A computer simulation model can be used as a tool to help explain the impact of drought stress on plant growth and development because it integrates the complex soil–plant-atmosphere system through a set of mathematical equations. The objectives of this study were to determine the impact of different irrigation scheduling regimes on peanut growth and development, to determine the capability of the CSM-CROPGRO-Peanut model to simulate growth and development of peanut, and to determine the relationship between yield and the two cumulative drought stress indices simulated by the peanut model. The CSM-CROPGRO-Peanut model was evaluated with experimental data collected during two field experiments that were conducted in four automated rainout shelters located at The University of Georgia, USA, in 2006 and 2007. Irrigation was applied when the simulated soil water content in the effective root zone dropped below a specific threshold value for the available soil water capacity (AWC). The irrigation treatments corresponded to irrigation thresholds (IT) of 30, 40, 60, and 90 % of AWC. The results showed that growth and development was reduced for the 30 and 40 % IT treatments which resulted in yield reductions that were 92 and 45 %, respectively, of the 90 % IT treatment. The Cropping System Model (CSM)-CROPGRO-Peanut model was able to accurately simulate growth and development of peanut grown under different irrigation treatments when compared to the observed data. We found an inverse relationship between the two simulated total cumulative drought stress indices for leaf growth (expansion) and photosynthesis and simulated pod yield. Knowing the cumulative drought stress value prior to harvest maturity could help with the prediction of potential harvestable yield.

BACKGROUND:The survival and distribution of enteric pathogens in soil and lettuce systems were investigated in response to several practices (soil amendment supplementation and reduced watering) that could be applied by home gardeners.RESULTS:Leaf lettuce was grown in manure compost/top soil (0:5, 1:5 or 2:5 w/w) mixtures. Escherichia coli O157:H7 or Salmonella was applied at a low or high dose (10(3) or 10(6) colony-forming units (CFU) mL(-1) ) to the soil of seedlings and mid-age plants. Supplementation of top soil with compost did not affect pathogen survival in the soil or on root surfaces, suggesting that nutrients were not a limiting factor. Salmonella populations on root surfaces were 0.7-0.8 log CFU g(-1) lower for mid-age plants compared with seedlings. E. coli O157:H7 populations on root surfaces were 0.8 log CFU g(-1) lower for mid-age plants receiving 40 mL of water compared with plants receiving 75 mL of water on alternate days. Preharvest internalization of E. coli O157:H7 and Salmonella into lettuce roots was not observed at any time.CONCLUSION:Based on the environmental conditions and high pathogen populations in soil used in this study, internalization of Salmonella or E. coli O157:H7 into lettuce roots did not occur under practices that could be encountered by inexperienced home gardeners.

The effect of atmospheric water vapor (AV) on plants has mostly been neglected in climate impact studies. The objectives of this study were to determine the effect of AV on photosynthesis (Pn), dry matter production (DM), transpiration (Tr), leaf conductance (gl) and water use efficiency (WUE), in climate controlled chambers. The relative humidity (RH) was held near 30, 60, and 85%. DM and WUE increased with RH. δDM/δRH ~ 0.3 from 30% to 60% and ~2.2 from 60% to 85%, δWUE/δRH ~0.2 for all RH's. The improved WUE at a rate of 0.2 units for each percent of increased RH resulted from a synergy between larger gl and lower Tr at high RH. This conclusions carries a bleak message to dry regions.

Spatial salinity mapping with a mobile sensor platform allowing GPS-labeled data on turfgrass areas would facilitate site-specific leaching programs for salinity management. A salinity monitoring device (SMD) based on 4-Wenner array electrical resistivity (ER) electrode configuration was developed for turfgrass sites and tested on three soils at Griffin, GA and a golf course fairway in Naples, FL on two dates where the fairway received saline irrigation water. Using directed soil sampling, the SMD resulted in soil apparent soil electrical conductivity (ECa) vs. laboratory saturated paste extract electrical conductivity (ECe) linear relationships with r(2) of 0.59 to 0.87 (p < 0.0002) for 0 to 10 cm and 0 to 20 cm zones at Griffin, GA. For two mapping events varying two-to threefold in salinity levels at the golf course fairway, the ECa vs. ECe linear regressions exhibited similar slopes, different intercepts (due to two to threefold difference in background salinity), and r(2) of 0.53 to 0.58 (p < 0.002). On another fairway, a detailed spatial salinity map using geographic information systems (GIS) methods was developed using a sampling grid of 2 by 3 m, which was well within the 19 m range determined for spatial autocorrelation of the data. Our data suggest the empirical methods developed for agricultural soils for relating ECa to ECe and for determining average ECa of discrete subsurface zones may differ under turfgrass conditions due to stratification of the surface organic matter layer influencing water holding capacity, soluble salt retention, and averaging ECa within a subsurface zone.

Environmental pests may serve as reservoirs and vectors of zoonotic pathogens to leafy greens; however, it is unknown whether insect pests feeding on plant tissues could redistribute these pathogens present on the surface of leaves to internal sites. This study sought to differentiate the degree of tissue internalization of Escherichia coli O157:H7 when applied at different populations on the surface of lettuce and spinach leaves, and to ascertain whether lettuce-infesting insects or physical injury could influence the fate of either surface or internalized populations of this enteric pathogen. No internalization of E. coli O157:H7 occurred when lettuce leaves were inoculated with 4.4 log CFU per leaf, but it did occur when inoculated with 6.4 log CFU per leaf. Internalization was statistically greater when spinach leaves were inoculated on the abaxial (underside) than when inoculated on the adaxial (topside) side, and when the enteric pathogen was spread after surface inoculation. Brief exposure (similar to 18 h) of lettuce leaves to insects (5 cabbage loopers, 10 thrips, or 10 aphids) prior to inoculation with E. coli O157:H7 resulted in significantly reduced internalized populations of the pathogen within these leaves after approximately 2 weeks, as compared with leaves not exposed to insects. Surface-contaminated leaves physically injured through file abrasions also had significantly reduced populations of both total and internalized E. coli O157:H7 as compared with nonabraded leaves 2 weeks after pathogen exposure.

Spatial and temporal variation of soil, climate, plants and irrigation requirements are challenges for modern agriculture and complex turfgrass sites. Precision agriculture (PA) evolved to improve site-specific management based on obtaining site-specific information. The focus of this concept paper is on the emerging area of precision turfgrass management (PTM) with attention given to: (a) comparing the concepts of PTM and PA in terms of driving forces and challenges that must be addressed for PTM to progress in science and practice and (b) discussion of specific field mapping applications (purposes) for different turfgrass situations such as golf courses, sod production fields and sports fields. The field applications relate to site-specific management of irrigation, salinity, fertilizer application and cultivation. To illustrate the potential for PTM, different approaches that may be necessary for PTM compared to PA are discussed. The initial factor that hindered the adoption of PTM has been the lack of mobile sensor platforms that can determine both key soil and plant properties for turfgrass situations. This paper concentrates on PTM field applications that involve mapping of both soil and plant attributes, in contrast to only optical sensing mapping.

An increase in atmospheric CO2 concentration ([CO2]) together with other climate change factors could greatly affect agricultural productivity. Understanding the impact of the change in atmospheric [CO2] in conjunction with the ongoing global change is crucial to prepare for mitigation and any adaptation for future agricultural production. The main goal of this project was to study the time-course pattern of cotton plant growth in response to [CO2] and temperature to investigate the hypothesis that whether response to elevated [CO2] would change at different temperatures. An experiment was conducted in the controlled-environment chambers of the Georgia Envirotron with two different day/night temperatures levels, e.g., 25/15 °C and 35/25 °C, and three CO2 concentrations, e.g., 400, 600 and 800 μmol l−1. The experimental design was completely randomized with four replicates (plastic containers) per treatment. Growth analysis was conducted at bi-weekly intervals during the growing season. In addition, leaf area, leaf dry mass, root dry mass, square dry mass, boll dry mass and total above dry mass per plant were also measured at each sampling. Plant traits, including plant height, number of leaves, number of squares and number of bolls were recorded weekly. The number of days to emergence, squaring, flowering and maturity were also observed. The results showed that by increasing [CO2] to 600 μmol l−1 total biomass increased at both temperature levels, but a further increase of [CO2] up to 800 μmol l−1 increased total biomass only at the temperature of 35/25 °C. Throughout the growing season, there was no significant effect of [CO2] levels on LAI. Increasing temperature from 25/15 °C to 35/25 °C had a positive impact on LAI across all CO2 levels (P < 0.05). Increasing CO2 from 400 to 600 μmol l−1 significantly increased the number of squares by 31.4%, but a further increase to 800 μmol l−1 caused a 6.6% decrease (non-significant) in the number of squares. The interactive effects of [CO2] and temperature indicated that at a higher temperature, CO2 would be more beneficial as we proceed towards the end of the growing season. However, further studies are needed to really understand the interaction between higher [CO2] and temperature levels and cultivar characteristics.

The interpretation of plant growth in terms of cumulated intercepted or absorbed solar radiation, and the efficiency with which this energy is used for dry matter production, has received much attention in the literature. Although the concept of plant radiation use efficiency is perfectly sound in theory, it may be difficult to use this technique predictively because the values for radiation use efficiency for a given crop may vary with site and season. Analysis and experimental data are used to demonstrate the methodological weaknesses of a simplistic interpretation of crop growth in terms of cumulated intercepted energy. When crop growth and radiation interception data are analyzed in a way that avoids these methodological weaknesses, the results show that under normal field conditions corp growth rates are not correlated with the rates of interception of solar energy. Also, although the oversimplifications of the early research have been recognized, we argue that there is still too much emphasis placed on the correlative relationship between cumulated intercepted energy and crop growth.