Study assesses landscape effects on biomass crop yields

By Anna Austin
Posted March 30, 2010, at 3:27 p.m. CST

Understanding biomass productivity on specific landscape positions is essential to realizing the highest financial returns on the integration of herbaceous and woody biomass crops at the field scale while providing a reliable and consistent feedstock source that meets quality specifications for the bioenergy market, according to a recent University of Minnesota study.

Led by associate professor Gregg Johnson, the research team investigated the differences in woody and herbaceous crop productivity and biomass yield of crops planted on seven varying landscape positions at the University of Minnesota's Agricultural Ecology Research Farm, part of the Southern Research and Outreach Center in Waseca, Minn. Terrain features were analyzed using Geographic Information Systems technology.

Crops evaluated in the study were alfalfa, corn stover, corn, grain, willow (two clones), cottonwood, poplar and switchgrass. Landscape positions included summit (excellent water drainage but visible erosion), depositional (receives water from two hill slopes and is characterized by poor drainage and accumulated topsoil), flat (poorly drained but has retained topsoil), and four hill slopes with east, south, southwest and north aspects.

The researchers recognized that harvest intervals between woody and herbaceous crops are different-willow is typically harvested after three years of growth, whereas switchgrass is harvested annually-and adjusted sampling methods accordingly. Willow data represented growth in the second year post-coppice, whereas poplar and cottonwood data represented third-year growth; alfalfa, switchgrass, and corn data represented combined yields from 2006 and 2007.

The study also takes into account the fact that soil physical and chemical properties change depending on landscape position. Soil nitrogen, phosphorous, potassium, profile darkness index, specific catchment area and compound terrain index were denoted as a single value for each landscape position and tested for significance within each species across all seven landscape positions.

Key findings of the study included:

• Total switchgrass and biomass yields were lower at the depositional, south hill slope, southwest hill slope and north hill slope compared with other landscape positions.

• Cottonwood biomass yields were consistent across all positions, showing no differences in yield among sites.

• Poplar biomass yield was lower at the depositional position compared with all other positions.

• Cottonwood and poplar did not display significant correlations between biomass yields and soil/terrain attributes.

• High productivity of both willow clones at the depositional and flat positions relative to other landscape positions indicate that willow is a good cropping option in landscape positions with saturated, anaerobic soils.

• Total alfalfa yield was lower at the depositional and west hill slope landscape positions compared with all other positions. Alfalfa biomass at the west hill slope position, however, was higher than the depositional position but lower than the other positions.

• Total corn stover yield was significantly lower at the depositional and flat landscape positions compared with all other positions; yields were higher where soil moisture was less compared with landscape positions with saturated soils.

The researchers believe the study provides a first step in developing cropping systems that provide a knowledge-based approach to crop selection and placement on the landscape with the goal of functional optimization.

"The Effect of Landscape Position on Biomass Crop Yield" was published in the March/April 2010 issue of Agronomy Journal.