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 6657-12130-00D, which started in May 2011 and continues research from Project Number 6657-12000-005-00D. Guidelines for designer biochar tailored to improve specific soil properties: Designer biochars were produced and their impact determined on improving carbon sequestration, fertility, and water holding capacity of sandy soils. From these results, guidelines for their creation and specific uses were developed. In response to objective 1, designer biochars and blends with other feedstocks were successful at improving targeted soil limitations. Responses of biochars to microbial communities and nutrient processing: Under objective 1, the impact of a biochar on the involvement of soil microbial communities and their ability to produce genes necessary to fix or convert N into plant nutrient forms were determined. It was found that biochar stimulated the abundance of genes critical for nitrogen cycling. Moreover, it demonstrated that this biochar was not detrimental to soil microbial communities. Improvement in soil profile organic carbon contents using switchgrass: In response to Objective 2, a multi-year switchgrass field study revealed that switchgrass significantly improved soil organic carbon contents in profiles down to three feet deep. Annual soil coring in the field over four years revealed that 1) soil organic carbon contents doubled in concentration within one year of production and 2) these concentrations were maintained throughout the four year study. Switchgrass production can improve soil carbon sequestration while also providing above ground biomass for bioenergy production. Sustainable corn stover removal in sandy agricultural soils: In bioenergy production systems in the Coastal Plain, corn residue is removed for processing, but some residue must be returned to maintain soil health. In response to Objective 2, crop yields, soil fertility, and microbiological properties were measured in plots under different rates of residue removal. After 4 years of residue removal, grain yields were not influenced, the abundances of microbial communities were shifted to favor fungi, and there were topsoil potassium and phosphorus concentrations declines. Corn residue harvesting can occur on sandy soils, but eventually soil nutrients removed with corn residue will need replenishment. Long-term impacts of tillage and row crop management on soil organic carbon levels: After decades of conventional tillage using typical row crops in sandy coastal plain soils, their organic carbon contents have declined to very low levels. In response to objective 2, a side-by-side comparison study after 34 years showed continual increase in soil organic carbon levels under conservation tillage; conservation tillage promotes slow carbon accumulation (< 0.1% over year at 0-4 cm depth). Maintaining these long-term tillage plots is of immense scientific value for climate modelers because it provides field data on rates of carbon lost and accumulated and associate shifts in soil health.
1. Sandy soils of the SE USA coastal plain region are naturally poor in nutrients, contain low organic carbon contents, and have meager abilities to retain water and nutrients that affects long-term productivity of these soils. In spite of these soil conditions, typical row crops as well as biofuel crops can be successfully grown with appropriate management practices that enhance soil organic carbon and plant nutrient contents. Scientists with the USDA-ARS examined strategies to improve these soil limitations by using tillage, crop management, and biochar as a soil amendment. Conservation tillage, switchgrass production, and biochar application were found to rebuild soil organic carbon contents as well as improve plant available nutrients. Biochars produced from different feedstocks and processing conditions were found to improve specific soil characteristics such as water infiltration and holding capacity. Agricultural producers, biochar users and other stakeholders can use these three different management strategies to improve the sandy soils organic carbon contents, fertility and water holding capacity.
2. Biochar is a solid material that is a byproduct from the biofuel processing industry. Because it contains both organic carbon compounds and inorganic elements it is viewed as an excellent soil amendment. The inorganic portion from biochar serves as a good source of plant nutrients while the organic portion can improve soil organic carbon levels, and retention of nutrients. However, biochars interaction with soil microbial communities and nutrient turnover processes in sandy soils is unknown. Scientists with the USDA-ARS evaluated the impact of several different biochars on the ability of soil microbial communities to produce enzymes involved with nitrogen cycling. During nitrogen cycling in soils, the enzymes convert unavailable nitrogen forms to plant available nitrogen forms. Results from this research show that biochars have no negative impact on nitrogen enzyme production and do not interfere with microbial nitrogen conversions processes that provide available nitrogen for crops. Agricultural operators as well as other stakeholders can benefit from applying biochars to sandy soils since it did not interfere with nitrogen conversion into plant available forms.
3. Plant productivity of pastures used for grazing animals in Florida is affected by frequent flooding from tropical storms. Severe reduction in plant growth due to soil flooding can place stress on both forage production and cattle performance potentially reducing farm income. In response to the issue of flooding and reduced plant growth, scientists from the USDA-ARS examined the effects of flood duration and fertilizer management on the growth response of three typical pasture forage species. The forage species were subject to different periods of flooding with variable levels of fertilizer added in between flooding periods. Results verified that forage growth varied with flood duration, however, a new management option was found involving stimulating forage growth using nitrogen fertilizers. Stakeholders in the animal production sector who depend on forage grazing can benefit using these new pasture management options in storm prone areas of Florida and other Gulf coast states.
Ducey, T.F., Ippolito, J.A., Cantrell, K.B., Novak, J.M., Lentz, R.D. 2013. Addition of activated switchgrass biochar to an aridic subsoil increases microbial nitrogen cycling gene abundances. Applied Soil Ecology. 65:65-72.