1a. Objectives (from AD-416):
Obj 1: Quantify the environmental factors that affect the degree of crop drought stress. Sub-obj 1A Assess the effects of rising atmospheric CO2 concentration on crop coefficients used in deficit irrigation scheduling systems. Sub-obj 1B Relate seasonal plant stress and water use efficiency responses of crop plants to irrigation scheduling techniques using stable carbon isotope discrimination. Sub-obj 1C Identify active root areas under sub-surface irrigation to determine optimal cultivar for dryland management. Obj 2: Develop crop management strategies that enhance water use efficiency. Sub-obj 2A Quantify the effects of wind speed, tillage management, and irradiance on surface water evaporation. Sub-obj 2B Identify changes in microbial and chemical characteristics that may impact water availability and productivity in dryland production. Obj 3 Develop a framework of methods and models for quantifying and studying the risks associated with water from rainfall for dryland agriculture over the Southern High Plains and other dryland agricultural regions. Sub-obj 3A Evaluate the ability of current weather generator configurations to reproduce the distributional characteristics of Southern High Plains summer weather variability. Sub-obj 3B Run calibrated and validated cotton and sorghum crop models with both observed and stochastically generated weather inputs to generate simulated dryland yield outcomes. Sub-obj 3C Convert modeled yield outcomes generated with simulated weather data into net profit outcomes to form corresponding profit distributions for dryland cotton and sorghum production. Obj 4: Evaluate management practices that prevent soil degradation by soil erosion in semiarid cropping and rangeland systems. Sub-obj 4A Investigate soil redistribution & dust emissions from agro-ecosystems including rangelands & native plant communities under the stressors resulting from climate change. Sub-obj 4B Evaluate management systems in terms of multi-decadal erosion rates estimated from radioisotope inventories. Obj 5: Evaluate management practices to increase soil water availability and contribute to higher water and nutrient use efficiencies. Sub-obj 5A Partitioning of evapotranspiration to water evaporation from soil & crop surfaces for dryland & irrigated cropping systems across different N fertilizer management strategies. Sub-obj 5B Investigate changes in groundwater quantity & quality that may affect cropland production in semiarid & arid regions. Obj 6: Develop management practices that contribute to maintaining microbial diversity and functions needed to improve soil health, ensure ecosystem sustainability, and maintain crop productivity under a changing climate. Sub-obj 6A Compare the effects of different management practices in semiarid regions on soil health indicators including the microbial community size, diversity & functions. Sub-obj 6B Characterize the effects of climatic events on soil health & the effects of future climate change (CO2, temperature and rainfall) on agro-ecosystems by measuring root biomass, soil microbial diversity & soil organic matter pools.
1b. Approach (from AD-416):
Sustainable agriculture, with emphasis on conservation of natural resources, is a challenge in the semiarid climate of the Southern High Plains (SHP). Of concern is developing cropping systems that cope with climate change, depletion of aquifers used for irrigation, and growing seasons characterized by frequent droughts and erratic rainfall. Climate change is expected to impose general global challenges but, clearly, solutions to these problems will be site specific. Within a framework to quantify and study the risks associated with dryland agriculture, we need sustainable agricultural systems that optimize productivity, conserve water, control soil erosion and improve soil health for agricultural production in semiarid regions and in a changing climate. We will continue long-term research that identifies management practices that impact water availability in dryland farming vs. lands in the Conservation Reserve Program. Our goal is to provide agricultural producers with tools to manage limited water resources in the semi-arid environment of the SHP. New technologies for exposing crops in the field to elevated levels of atmospheric CO2 concentration will be used to monitor hourly and daily whole canopy water use efficiency by simultaneously measuring the ratio of net CO2 assimilation to evapotranspiration. Optimum irrigation scheduling techniques will be determined from stable carbon isotope discrimination while optimal cultivars for dryland agriculture will be selected by identifying and comparing active rooting areas. This multifaceted research program will provide the knowledge base for optimizing the use of scarce water resources in arid and semi-arid regions where ground water resources are being depleted.
3. Progress Report:
In September 2017, the objectives and milestones of the research project 3096-12610-001-00D, entitled Improving the Productivity and Climatic Resilience of Agricultural Production Systems in Semiarid and Arid Ecosystems were added to this project. As the impacts of climate variability become more intense, plant breeders need simple tools to screen for traits that may result in higher water use efficiency, i.e., more crop yield with less water. Within this first year of our plan, we explored whether seasonal water use efficiency could be assessed by analyzing oil extracted from cotton seeds at harvest-time (Sub-objective 1B). Standard American Oil Chemist Society methods of seed oil extraction were compared to modified methods that use less harmful solvents for oil extraction. We are currently scaling these methods down to a micro-scale and comparing these to other extraction methods to ensure there is no effect on subsequent analyses. Current field work consisted of growing several cotton cultivars with release dates spanning a century under controlled irrigation conditions to ensure material is on hand for analyses of trends in water use efficiency as measured by stable carbon isotope analysis. A new tool to quantify root-water uptake on cultivars to be grown under dryland conditions was evaluated (Sub-objective 5B). A prototype sensor that measures soil water content using a novel circular design was tested using a fritted clay material that has a wide range of soil water content (0 to 55 % by volume). A 12–inch diameter PVC pipe was cut and used as a pot. Holes were drilled into the bottom to drain water, and a stainless steel was placed in vertical strips 5-cm apart starting from the bottom. Each strip of 5 bolts had an identical vertical strip on the opposite side of the pot making 3 sets of conductivity meters at 5 different heights. Each bolt can be tested for conductance and thus create a 3-dimensional map of conductivity across the depth of the pot. A computer fitted with a special running board and relay modules that power the voltage sent to the individual conductance cells was used to run the program and measure the conductivity across all bolts. This setup of a pot, computer/sensor, and program will be tested for performance using increasing volumes of salt water to detect the movement of the salty water through the fritted clay. Once the movement of salt water into the fritted clay profile is demonstrated, a cotton plant will be planted and allowed to develop to the 1st square. A new solution of salt water will be prepared with a source that is isotopically enriched compared to the tap water and plant samples will be taken to determine if the cotton plant is using the new water substituting for rainwater. This is essential information needed to evaluate what cultivars are more efficient in using rainfall under dryland conditions. An important component of water use efficiency is to minimize soil water evaporation as affected by management practices (Sub-objective 3A). For this purpose we designed experiments on a wind tunnel to evaluate the effects of wind and tillage on evaporation. We purchased materials and equipment to maintain a constant air temperature and high vapor pressure deficit for a 15-m wind tunnel with 4 weighing lysimeters to measure evapotranspiration. The monolith shells and extractor were fabricated and are ready for monolith extraction. The region is currently in a state of extreme drought and the soils are too dry and hard that prevent us from obtaining hydrologically intact soil monoliths. The project will proceed with installation of climate control equipment and testing of the system. Furthermore, quantifying the partitioning of water evaporation from the soil and crop to increase crop yield while minimizing the loss of water from the soil is critical in cropping systems. Given the loss of a scientist in our unit we modified our research related to the partitioning of evapotranspiration for dryland and irrigated cropping systems. We are currently using an energy water balance simulation model developed by a scientist in the unit (Objective 3). An important input to this model is the intensity and duration of rainfall events and their impact on infiltration and runoff. One way to obtain these data is by using a rain simulator. To expedite and facilitate the transport of the rain simulator to the field was to attach the simulator to the cargo trailer, which was modified by cutting out the floor under the rain simulator and removing the axles and replacing them with axle-less wheel hubs. Additionally, a remote control trailer mover rated for 3,300 lbs was purchased. In the end we will have a portable rain simulator that can be pulled using a truck-hitch to field sites of interest and can be operated as remote controlled rain simulator by 1–2 people rather than 3–4. Other input soils data for the model are the soil hydraulic properties of the major soil series on the Texas High Plains. For this purpose, equipment was set up to make measurements on soil cores sampled from Brownfield and Amarillo, Texas soil series. These measurements include infiltration, soil water holding capacity, soil water retention curve and saturated hydraulic conductivity. Simulation models were used to evaluate risk assessment associated from dryland cropping systems across the semiarid Texas High Plains (Objective 3). For publishable results, it is important to use correct historical weather input data. Data sets were subjected to quality control tests. Weather input (5 and 15 minute) data of air temperature, precipitation, radiation, and wind for 21 West Texas Mesonet stations during the 2005–2017 period were averaged or summed into daily averages or totals. Statistical analyses of these data sets are underway using several computer models. The CROPGRO-Cotton model was run using weather inputs from the 21 West Texas Mesonet stations over an 11 year-period, and repeated under 32 management options. A journal paper describing this work was submitted for publication. Further, these results will be reported at the August 2018 Cropping Systems Research Laboratory Field Day, the December 2018 American Geophysical Union meeting, and the January 2019 Beltwide Cotton Meeting. The cotton lint yield and soil water content data that were provided by a Bushland, Texas ARS collaborator were evaluated and used to calibrate and initialize the DSSAT CROPGRO-Cotton and CROPGRO-Sorghum models. An associated paper was submitted giving estimates of dryland cotton lint yield variation and profit risk under a range of management options. Another element of our research project is to evaluate management practices that diminish soil erosion in cropping and rangeland systems (Objective 4). Multiple natural and agricultural surfaces at 25 different locations in Texas, New Mexico, Arizona, Colorado, and Utah were tested for respirable dust emissions using a portable in-situ wind erosion laboratory (PI-SWERL). Data were analyzed and summarized, and preliminary results were presented at the 10th International Conference on Aeolian Research in Bordeaux, France 25–29 June 2018 and at the 2018 Soil and Water Conservation Society Annual International Conference. Results indicated that many dust emission models overestimate emission by failure to consider surface crusting and that the differences between the emission rates from a crusted surface and a disturbed surface are often greater than an order of magnitude. Access to sample processing facilities has been unavailable up until autumn, 2018. However, previously collected samples were prepared and reagents acquired for analysis which is anticipated in October and November 2018. Reference locations will be sampled during the early spring of 2019. Samples from cropped lands will be collected in late spring of 2019. We continue to sample several wells across the Texas High Plains to evaluate changes in groundwater quantity and quality that may affect future dryland cropland production (Sub-objective 5B). In addition to our sampling regime, we are evaluating changes in salinity with depth inside each sampled well. We purchased a depth-to-water meter that has a probe to measure salinity as well. This will allow us to measure changes in salinity with depth, creating a profile for each sampled well. These profiles will then be compared from October to March to quantify if the salinity of each well is changing over time. Changes in soil microbial and chemical properties are indicators of productivity under dryland conditions (Objective 6). We began our soil sampling and installed neutron probes to measure soil water content, and rainfall on Conservation Reserve Program and dryland sites designated for this experiment. Our aim is to establish linkages of the microbial component that is essential to improve soil water holding capacity and productivity. We also continue to collect soil samples in several producer sites to evaluate changes in soil microbial communities that could be related to soil water conservation under the current climate variability. These soil samples were collected starting in 2011, when a record drought/heat wave occurred on the Texas High Plains. Further, we are also evaluating soil microbial data as affected by different management scenarios between 2015–2017. We are currently experiencing another drought and with our sampling scenario we have an opportunity to test the microbial response to climate variability under semiarid conditions. Scientists contribute to two big databases. One scientist is a member of the steering committee for the USDA-ARS Nutrient Use and Outcome database (NUOnet). Another scientist leads the Soil Biology Group comprised of 15 ARS scientists within the Greenhouse Gas Reduction through Agricultural Carbon Enhancement network.
1. Early planted rain-fed cotton yields more lint. As the Ogallala Aquifer levels decline, cotton producers on the Southern High Plains (SHP) need information on management practices that maximize crop yields and profits without irrigation. However, many of the potential combinations of management practices have not been investigated. Therefore, ARS scientists at Lubbock, Texas used a crop model driven by weather inputs from 21 west Texas Mesonet stations (2005–2016) and 32 combinations of planting dates, fertilizer levels, and seeding rates. Earlier planting dates had the greatest positive yield effect, with the lint yields increasing by 145 pounds per acre when planted on May 15th compared to June 5th. Lower plant densities also had a positive effect on profits. These crop simulations suggest planting on or before May 15 at a low plant density should maximize profitability and minimize loss on the SHP.
2. Characterization of a sugar cane aphid resistant sorghum. As irrigation-water is depleted, producers over the Ogallala Aquifer need access to drought tolerant crops, like sorghum, which can be grown under rain-fed conditions. However, profits of sorghum production are low compared to other crops. Also, controlling problems created by the new pest, sugar cane aphid, force growers to use insecticides, increasing the costs of crop production and lowering profits. ARS scientists from Lubbock, Texas characterized a mutant sorghum that has thick, narrow leaves, which showed resistance to the aphid and was drought tolerant. Incorporation of this trait into breeding programs could result in sorghum lines with greater drought and resistance to sugar cane aphid, which should lower production cost and increase profitability.
3. A framework to understand seasonal water fluctuations in the Ogallala Aquifer. On the Texas High Plains, groundwater pumping for irrigation has led to a significant depletion of the resources. As the volume of groundwater decreases, farmers need a better understanding of seasonal changes in groundwater availability and pumping rates to manage their withdrawals over the growing season. Water levels are generally observed to decline during the growing season and gradually recover when irrigation wells are switched off. However, these changes in depth to groundwater are difficult to compare and interpret. In an attempt to better understand this process, a theoretical framework was developed by ARS scientists from Lubbock, Texas and scientists from Texas Tech University. The resulting curves can be readily interpreted and compared to provide insight into seasonal irrigation patterns. Such information will provide irrigators a better estimate of groundwater availability especially later in the growing season.
4. Enhanced water use efficiency in peanuts. Carbon dioxide levels in the air have increased over the past half century. However, the effects of this increased carbon dioxide on crops is not fully understood. Therefore, ARS scientists from Lubbock, Texas examined the response of peanuts to increased carbon dioxide levels in the air under field conditions using special chambers. We discovered that the numbers of tiny pores (stomata) in peanut leaves decreased at higher carbon dioxide. Because these tiny pores also transport water out of leaves, these results suggest a mechanism where peanuts will exhibit greater water use efficiency at higher carbon dioxide levels. These results are of interest to plant physiologists, agronomists and crop breeders to better understand how crop plants can adapt to climate change.
5. Analysis of air temperatures indicate that the summer climate of the U.S. Midwestern Corn Belt has not changed. There are concerns that increases in atmospheric carbon dioxide will increase air temperatures. However, it is not well understood how changes in summer air temperatures will affect crop production in various regions of the United States. Therefore, ARS scientists at Lubbock, Texas analyzed trends in mean summer maximum and minimum temperatures from 1895 to 2015 for the important U.S. crop growing regions. Warming trends in summer minimum temperatures were found over almost all of the U.S. and increasing summer maximum temperatures were found in the west and northeast. However, no significant increases in summer temperatures were found from 1970 to 2015 for the key crop production region of the Midwestern Corn Belt. This research shows that the summer temperatures of the important agricultural region of the Midwestern Corn Belt have been stable in recent decades.
6. Analyses of multiple soil enzymes in one sample provides a new index of soil health. Farmers are interested in how cropping practices promote soil health or degrade soils. Producers need simple soil health tools to assist their selection of sustainable soil management practices. However, simple measures of soil health have been difficult to develop. Although enzyme activities are sensitive to management and represent measures of soil functions, the current protocols are time-consuming because each enzyme is measured separately. Therefore, ARS scientists in Lubbock, Texas and Minnesota developed an assay of multiple enzyme activities on the same soil sample, providing a protocol adaptable to many climatic zones and cropping systems. This method provides an index related to soil health. Our expectation is that the new assay will enable producers and land owners to assess soil health and adopt cropping practices that increase soil health.
7. Surface crusting affects the extent of soil movement by wind. Wind erosion can cause considerable damage to cropland and natural ecosystems in arid and semi-arid regions. However, the factors that affect the extent of soil erosion by wind are poorly understood. It is well established that soil texture affects wind erosion; however models using primarily soil texture as a variable tend to overestimate actual rates of soil movement by wind. Therefore, ARS scientists at Lubbock, Texas investigated the effects of soil surface crusting on wind erosion, using a portable wind erosion unit. These results confirmed the importance of surface crusting in sediment movement by wind, and will help refine wind erosion models and guide conservation management practices.
8. Wind erosion of soils in arid grassland occurs and is worst in shrubby ecosystems. Arid grasslands and shrubby ecosystems are dominant land types in the Southwestern United States and other arid regions world-wide. These regions tend to be characterized by relatively high wind velocities. However, estimates of soil or sediment movement by wind are not fully developed. ARS scientists at Lubbock, Texas measured sediment transport at locations in the Sevilleta National Wildlife Refuge in central New Mexico. Results revealed greater sediment transport rates in shrub communities than in desert grasslands; however, transport also occurred in desert perennial grasslands. These results dispute the widely held belief that soils under arid perennial grasslands were not transported by wind.
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