Biophysical interactions in perennial biomass alley cropping systems

Authors: Gamble, Joshua; JOHNSON, GREGG - University Of Minnesota; CURRENT, DEAN - University Of Minnesota; WYSE, DONALD - University Of Minnesota; ZAMORA, DIOMEDES - University Of Minnesota; SHEAFFER, CRAIG - University Of Minnesota

Submitted to: Agroforestry Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2018
Publication Date: 1/17/2018
Citation: Gamble, J.D., Johnson, G., Current, D., Wyse, D., Zamora, D., Sheaffer, C. 2018. Biophysical interactions in perennial biomass alley cropping systems. Agroforestry Systems. 93:901-914. https://doi.org/10.1007/s10457-018-0188-8.
DOI: https://doi.org/10.1007/s10457-018-0188-8

Interpretive Summary: Agroforestry represents one approach to increase ecosystem services from agricultural lands. However, competition between trees and crops in agroforestry systems can reduce crop yields. Our objective was to evaluate competition for light, water, and nitrogen in an alley cropping agroforestry system composed of a native grass (prairie cordgrass) or an 11-species native grassland mixture planted between rows of shrub willow bioenergy crops. Research was conducted at two sites in Minnesota (Granada & Empire, MN). We found that water and nitrogen availability were reduced adjacent to tree rows at both sites. Light availability depended on alley (tree row) orientation, with light availability being greater in west-east (Granada) than in north-south (Empire) oriented alleys. No crop yield decline was observed at Granada, but at Empire crop yield declined close to tree rows for both prairie cordgrass and the native grassland mixture. Our analysis suggests that competition for light and water were the reason for this decline. Our findings are important for the design of bioenergy crop-based agroforestry systems because they demonstrate that 1) a west-east alley orientation favors better crop yield; 2) Given appropriate alley orientation (and assocated light availability), water and nitrogen use by shrub willow has little impact on growth and yield of prairie cordgrass and a native grassland mixture. This information can inform the design of additional research or field scale agroforestry systems. The findings of this research will be of interest to researchers, and producers/producer groups with interest in agroforestry and bioenergy produciton systems.

Technical Abstract: .Understanding the nature and degree of competition between trees and co-planted crops in agroforestry systems can inform management decisions, future species selection, and system design., We measured variation in herbaceous biomass yield, photosynthetically active radiation (PAR), soil water potential, and soil NO3 in alley cropping systems consisting of prairie cordgrass (Spartina pectinata) or an 11-species native grass-forb-legume polyculture planted between rows of shrub willow (Salix purpurea L. ‘Fish Creek’) at two Minnesota sites. At Empire, biomass yield increased with distance from the tree row for both alley crops, as did PAR and NO3 availability. At Granada, no spatial pattern in crop yield was evident, despite reduced PAR and NO3 availability adjacent to tree rows. At both sites, patterns in soil water potential suggested that trees competed with crops for soil water within 2.4 m of tree rows, but had a facilitative effect on crop water use at 4.8 m. Alleys had differing cardinal orientations at the two sites, and light availability was lower in a north-south alley (Empire) than in west-east and northwest-southeast orientations (Granada). At Empire, mixed effects analysis indicated that competition for light and soil water were responsible for reductions in crop yield. For every 100 µmol m-2 s-1 increase in PAR, model estimated herbaceous crop yield increased by 623 kg DM ha-1. For every 20 kPa increase in average daily water potential, model estimated herbaceous crop yield increased by 1,038 kg DM ha-1. Alley cropping systems comprised of shrub willow and herbaceous perennial biomass crops should avoid north-south row orientations to minimize shading. Prairie cordgrass and native polyculture biomass yield showed similar spatial patterns, though prairie cordgrass had higher yields at Empire.