Location: Southeast Watershed ResearchTitle: Soil nitrogen dynamics and leaching under conservation tillage in the Atlantic Coastal Plain, Georgia, USA
|Strickland, Timothy - Tim|
|Hubbard, Robert - Retired ARS Employee|
|Bosch, David - Dave|
Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2016
Publication Date: 9/6/2017
Citation: Pisani, O., Strickland, T.C., Hubbard, R., Bosch, D.D., Coffin, A.W., Endale, D.M., Potter, T.L. 2017. Soil nitrogen dynamics and leaching under conservation tillage in the Atlantic Coastal Plain, Georgia, USA. Journal of Soil and Water Conservation. 72(5):519-529. https://doi.org/10.2489/jswc.72.5.519.
Interpretive Summary: Strip tillage (ST) and the maintenance of plant residues on cropped fields are conservation practices that can increase subsurface nutrient loadings, soil carbon (C) and nitrogen (N) accretion, and reduce sediment runoff in the southeastern Coastal Plain region of Georgia. Here, we evaluated tillage impacts on soil N speciation and leaching, and examined possible associations to N availability and to soil microbial biomass. Tillage treatments were ST and conventional tillage (CT). Sets of PVC cylinders were installed in the soil over a five-year period in a rotational cotton and peanut production system with winter cover crops. Upon retrieval, the soils in the cylinders were analyzed for inorganic N, total N, total C and microbial biomass. Leached NO3-N was captured on anion exchange resin placed in bags at the bottom of each cylinder. Both tillage treatments resulted in an increase in the soil C content over the five-year study period, indicating the importance of winter crop covers to soil quality. The total N content also increased, but to a greater extent with ST compared to CT practices, indicating that ST practices can increase soil quality in sandy soils. Temporal patterns in NO3-N leaching were not different between CT and ST treatments and a high amount of NO3-N leaching was observed after the application of poultry litter. Our results suggest that leaching from the top 15 cm of soil may be an important pathway of N loss from the rooting zone of sandy soils of the southeastern Coastal Plain. Regardless of tillage, the soil microbial biomass represented a small percentage of the total N and the five-year average was higher in ST compared to CT. Minimizing NO3-N in the soil from reaching ground and surface waters while increasing crop productivity represents a major challenge. The use of ST in conjunction with winter cover crops may improve plant N availability in the sandy landscapes of the southeastern Coastal Plain region.
Technical Abstract: Conservation tillage (CsT) involves management that reduces soil erosion by maintaining crop residue cover on farm fields. Typically, both infiltration and soil organic matter increase over time with CsT practices. We compared the impact of a commonly used CsT practice, strip tillage (ST), to conventional tillage (CT) management on soil nitrogen (N) dynamics and leaching, and examined associations to soil N availability and microbial biomass. A winter cover crop was used in both tillage treatments. The study was conducted over a five-year period during rotational cotton and peanut production in the Atlantic Coastal Plain region in Georgia, USA. Fertilizer and poultry litter were applied ahead of the cotton crops. Sets of PVC cylinders were filled with soil from each of six plots, 3 in ST and 3 in CT, and maintained in situ in their respective plots for sixteen intervals of about 90 days. After retrieval, the soil in each cylinder was analyzed for inorganic N (NH4+ and NO3-), total N, total carbon and microbial biomass. Leached NO3--N was captured on anion exchange resin-filled bags attached to the bottom of each cylinder. Throughout the study period, the ST and CT soil carbon content increased by 22 and 23%, respectively. Total soil N content increased 27% with ST compared to 22% with CT. Temporal patterns in NO3--N leaching were not different between CT and ST treatments and a high amount of NO3--N leaching was observed after the application of poultry litter. The cumulative amount of NO3--N leached from soils throughout the five-year study was 141 and 122 kg N ha-1 with CT and ST practices, respectively. Results suggest that leaching from the top 15 cm of soil may be an important pathway of N loss from both CT and ST cropping systems in the region. Regardless of tillage, soil microbial biomass N was equal to or higher than the total inorganic N, but still represented a small percentage (up to 9%) of the total soil N. Overall, microbial biomass N was higher in ST compared to CT. Minimizing NO3--N in the soil from reaching ground and surface waters while increasing crop productivity represents a major challenge. The use of ST in conjunction with winter cover crops may improve plant N availability by more than 27 kg ha-1 yr-1 in the sandy landscapes of the southeastern Coastal Plain region through microbial cycling of organic N while reducing subsurface NO3--N losses.