Effects of Soil Fumigation and Seeding Regimes on Secondary Succession in a Semiarid Shrubland

In order to ascertain the degree to which disturbance and subsequent recovery of belowground biotic components (mycorrhizal and decomposer systems) influence successional dynamics, a portion of semiarid shrubland in northwest Colorado was mechanically disturbed in 1984. Two treatments, soil fumigation (fumigated with methyl bromide and not fumigated) and seeding (early-seral species, late-seral species, and not seeded) were imposed on 500 m2 plots in each of four replications. Aboveground annual production by species, and decomposition rates were measured in 1991, 7 years after the initial disturbance and treatments. Mycorrhizal infection potential had been previously measured at this site from 1984-1988. Seeding to late-seral species resulted in greater production rates (and greater community composition) of late-seral species, whereas seeding to early-seral species had only a minor effect when compared to unseeded plots 7 years after disturbance. Fumigation slowed the rate of succession on unseeded plots, primarily by decreased production of perennial grasses. Mycorrhizal infection potential, initially greatly reduced by the disturbance and by fumigation, recovered to near-background levels on unfumigated plots but not on fumigated plots after 4 years. Decomposition experiments suggest that seeding may have facilitated recovery of the decomposer system after initial disturbance and fumigation. Our results suggest that the redevelopment of soil biotic communities following disturbance has a significant impact on successional dynamics, particularly the replacement of early-seral annuals by mid-seral perennial grasses.     

Effects of Nighttime Air Temperature During Kernel Development of Field‐Grown Rice on Physicochemical and Functional Properties

Elevated nighttime air temperatures (NTATs) occurring during critical grain‐filling stages affected rice physicochemical properties, which impacted functional quality. Six cultivars were grown at multiple field locations from northern to southern Arkansas during 2007 to 2010. Nighttime temperatures were recorded throughout production at each of the locations, and 95th percentiles of NTATs were calculated for each cultivar's reproductive (R) stages. Amylose content and crude protein content decreased linearly, whereas total lipid content increased linearly, with increasing NTATs occurring during the grain‐filling stages (R6–R8). Effects of NTAT on proximate composition influenced functional properties. Peak viscosities increased linearly as NTAT increased, whereas setback viscosities decreased. Setback viscosities were linearly correlated to NTATs for medium‐grain cultivars, but correlations were quadratic for the long‐grain cultivars. Gelatinization temperatures increased linearly with increasing NTAT. The R stages in which correlations were strongest varied by cultivar and by property, hypothesized to result from differences in kernel development patterns among cultivars. These findings have significant implications for rice production scientists and processors, in that understanding the effects of NTAT on physicochemical and functional properties may help explain and reduce quality variation.     

Comparative evaluation of compost humic acids and their effects on the germination of switchgrass (Panicum vigatum L.)

Purpose

This study aimed to investigate comparatively the main chemical and physico-chemical properties of the humic acid (HA) fraction of three different composts and to evaluate the bioactive effects of these HAs on the germination and early growth of four populations of switchgrass.

Materials and methods

Three compost HAs isolated from a green compost (HA_GC), a mixed compost (HA_MC), and a coffee compost (HA_CC) were characterized for some chemical and physico-chemical properties, such as ash content, elemental composition, total acidity, carboxylic and phenolic OH group contents, E₄/E₆ ratio, Fourier Transform infrared (FT IR), and fluorescence spectroscopies. In subsequent experiments conducted in vitro in a climatic chamber under controlled conditions, the bioactive effects of the three HAs at concentrations of 10, 50, and 200 mg?L^?1 were tested on the germination and early growth of four switchgrass (Panicum virgatum L.) populations, the octaploids Shelter, Shawnee and Dacotah, and the tetraploid Alamo.

Results and discussion

The ash content and the E₄/E₆ ratio were, respectively, much higher or slightly higher for HA_CC than for the other two HAs. HA_MC showed the lowest C and H contents and the highest O content, whereas HA_GC had the highest N content. The total acidity and phenolic OH group content followed the order: HA_MC?>?HA_CC?>?HA_GC. The fluorescence analysis of the three HAs evidenced a common fluorophore unit possibly associated to simple aromatic structures, such as phenolic-like, hydroxy-substituted benzoic and cinnamic acid derivatives. The FT IR spectra of all HA samples indicated the presence of aromatic phenolic structures. Significant beneficial effects were produced by any HA on switchgrass germination and early growth as a function of the population tested and the HA dose.

Conclusions

Results of this study demonstrated that the addition of compost HAs to the germination medium of four switchgrass populations positively influenced the germination process and the growth of primary root and shoot. Significant correlations were found between HA bioactivity and some HA properties. These results suggest a possible use of compost as soil amendment in areas where switchgrass grows naturally or is cultivated.     

The role of lysine amino nitrogen in the biosynthesis of mousy off-flavor compounds by Dekkera anomala

Mousy off-flavor is an insidious and economically disastrous microbiologically derived spoilage characteristic of wine and other fermented beverages. Tainted wines are rendered unpalatable and there is currently no satisfactory procedure for removal of the off-flavor. Here we report the confirmation of that both d- and l-lysine can act as a precursor for the formation of mousy off-flavor N-heterocycles. Further, through the use of stable isotope feeding experiments, we could establish that a pentylamine group from lysine is incorporated into the piperideine moiety of two off-flavor N-heterocycles. A biochemical pathway for the formation of mousy off-flavor compounds is proposed.     

A review of downscaling methods for remote sensing-based irrigation management: part I

High-resolution daily evapotranspiration (ET) maps would greatly improve irrigation management. Numerous ET mapping algorithms have been developed to make use of thermal remote sensing data acquired by satellite sensors. However, adoption of remote sensing-based ET maps for irrigation management has not been feasible due to inadequate spatial and temporal resolution of ET maps. Data from a coarse spatial resolution image in agricultural fields often cause inaccurate ET estimation because of a high level of spatial heterogeneity in land use. Image downscaling methods have been utilized to overcome spatial and temporal scaling issues in numerous remote sensing applications. In the field of hydrology, the image downscaling method has been used to improve spatial resolution of remote sensing-based ET maps for irrigation scheduling purposes and thus improves estimation of crop water requirements. This paper (part I) reviews downscaling methods to improve spatial resolution of land surface characteristics such as land surface temperature or ET. Each downscaling method was assessed and compared with respect to their capability of downscaling spatial resolutions of images. The companion paper (part II) presents review of image fusion methods that are also designed to increase spatial resolutions of images by integrating multi-spectral and panchromatic images.     

ET mapping for agricultural water management: present status and challenges

Evapotranspiration (ET) is an essential component of the water balance. Remote sensing based agrometeorological models are presently most suited for estimating crop water use at both field and regional scales. Numerous ET algorithms have been developed to make use of remote sensing data acquired by sensors on airborne and satellite platforms. In this paper, a literature review was done to evaluate numerous commonly used remote sensing based algorithms for their ability to estimate regional ET accurately. The reported estimation accuracy varied from 67 to 97% for daily ET and above 94% for seasonal ET indicating that they have the potential to estimate regional ET accurately. However, there are opportunities to further improving these models for accurately estimating all energy balance components. The spatial and temporal remote sensing data from the existing set of earth observing satellite platforms are not sufficient enough to be used in the estimation of spatially distributed ET for on-farm irrigation management purposes, especially at a field scale level (∼10 to 200 ha). This will be constrained further if the thermal sensors on future Landsat satellites are abandoned. However, research opportunities exist to improve the spatial and temporal resolution of ET by developing algorithms to increase the spatial resolution of reflectance and surface temperature data derived from Landsat/ASTER/MODIS images using same/other-sensor high resolution multi-spectral images.