Astrid Volder

Cultivar evaluations for drought tolerance and irrigation management are very important in water-limited, arid regions of the United States. This study was conducted to investigate the effect of deficit irrigation (50% vs. 100% crop evapotranspiration, ETc) on three melon (Cucumis melo L.) cultivars (Mission and Da Vinci, reticulatus type and Super Nectar, inodorus type). Overall, deficit irrigation significantly reduced photosynthetic rate (Pn) by 30% and stomatal conductance (gs) by 21%. The highest average Pn (20.53 µmol·m-2·s-1 of CO2) and gs (0.31 mol·m-2·s-1 of H2O) were recorded in Mission and Super Nectar, respectively. Transpiration rate and leaf water use efficiency were not significantly affected by either irrigation or cultivar. Throughout the development period, physiological traits were affected by cultivar and irrigation regimes. At fruit set Pn and gs were reduced with deficit irrigation in all cultivars but recovered only in cv. Da Vinci. Deficit irrigation signific...

In multispecies systems, facilitation and complementarity can offset some of the negative effects of interspecies competition. This can lead to more efficient use of resources by the plant community as a whole, resulting in an increase in productivity. Overyielding, a phenomenon whereby plant production in mixture exceeds that of production in monoculture, has been attributed to complementary use of resources by different plant functional types. Different combinations of peanut, watermelon, okra, cowpea and pepper in single crop and various intercropping combinations were investigated in a low-input organic system in Texas. Each species was selected to perform a specific function within the system. Results from land equivalent ratio (LER) and per plant production calculations show that the intercropping combination with peanut, watermelon and okra (Wpwo) and peanut, watermelon, okra and cowpea (Wpwoc) consistently overyielded and performed the best overall in both 2011 and 2012. Pla...

Placing impermeable pavement around existing trees can cause declines in tree growth and health due to reduced water infiltration and soil surface gas exchange.Using pervious concrete, with greater water infiltration and gas permeability, could be a good alternative. The purpose of this study was to test soil respiration, root growth and soil extract chemistry in root zones of American sweetgum (Liquidambar styraciflua) as affected by pavement. The experimental setup consisted of twenty-five sweetgum trees, with root zones covered by standard concrete (five plots), pervious concrete (10 plots) or left uncovered (control, 10 plots). Each plot was outfitted with access points for soil respiration measurements. Soil respiration was measured monthly on two access holes per plot, with three sub-measurements per access hole. Data collected from February 2008 to January 2009 indicated that soil respiration correlated with seasonal soil temperatures. We observed tremendous variability in so...

Ecosystem services have been defined as the benefits that human populations derive directly or indirectly from ecosystem functions. These services range from the obvious, such as provision of food and fiber and timber for homes, to the less obvious, such as microbial nutrient cycling in soil and environmental cooling by vegetation. This chapter discusses the services, resources, and benefits provided in natural and human dominated ecosystems.

Humans significantly affect their ecosystem. Nowhere is this more evident than in our towns and cities around the world. We have options when it comes to the sustainability of our cities. We have to pay attention to meeting the needs of today without compromising the needs of the future. However, to truly understand those options, we need to have the best knowledge available so that we can make the best decisions possible. It has everything to do with the stewardship of our natural resources, while at the same time using those resources to meet the needs of today’s urban population. This volume deals with the impacts of urbanization on the environment— soils, air, and water quality, the animals and humans who live there—and offers some solutions to contemporary problems. Its coverage exemplifies the wide range of specialties in the agronomic sciences and shows how scientists define ecosystem functions and solve problems. To read this book will give instruction in how agronomy, an ar...

The presence of vegetation is thought to reduce loss of soil substrate after roof installation; however, few attempts have been made to quantify this effect. Twelve green roof modules placed at a 2% slope were used to quantify the effect of wind, precipitation intensity ,vegetation and vegetation type on modular green roof substrate depth. The presence of vegetation reduced substrate loss immediately after installation of equipment, yet had little effect on substrate depth once the substrate had settled. Neither wind speed nor precipitation rate had a direct effect on substrate depth, although after some large rainfall events substrate depth increased due to media expansion caused by the retained water. Overall we observed negligible substrate depth decrease, regardless of vegetation presence, wind speed or precipitation intensity.

Green roofs can improve urban environments by reducing the amount of runoff and in some cases improve the quality of runoff leaving urban areas. Water quality and soil chemistry of four green roofs in Houston that harvest and recycle rainwater and irrigation runoff were investigated. The green roofs vary in age from 2.5 to 8 years. Continuous recycling of water is expected to decrease soil and water quality and in turn decrease plant productivity. Soil cores, irrigation samples, and runoff samples were collected and analyzed. Preliminary irrigation samples indicate that the sodium absorption ratios (SAR) are below 2 which are not concerning. Electrical conductivity is relativley high (450, 450 475, 300 µS/cm respective of age) in the irrigation water compared to the soil (all below 200 µS/cm). Soil organic matter percentage was rather high for a green roof substrate ranging from 15% to 18%. Other nutrient concentrations in the soil do not appear to be high enough to become problemat...

ABSTRACT Background/Question/Methods Crop rotations during the heat of Texas’ summers are limited due to the poor availability of crops that can withstand the high temperatures. Additionally, management practices that enhance or sustain soil and crop productivity while reducing inputs can increase producer profit and reduce the potential for nutrient runoff and leaching. We are currently investigating different combinations of watermelon, peanut, okra, cowpea and pepper in single crop and various intercropping combinations and their effects on ecosystem services and plant productivity. Each component crop was selected to perform a specific function within the system. Specifically, we are assessing the effects of plant functional diversity on soil temperature, soil moisture, and soil health (organic matter content, microbial C and N, total and organic C and N) in a system following strict organic guidelines. A randomized complete block design with 3 replicates was utilized for this study. Results/Conclusions Although data analysis is ongoing, preliminary observations suggest that intercropping combinations utilizing watermelon reduce soil temperatures and promote short-term soil moisture retention. Temperatures were reduced by between 2 and 3°C on average and short-term soil moisture retention was increase by 25% VWC in these treatments. Okra benefited most from intercropping when compared to its monocrop with an increase in soil moisture content of 46% VWC. Contradictory to our hypothesized outcome, preliminary results from soil microbial biomass analysis suggest a decrease in soil microbial C in the intercropping combination of peanut, watermelon and okra as compared to peanut, watermelon and okra grown in monocrop, 701, 940, 955 and 1161 µg C/g dry soil respectively. There was no significant difference in soil microbial N between the 4 treatments. We are currently conducting root trait analysis in addition to analyzing other soil chemistry parameters to help explain these observations. The preliminary information gathered from this investigation has the potential for alleviating heat and soil moisture stress on crops during the peak of the summer heat in Texas. However, the potential effects of these systems on soil health and nutrient cycling have yet to be conclusively determined from this study.

... Mechanistic modeling using an optimization or cost-benefit approach can be a powerful tool in ... required for root con-struction, growth, ion uptake and maintenance, as well as costs associated with ... 8.2.4 Variation in Root Life Span in Different Environments and Among Species ...

Pecan is an important nut crop grown throughout much of the southern U.S, with New Mexico, Georgia, and Texas ranked as the leading producers. The commercial pecan nursery industry currently relies on improved cultivars grafted on rootstocks derived from open-pollinated seeds. Seedstocks are chosen in relation to their geographical origin and general historical performance as rootstocks. Despite the fact that certain seedstocks are recommended more than others for particular soil or climate conditions, little is known about the physiology of known rootstock cultivars of pecan. An experiment was conducted to investigate the physiological differences between two open-pollinated pecan seedlings (Apache and Elliott) grown in field conditions. Traditionally, ‘Apache' has been recommended for the dryer regions of the pecan producing area, whereas ‘Elliott' is more frequently used in the more humid southeast. The study was conducted from May to September 2007 on rain-fed, six-year-...

Increased continuous irrigation due to drought conditions and above average temperatures, and resulting salt buildup in soils, can lead to a decline in yields in salt-sensitive species such as watermelon. This greenhouse investigation is phase one of a two-phase study aimed at assessing the potential benefits of utilizing halophytic species as companion crops to watermelon in salt-affected soils. From this initial screening, two species will be selected for intercropping with watermelon in a field setting. Based on a set of criteria, the six species chosen for this screening were four-wing saltbush (Atriplex halimus), barley (Hordeum vulgare), garden orache (Atriplex hortensis), purslane (Portulaca oleracea), saltwort (Suaeda salsa), and wheat (Triticum aestivum). Treatments of 0, 3, and 6 dS/m irrigation water were applied to plants over a 5-week period and plant species were replicated 5 times within each treatment level in a randomized complete-block design. Preliminary results f...

After an outbreak of blotch leafminer (Cameraria caryaefoliella) on field-grown pecan (Carya illinoinensis) trees in 2010, an experiment was conducted to evaluate the consequences of the injury on carbon assimilation and photosynthetic efficiency, and, in particular, to assess if low-to-moderate injury induces a compensatory increase in photosynthesis. Gas exchange and light-adapted fluorescence were measured on non-injured portions of the leaflet lamina adjacent to the injured area as well as on portions of leaflets that included leafminer injury. Results indicate that damage of the photosynthetic apparatus did not extend beyond the injured areas by leafminers. Furthermore, although a strong relationship between the proportion of leafminer injury and area-based net CO2 assimilation rate of injured leaflet tissue was found, there was no evidence that pecan leaves were able to compensate for leafminer injury by upregulating CO2 assimilation in leaflet tissue that was unaffected.

Citrus production in Texas, currently valued at approximately $75 million, is the third largest citrus industry in the U.S., with Hidalgo and Cameron Counties in the Lower Rio Grande Valley (LRGV) accounting for more than 98% of bearing acres. In recent years, the citrus industry in the U.S. and the LRGV in particular, has been facing numerous challenges with emerging diseases and recurrent droughts. Increased water deficits and other drought-related issues such as increased soil salinity have prompted the need for efficient water management strategies, including alternative water sources, and adoption of stress tolerant varieties to mitigate the effects of drought, salinity, and to meet population needs along the U.S.–Mexico border. Currently, the Rio Grande River provides most of the irrigation and domestic water in the LRGV, but proximity to the Gulf of Mexico limits groundwater use for crop irrigation in this area due to salt-water intrusion. Grafting can enhance plant yield, di...

As climate change impacts rainfall distribution and frequency many agricultural producers are turning to alternative water sources as supplemental irrigation. Often these sources are of low quality and high in salinity. Glycophytic crops, which include most agricultural crop species, are negatively impacted by salt stress. This results in a dramatic decrease in yield and quality when salt is present in the soil. Citrus, a salt sensitive crop, tolerates less than 2 dS m-1 of salt before yields are reduced. Sour Orange (SO) is a common rootstock used in the citrus industry, however, it is susceptible to Citrus Tristeza Virus (CTV) which has led to the decline of its use in recent years. Several newer rootstock varieties are CTV resistant; C22 and C146 rootstocks are among the most promising but have not been tested for their salinity tolerance. The objectives of this experiment were to determine the impacts of salinity on grafted and non-grafted citrus rootstocks by taking physiologic...

Background/Question/Methods Fully understanding the combined effect of elevated CO2 and climate warming on nitrogen (N) cycling in pastures requires an understanding of changes in tissue N and C:N ratios in response to climate and management treatments. In addition, it requires a full accounting of above- and belowground biomass production. We examined the effects of elevated atmospheric CO2 concentration, atmospheric warming and clipping frequency on tissue C and N concentrations and biomass responses of the pasture grass Phalaris aquatica. Phalaris aquatica swards were grown in the field within six transparent temperature gradient tunnels - three at ambient atmospheric CO2 concentrations and three at 750 ppm CO2 concentration. Within each tunnel there were three air warming treatments; no warming (ambient control), +2.2 / +4.0 oC above ambient day/night warming, and +3.0 oC continuous warming. Within each warming treatment there were two clipping frequencies, low and high. Treatme...

Water stress alters biomass allocation strategies of crop plants, resulting in changes in root growth patterns in time and space. Understanding these changes will assist in screening cultivars for drought tolerance traits in melons. This study was conducted to investigate the effect of deficit irrigation (50% vs. 100% crop evapotranspiration, ETc) on root growth of three melon (Cucumis melo L.) cultivars (Mission and Da Vinci, reticulatus type and Super Nectar, inodorus type). Root length intensity (RL; mm·cm-2) was measured using the minirhizotron method six times at biweekly intervals during 2012 growing season, and at final harvest with the soil core method. Minirhizotron data showed that RL increased significantly up to 70 days after planting (DAP), with no significant differences among 70, 84, 98, and 112 DAP. Both minirhizotron and soil core methods showed similar root growth trends at final harvest, concluding that deficit irrigation significantly enhanced root growth in &#39...

Summary • This study examined the effects of warming, elevated atmospheric CO 2 and cutting regimen on the growth of Phalaris aquatica cv. Holdfast swards. • Six temperature gradient tunnels (TGT) were used to manipulate both air temper- ature and atmospheric CO 2 concentrations (ambient and 750 ppm). Within each tunnel, there were three temperature treatments: no warming, constant warming

ABSTRACT Increasing concentrations of greenhouse gases are projected to elevate global surface air temperatures by 1.1 to 6.4°C by the end of the century, and potentially magnify the intensity and variability of seasonal precipitation distribution. The mid-latitude grasslands and savannas of North America are predicted to experience a shift towards drier summers and wetter spring and fall seasons. The purpose of this study was to quantify belowground C and N storage in soils and roots of dominant oak savanna plant species under experimental warming and rainfall manipulation. Research was conducted at the Texas A&M Warming and Rainfall Manipulation (WaRM) Site in College Station TX where eight 9x18m rainout shelters and two unsheltered controls were established in post oak savanna in 2003. Replicate (n = 4) annual rainfall redistribution treatments were applied at the shelter level (long term mean vs. 40% of summer redistributed to fall and spring with same annual total). Warming treatments (ambient vs. 24-hr IR canopy warming of 1-3°C) were applied to planted monocultures of the dominant tree (post oak and juniper) and grass (little bluestem) species and two tree-grass combinations within each shelter in native soil. Soil organic carbon (SOC) and soil total nitrogen (STN) were quantified on soil cores taken to 10 cm depth in 2009 after 6 yrs of temperature and rainfall manipulation. SOC ranged from 800-1100 g C m-2 and STN ranged from 59-76 g N m-2 across all treatment combinations. Neither SOC nor STN was affected by plant species composition. Values for SOC were highest in the control rainfall plots for both warmed and ambient temperature treatments, whereas highest values for STN were in warmed plots with control rainfall. Lowest values for SOC and STN were found in warmed plots with redistributed rainfall. Therefore, 1-3°C warming coupled with drier summers appears to reduce SOC and STN storage, perhaps due to water limitations on primary production and more rapid rates of decomposition in response to warming. These changes in soil C and N storage in response to global change drivers may have important implications for net primary production, soil fertility, carbon storage, interspecific interactions, and vegetation dynamics in the oak savanna region of North America.