Topographic Effects on Spring Wheat Yields and Water Use

Abstract

Water redistribution in a complex landscape needs to be quantified in order to determine field productivity. Landscape effects on water use and spring wheat (Triticum aestivum L.) yields were studied by monitoring two fields at each of two locations in North Dakota for 5 years. Four soil series at different positions within each field were monitored: the Zahl loam series (fine‐loamy, mixed Entic Haploboroll) on hilltops and shoulder positions, the Williams loam series (fine‐loamy, mixed Typic Argiboroll) on side slopes and hilltops, the Bowbells loam series (fine‐loamy, mixed Pachic Haploboroll) on footslopes and toeslopes, and the Tonka silt loam series (fine, montmorillonitic, frigid Argiaquic Argialboll) in small undrained depressional areas. Topographic factors were calculated at each site by measuring the slope in four directions, 90° apart, and adding the slopes together. If a slope was downward toward a site, it was considered positive, if a slope was upward toward a site it was considered negative. This number, if positive, would indicate that runon water would be added to the site and, if negative, water would be lost from the site due to runoff. Topographic factors were calculated 3, 6, 15, and 30 m from each site. As expected, wheat yields from the four soils were in the order Tonka > Bowbells > Williams > Zahl. Spring wheat grain yields ranged from 5.1 Mg ha−1 on Bowbells in 1985 to no yield in 1988 at the Underwood location. Spring wheat grain yields were generally correlated to total water use. When the topographic factor was added into the regression of yield vs. total water use, the coefficient of determination, R2, increased in the first 3 yr. The last 2 yr of the study were drought years and the topographic factor accurately reflected the lack of water redistribution in those years. Topographic factors measured 15 m from the site gave the highest R2 values.

Slope position and subsoiling effects on soil water and spring wheat yield

“…Crops on upper slope positions consume less water than on lower slope positions when there is abundant stored soil water near the surface, such as fallowed land in the semiarid northern Great Plains (Munn et al 1982;Halvorson and Doll 1991) or crop- For personal use only.…”

“…2). When stored soil water in the surface is low, such as for crops seeded on crop stubble in the northern Great Plains, water use at upper slopes is generally equal to or higher than that at lower slopes (de Jong and Rennie 1969;Halvorson and Doll 1991). This has been related to stubble-seeded crops exploiting available soil water reserves more thoroughly than fallow crops to complete their life cycle (Brown and Miller 1978).…”

“…The addition of topsoil (Verity and Anderson 1990) or manures (Ayres et al 1985) was necessary to increase the productivity of upper slopes to that of lower slope positions. Developing clear relationships between slope position and crop productivity or soil water regime has been difficult because of the confounding influences of three-dimensional slope curvature (Sinai et al 1981;Simmons et al 1989;Halvorson and Doll 1991) or of differing slope aspect (Spratt and McIver 1972;Jones et al 1989).…”

Spatial Relation of Apparent Soil Electrical Conductivity with Crop Yields and Soil Properties at Different Topographic Positions in a Small Agricultural Watershed

“…A study by Florinsky et al [28] showed that the topography influence on soil properties and residual phosphorus decreased with depth. However, the influence of topography on crop yields has been reported over relatively small scales [29,30].…”

Topography impact on nutrition content in soil and yield

“…Halvorson and Doll (1991) observed lower influence of topography on yield in dry years than in wet ones. They related it to lower amounts of water available for topographical redistribution during dry years.…”