Soil Science Exit Seminar
Mary Pershing, M.S. Student, Soil Science, NCSU, will present an exit seminar titled:
“Evaluating the Flush of CO2 as a Short-Term Biological Indicator of Soil Nitrogen Availability” (under the direction of Dr. Alan Franzluebbers)
on 30 September 2016 at 9:00 am in the McKimmon Room (2223 WMS).
All are welcome to attend.
Determining the appropriate nitrogen (N) rate for field crops is critical to farm economics and environmental protection. In North Carolina, N fertilizer recommendations are not modified by residual inorganic N or biologically active N, but only by realistic yield expectation set for each soil type and crop. However, due to increasingly popular conservation management practices such as cover cropping and no-till farming, residual N can remain in the soil in a biologically active form for potential plant uptake, resulting in greater supply of N than expected. Measuring biologically active carbon (C) is strongly related to net N mineralization, and may be less complicated, expensive, and time consuming than measuring biologically active N, due to the rapidly changing nature of soil N. Soil samples (n=759) from research stations and private farms representing three physiographic regions of North Carolina (coastal plain, piedmont, and mountains), as well as from cooperating locations in Virginia, Pennsylvania, Oklahoma, Nebraska, and Georgia were analyzed for various soil chemical and biological properties in the laboratory and utilized in four separate greenhouse growth trials. Unfertilized Sorghum bicolorwas grown for eight weeks in each soil sample to test for N availability. Dry matter accumulation and N concentration of plants were measured, which allowed for determination of above ground plant N uptake. The flush of CO2 following rewetting of dried soil was a key indicator of interest, as was net N mineralization during 24 days, soil microbial biomass C, particulate organic C and N, and total organic C and N. In Greenhouse Trial 1, the flush of CO2 was the second best indicator of greenhouse growth (R2=0.78) behind net N mineralization (R2= 0.81). In Greenhouse Trial 2, total soil N was the best indicator of greenhouse growth (R2 = 0.82). In Greenhouse Trial 3, the flush of CO2was the best indicator of greenhouse growth (R2 = 0.96). In Greenhouse Trial 4, the flush of CO2 was the second best indicator of plant N uptake (R2=0.83) behind net N mineralization (R2= 0.88). Among all samples, the flush of CO2 explained 69% of the variation in N uptake. The slope to predict greenhouse growth in soils from Oklahoma, Georgia, and Pennsylvania, was significantly different from Virginia and North Carolina. The interaction effect of state on the flush of CO2 improved prediction of dry matter production from 50 to 71% and of plant N uptake from 68 to 89%. Samples originating from NC and VA (n=516) were predicted by the flush of CO2 with an R2=0.81 for plant N uptake and R2=0.66 for dry matter production. The biologically active fraction of organic matter was the most dominant and consistent way to determine plant N uptake in this study (i.e. through net N mineralization and potential C mineralization). Sometimes soil nutrient concentrations and initial inorganic N were additionally helpful. In conclusion, the flush of CO2 has the potential to be a simple, rapid, and reliable predictor of potentially available N in the mid-Atlantic United States.