Gregory W. McCarty

Acquisition of NIR-Green-Blue Digital Photographs from Unmanned Aircraft for Crop Monitoring

Payload size and weight are critical factors for small Unmanned Aerial Vehicles (UAVs). Digital color-infrared photographs were acquired from a single 12-megapixel camera that did not have an internal hot-mirror filter and had a red-light-blocking filter in front of the lens, resulting in near-infrared (NIR), green and blue images. We tested the UAV-camera system over two variably-fertilized fields of winter wheat and found a good correlation between leaf area index and the green normalized difference vegetation index (GNDVI). The low cost and very-high spatial resolution associated with the camera-UAV system may provide important information for site-specific agriculture.

Near infrared reflectance spectroscopy for the analysis of agricultural soils

The objective of this work was to investigate the usefulness of near infrared (NIR) reflectance spectroscopy in determining: (i) various constituents (total N, total C, active N, biomass and mineralisable N, and pH), (ii) parameters (soil source, depth from which sample was obtained, type of tillage used) and (iii) rate of application of NH4NO3 fertiliser) of low organic matter soils. A NIRSystems model 6250 spectrometer was used to scan soil samples (n = 179) obtained from experimental plots at two locations with three replicate plots under plow and no till practices at each location with three rates of NH4NO3 for each plot (2 × 3 × 2 × 3). For each of these, samples were taken from five depths for a total of 2 × 3 × 2 × 3 × 5 or 180 samples (one sample lost). The results demonstrated that NIR reflectance spectroscopy can be successfully used to determine some compositional parameters of low organic matter soils (particularly total C and total N). It is also apparent that for non-biological parameters (excluding soil type as reflected by source) such as the depth from which the sample was obtained, the rate of application of NH4NO3 fertiliser and the form of tillage used, that NIR reflectance spectroscopy is not very useful, unless a very limited set of samples is used (i.e. single tillage and location). For other determinations, such as pH, biomass N and active N, the results may be useful depending on the exact needs in question. Finally, from the results presented here, NIR reflectance spectroscopy was not successful in determining soil N mineralisable in 21 days.

COMPARISON OF NEAR INFRARED AND MID INFRARED DIFFUSE REFLECTANCE SPECTROSCOPY FOR FIELD-SCALE MEASUREMENT OF SOIL FERTILITY PARAMETERS

Data-intensive technologies such as precision agriculture require new approaches for acquisition of soil data on landscapes. We compared the ability of near infrared (NIR; 400-2500 nm) and mid infrared (MIR; 2,500-25,000 nm) spectroscopy for field-scale acquisition of soil fertility parameters. Samples were obtained in a grid pattern (25 m spacing) from the surface (0-10 cm) and sub-surface (10-30 cm) samples collected at 272 locations. Samples were analyzed for organic C and total N, texture (clay, silt, and sand), soil pH, and Mehlich I extractable Ca, K, Mg, and P. We found that chemometric analyses NIR and MIR provided good calibrations for organic carbon, total N, and soil texture. To varying degrees of precision, these regions also calibrated for pH and exchangeable Ca, Mg, and K. Exchangeable P did not form useful calibrations in either spectral region. In all cases, MIR calibrations were better than those formed in the NIR region. Test of calibrations based on one-third of the samples was used to predict the remaining samples. This demonstrated the strategy of developing field-scale calibrations for the spectral regions by chemical analysis of a small sub-set of samples for the prediction of large numbers of samples. This approach can be used to accurately map the spatial distribution of soil properties within agricultural landscapes. These studies demonstrate the utility of infrared spectral approaches for generating the spatial soil properties data needed to implement precision agriculture technology.

Denitrification and degassing in groundwater estimated from dissolved dinitrogen and argon

Abstract The groundwater concentrations of dinitrogen (N2) and argon (Ar) were measured in a transect of a Danish riparian wetland in order to estimate N2 production from denitrification, the concentration of Ar being used as an internal tracer for degassing. Dissolved N2 increased by 135 μM N2-N. Simple calculations incorporating the decrease in groundwater dissolved Ar and the partial pressure of N2 revealed that 376 μM N2-N was degassed along the transect. Total denitrification thus amounted to 511 μM N2-N, correlating well with the measured NO3− reduction of 503 μM NO3-N. The total partial pressures of dissolved gases (N2, O2, Ar, and CO2) exceeded the hydrostatic pressure, thus confirming that degassing was a plausible mechanism for loss of dissolved gases in this riparian wetland. This study provides strong evidence that losses of dissolved Ar along a transect parallel to groundwater flow can be used to assess the amount of dissolved N2 degassed and thereby permit estimates of N2 production under conditions without conservation of gases within the groundwater system.

Quantitative analysis of agricultural soils using near infrared reflectance spectroscopy and a fibre-optic probe

The objective of this work was to investigate the usefulness of near infrared (NIR) reflectance spectroscopy in conjunction with a fibre-optic probe for determining various constituents (total N, organic C, active N, biomass and mineralisable N and pH) in agricultural soils. A NIRSystems model 6500 spectrometer equipped with a fibre-optic reflectance probe was used to scan soil samples (n = 180) obtained from experimental plots at two locations with three replicate plots under plow and no till practices at each location with three rates of NH4NO3 for each plot (2 × 3 × 2 × 3 = 36). For each of these, samples were taken from five depths for a total of 2 × 3 × 2 × 3 × 5 or 180 samples. Optimal calibrations were achieved using first derivative spectra, and only data from 1100 to 2300 nm, with every 20 data points averaged from 1900 to 2300 nm. Compared to results achieved using a spinning cup, the use of the probe resulted in more concentration outliers (up to 6% with probe and none with the spinning cup), the reason for which is unknown. Otherwise, the final calibration results were quite similar to those achieved using a spinning cup to obtain spectra, with calibration (outliers removed) R2 and RMSD/Mean of 0.96, 6.6; 0.95, 6.5; 0.88, 15.3; and 0.80, 19.3; for organic C, total N, active N and biomass N, respectively. The R2 and RMSD for pH were 0.80 and 4.5 pH units, respectively. In summary, the work presented here demonstrated that NIR spectroscopy, based on data obtained using a fibre-optic probe, can be successfully used to determine compositional parameters of agricultural soils (particularly organic C and total N). However, there appeared to be a greater problem with outliers when using a fibre-optic probe than was true when obtaining spectra using a spinning cup.

Evaluation of coal combustion byproducts as soil liming materials: their influence on soil pH and enzyme activities

There is considerable interest in the use of coal combustion byproducts as soil liming materials in agricultural production, but there is concern that such use may be detrimental to the quality of agricultural soils. To evaluate these byproducts as liming materials and address issues related to soil quality, we compared the influence of different amounts of four combustion byproducts [fly ash and bed ash from a fluidized bed combustion furnace, lime-injected multistage burner residue, and spray dryer residue] and CaCO3 on soil pH and activities of urease, phosphatase, arylsulfatase, and dehydrogenase in an acidic soil. Studies comparing the influence of the combustion byproducts and CaCO3 on soil pH showed that on a weight basis of application, substantial differences were observed in the ability of these materials to influence soil pH but that such differences decreased markedly after the data were transformed to a CaCO3 equivalent basis of application. Analysis of covariance for these transformed data indicated that whereas the liming abilities of fly ash and CaCO3 were not significantly different when compared on the CaCO3 equivalent basis, those of bed ash, multistage burner residue, and spray dryer residue were less than that of CaCO3. Studies comparing the influence of the byproducts and CaCO3 on soil enzyme activities showed that the effect of these liming materials on the enzyme activities studied was largely due to their influence on soil pH. The relationships obtained between soil pH and enzyme activities in soil amended with the liming materials generally demonstrated the marked similarities in the influence of the combustion byproducts and CaCO3 on these activities when observed within the domain of soil pH. These studies showed that the combustion byproducts tested functioned as soil liming materials in a manner similar to that of CaCO3 and seemed to have little adverse effect on soil quality.

Can Near or Mid‐Infrared Diffuse Reflectance Spectroscopy Be Used to Determine Soil Carbon Pools?

Abstract The objective of this study was to compare mid‐infrared (MIR) an near‐infrared (NIR) spectroscopy (MIRS and NIRS, respectively) not only to measure soil carbon content, but also to measure key soil organic C (SOC) fractions and the δ13C in a highly diverse set of soils while also assessing the feasibility of establishing regional diffuse reflectance calibrations for these fractions. Two hundred and thirty‐seven soil samples were collected from 14 sites in 10 western states (CO, IA, MN, MO, MT, ND, NE, NM, OK, TX). Two subsets of these were examined for a variety of C measures by conventional assays and NIRS and MIRS. Biomass C and N, soil inorganic C (SIC), SOC, total C, identifiable plant material (IPM) (20× magnifying glass), the ratio of SOC to the silt+clay content, and total N were available for 185 samples. Mineral‐associated C fraction, δ13C of the mineral associated C, δ13C of SOC, percentage C in the mineral‐associated C fraction, particulate organic matter, and percentage C in the particulate organic matter were available for 114 samples. NIR spectra (64 co‐added scans) from 400 to 2498 nm (10‐nm resolution with data collected every 2 nm) were obtained using a rotating sample cup and an NIRSystems model 6500 scanning monochromator. MIR diffuse reflectance spectra from 4000 to 400 cm−1 (2500 to 25,000 nm) were obtained on non‐KBr diluted samples using a custom‐made sample transport and a Digilab FTS‐60 Fourier transform spectrometer (4‐cm−1 resolution with 64 co‐added scans). Partial least squares regression was used with a one‐out cross validation to develop calibrations for the various analytes using NIR and MIR spectra. Results demonstrated that accurate calibrations for a wide variety of soil C measures, including measures of δ13C, are feasible using MIR spectra. Similar efforts using NIR spectra indicated that although NIR spectrometers may be capable of scanning larger amounts of samples, the results are generally not as good as achieved using MIR spectra.

Near infrared reflectance spectroscopy for the determination of biological activity in agricultural soils

The objective of this work was to investigate the usefulness of near infrared (NIR) reflectance spectroscopy in determining biological activity in agricultural soils. A Foss-NIRSystems model 6500 spectrometer, equipped with a spinning sample cup module, was used to scan 179 soil samples obtained from experimental plots at two locations with three replicate plots under plough and no-till practices at each location with three rates of NH4NO3 for each plot with samples taken from five depths for a total of 180 samples (one sample lost). Biological activity as measured by four enzymes (dehydrogenase, phosphatase, arylsulfatase and urease) and nitrification potential was determined by conventional methods and NIR reflectance spectroscopy. Investigations showed NIR reflectance spectroscopy to be capable of determining biological activity as reflected by the four enzymes and nitrification potential to at least some degree. With the best R2 in the range of 0.8, the results, while positive, were not as good as found previously for many other components (i.e. total C and N) in the same sample set. Efforts at simple discrimination into high, medium and low activities were not successful, and for the most part, calibrations based on subsets, such as samples from only one location, were not found to be an improvement. Correlation analysis indicated that measures of biologically-active nitrogen might be the basis for these determinations. Finally, while further research will be needed to define clearly the basis for, limitations to and usefulness of NIR reflectance spectroscopy in determining biological activity in soil samples, the results presented indicated that NIR reflectance spectroscopy might be useful for the rapid determination of such activity in cases where extreme accuracy is not required, such as spatial mapping.

Effects of N fertilizer treatments on biologically active N pools in soils under plow and no tillage

Abstract Studies assessing the effects of different tillage and N fertilizer management practices on distributions and amounts of various C and N pools in soil can provide information about the influence of such management on the quality of organic matter in agricultural soils. To assess the influence of management on soil quality, we characterized the organic matter by measurements of total N, organic C, microbial biomass N and active N in the 0–20cm profiles of soil from long-term field experiments containing plots under treatments of plow or no tillage and 0, 135, or 270kgNha–1 fertilizer. Previous work had established that on the basis of the crop growth requirement of maize, these application rates of fertilizer N provide amounts of N that are deficient, sufficient, and excessive, respectively. The studies reported provide evidence that the sufficient amount of fertilizer N stimulated formation of the biologically active pools of N (biomass N and active N) in soils under no tillage treatments, but the excessive amount of fertilizer N tended to suppress these pools. The results demonstrated that these influences of excessive N fertilization were not reflected in distributions of total N or total organic C in soil profiles but became evident with the measurements of biologically active N. This suggests that such measurements can provide information related to the influence of different management practices on soil quality.

An Improved ASTER Index for Remote Sensing of Crop Residue

Unlike traditional ground-based methodology, remote sensing allows for the rapid estimation of crop residue cover (fR). While the Cellulose Absorption Index (CAI) is ideal for fR estimation, a new index, the Shortwave Infrared Normalized Difference Residue Index (SINDRI), utilizing ASTER bands 6 and 7, is proposed for future multispectral sensors and would be less costly to implement. SINDRI performed almost as well as CAI and better than other indices at five locations in the USA on multiple dates. A minimal upgrade from one broad band to two narrow bands would provide fR data for carbon cycle modeling and tillage verification.