Submitted to: Agronomy Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/28/2005
Publication Date: 4/11/2006
Citation: Johnson, J.M., Allmaras, R.R., Reicosky, D.C. 2006. Estimating source carbon from crop residues, roots and rhizodeposits using the national grain-yield database. Agronomy Journal. 98:622-636. Interpretive Summary: Concern about climate change calls for more information on how carbon moves through plants and soil in farming systems. Soil organic matter is the net result of plant and animal material inputs and carbon losses due to respiration by soil organisms (including plant roots and microbes). Carbon stored in soil is sensitive to land management changes such as conversion of native lands to cropland, changes in crop rotation, and changes in tillage depth and frequency. The ability of a soil to store carbon also depends on climate and soil type. This paper reviews the amount of carbon produced and returned to the soil from major crops in the United States from historical, current and future perspectives. The review shows changes in biomass produced and left on the field has increased and that together with reducing tillage has resulted in agriculture building soil organic matter, thus storing carbon. Knowing how much biomass is available and the minimum amount of carbon needed to be put into the soil is a critical step in establishing guidelines for harvesting crop biomass. Crop biomass such as corn stalks is a potential domestic and renewable source of energy. The growing interest in using crop biomass as renewable energy demands that we have accurate estimates of the carbon inputs needed to maintain soil organic matter for long-term soil sustainability and to protect the soil from erosion. The review clearly identifies the need for more research especially in no tillage and conservation tillage systems. The developing biomass energy industry, policy makers and regulatory agencies, such as NRCS, will benefit from accurate knowledge of how management decisions affects stored carbon. This information allows agriculture to reduce negative impacts on global climate changes and leads to improved soil and environmental quality.
Technical Abstract: Concern about potential climate change has called for more knowledge delineating the total carbon (C) cycle with emphasis on agricultural systems. Our objectives are to: 1) discuss historical aspects of C management in agriculture; 2) review harvest index (HI) and root C-to-shoot C ratios (k) of some major crops; 3) estimate total source C production relative to source C inputs critical for soil organic C (SOC) maintenance. Source C estimates provide an easy, indirect method of predicting C. The United States national yield databank, empirically-derived HI and k were used to estimate the root plus shoot C for barley, corn, oat, sorghum, soybean, sunflower and wheat. In 1940, total root plus shoot source C ranged among crops from 1.4 to 2.7 Mg C ha-1 increasing to 1.5 to 6.8 Mg C ha-1 by 2000. The critical vegetative residue C for moldboard plowed management ranged from 1.0 Mg C ha-1 in the Pacific NW to 3.7 Mg C ha-1 in the Corn Belt. A corn grain yield of 10 Mg ha-1 with a HI of 0.53 produces 8.9 Mg ha-1 stover, assuming a critical vegetative source C of 2.3 Mg C ha-1 about 3.2 Mg biomass ha-1 could be harvested, but with a critical vegetative source C of 3.7 Mg C ha-1, loss of SOC would be expected. Source C from corn was estimated with k values of 0.6 and 1.2; such estimates of k values are needed for other crops to estimate total source C available.