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ARS Home » Pacific West Area » Pendleton, Oregon » Soil and Water Conservation Research » Research » Publications at this Location » Publication #286382

Title: Root to shoot ratios and belowground biomass distribution for Pacific Northwest dryland crops

Author
item Williams, John
item Reardon, Catherine - Kate
item Mccool, Donald - Retired ARS Employee
item Douglas, Clyde - Retired ARS Employee
item Albrecht, Stephan - Retired ARS Employee
item Rickman, Ron - Retired ARS Employee

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2012
Publication Date: 8/23/2013
Publication URL: http://handle.nal.usda.gov/10113/58481
Citation: Williams, J.D., Reardon, C.L., Mccool, D.K., Douglas, C.L., Albrecht, S.L., Rickman, R.2. 2013. Root to shoot ratios and belowground biomass distribution for Pacific Northwest dryland crops. Journal of Soil and Water Conservation. 68(5):349-360.

Interpretive Summary: Roots, cereal crowns, and stems growing beneath the soil surface provide important resistance to soil erosion. Incorporating how this material is distributed into soil erosion models will improve model performance and our ability to evaluate soil and water conservation efforts. We measured the belowground biomass of wheat, spring peas, and winter canola crops grown in the dryland cropping region of the Pacific Northwest and found 70% of the root mass in the top 4 inches of soil in wheat and canola crops and the top 6 inches of soil in pea crops. These findings are in agreement with Revised Universal Soil Loss Equation (RUSLE2) Science Documentation, which indicates that an average of 74% of root mass is in the top 6 inches of the profile. Root-to-shoot biomass ratios in mature wheat ranged from 0.13 to 0.17, substantially lower than the value of 0.25 used in the Water Erosion Prediction Project (WEPP) model. More accurately representing root development, particularly in winter crops, could improve WEPP performance in the Pacific Northwest.

Technical Abstract: Roots, cereal crowns, and stems growing beneath the soil surface provide important resistance to soil erosion. Understanding the amount and distribution of this material in the soil profile could provide insights into resistance to soil erosion by water and improve performance of soil erosion models such as RUSLE and WEPP. Erosion models use built-in or external crop growth models to populate crop yield and live aboveground and associated belowground biomass databases. We examined two data sets from the dryland small grain production region in the Pacific Northwest to determine root to shoot ratios, the vertical distribution of root and attached belowground biomass, and incorporated residue from previously grown crops. Data were collected in 1993, 1994, 1995, and 2000 from short-term no-till and conventional tillage experiments conducted near Pendleton, OR and Pullman, WA, and in 1999 and 2000 from long-term experiments representative of farming practices near Pendleton, OR. The crops sampled in the short-term data set included soft white winter and spring wheat (Triticum aestivum L.) (WW and SW, respectively), spring peas (Pisum sativum L.) (SP), and winter canola (Brassica napus L.) (WC). Crops sampled in the long-term study included WW, SW, and SP. Data were collected at harvest in both data sets, and during three phenologic stages in each of the crops in the short-term data set. We found greater than 70% of root mass is in the top 10 cm (3.9 in) of the soil profile with the exception of spring peas, which had 70% of root mass in the top 15 cm (5.9 in) of the soil profile. WC produced significantly more belowground biomass near the soil surface than WW, SW, or SP. Root-to-shoot biomass ratios in mature wheat ranged from 0.13 to 0.17, substantially lower than values used in WEPP (0.25). In the long-term experiments, soil of the conventionally tilled continuous winter wheat (CWW) plots contained significantly greater belowground biomass than soil of conventionally tilled winter wheat/fallow (CR) and no-till winter wheat/fallow (NT) treatments. There was no significant difference between CWW and conventionally tilled winter wheat/ spring pea (WP), however CWW returns more residue than WP, the year peas are grown. More accurately representing root development, particularly in winter crops, could improve WEPP performance in the Pacific Northwest.