CO2 and H2O exchange of crop ecosystems in the Southeast

Summary

In 2020 we conducted (1) experiments and quantify the influence of different tillage practices (strip till vs. conventional till) on peanut water-use efficiency and yield at the Sunbelt Expo, Moultrie, GA, (2) experiments on peanut water-use efficiency and yield influenced by seed rate at the UGA Southwest Research and Education Center, Plains, GA , (3) experiments in a micro-irrigated commercial pecan orchard King Spring Pecans, Hawkinsville, Georgia with the goal of developing a model for irrigation and water-use efficiency management in pecan tree growth, (4) processing data and analyzing results on the influence of planting date on peanut water-use efficiency and yield, (5) a study using an economical micro-drone equipped with a camera sensitive to water content changes in the golf turf to develop a low-cost irrigation scheduling methodology, (6) finalizing our work on the influence of different peanut planting patterns (single-row vs. twin-row) on its water-use efficiency and yield, and (7) finalizing our work on quantifying carbon dioxide stored by Spartina Alterniflora L. one of the most productive ecosystems on earth on the Georgia Coast near Sapelo Island.

Situation

Peanut is one of the important row crops in Southeast USA, especially in Georgia. With increasing drought frequency, it has been crucial to improve water-use efficiency while maintaining high peanut yields through different management practices. One such practice is tillage. Conservation tillage is believed to be one of the ways to save water and preserve soil and microbes, while conventional tillage also has its advantages in terms of creating fine seedbeds and a weed-free environment for crops. One aspect of peanut experiments in 2020 was to study quantitatively the influence of tillage on peanut water use efficiency and yield. Another practice is the planting seed rate. Seeds are one of the most expensive variable input (18% of variable cost) in peanut production. A higher seed rate results in increased competition between plants for water, space, and light and higher seed cost. On the other hand, a lower seed rate can cause increased loss from TSWV. Therefore, this aspect of peanut experiments in 2020 was to quantify the impact of three different seed rates on both peanut water-use efficiency and yield and determine the optimum seeding rate. Peanut planting pattern and planting date are also important practices that affect peanut water-use efficiency and yield. We analyzed results from previous experimental data, presented the results at a national conference, wrote and submitted a related peer-review article in 2020. Georgia is the one of the largest producers of pecan in United States. Pecans require ample amount of water during the growing season to produce quality nuts. The water requirement of the trees is more than its supply through rainfall: thus, to fulfill its water needs frequent irrigation must supplement rainfall every season. A slightest water stress during kernel filling stage can result in degradation of the quality of nuts. An increasingly drier climate in the Southeast of the US coupled with increasing regional competition for water, suggest that studies related to sustainable irrigation and enhancing WUE are rapidly becoming important. Thus, the aim of the study is to optimize existing water resources and to enhance water-use efficiency to maximize yield. Several studies had been already conducted on pecans with respect to irrigation, primarily in the Southwest. However, our goal is to provide a water-use model considering different environmental factors for micro-irrigated orchards in the Southeast. Therefore, our main objective is to enhance the WUE of pecans and to provide guidance to growers to optimize the irrigation timings during the growing season. With water conservation rapidly becoming a source of concern in the state, conservation of water resources is quickly becoming a priority for golf course superintendents. While golf courses have historically been proactive in addressing efficient irrigation, increasingly limited water resources require a more quantitative approach to determine the degree of water stress so that the optimum amount of water is applied on golf courses. In 2020, we processed and analyzed the 2019-fall experiment with a low-cost drone technology hosting a multi-spectral camera to assess the optimum amount of water used by turf in golf courses and the spatial distribution of water stress, in an effort to seek the optimum irrigation schedule by identifying the water deficit. A little understood ecosystem in the state is the coastal one. Salt marshes are among the most productive and dynamic ecosystems on Earth and globally sequester an average of 210 g C m−2 yr−1. To understand the role of this ecosystem in the carbon cycle and its changes as a result of rapid climate change and human disturbance, a baseline record particularly on carbon dioxide (CO2) exchange between this ecosystem and atmosphere needs to be established. The goal of this study is to determine the effects tide events on the exchange of CO2 in a salt marsh ecosystem dominated by Spartina alterniflora using the eddy-covariance method near Sapelo Island, GA. One peer-review article had already appeared in a high impact peer-review publication and another one is being finalized.

Response

1. Peanut crop with different tillage methods In 2020, two large, adjacent fields at the Sunbelt Expo, Moultrie, GA were selected for the experiment. Peanuts were planted on two types of tillage systems: strip tillage in one field and conventional tillage in another field. Peanut cultivar Georgia-06 was used in both fields. Three-dimensional wind components, temperature, and concentration of water vapor and carbon dioxide were measured in a sampling frequency of 10 Hz with the eddy-covariance method. The data are collected to estimate peanut field evapotranspiration and CO2 exchange with the atmosphere that indicates the canopy respiration (with night data) and photosynthesis (with daytime data) at the field scale. The leaf area index was measured weekly in each field. Soil samples were taken in each field to measure soil physical properties before field tillage and at the end of peanut growth. Evapotranspiration, CO2 fluxes, and water-use efficiency were calculated by using software EddyPro and Matlab. 2. Peanut crop with different planting seed rates In 2020, three large, adjacent fields at the UGA Southwest Research and Education Center, Plains, GA were selected for the experiment. Peanuts were planted in three seed rates: 4.5, 7, and 9.5 seeds per foot. Peanut cultivar Georgia-06 was used in both fields. Three-dimensional wind components, temperature, and concentration of water vapor and carbon dioxide were measured in a sampling frequency of 10 Hz with the eddy-covariance method. The data are collected to estimate peanut field evapotranspiration, CO2 exchange with the atmosphere, and water-use efficiency at the field scale. The leaf area index was measured weekly in each field. Yield and its component sampling were taken when peanut was dug out and harvested. Data analysis is ongoing. 3. Model for yield and irrigation needs in Pecan Stem water potential and crop coefficient data collected in 2019 provided convincing evidence that water stress generally occurs at nut enlargement stage which can ultimately affect the quality and yield of the nuts. In 2020, a series of experiments were conducted in a micro-irrigated commercial pecan orchard King Spring Pecans, Hawkinsville, Georgia. Fluxes of carbon and water vapor have been measured at field scale with an eddy-covariance system. Soil moisture content has been measured with Time Domain reflectometer at three different depths and at two different soil types for making comparison of lateral movement of water in the orchard. Individual tree transpiration data has also been collected by sap flow sensors at both contrasting soil types. Along with these measurements, irrigation treatment of different irrigated water amount has been conducted so that the data output of soil moisture conduct can be used for modeling. A numerical model HYDRUS 1-D will be used to simulate soil water movement to estimate irrigation requirements given the weekly quantified precipitation forecasts to optimize root water uptake for next growing season. The model will be calibrated using previous dataset and the calibrated model will be used to estimate crop water-use under different irrigation scenarios. i) Current rate and amount of applied irrigation water; ii) Half the rate but double the amount of applied irrigation water and iii) Double the rate but half the amount of applied irrigation water. We expect to evaluate if a different irrigation scenario would have resulted in greater root water uptake. This result will be used to determine if the current irrigation scheduling practices are optimum or can be altered to enhance root water uptake. We will create a table suggesting the weekly irrigation amounts and timings under different weather scenarios and antecedent moisture conditions. Estimate potential crop water use for the pecan trees weekly using the models developed in a) for possible future weather conditions. Processing and analysis of the data for year 2020 will be conducted after the harvesting in late November. 4. Peanut crop with different planting dates In 2020, we processed previous experimental data and analyzed results on the influence of planting date on peanut water-use efficiency and yield, by combing together experiments of three years. A peer-reviewed paper is in preparation. 5. Optimum scheduling of water application on golf courses in the state In 2020, we processed and analyzed the 2019-fall experimental data set. It included the evapotranspiration and crop coefficient at the field scale with the eddy-covariance method, soil water content and soil temperature, turfgrass water content and water potential, and NDVI image data of the golf course with a low-cost drone technology hosting a multi-spectral camera. The results are used to assess the optimum amount of water used by turf in golf courses and the spatial distribution of water stress, in an effort to seek the optimum irrigation schedule by identifying the water deficit. 6. Peanut crop with different planting patterns In 2020, we revised the peer-reviewed paper on the influence of planting pattern on peanut water-use efficiency and yield and resubmitted for publication. 7. Salt marsh Spartina In 2020, we worked on the paper writing related to the exchange of CO2 in a salt marsh ecosystem dominated by Spartina alterniflora near Sapelo Island, GA. We have one peer-reviewed paper published, one paper is currently being revised based on reviewers’ comments. A third one is in internal review.

Impact

1. Peanut crop with different tillage methods The preliminary result suggested that trip tillage had greater water-use efficiency and yield as compared to conventional tillage. A greater leaf area index was observed in the strip tillage suggesting more photosynthesis and yield. For the second year, data analysis is being conducted. 2. Peanut crop with different planting dates Results suggest that the late planting date (early June) presents the largest water-use efficiency (20-65% higher than the earlier planting dates in late April and at middle May over three years) during the early growing stage and the greatest yield (14-30% greater than the other two planting timings over three years). However, the late planting date carries an increased risk of low temperature late in the season which can reduce yield in many years. 3. Peanut crop with different planting patterns Results suggest that, in 2016, the early canopy closure of the twin-row crop resulted in a greater CO2 flux and water-use efficiency by 31.8% and 27% early in the season, respectively. In mid and late peanut growth stages in 2018, with high precipitation and low vapor pressure deficit, the water-use efficiency and CO2 flux of twin-row planted peanut were greater than single-row by 9% and 7-10%, respectively. The twin-row peanut yield was greater than single-row in 2018. These results suggest that with high precipitation and low vapor pressure deficit, greater water-use efficiency of twin-row peanut could be one of the reasons for its greater yield as compared to single-row peanut. 4. Salt marsh Spartina We found that the net ecosystem exchange of salt marsh dominated by Spartina alterniflora in the Sapelo Island, Georgia was ~ 60% greater during neap high tides than during spring high tides; the largest differences occurred early in the growing season. The effect of tidal flooding varied continuously with the degree to which plants were inundated versus emergent. The total monthly reduction (less negative) in daytime net ecosystem exchange due to flooding was 7-38% and 1-64% in 2014 and 2015 respectively. The highest CO2 flux reductions were observed early and during the peak growing season (February, March, April and May) and the lowest during the summer season in both years. Our findings suggest that daytime CO2 flux was reduced (less negative) 30-40% during the peak growing season due to tidal flooding. A better understanding of the impact of seasonal tidal flooding on net ecosystem exchange may allow more sophisticated predictions of how sea level rise will affect marsh function and survival over the coming century.

State Issue

Sustainability, Conservation, & the Environment

Details

• Year: 2020
• Geographic Scope: Multi-State/Regional
• County: Colquitt
• Location: Southwest Georgia Research and Education Center, Plains
• Program Areas:
  • Agriculture & Natural Resources