1a. Objectives (from AD-416)
The goal of this research will be to obtain knowledge and develop tools that will enable planners, decision makers, and producers to more effectively manage, conserve, and protect water resources. Specific objectives are as follows: 1)Develop cotton and peanut production systems for humid areas that are based on site-specific water and nutrient applications, 1a)Develop water management strategies in humid areas that optimize spatial and temporal water applications, 1b)Develop and explore spatial nutrient management for irrigated and non-irrigated crops in humid areas; 2)Develop practices that increase crop water use efficiency in rainfed/irrigated cropping systems in relation to tillage, irrigation, and crop management practices; and 3) Develop practices and technologies that enhance denitrification and expand the knowledge of microbial communities including their genetics and implication on geospecific disease in riparian buffers, wetlands, and streams for improving water quality.
1b. Approach (from AD-416)
This 5-year project utilizes a systems approach to identify and develop strategies for improved spatial management of water and nutrients. The project explores the spatial components of irrigation, tillage, and nutrient management. In spatial irrigation, the project will focus on identifying strategies for managing a site-specific irrigation system to conserve water and nutrients while maintaining cost effective production. In tillage management, the project will focus on efficiency of water use using tillage practices that will improve infiltration and soil water-holding capacities under site-specific irrigation to determine the spatial uptake and water use efficiency to improve spatial water management. In nutrient management, the project will focus on both in-field and off-site management. In-field nutrient management will focus on spatial nitrogen applications on cotton and Coastal bermudagrass to improve crop production and reduce the impact of off-site nitrogen movement. Off-site nitrogen and water management will focus on understanding the geospatial variability of microbial communities along with nitrous oxide emissions from riparian buffers, wetlands, and streams.
3. Progress Report
A peanut irrigation experiment was designed to assess the potential of the irrigation scheduling model ‘Irrigator Pro’ as a tool for site-specific irrigation; it was conducted on the Center’s site-specific irrigation facility for a fourth year. Three spatial irrigation methods were used a) individual soil types within plots watered based on soil water tension readings, b) individual soil types based on an Irrigator Pro scheduling, and c) whole plot watering based on the Irrigator Pro scheduling. Canopy temperatures and vegetative indices were measured during the growing season to evaluate spatial variability within and among the irrigation treatments. Soils from the various irrigation treatments were collected to evaluate the residual nitrogen contents. Infiltration rates and water contents were measured in selected plots to relate water use efficiency to site-specific irrigation management; data analyses are underway. To evaluate spatial nutrient management for irrigated crops in humid regions, an experiment using the site-specific center pivot irrigation system was conducted for two years to evaluate nitrogen and irrigation interactions on Coastal bermudagrass forage yield and quality. The study included 4 irrigation amounts, 3 nitrogen rates, 2 cutting frequencies, and 3 replications (72 plots). Experimental design was a split-plot with cutting frequency as main plots and the irrigation by nitrogen levels as subplots. Vegetative indices were measured during the growing season and biomass samples collected for forage nitrogen concentration and forage ruminant nutritive quality. In the current year, we are evaluating the use of the vegetative indices to spatially apply nitrogen to the bermudagrass crop. With commercial instruments available, soil electrical conductivity is a relatively easy way to identify differences in fields for soil physical properties. Field experiments were conducted with cotton and peanuts in an attempt to identify how soil electrical conductivity can be used to improve spatial water and N fertilizer applications. Microbial communities were examined in riparian buffer zones using DNA sequencing and real-time PCR. Two genes in the biological denitrification pathway, nirS and nosZ, were sequenced from twelve riparian buffer zone sites to correlate the effect between microbial populations and greenhouse gas emissions. Real-time PCR was performed to examine the correlation between microbial denitrification gene densities in riparian buffer soils with greenhouse gases produced by microbially-mediated pathways.
1. Variable Rate Irrigation Management: Traditional irrigation systems apply water at the same rate over an entire field. Site-specific irrigation allows precise amounts of water to be applied to specific areas where and when plants need them for optimal growth. An experiment was conducted to evaluate spatial management of both water and fertilizer on a site-specific irrigation system in Florence, South Carolina. Corn was grown in a field experiment using a center pivot irrigation system that had been modified to make site-specific applications of water and fertilizer. Treatments included three irrigation regimes, four nitrogen fertilizer amounts, and with four replications. As expected, corn grain yields increased with irrigation and nitrogen fertilizer, but how the corn crop responded varied among the three years. In two of the three years, corn grain yield increased with increased nitrogen fertilizer. These increases were greater with irrigation than with only rainfall. A regression analysis was then used to evaluate the yield response to combined fertilizer and water treatments. For the rainfed only treatment, yield response to nitrogen fertilizer was linear in all three years. The yield response to nitrogen fertilizer for the combined irrigation treatments was quadratic in two of three years. These results should be helpful in developing management strategies and decision support systems for profitable management of water and nitrogen fertilizer on spatially-variable soils in the southeastern Coastal Plain while conserving natural resources and protecting the environment.
2. Cotton response to conservation tillage during drought: Climate prediction models indicate that as greenhouse gasses continue to accumulate in the atmosphere, the southeastern US will experience more periods of drought. Production practices are needed that will maintain productivity during extended rain-free periods. ARS scientists at Florence, SC, in collaboration with Clemson University, found that during drought years, conservation tillage resulted in a 25% yield increase compared to conventional tillage. These results will be used by researchers and extension personnel in the development of improved cotton production practices that help ensure sustainable production in a changing climate.
3. Potential impacts of biomass feedstock production on water resource availability: High fuel costs have scientists looking for alternatives to oil. One alternative is bioenergy from waste materials and crops. Bioenergy has the added benefit of mitigating the effects of reducing greenhouse gases, which may affect climatic change. However, use of crops to provide significant amount of bioenergy involves new challenges for agriculture including management of water resources for both fuel and food. We reviewed and assessed potential bioenergy production based on its impact on water resources and the impact of water resources on bioenergy sustainability. Water is already a limited resource that is often globally over-allocated. When bioenergy crops are being selected, planners must assess water availability as well as the potential bioenergy crop water use. Additionally, climate and weather will impact water along with the production and sustainability of bioenergy crops. Diversity in bioenergy crops is needed to lessen potential supply disruptions due to crop failures or weather-related events. Corn has been shown to be highly impacted by weather and water. However, improved crops, water management, recycled water, and new technologies for bioenergy conversion offer opportunities for sustainably producing bioenergy crops.
Stone, K.C., Hunt, P.G., Cantrell, K.B., Ro, K.S. 2010. The potential impacts of biomass feedstock production on water resource availability. Bioresource Technology. 101:2014-2025.