Estimating Source Carbon from Crop Residues, Roots and Rhizodeposits Using the National Grain‐Yield Database

Abstract

Crop residue management received little attention until about 1970. Records of crop residue production are limited, but crop yield databases have been available since 1865. Carbon sequestration and other conservation benefits require a detailed knowledge of crop residue production and management. Our objectives are to: (i) review grain and biomass yield, harvest index (HI), and root C/shoot C ratios (k) of major grain crops in the USA; (ii) discuss historical agriculturalpractice impacts on soil organic C (SOC); and (iii) compare estimates of total (above-and belowground) source C production (ESC) relative to minimum source C inputs required to maintain SOC (MSC). Aboveground MSC input averaged 2.5 6 1.0 Mg C ha 21 yr 21 (n 5 13) based on moldboard plow sites and 1.8 6 0.44 Mg C ha 21 yr 21 (n 5 5) based on no-till and chisel plow sites. These MSC values included only aboveground source C, thus underestimate the total MSC. When ESC is estimated from k, including rhizodeposition (k rec ), the true magnitude of the C cycle is at least twice that when ESC is estimated using k excluding rhizodeposition (k his ). Neglecting rhizodeposition C underestimates the net production of C in cropland. Current yields and measured MSC predict continued SOC loss associated with soybean [Glycine max (L.) Merr.] and some wheat (Triticum aestivum L.) production management unless conservation tillage is used and ESC is increased. The adequacies of ESC to maintain SOC has direct implications for estimating the amount of crop residue that can be harvested and yet maintain SOC.

Engineering, nutrient removal, and feedstock conversion evaluations of four corn stover harvest scenarios

“…In comparison to estimates by Graham et al [6], our normal cut scenario collected only 0.07 Mg ha À1 less than their estimate, but the amount of residue left on the soil in our study ($24%) was less than their prediction ($32%). This may appear to be sufficient residue for surface cover, but the amount of C returned to the soil was only 25-30% of that suggested by Johnson et al [28] as being needed to maintain soil organic matter.…”

“…Tollenaar [27] reported that harvest index differed very little among several era hybrids when grown at their optimum plant population in Ontario. Harvest index and other ratios of grain and stover have been employed to estimate source carbon from corn residues, roots, and rhizodeposits as well as stover yield [28,29].…”

Corn Belt soil carbon and macronutrient budgets with projected sustainable stover harvest

“…In practice, how much crop residue can be sustainably removed at a field scale depends on local climate, soil type, and management practices (Johnson et al, 2006), particularly on the baseline SOC level (Senthilkumar et al, 2009;Tan and Liu, 2013). Long-term cultivation would reduce the SOC content of a soil with a high baseline SOC content because such a soil tends to need more residue retained in the field to sustain the SOC stock than the soil having a lower SOC content (Tan et al, 2012).…”

“…The MSR values are generally higher in the Corn Belt than other areas. Johnson et al (2006) documented a range from 5.25 to 12.50 Mg ha À1 of stover needed to maintain SOC content in the Corn Belt soils. Varvel and Wilhelm (2008) suggested that a stover yield of 6.0 Mg ha À1 is required to maintain SOC levels in the western Corn Belt.…”

“…Excessive residue removal will enhance soil erosion, degrade soil physical properties and reduce the soil organic carbon (SOC) pool (Hammerbeck et al, 2012;Khanal et al, 2014). To define how much residue is required to maintain soil fertility, Johnson et al (2006) proposed the minimum source carbon concept and used it to estimate the minimum amount of crop residue that needed to be retained to sustain soil carbon levels for continuous corn and corn-soybean systems in the U.S. Corn Belt. Wilhelm et al (2007) also defined the minimum amount of stover retention as a function of soil erodibility, tolerable soil loss, surface slope, tillage method, cropping system, and grain yield.…”