1a. Objectives (from AD-416)
1. Develop new tools and a knowledge base that will enable decision makers to more effectively manage and conserve water resources. 1.a Design and test sensors that will quantify the level of plant water stress in growing crops and can be used to make irrigation decisions. 1.b Determine the relationship between crop productivity and applied water as a function of environmental factors so that irrigation can be managed for optimal use of all available water. 2. Develop and evaluate techniques and methodologies that maintain efficient agricultural production under deficit irrigation and dryland production. 2.a Design and evaluate water management strategies that optimize water use and crop production with limited well capacity. 2.b Define and evaluate crop management systems to facilitate the transition from irrigated to dryland cropping, considering crop species and varieties, cultural practices, and that incorporate long range weather prediction. 3. Identify changes in soil microbial, chemical, and physical properties affecting soil water availability and develop management practices that impact soil properties to sustain and improve crop production where water supply is in transition from limited irrigation to rainfed production. 4. Develop Best Management Practices based on a growing region's climate variability. 4.a Develop optimal planting strategies that integrate seasonal climate forecast information into agricultural managment. 4.b Develop software tools that provide detailed knowledge of precipitation, temperature stress, and evapotranspiration and demand to producers and plant breeders.
1b. Approach (from AD-416)
Develop and evaluate techniques and methodologies that utilize limited water resources efficiently to maintain economically viable deficit irrigated and dryland agricultural production systems. Develop new approaches, including acoustic detection of xylem cavitation and portable chamber technologies, to quantify the degree of crop drought stress and evaluate new and existing deficit irrigation strategies. Examine irrigation quantity and application rate effects on water use efficiency using the BIOTIC protocol for irrigation scheduling. Explore the efficiency of subsurface drip irrigation for storing water from low capacity wells in the soil during the fallow season. Determine the feasibility of enhancing water infiltration with adapted grasses and use water stored in playa lakes for forage production. Evaluate new crop species and cultural practices for facilitating the transition from irrigated to dryland cropping systems. Determine the effects of crop rotations and residue management systems on soil microbial, chemical, and physical properties including effects on soil water availability, infiltration, and rainfall capture efficiency. Assess the influence of row spacing and planting patterns on water use efficiency of different cropping systems. Use seasonal climate forecasts to develop optimal planting strategies and software tools to provide detailed predictions of precipitation, temperature stress, and evapotranspiration demand for producers and plant breeders. This multifaceted research program will provide the knowledge base for optimizing the use of scarce water resources especially in arid and semi-arid regions where ground water resources are being depleted.
3. Progress Report
As plants undergo increasing levels of drought stress, water inside xylem elements in the plant's stem collapse or cavitate and emit sound energy that can be detected in order to quantify the amount of drought stress a plant is experiencing. Spectral distribution of acoustic energy from xylem cavitation events was investigated in greenhouse grown cotton. A playa (or pan) is a dry or ephemeral lake bed that fills with run-off water following rainfall events and are a common feature of the landscape in the semi-arid Southern High Plains of the United States. Research plots of the forage crop Gamagrass has been established in several playas. Selected playas have been instrumented with sensors to monitor water depth throughout the year. It was found that the frequency and duration of the hydroperiod varies from playa to playa. Hence, some playas are better suited to forage production using monocultures of Eastern Gamagrass than others. Crop photosynthesis, dark respiration and transpiration are all major crop physiological processes that respond to environmental variables, including drought stress. A portable, open transparent chamber system for measuring canopy gas exchanges was developed and tested. With minor chamber effect, the chamber accurately estimates E for many field applications such as comparison of canopy gas exchanges and water use efficiencies among irrigation treatments. The value of El Nino–Southern Oscillation (ENSO) forecast information to combined winter wheat and cattle grazing production systems over the U.S. Southern High Plains was estimated via computer simulation. Profit outcomes were derived from the simulations based on four production scenarios that assumed wheat prices varying about either historical ($3.22 bu-1) or elevated ($7.00 bu-1) means, and returns on live weight gain consistent with the grain producer leasing pasturage ($0.75 kg-1) or owning cattle ($2.42 kg-1). This suggests that when forecast information is not available – which is the case in most growing regions during most years - producers might profit from following management practices that are best for the growing region's climatology. (NP211, Component 4a)
1. An Open System for Measuring Canopy Gas Exchanges: There is an urgent research need for the ability to monitor crop water loss, crop photosynthetic net carbon gain and instantaneous crop water use efficiency under a wide range of experimental conditions from the field to the greenhouse. We have completed construction and testing of three CETA (Canopy Evapo-Transpiration and Assimilation) chambers that measure crop water loss and crop photosynthesis continuously at 10-second intervals throughout the day. These chambers will provide precise physiological measurement of crop responses to the environment, including drought stress. This chamber system has been tested against independent measurements using weighing scales, and good agreement was found between the CETA chambers and the weighing scales. A complete description of the design, operation and testing of this chamber system has been accepted for publication and is currently in press at Agronomy Journal. (NP211, Problem Area 2)
2. Managing Soil Properties through Dryland Cropping Systems Intensities:I n some areas of the Southern High Plains, available irrigation water is becoming scarce due to the small amount of groundwater recharge occurring to the Ogallala aquifer. Changes in soil properties (i.e., organic matter content, soil microorganisms) can improve the potential of soils to store water for crop production in dryland cropping areas. ARS scientists from Lubbock, Texas, evaluated a High Biomass Crop dryland study and have shown that soil microbial populations were higher in winter cover crop rotations after only 3 years compared to continuous cotton or cotton-sorghum systems. Soil water infiltration rates were higher in cropping systems under no-tillage compared to conventional tillage. Although rapid improvements in soil properties have been observed, total weight and lint yield of cotton were similar in Ct-Ct compared to the rotations after 5 years. Thus, continuation of this study is important to further evaluate and confirm these trends as indicators of soil changes including the potential of soil as a water storage-reservoir for dryland crop production. (NP211, Problem Area 2)
3. ENSO forecast value to dual-purpose wheat production over the Southern High Plains: In semi-arid regions rainfall is the determining factor in the profitability of dryland agriculture. In such areas, forecasts of growing season precipitation before planting might allow producers to make management decisions that exploit wet growing seasons, or limit the producer's risk during dry conditions. A computer simulation approach was used here to determine how managers of combined wheat and cattle grazing production systems over the U.S. Southern High Plains should respond to El Niño–Southern Oscillation (ENSO) forecast information to maximize their profits. These simulations were conducted under a limited number of production and cost conditions. In the future, Visual Basic risk management applications capable of testing arbitrary production scenarios and cost conditions might be developed based on this simulation approach. Thus for a given set of either climatological or ENSO phase conditions, and current or projected market conditions defined by the user, such applications might propose a best management practice for a particular forecast condition and present distributions of possible profit outcomes. (NP 211, Problem Areas 2 and 5)
5. Significant Activities that Support Special Target Populations
Mauget, S.A., Ko, J. 2008. A two-tier statistical forecast method for agricultural and resource management simulations. Journal of Applied Meteorology and Climatology. 47(6):1573-1589.