Hydrologic modeling of conservation farming practices on the Palouse Joshua Van Wie a , Jennifer Adam a , Jeff Ullman b a Department of Civil and Environmental Engineering, b Department of Biological Systems Engineering, Washington State University. Introduction
Hydrologic modeling of conservation farming practices on the Palouse
Joshua Van Wie a, Jennifer Adam a, Jeff Ullmanb
a Department of Civil and Environmental Engineering, b Department of Biological Systems Engineering, Washington State University
The agricultural practice of field tillage has dramatic effects on surface hydrologic properties, significantly altering the processes of infiltration, evaporation, and runoff. In dryland farming regions such as the Palouse of the Pacific Northwest it is essential to maintain an adequate and reliable water supply as water is the limiting factor to crop yield in most years (Pannkuk, 1998).
Conservation techniques leave a greater amount of crop residue on the surface after harvest that provides a physical barrier against runoff and evaporation (Fuentes, 2003) in addition to increasing infiltration by regulating soil temperature during cold weather (Singh, 2009). The purpose of this study is to investigate no-till methods and to simulate the over-winter water savings that may occur under widespread adoption of these methods using hydrologic modeling.
Tillage effects are represented in DHSVM by adjusting soil and vegetation parameters according to the intensity of tillage. The model is calibrated and verified using field scale runoff data from land under conventional and no-till management.
The accuracy of DHSVM is determined by error statistics that evaluate the ability of the model to predict historical streamflows. Preliminary model runs for the North Fork Palouse River resulted in a Nash-Sutcliffe coefficient of 0.76 out of maximum possible value of 1.0 and a volume error of 2.3% for a 10-year simulation. These results compare well with previous applications of DHSVM.
Further work is necessary to insure that the model is accurately predicting at both the field scale and the watershed scale. It is important to thoroughly understand the implications of field studies on the entire watershed as increased retention of water through the winter months and a higher soil water content at the beginning of the growing season may have the potential to increase crop yields in this arid region.
τ (Ri) = transmittance
ΔR = residue area index
Ω = clumping index
L = longwave radiation
fN+1 = view factor
ε = emissivity of atmosphere or ground surface
σ= Stefan-Boltzmann constant
T= temperature of atmosphere or ground surface
Soil moisture contents are shown for the North and South forks of the Palouse River basin in early April under two scenarios:
Heavy conventional tillage represented by bare soil and low albedo during the winter months.
No-till modeled with an understory and high albedo during the winter.