a b s t r a c t a r t i c l e i n f oRemote sensing technology can rapidly provide spatial information on crop growth status, which ideally could be used to invert radiative transfer models or ecophysiological models for estimating a variety of crop biophysical properties. However, the outcome of the model inversion procedure will be influenced by the timing and availability of remote sensing data, the spectral resolution of the data, the types of models implemented, and the choice of parameters to adjust. Our objective was to investigate these issues by inverting linked radiative transfer and ecophysiological models to estimate leaf area index (LAI), canopy weight, plant nitrogen content, and yield for a durum wheat (Triticum durum) study conducted in central Arizona over the winter of 2010-2011. Observations of crop canopy spectral reflectance between 268 and 1095 nm were obtained weekly using a GER 1500 spectroradiometer. Other field measurements were regularly collected to describe plant growth characteristics and plant nitrogen content. Linkages were developed between the DSSAT Cropping System Model (CSM) and the PROSAIL radiative transfer model (CSM-PROSAIL) and between the DSSAT-CSM and an empirical model relating NDVI to LAI (CSM-Choudhury). The PEST parameter estimation algorithm was implemented to adjust the leaf area growth parameters of the CSM by minimizing error between measured and simulated NDVI or canopy spectral reflectance. A genetic algorithm was implemented to identify the optimum combination of remote sensing observations required to optimize simulations of LAI through model inversion. The relative root mean squared error (RRMSE) between measured and simulated LAI was 24.1% for the CSM-PROSAIL model, whereas the stand-alone PROSAIL and CSM models simulated LAI with RRMSEs of 40.7% and 27.8%, respectively. Wheat yield was simulated with RRMSEs of 12.8% and 10.0% for the lone CSM model and the CSM-PROSAIL model, respectively. Optimized leaf area growth parameters for CSM-PROSAIL were different among cultivars (p b 0.05), while those for CSM-Choudhury were not. Only two observations, one at mid-vegetative growth and one at maximum vegetative growth, were required to optimize LAI simulations for CSM-PROSAIL, whereas CSM-Choudhury required four observations. Inverting CSM-PROSAIL using hyperspectral data offered several advantages as compared to the CSM-Choudhury inversion using a simple vegetation index, including better estimates of crop biophysical properties, different leaf area growth parameter estimates among cultivars (p b 0.05), and fewer required remote sensing observations for optimum LAI simulation.Published by Elsevier Inc.

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A study was conducted to determine the diversity of 2-, 3-, and 4-chlorobenzoate (CB) degraders in two pristine soils with similar physical and chemical characteristics. Surface soils were collected from forested sites and amended with 500 microg of 2-, 3-, or 4-CB g(-1) soil. The CB levels and degrader numbers were monitored throughout the study. Degraders were isolated, grouped by DNA fingerprints, identified via 16S rDNA sequences, and screened for plasmids. The CB genes in selected degraders were isolated and/or sequenced. In the Madera soil, 2-CB and 4-CB degraded within 11 and 42 d, respectively, but 3-CB did not degrade. In contrast, 3-CB and 4-CB degraded in the Oversite soil within 14 and 28 d, respectively, while 2-CB did not degrade. Approximately 10(7) CFU g(-1) of degraders were detected in the Madera soil with 2-CB, and the Oversite soil with 3- and 4-CB. No degraders were detected in the Madera soil with 4-CB even though the 4-CB degraded. Nearly all of the 2-CB degraders isolated from the Madera soil were identified as a Burkholderia sp. containing chromosomally encoded degradative genes. In contrast, several different 3- and 4-CB degraders were isolated from the Oversite soil, and their populations changed as CB degradation progressed. Most of these 3-CB degraders were identified as Burkholderia spp. while the majority of 4-CB degraders were identified as Bradyrhizobium spp. Several of the 3-CB degraders contained the degradative genes on large plasmids, and there was variation between the plasmids in different isolates. When a fresh sample of Madera soil was amended with 50, 100, or 200 microg 3-CB g(-1), 3-CB degradation occurred, suggesting that 500 microg 3-CB g(-1) was toxic to the degraders. Also, different 3-CB degraders were isolated from the Madera soil at each of the three lower levels of 3-CB. No 2-CB degradation was detected in the Oversite soil even at lower 2-CB levels. These results indicate that the development of 2-, 3-, and 4-CB degrader populations is site-specific and that 2-, 3-, and 4-CB are degraded by different bacterial populations in pristine soils. These results also imply that the microbial ecology of two soils that develop under similar biotic and abiotic environments can be quite different.

-Hybrids of Sorghum sudanensis (sudangrass) and Sorghum bicolor genotypes can produce high amounts of biomass, sorgoleone (a long chain hydroquinone), and other phytotoxic substances. Shoots and roots of a sorghum-sudangrass hybrid (cv. Trudan 8) were collected 10, 20, 30, 40, and 50 days after emergence. Four concentrations of aqueous extracts from the shoots and roots (0, 0.4, 2, and 10 g L -1 , w/v) were used to treat seeds of lettuce (Lactuca sativa), tomato (Lycopersicum sculentum), purslane (Portulaca oleracea), and pigweed (Amaranthus retroflexus). Seed germination of lettuce, tomato, and pigweed was inhibited by extracts from sorghum-sudangrass shoots at 10 g L -1 when made from sorghum-sudangrass plants 20 days or less in age. Seed germination of purslane was not inhibited by any sorghum-sudangrass extract. Growth of the four species evaluated were systematically inhibited when treated with 10 g L -1 extracts from sorghum-sudangrass shoots harvested up to 10 days after emergence.Keywords: allelopathy, germination inhibition, lettuce (Lactuca sativa), tomato (Lycopersicum sculentum), pigweed (Amaranthus retroflexus) and purslane (Portulaca oleracea).RESUMO -Os capins híbridos obtidos pelo cruzamento entre Sorghum sudanensis (capimsudão) e genótipos de Sorghum bicolor possuem alto potencial para produção de biomassa e para controle de plantas daninhas pela produção de substâncias fitotóxicas, como o sorgoleone (uma hidroquinona de cadeia longa). Sementes de alface (Lactuca sativa), tomate (Lycopersicum sculentum), beldroega (Portulaca oleracea) e caruru (Amaranthus retroflexus) foram submetidas a tratamentos com extratos aquosos da parte aérea e das raízes do híbrido de sorgo com capim-sudão, cv. Trudan 8, colhido em cinco diferentes estádios de crescimento (10, 20, 30, 40 e 50 dias após a emergência). Os extratos foram preparados em quatro concentrações (0, 0,4, 2 e 10 g L -1, p/v) e aplicados em quatro repetições. Após os tratamentos, a germinação e o comprimento de plântulas das espécies foram avaliados. A germinação de sementes de tomate, caruru e alface foi inibida pelos extratos da parte aérea das plantas de Trudan 8, na concentração de 10 g L 1 , colhidas até os 20 dias após a emergência. A germinação de sementes de beldroega, no tocante à porcentagem de germinação, não foi inibida pelos extratos de Trudan 8. O crescimento das quatro espécies avaliadas foi inibido quando tratadas com extratos aquosos da parte aérea de Trudan 8, colhida até os 10 dias após a emergência, na concentração de 10 g L -1. Palavras-chave: alelopatia, inibidor de germinação, alface (Lactuca sativa), tomate (Lycopersicum sculentum), caruru (Amaranthus retroflexus) e beldroega (Portulaca oleracea).

Cotton response to fruiting branch removal (FBR) is critical information in estimating plant recovery potential and making management decisions after hail storms or other physical damages. Fruiting branches were removed at first bloom (R8), 2.5‐cm boll (R12) and peak bloom (R16) growth stages. Five FBR treatments were conducted at each of the above three growth stages: 0 %, 25 %, 50 %, 75 % and 100 %. At harvest, five plants were randomly chosen from each plot and branches separated into three groups: vegetative, lower and upper fruiting branches. Lower fruiting branches were from the nodes where FBR treatments were conducted, whereas upper fruiting branches were the new branches developed after FBR. Seed cotton weight, open boll number and node number in each group were recorded. Fruiting branch removal increased boll number, boll size and boll/node on the upper fruiting branches, which compensated yield loss on lower fruiting branches. Generally, FBR at the first bloom reduced cotton yield more than it did at the 2.5‐cm boll and peak bloom growth stages when FBR percentage was lower than 75 %. The removal of all 16 fruiting branches at peak bloom reduced cotton yield by 16.8 %, indicating remarkable compensation ability by cotton plants in climates with a long growing season.

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