Soil-test biological activity in corn production systems: II. Greenhouse growth bioassay

Authors: Franzluebbers, Alan; PERSHING, MARY - North Carolina State University

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2018
Publication Date: 5/10/2018
Citation: Franzluebbers, A.J., Pershing, M.R. 2018. Soil-test biological activity in corn production systems: II. Greenhouse growth bioassay. Soil Science Society of America Journal. 82:696-707.

Interpretive Summary: Soil testing for nitrogen availability in cropping systems requires a rapid and reliable indicator to assess nitrogen availability. Scientists from USDA-ARS in Raleigh NC and North Carolina State University evaluated the plant growth responses of a test crop planted in unamended soils collected from 47 fields throughout North Carolina and Virginia. Plant dry matter and nitrogen uptake of the test crop during 6-8 weeks of growth in the greenhouse was highly related to both organic and inorganic nitrogen fractions. However, a simple, rapid, and reliable indicator based on simple microbial activity (the flush of CO2) was equally associated with plant growth responses. Low cost and short time required for this simple indicator makes it suitable for soil testing, because it was robust in predicting plant growth. The strong association of the flush of CO2 with plant N uptake under semi-controlled greenhouse conditions corroborated use of the flush of CO2 as a rapid and reliable indicator of soil N availability. These results will be valuable for farmers wanting to make efficient applications of nitrogen to enhance profit and steward natural resources.

Technical Abstract: Soil N mineralization is variably affected by management and edaphic conditions. A routine soil test is needed to make better predictions for N fertilizer recommendations to cereal grains on different soil types and landscape settings. We collected soils from 47 corn production fields in North Carolina and Virginia at depths of 0-10, 10-20, and 20-30 cm and evaluated soil C and N characteristics in association with sorghum-sudangrass dry matter production and N uptake during 6-8 weeks of growth in the greenhouse. Plant dry matter and N uptake were strongly associated, as expected. Plant available N (summation of net N mineralization during 24 d of aerobic incubation and residual inorganic N) had the strongest association with plant dry matter production (r2 = 0.74). However, the flush of CO2 during 3 d following rewetting of dried soil was the single most effective variable in predicting N uptake (r2 = 0.77). Multiple regression models often chose the flush of CO2 as the dominant factor with 3-5 additional variables of significance, yielding strength of association of 0.88-0.90. Multiple regression models suggested that combination of the flush of CO2, residual inorganic N, and total soil N concentration provided the strongest predictive capabilities of N availability balanced with limited soil-testing resources (time and labor). The strong association of the flush of CO2 with plant N uptake under semi-controlled greenhouse conditions corroborated use of the flush of CO2 as a rapid and reliable indicator of soil N availability.