Soil‐Test Biological Activity with the Flush of CO₂: I. C and N Characteristics of Soils in Corn Production

Abstract

Nitrogen limits crop production when insufficient and harms the environment when excessive. Tailoring N inputs to cropping systems remains a high priority to achieve production and environmental goals. We collected soils from 47 corn (Zea mays L.) production fields in North Carolina and Virginia at depths of 0 to 10, 10 to 20, and 20 to 30 cm and evaluated soil C and N characteristics in association with soil N mineralization. Soil organic C at a depth of 0 to 10 cm varied among sites from ~10 to 80 g kg -1 , and generally declined with depth because of many sites with no-tillage management. N itrogen (N) is considered the most limiting nutrient in plant production. In many cases, demand for N by highly productive crops far exceeds the N that can be supplied by soil. Sources of N from soil are residual inorganic N from previous cropping or organic forms of N in soil organic matter and plant and animal residues, which must be mineralized in synchrony with decomposition processes. Insufficient N leads to low biomass production as a result of limited protein synthesis and low photosynthetic activity, all of which causes cascading negative effects on water-use efficiency, biological activity, ecosystem functioning, economic return from farm capital investment, and social welfare of farming communities (Smil, 2002;Tilman et al., 2011). In contrast, excessive N leads to susceptibility of crops to invasion by pests, leakage of N from the soil and plant systems to the environment causing air and water pollution, and loss of investment from costly inorganic N inputs (Vitousek et al., 1997;Hatfield and Follett, 2008).Nitrogen availability in soils has been investigated for decades (Waksman and Starkey, 1924;Fribourg and Bartholomew, 1956;Stanford, 1968;Jenkinson and Powlson, 1976;Jansson and Persson, 1982;Campbell et al., 1991), yet reliable predictions of N fertilizer application rate to optimize cereal grain yields have been elusive (Balkcom et al., 2003). Early investigations to optimize inorganic N inputs focused on defining potentially mineralizable N from a nonlinear function derived from inorganic N released through successive leaching and incubation (Stanford and Smith, 1972). This methodology has been considered the best estimate of soil N mineralization potential, despite (i) the long time period for evaluation (32 wk Core Ideas• Soil nitrogen mineralization can be predicted with the flush of CO 2 .• Soil texture does not alter the relationship between the flush of CO 2 and N mineralization.• Large quantity of mineralizable N in surface soils is possible with conservation management.• The flush of CO 2 is an appropriate indicator for soil-test biological activity.• The flush of CO 2 is a rapid and reliable indicator of soil N availability.

Comparing Biological and Conventional Chemical Soil Tests in Long‐Term Tillage, Rotation, N Rate Field Study

“…Culman et al (2013) reported a lack of management (tillage) system effect on Solvita CO 2 and suggested that treatment differences could have been masked by spatial heterogeneity in the field. The Solvita test has been used to predict crop N uptake and soil N availability (Franzluebbers, 2018; Franzluebbers et al, 2018), but there are concerns regarding cross‐laboratory reproducibility of results (Sullivan and Granatstein, 2015; Wade et al, 2018). Standardized protocols would improve the robustness of CO 2 flush tests, as demonstrated by variations in mineralizable C resulting from procedural differences including water delivery method (Franzluebbers and Haney, 2018; Wade et al, 2018).…”

“…In North Carolina, Roper et al (2017) reported that biological tests did not adequately differentiate between long‐term management systems, though tillage did affect WEON and total Haney N on two out of three soils, and soil health test results were not correlated with crop yields. The relationship of CO 2 flush with crop N uptake has already been established (Haney et al, 2001); recent research indicates that CO 2 flush is also strongly associated with N availability in the field (Franzluebbers, 2016, Franzluebbers et al, 2018). Additional work is still necessary for Solvita and other Haney indicators to predict biologically available N across a broader range of soils and management systems.…”

Soil‐Test Biological Activity with the Flush of CO2: II. Greenhouse Growth Bioassay from Soils in Corn Production

“…Soil physical, chemical, and biological properties were described more fully in Franzluebbers et al (2018). Briefly, laboratory methods included:…”

Combination of biological and chemical soil tests best predict maize nitrogen response

“…The five routine soil measurements included: pH in water and 0.01 CaCl 2 (soil/solution ratio of 1:2.5, w/w), Mehlich III extractable phosphorus (soil test P or STP), Mehlich III extractable K (STK), and bulk density. We used a 300‐d aerobic incubation as the benchmark for estimated net N mineralization, as long‐term incubations have been found to be the most accurate in predicting N‐supplying power of soils (Campbell, Ellert, & Jame, 1993; Franzluebbers, Pershing, Crozier, Osmond, & Schroeder‐Moreno, 2018; Stanford, Legg, & Smith, 1973). We hypothesized that this test would best predict N response type, but realize this length of an incubation is not feasible for a soil N test, so we wanted to look at which rapid N tests of plant‐available N (Table 1) would correlate with the 300‐d incubation test.…”