designed (produced under specific conditions) and characterized will be catalogued and matched to the needs of these soils – to improve fertility, increase water holding capacities, and reduce root penetration resistance. Designed biochars and/or biochar blends will be lab tested in soils for effectiveness as recalcitrant SOC amendments. Second, impacts of alternative management and crops on SOC levels will be studied in field experiments with residue addition/removal at the surface and residue addition at root depths. In one case, cover crops will replace removed residues. Technologies resulting from these lines of research will improve soil physical, chemical, and microbial properties for enhanced soil quality, water retention, and crop/bioenergy productivity. These improvements help meet administration goals of enhanced food security, sequestered C, and reduced greenhouse gas (GHG) emissions. The immediate beneficiaries are Coastal Plain agribusinesses and farmers. The ultimate beneficiaries will be individuals and families who will be provided with sufficient food and clean water. More effective soil and crop management will enable agriculture and other sectors of society to share water/soil resources, maintain environmental quality, and improve food production.
3. Progress Report:
This report documents progress for the parent Project 6657-12130-002-00D, which started in May 2011 and continues research from Project Number 6657-12000-005-00D. Development of designer biochar tailored to improve specific soil properties: Biochar can be designed for specific soil improvements by changing feedstock blending ratios, pyrolysis temperatures, and by pelletization. In response to Objective 1, designer biochars incubated in soil were effective at improving soil quality. These results corroborate that biochars can be tailored to modifying specific soil properties. Response of soil microbial communities to biochar: Under Objective 1, biochar’s impact on soil microbial genetics was investigated by incubating soil with switchgrass biochar. The genes associated with microbial nitrogen cycling were extracted and quantified. These genes showed a stimulation in response to biochar implying that switchgrass biochar was not detrimental to soil microbial communities. Improvement in soil profile soil organic carbon contents using switchgrass: In response to Objective 2, a switchgrass field study revealed that profile (0 to 90-centimeter deep) soil organic carbon contents increased due to the crop’s deep root system. Annual soil coring revealed that soil organic carbon contents increased within the first year and were maintained throughout the study. Under variable climatic conditions, switchgrass was capable of improving soil carbon sequestration levels while also providing sufficient crop biomass for bioenergy production. Sustainable corn residue removal in sandy agricultural soils: Bioenergy production in the Coastal Plain region requires crop residues, but some residue must be returned to soil for nutrient replenishment. In response to Objective 2, crop yields, compositional analyses, and soil fertility levels are measured from plots under different rates of residue removal. Crop yields in three of the project’s four years were variable, but plant compositional and thermal energy values have remained near steady. Harvesting crop biomass can remove plant nutrients concomitantly lowering soil nutrient levels. Long-term increases in soil organic carbon with conservation tillage: In response to Objective 2, the amount of carbon sequester was examined in conservation tillage systems. In these side-by-side conservation and conventional tillage plots, conservation tillage has shown a surface (0 to 4-centimeter depth) carbon-enriched layer formed over 25 yrs; conservation tillage promotes slow carbon accumulation (< 0.1% per yr). This long-term study is important for scientists because it demonstrates rates of carbon sequestered under different tillage practices.
1. Rebuilding soil organic carbon levels in southeastern Coastal Plain soils. Agricultural production in the Coastal Plain region of the USA is hampered by highly weathered sandy soils that have inherently low soil organic carbon contents and a meager ability to retain water and nutrients. To increase crop productivity in these soils, strategies using crop management or adding amendments are needed that can successfully rebuild carbon, while also increasing nutrient and water retention. Conservation tillage under typical row crop production was found to be a slow promoter of carbon accumulation and carbon storage under switchgrass can be transitory. A more rapid and longer lasting improvement in soil quality was found using biochar, which mixed into soil at 1 to 2% by weight vastly improved the soil organic carbon content and increased nutrient and water retention. This resulted because of the recalcitrant structures of the carbon within biochar. The degree of soil quality improvement using biochars was dependent on feedstock selection and pyrolysis conditions. In total, the scientists at ARS Florence have shown that biochars can improve the soil’s ability to retain more carbon, pesticides, nutrients and water for enhanced crop production without harming soil microbial populations.
Raczkowski, C.W., Mueller, J.P., Busscher, W.J., Bell, M.C., Mcgraw, M.L. 2012. Soil physical properties of agricultural systems in a large-scale study. Soil & Tillage Research. 119:50-59.