Latent heat flux estimation in clear sky days over Indian agroecosystems using noontime satellite remote sensing data

A simplified evaporative fraction (Λ) based single-source energy balance scheme was tested with moderate resolution (1 km) noontime satellite observations to evaluate clear sky latent heat flux (λE) estimates over diverse agricultural landscapes. This approach uses two-dimensional (2D) scatter between land surface temperature (LST) and albedo to determine Λ. The operational utility of this scheme was demonstrated for estimating regional evapotranspiration and consumptive water use during rabi (November to April) crop growing season to predict pre-harvest wheat yield (error within 15.9% of reported mean) using time series data. The existence of triangular relations between Λ and LAI (leaf area index) or NDVI (normalized difference vegetation index) was found with basal line (hypotenuse) linearly coupled with LAI or NDVI at low level of surface soil wetness. The analysis of diurnal course of in situ Λ proved the validity of constant-Λ hypothesis over pure, uniform, homogeneous crop canopies but showed irregular and wave-like patterns over heterogeneous, mixed crop canopies. The root mean square error (RMSE) of noontime and daytime average λE estimates with respect to in situ λE measurements were also smaller over homogeneous agricultural canopies (41 and 23 W m⁻²) with correlation coefficients (r) 0.94 and 0.96, respectively, from 135 clear sky datasets as compared to RMSE over heterogeneous ones (59 and 28 W m⁻² with r = 0.66 and 0.82, respectively from 22 datasets). The intercomparison with another Λ based approach (LST–NDVI 2D scatter) showed the supremacy of Λ determined from LST–albedo 2D scatter. The efficiency of LST–NDVI scatter was better during the dry down or water limited phases of crop growth only. The uncertainties of λE estimates were attributed to errors in core radiation budget inputs, relative loss of conservativeness of Λ due to canopy heterogeneity, and the inherent limitations of the single-source approach. There is further scope to reduce present λE uncertainties by combining the new findings on Λ (LST–albedo scatter)–NDVI triangular relations, diurnal Λ and two-source radiation budget.     

Modelling regional level spatial distribution of aphid (Lipaphis erysimi) growth in Indian mustard using satellite-based remote sensing data

Abstract

We developed a procedure for preparing a model for mapping spatially distributed zones of aphid pest (Lipaphis erysimi) outbreaks at a regional level. This study employed near-surface meteorological parameters derived from National Oceanic and Atmospheric Administration (NOAA) Television and Infra-Red Operational Satellites (TIROS) Operational Vertical Sounder (TOVS) data and field observations of disease infestation. The study area comprised three sites representing semi-arid and sub-humid regions of dominant Indian mustard (Brassica juncea L.)-growing regions of India. A model based on TOVS-derived cumulative surface air temperature and minimum specific humidity (SpH) was developed to estimate the date of ‘aphid onset’ (first appearance), date of peak infestation and location of severity with respect to aphid population density. Aphid population growth rate during the linear growth phase between aphid onset to peak was computed using SpH-weighted temperature and dates of sowing of the crop (crop age). Sowing dates of mustard crop, of northwest India, were obtained from spectral growth profiles derived from time series remote sensing (RS) products of the SPOT-4 VEGETATION sensor. Estimated dates of peak aphid infestation and peak population showed a strong match with the observed data. The location of peak aphid population density was depicted in each spatial grid of 25×25 km² for parts of northwest India. The simulated aphid population build-up and date of peak population density was validated with observed data for an unknown site in the Sriganganager district, Rajasthan state, India. Comparison of predicted dates of attaining peak aphid population with observations showed a deviation of ±7 days. After validation, the regional level model was applied over a large area of a mustard-growing region for varying dates of sowing, surface air temperature and specific humidity, to show the spatial distribution of aphid growing severity zones (population density) and to predict dates of severe aphid infestation (peak population) at each grid level in the region.     

Are roads and railroads barriers to bumblebee movement in a temperate suburban conservation area?

We investigated how habitat fragmentation affects the movement of marked bumblebees between plant patches in a temperate conservation area in metropolitan Boston, Massachusetts. Our study was conducted on populations of sweet pepperbush (Clethra alnifolia L. f.) separated by a road and natural woodland, and buttonbush (Cephalanthus occidentalis L.) separated by a railroad. Bumblebees showed high site fidelity and only rarely crossed roads or railroads. When bees captured at one sweet pepperbush population were moved across a road to a new sweet pepperbush population and released, they returned to their original site, some within 20 min of their capture. When all inflorescences were removed from one sweet pepperbush patch, most bees moved to another sweet pepperbush population on the same side of the road. The results show that while bumblebees have the ability to cross a road and railroad, these human structures may restrict bumblebee movement and act to fragment plant populations because of the innate site fidelity displayed by foraging bees. Moreover, marked bees were almost never observed to move between populations unless they were displaced, or forced to seek additional forage sites.     

Mutation scan screening of Echinococcus granulosus isolates of Indian origin

During the present investigation a total of forty Indian animal isolates were screened by single strand conformation polymorphism (SSCP) collected from sheep, goat, cattle and buffalo. The result of the study indicated that nuclear variants of Echinococcus granulosus were present in both small and large ruminants. SSCP phenotypes of AgB, intron of actin II and Hbx-2 have been deduced. Presence of nuclear variants due to mutation of E. granulosus has been discussed depending on hypotheses imparted earlier in literature. High polymophism of AgB demands further investigation because the gene is related with immune evasion and infectivity. This communication reports for the first time the comparative profile of Indian goat, sheep, cattle and buffalo isolates of E. granulosus complex.     

Degradation of oxadiazon in Kalyani alluvial soil

Residual fate and behaviour of the herbicide oxadiazon in Kalyani soil, paddy straw and grain were studied under subtropical conditions, in West Bengal following application @ 1 kg and 2 kg ha⁻¹. Dissipation of oxadiazon in soil followed first-order kinetics and DT₅₀ values ranged from 44 to 45 days. Residues at harvest in paddy grains and straw were also studied. Degradation of oxadiazon after 60 days of incubation at 28(± 1) °C in alluvial soil at water holding capacity yielded 10 metabolites of which four were characterised by spectroscopy. © 1999 Society of Chemical Industry     

Application of SALTMOD in Coastal Clay Soil in India

SALTMOD is a simulation model whichpredicts root zone soil salinity, drainagewater quality and water table depth inagricultural land under differentgeo-hydrological conditions and varyingwater management scenarios. The model wasapplied to the data from coastal AndhraPradesh of India where subsurface drainagesystem is laid out at several drainspacings at the experimental site. Fielddata for 1999, 2000 and 2001 were collectedfrom 35 and 55 m drain spacing plots forSALTMOD application. Modelling was doneconsidering two simulation approaches. Thefirst approach (Simulation-I) used the sameinitial values for the entire simulationperiod. In the second approach(Simulation-II), the computations wereperformed year-by-year, giving each yearthe current input values obtained from thesimulation results of the previous year.Results of these two approaches weredifferent from each other. Simulation-IIgave better predictions than that ofSimulation-I in terms of closeness to theobserved values. Simulation results ofsoil salinity in the root zone, drainagewater quality and quantity and depth towater table revealed that the salinity ofroot zone was predicted more accuratelythan that of drainage water quality anddepth to water table. Also throughsimulation, it was found that the salinityof drainage water was relativelyindependent of the root zone soil salinity. Model application study suggests thatSALTMOD can be used with confidence toevaluate various drain spacings of asubsurface drainage system and facilitatereasonable prediction of the reclamationperiod.     

Effects of Sesbania rostrata and Azolla microphylla incorporation on transformation of applied zinc and copper in lateritic rice soils with different flooding regimes

Fixation of Zn and Cu applied to tropical rice-growing lateritic soils rich in Fe-oxides may be reduced if the soils are kept flooded for a few days before their application. There may be a further reduction if such flooding is combined with incorporation of green manures. To investigate this effect, a laboratory experiment was conducted to study the effect of different periods (0 and 15 days) of preflooding combined with (0 and 0.50% of soil weight) Sesbania rostrata and Azolla microphylla incorporation as green manures on the transformation of applied Zn and Cu in two lateritic rice-growing soils. Recovery of added Zn/Cu in DTPA (diethylene triamine pentaacetate)-extractable form was always found to be higher when they were applied after the soils were maintained in a flooded state for 15 days than when applied immediately after flooding; this effect was more prominent in respect of Cu. Contrary to expectations, green manure incorporation along with preflooding caused a significant decrease in recovery of Zn/Cu; the effect, however, showed a decreasing trend as incubation progressed. The effect was more marked with A. microphylla than with S. rostrata, particularly with Cu. Possible causes of such changes and their implications on the Zn/Cu nutrition of rice are discussed. Received: 7 August 1995