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
1) Data were collected from a peanut experiment designed to assess the potential of the irrigation scheduling model ‘Irrigator Pro’ as a tool for site-specific irrigation. The irrigation experiments were conducted on the Center’s site-specific irrigation facility for a third year to assess three spatial irrigation scheduling methods. The three spatial irrigation treatments were a) individual soils within plots based on tensiometers, b) individual soils based on an Irrigator Pro, and c) whole plot irrigation based on the Irrigator Pro. 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. 2) To evaluate spatial nutrient management for irrigated crops in humid regions, an experiment using the site-specific center pivot irrigation system was conducted for a second year to evaluate nitrogen and irrigation interactions on Coastal bermudagrass forage yield and quality. The study includes 4 irrigation amounts, 3 nitrogen rates, 2 cutting frequencies, and 3 replications (72 plots). Experimental design is a split-plot with cutting frequency as main plots and the irrigation by nitrogen levels as subplots. Canopy temperatures and vegetative indices were measured during the growing season and biomass samples collected for forage nitrogen concentration and forage ruminant nutritive quality. 3) To develop practices or technologies that enhance denitrification in riparian buffers and wetlands for improving water quality in streams: Substantial progress was made in the quality assurance and quality control of direct measurements via photoacoustic analysis technology. In particular, the lower limit validity relative to the lower limits of emission being commonly reported from global investigations of wetlands. This is important because most of the wetlands will have significant denitrification capacities. Yet, only a few will produce significant quantities of nitrous oxide. Thus, it is extremely important to know that the negative emission measurements are valid. Site selection has progressed in VA so that sampling and measurements are proceeding. The MD and NC site selection and sampling will begin within a few weeks.
1. Variable Rate Irrigation Management: Improved spatial analysis: Variable rate or site-specific irrigation provides farmers with the ability to allocate limited water resources while potentially increasing profits. However, lack of basic knowledge about spatial and treatment-varying crop response to irrigation hinders irrigation management. In the emerging field of site-specific or precision agriculture, varying crop responses are important, so statistical methods are needed that simultaneously explain both treatment and the spatial variation. A methodology was developed that explains the variations and also provides estimates of the uncertainty in the result. The methodology was demonstrated with an example of corn yield data obtained under site-specific irrigation and it can be implemented using any of a number of standard statistical software packages. This new statistical methodology provides a much needed tool for crop advisors to better account for spatial variation in precision agricultural research.
2. Subsurface Drip Irrigation for Narrow-row Corn Production: Short-term droughts occur about every other year in the southeastern US Coastal Plains and frequently cause water stress in plants, reduced yields, and decreased farm income. Irrigation can help to reduce the impact of these problems. Although sprinkler irrigation is the most commonly used method to water agronomic crops in the region, drip irrigation offers the potential to conserve soil water and reduce evaporation. We investigated feasibility of utilizing subsurface drip irrigation in combination with corn planted in narrow-rows. In a two-year study, corn was planted in narrow (38-cm) rows on an irrigation site that had subsurface drip tubes buried 0.3 meters below the soil surface and spaced at both 1 and 2 meters apart. We found that the distance of the corn rows from the subsurface drip lateral influenced the crop growth and grain yield. Plant biomass, plant nitrogen, ear length, and grain weight all decreased significantly with distance from the subsurface drip irrigation laterals. These results demonstrate that both irrigation systems and cropping practices could be easily optimized for both profitability and conservation of limited water resources.
3. Forage Quality and Energy Content of Subsurface Drip Irrigated Coastal Bermudagrass: Land application of animal waste from livestock treatment systems in the eastern US is both an environmental and social concern. To address these concerns, we installed and evaluated a subsurface drip irrigation system for advanced-treated swine effluent application to coastal bermudagrass hay. We then evaluated both the forage quality and the energy content of harvested bermudagrass hay as a potential biofuel. The forage quality was evaluated by feeding hay grown on the irrigation system to wether sheep. We found that the irrigation system produced adequate quality bermudagrass hay for ruminant production systems. The energy content of the bermudagrass hay from the irrigation system ranged from 127 to 251 Mega Joule per ha. Hay grown with effluent had higher yields and greater energy content per hectare. These results demonstrated that a subsurface drip irrigation system for advanced-treated swine effluent application can produce quality hay forage and bioenergy while protecting environmental quality.
4. Assessment of Microbial Community Structures in Riparian Buffer Zones Adjacent to High Ammonia Load Agricultural Lands: Riparian buffers are a best management practice utilized extensively in the protection of freshwater ecosystems from agriculturally generated nitrate pollution. While there are several routes for nitrate removal from riparian buffer zones, microbial mediated denitrification is thought to serve as the primary mechanism. While several studies have looked at the microbial community structure of riparian buffer zones, none of these studies were performed in riparian buffer zones adjacent to areas receiving heavy nitrate loads. Riparian buffers located next to fields receiving high nitrate loads are of particular importance because studies have indicated that these riparian buffers have a higher propensity for nitrous oxide – a greenhouse gas – emissions. We employed microbial fingerprinting methods and 16S rDNA gene sequencing to examine the diversity and microbial community structure of a Coastal Plain riparian buffer zone system and identified a positive correlation between the microbial phylum Proteobacteria and both complete and incomplete denitrification. Addressing environmental conditions conducive to the propagation of micro organisms capable of complete nitrification has the potential to improve riparian buffers as a better management practice for reduction of both nitrate pollution and emission of greenhouse gases.
Holan, S., Wang, S., Arab, A., Sadler, E.J., Stone, K.C. 2008. Semiparametric Geographically Weighted Response Curves with Application to Site Specific Agriculture. Journal of Agricultural, Biological, and Environmental Statistics. 13(4):424-439.