Thomas J. Sauer

Managing Soils to Achieve Greater Water Use Efficiency

Water use efficiency (WUE) represents a given level of biomass or grain yield per unit of water used by the crop. With increasing concern about the availability of water resources in both irrigated and rainfed agriculture, there is renewed interest in trying to develop an understanding of how WUE can be improved and how farming systems can be modified to be more efficient in water use. This review and synthesis of the literature is directed toward understanding the role of soil management practices for WUE. Soil management practices affect the processes of evapotranspiration by modifying the available energy, the available water in the soil profile, or the exchange rate between the soil and the atmosphere. Plant management practices, e.g., the addition of N and P, have an indirect effect on water use through the physiological efficiency of the plant. A survey of the literature reveals a large variation in measured WUE across a range of climates, crops, and soil management practices. It is possible to increase WUE by 25 to 40% through soil management practices that involve tillage. Overall, precipitation use efficiency can be enhanced through adoption of more intensive cropping systems in semiarid environments and increased plant populations in more temperate and humid environments. Modifying nutrient management practices can increase WUE by 15 to 25%. Water use efficiency can be increased through proper management, and field-scale experiences show that these changes positively affect crop yield.

Crop residue effects on surface radiation and energy balance — review

SummaryCrop residues alter the surface properties of soils. Both shortwave albedo and longwave emissivity are affected. These are linked to an effect of residue on surface evaporation and water content. Water content influences soil physical properties and surface energy partitioning. In summary, crop residue acts to soil as clothing acts to skin. Compared to bare soil, crop residues can reduce extremes of heat and mass fluxes at the soil surface. Managing crop residues can result in more favorable agronomic soil conditions. This paper reviews research results of the quantity, quality, architecture, and surface distribution of crop residues on soil surface radiation and energy balances, soil water content, and soil temperature.

Sensible Heat Observations Reveal Soil-Water Evaporation Dynamics

Soil-water evaporation is important at scales ranging from microbial ecology to large-scale climate. Yet routine measurements are unable to capture rapidly shifting near-surface soil heat and water processes involved in soil-water evaporation. The objective of this study was to determine the depth and location of the evaporation zone within soil. Three-needle heat-pulse sensors were used to monitor soil heat capacity, thermal conductivity, and temperature below a bare soil surface in central Iowa during natural wetting/ drying cycles. Soil heat flux and changes in heat storage were calculated from these data to obtain a balance of sensible heat components. The residual from this balance, attributed to latent heat from water vaporization, provides an estimate of in situ soil-water evaporation. As the soil dried following rainfall, results show divergence in the soil sensible heat flux with depth. Divergence in the heat flux indicates the location of a heat sink associated with soil-water evaporation. Evaporation estimates from the sensible heat balance provide depth and time patterns consistent with observed soil-water depletion patterns. Immediately after rainfall, evaporation occurred near the soil surface. Within 6 days after rainfall, the evaporation zone proceeded 13 mm into the soil profile. Evaporation rates at the 3-mm depth reached peak values 0.25 mm h 1 . Evaporation occurred simultaneously at multiple measured depth increments, but with time lag between peak evaporation rates for depths deeper below the soil surface. Implementation of finescale measurement techniques for the soil sensible heat balance provides a new opportunity to improve understanding of soil-water evaporation.

Effects of crop residue cover and architecture on heat and water transfer at the soil surface

Different residue types and standing stubble versus distributed flat residues affect heat and water transfer at the soil surface to varying degrees. Understanding the effects of various residue configurations can assist in better residue management decisions, but this is complex due to various interacting influences. Therefore, modeling the effects of crop residues on heat and water movement can be an effective tool to assess the benefits of differing residues types and architectures for various climates. The purpose of this study was to test the ability of the Simultaneous Heat And Water (SHAW) model for simulating the effects of residue type and architecture on heat and water transfer at the surface and to evaluate the impacts of differing residue types and architectures on heat and water transfer in significantly different climates. The model was tested on bare tilled soils and corn, wheat and millet residues having varying amounts of standing and distributed flat residues for three separate locations: Ames, IA, Akron, CO and Pullman, WA. Modifications to the model were necessary to correctly simulate the effect of wind on convective transfer through a flat corn residue layer. Model efficiencies for simulated soil temperature approached or exceeded 0.90 for nearly all residue treatments and locations. The root mean square deviation for simulated water content compared to measured values was typically around 0.04 m3 m−3. Satisfied that the model could reasonably simulate the effect of residue type and architecture, the model was applied to simulate the effects of differing residue architectures to 30 years of generated weather conditions for four diverse climate stations: Boise, ID; Spokane, WA; Des Moines, IA; Minneapolis, MN. Simulated frost depths for bare and standing residues were typically deeper than for flat residues. Bare soil had the highest evaporation at all sites, and flat wheat residue generally had the lowest evaporation. The wetter climates (Des Moines and Minneapolis) tended to favor flat residues for reducing evaporation more so than the drier climates. Near-surface soil temperature under standing residues warmed to 5 °C in the spring by as much as 5–9 days earlier compared to bare and flat residue cover depending on location, which can have important ramifications for early seedling germination and plant establishment.

Surface energy balance of a corn residue-covered field

Abstract Crop residues on the soil surface have the potential to significantly affect the magnitude of individual components of the surface energy balance. Previous research has concentrated on residue effects on soil temperature and moisture early in the growing season. The objective of this study was to measure each of the surface energy balance components of a field during snow-free periods between successive growing seasons. A Bowen ratio system was used to measure surface fluxes within a no-tillage corn ( Zea mays L.) field near Ames, IA, USA. During the fall, large solar zenith angles and short daylengths resulted in −2 d −1 of available energy ( R n − G ). On overcast days with a dry surface, average daytime Bowen ratios ( β ) were β values were >2.3 and β values (1.0 and 1.5 on sunny vs. 0.87 and 1.84 on overcast days) while less available energy was used to evaporate water on sunny days ( 38% on overcast days). More energy was available (up to 12.9 MJ m −2 d −1 ) during the spring measurement interval with daytime Bowen ratios averaging 1.7 and 0.8 on sunny and overcast days, respectively. With overcast conditions and wet soil, evaporation approached potential rates predicted by both the Priestley–Taylor and Penman–Monteith equations. With clear skies and wet soil, Penman–Monteith estimates using a residue resistance term agreed well with measured values.

Characterizing the surface properties of soils at varying landscape positions in the Ozark highlands

Surface runoff of nutrients after land application of animal manures is influenced by climate, physical and chemical properties of the soil, and land use. The objective of this study was to characterize the surface soil properties from a riparian forest to an adjacent ridge top at a site in the Ozark Highlands. Sampling transects (60 m long) were established in five soil map units, 7.6-cm-diameter X 10-cm-deep cores extracted at 3-m intervals, and samples analyzed to determine relevant soil physical and chemical properties. Ponded infiltration measurements were also completed on four of the transects. Soil test phosphorus and phosphorus saturation ranged from 10 to 31.4 mg kg -1 and 9.1 to 18.4%, respectively, and reflect the recent history of limited poultry litter or fertilizer application. Soil samples from each transect had similar average silt content (range = 67.2-73.9%), but the soil in the riparian forest (Razort silt loam) had more clay and significantly less sand and coarse fragments. The Razort soil also had a higher cation exchange capacity (CEC) (20.7 cmol kg -1 ) and infiltration rate (5.29 cm h -1 ). Trends in clay content, infiltration rate, and CEC suggest that the riparian forest and adjacent alluvial pasture may act as nutrient sinks in this landscape. Results of this study will be combined with grazing management and hydrologic analyses to develop best management practices for poultry litter applications and to provide baseline data for the assessment of long-term effects of litter application on soil properties.

Spatial and diurnal below canopy evaporation in a desert vineyard: Measurements and modeling

Evaporation from the soil surface (E) can be a significant source of water loss in arid areas. In sparsely vegetated systems, E is expected to be a function of soil, climate, irrigation regime, precipitation patterns, and plant canopy development and will therefore change dynamically at both daily and seasonal time scales. The objectives of this research were to quantify E in an isolated, drip-irrigated vineyard in an arid environment and to simulate below canopy E using the HYDRUS (2-D/3-D) model. Specific focus was on variations of E both temporally and spatially across the inter-row. Continuous above canopy measurements, made in a commercial vineyard, included evapotranspiration, solar radiation, air temperature and humidity, and wind speed and direction. Short-term intensive measurements below the canopy included actual and potential E and solar radiation along transects between adjacent vine-rows. Potential and actual E below the canopy were highly variable, both diurnally and with distance from the vine-row, as a result of shading and distinct wetted areas typical to drip irrigation. While the magnitude of actual E was mostly determined by soil water content, diurnal patterns depended strongly on position relative to the vine-row due to variable shading patterns. HYDRUS (2-D/3-D) successfully simulated the magnitude, diurnal patterns, and spatial distribution of E, including expected deviations as a result of variability in soil saturated hydraulic conductivity.

Effect of corn or soybean row position on soil water.

Crop plants can funnel water to the soil and increase water content more in the row relative to the interrow. Because the row intercepts more soil water after rains and higher root density, the soil may also dry out more between rains than does soil in the interrow. The objectives of this study were to determine if there is a row position difference in soil wetting after rain and drying between rains, and to determine the seasonal nature of these differences. The first experiment examined soil water content 0 to 0.06 m in row, interrow, and quarter corn row positions for eight sites at specific times during a corn (Zea mays L.)-growing season. During the growing season, the second experiment examined automated soil water measurements at one site for two corn years and one soybean (Glycine max [L.] Merr.) year at row and interrow positions to 0.15-m depth. Soil water content changes were significantly greater in the row than the interrow for some mid-season dates. Temporal soil water changes showed that row wetting and drying dominated over interrow soil water changes for mid season. The mean ratio of row/(row + interrow) soil water changes for wetting was 0.76 and 0.77 for corn and 0.64 for soybean and for drying was 0.58 and 0.84 for corn and 0.60 for soybean. Soybean showed the row effect for a shorter time of the season (up to 71 days) compared with corn (up to 159 days).

Over-winter changes in radiant energy exchange of a corn residue-covered surface☆

Abstract Crop residues on the soil surface absorb solar radiation and have reflectivity properties that may differ significantly from the underlying soil. The objective of this study was to measure the temporal variation in solar radiation reflectivity and transmissivity of a corn ( Zea mays L.) residue layer under field conditions. Incident and reflected solar and visible radiation were measured in a field with standing corn stubble and com residue prostrate on the soil surface. Transmitted solar and visible radiation were measured with line sensors placed beneath the prostrate residue. Measurements were made during snow-free periods from October 1994 to April 1995. Mean reflectivity decreased from 0.20 ± 0.02, 0.12 ± 0.02, and 0.27 ± 0.03 for the solar, visible, and near-infrared wavebands during the fall, to 0.17 ± 0.01, 0.11 ± 0.01, and 0.22 ± 0.02 during the spring measurement period, respectively. Transmissivity of solar and visible radiation through the com residue layers was directly proportional to residue area index. Extinction coefficients for solar and visible radiation ranged from 0.79 to 0.96 and were higher in the fall for both wavebands. Diurnal patterns of reflectivity and transmissivity showed a sensitivity to the proportion of beam vs. diffuse radiation and wetness of the residue.

Mitigation Opportunities from Land Management Practices in a Warming World: Increasing Potential Sinks

Climate change will create changes in CO 2 , temperature, and precipitation in the plant and soil environment. The changes will not be uniform in time or space creating further uncertainty about the magnitude of the impact of climate change on agricultural systems. Increases in CO 2 will enhance plant growth; however, these increases will be offset by increased heat stress and soil water use leading to potential water deficits. Variations in observed CO 2 emissions are closely related to soil temperatures, thus increasing global temperatures may stimulate soil heterotrophic processes and increase soil organic carbon decomposition. Mitigation of N 2 O will result from improved N management; however, the impact will be dependent upon the soil water regime. Effective mitigation of CO 2 or N 2 O emissions will require an understanding of how the processes that affect emissions are influenced by climate change and how we can most effectively incorporate this knowledge into improved soil and crop management practices.