Shrinivasa K. Upadhyaya

A NIR Technique for Rapid Determination of Soil Mineral Nitrogen

The objective of this investigation is to determine the possibility of rapidly sensing soil mineral-N content using near infrared (NIR) reflectance. Simulation studies were conducted to determine the ability of Partial Least Squares (PLS) and Principal Components Regression (PCR) techniques to relate NIR spectral data to soil nitrate content in the presence of interfering effects and experimental noise. The simulation studies revealed that both PLS and PCR techniques were quite robust in predicting soil nitrate content provided the calibration set included the same interfering effects. These techniques failed completely if the prediction set contained interfering effects which were not included in the calibration set. This implies that a site-specific calibration is necessary for this technique to work successfully. Laboratory tests using Yolo loam and Capay clay soil samples as well as verification tests using field soils (Yolo loam and Capay clay) mixed with nitrogen fertilizer indicated that soil mineral-N content can be determined using the NIR technique provided site-specific calibration is used.

SEED LOCATION MAPPING USING RTK GPS

The potential use of a real-time kinematics (RTK) GPS receiver for seed mapping with a high level of accuracy was investigated. High-accuracy seed mapping can potentially be used in weed control and plant-specific crop management. A four-row Salvo 650 vacuum planter was retrofitted with an RTK GPS receiver. Four seed detector sensors (one per planting unit) were mounted directly above the planter shoes. These sensors detected the seeds as they fell through seed tubes. Two low-cost single-board computers were used to acquire data in real time and display it in the tractor cab. The first computer was interfaced to the RTK GPS unit to determine seed location and forward speed. The second computer was interfaced to a display unit mounted in the cab. The first computer obtained the GPS time and UTM coordinates every second and stored them with a reference time (time tag). This computer also monitored the seed detector sensors, time-tagged the seeds from each unit, and stored the information in memory. The second computer monitored the first computer and reported the planter’s performance through the display unit mounted in the tractor cab. Field tests were conducted to check the performance of this planter over two growing seasons. The first year test results indicated a need to control the sensitivity of the seed detector sensors used for seed detection. The second year tests showed that the improved system performed very well. The differences between the actual plant and the seed map generated by the RTK GPS based planter were in the range of 30 to 38 mm.

SENSING SOIL MOISTURE USING NIR SPECTROSCOPY

Seven California soils were studied to determine if near infrared (700 to 2500 nm) reflectance spectroscopy could be used to determine soil moisture content. Near infrared absorbance data in the 1400– to 2400–nm region correlated well (r 2 = 0.97, SEP = 1.3%, Bias = 0.2%) with soil moisture content when a partial least squares calibration model was used to estimate the moisture content of soil samples of the same soil type and particle size as those in the calibration data set. However, when the model was used to estimate the moisture content of a soil sample with a particle size which differed from those included in the calibration set, the performance was degraded due to large slope and bias errors (Bias = 4.0%, SEP = 2.2%). However, the high coefficient of determination (r 2 = 0.98) suggested that predictions for soil samples which differ from those included in the calibration set could be improved if the slope and intercept were corrected for a given site. An example validation of this type was shown where the SEP and bias were reduced from SEP = 2.1% and Bias = 6.0% to SEP = 1.0% and Bias = 0.9% after slope and bias correction.

Traction prediction equations for radial ply tyres

Abstract Three radial tyres (16.9R38, 18.4R38 and 24.5R32) were tested in two different soil types (Capay clay and Yolo loam), five different soil treatments (conditions) in each of the two soils, at three different axle loads and two different inflation pressures to obtain traction prediction equations for radial tyres. The field data were analysed to obtain traction prediction equations under varying soil and loading (vertical load, inflation pressure) conditions for radial ply tyres. Simulation studies were conducted to determine the effect of soil conditions, dynamic load on the axle and inflation pressure on the tractive performance of radial ply tyres. The results indicate that (i) changes in soil conditions influence tyre performance much more than changes in tyre loading and dimensions; (ii) in a given soil condition the 24.5R32 tyre appears to perform better than the other two tyres; (iii) the performance of the 18.4R38 tyre was similar to that of the 16.9R38 tyre, although at lower soil cone index values, the 18.4R38 tyre performed slightly better than the 16.9R38 tyre.

An instrumented device to obtain traction related parameters

Abstract A fully instrumented device to measure soil properties relevant to traction has been developed. The device can measure soil sinkage parameters (sinkage constant and exponent) utilizing sinkage plates, as well as soil shear parameters (maximum shear stress and shear modulus) using grouser plates. Moreover, this device can be used to measure soil come index. Field tests were conducted using three different rectangular plates (sinkage tests), and five different rectangular grouser plates (shear tests) in a firm and a tilled Yolo loam soil. The results of these tests show that the device works well in all three modes.

Development, Construction, and Field Evaluation of a Soil Compaction Profile Sensor

Studies have shown that an increased level of soil compaction leads to a reduction in infiltration characteristics of soil, which in turn leads to low soil moisture. Conventional methods of measuring soil compaction are tedious, time consuming, and expensive. The objective of this study was to develop and evaluate a soil compaction profile sensor (SCPS) that could assist in the assessment of the state of compactness of the soil profile in real-time. The device developed in this study consisted of eight cutting elements, designed to provide information on soil resistance to cutting for every 7.5 cm layer down to a total depth of 60 cm. The design produced a sensor with a backward-sloping rake angle and a total thickness of 5.1 cm. Extensive field tests were conducted during summer and fall of 2001 and spring of 2002 in loamy, clayey, and sandy fields. Within each soil type, three different moisture conditions were included in the test (low, medium, and high). Analysis of the test data revealed that the soil cutting force was a function of soil bulk density, moisture content, and the location of the cutting element within the soil profile. Additional analyses were conducted to relate soil cutting force profile to the cone index profile. The empirical relationship between predicted and measured profile sensor output had a coefficient of multiple determination (R2) of 0.977, indicating that the SCPS can potentially be used to make real-time measurements of soil strength profile.

FEASIBILITY OF DETECTING SOIL NITRATE CONTENT USING A MID–INFRARED TECHNIQUE

The long–range goal of this study was to develop a portable, soil nitrate sensor to determine soil nitrate content in–situ. The immediate objective of this study was to develop a rapid technique to determine soil nitrate content using diffuse reflectance spectroscopy in the mid–infrared (MIR) range. A Fourier Transform Infrared (FTIR) spectrophotometer was used to determine the MIR response of various concentrations of calcium nitrate solution in water. The results clearly showed the existence of a strong nitrate absorption peak at 7194 nm (1390 cm –1 ). For KBr–diluted soil samples, the ratio of the area under the nitrate absorbance peak (1360–1390 cm –1 ) to the water absorbance peak (1640–1660 cm –1 ) was proportional to nitrate concentration. Mid–infrared diffuse reflectance spectroscopy detected soil nitrate content at low concentrations in KBr–diluted soil samples. However, when undiluted soil samples containing varying amounts of nitrate content were tested in the MIR range, it was necessary to further condition the data with noise filtering techniques. Three noise removal techniques were compared to improve the spectral quality: (1) the Savitzky and Golay, (2) FFT filtering, and (3) wavelet denoising. The wavelet denoising technique resulted in the highest coefficient of determination (R 2 = 0.856) for nitrate prediction. These noise removal techniques could not remove specular reflection effects and band overlap. To overcome these problems, a continuous wavelet transform, which could remove specular reflection as well as minimize noise, was used to deconvolute the soil spectral data, resulting in a high correlation (R 2 = 0.878) between soil nitrate content and MIR diffuse spectral reflectance.

A model of Agrobacterium tumefaciens vacuum infiltration into harvested leaf tissue and subsequent in planta transgene transient expression

Agrobacterium-mediated gene transfer, or agroinfiltration, can be a highly efficient method for transforming and inducing transient transgene expression in plant tissue. The technique uses the innate DNA secretion pathway of Agrobacterium tumefaciens to vector a particular plasmid-encoded segment of DNA from the bacteria to plant cells. Vacuum is often applied to plant tissue submerged in a suspension of A. tumefaciens to improve agroinfiltration. However, the effects of vacuum application on agroinfiltration and in planta transient transgene expression have not been well quantified. Here we show that vacuum application and release act to drive A. tumefaciens suspension into the interior of leaf tissue. Moreover, the amount of suspension that enters leaves can be predicted based on the vacuum intensity and duration. Furthermore, we show that transient expression levels of an agroinfiltrated reporter gene vary in response to the amount of A. tumefaciens vacuum infiltrated into leaf tissue, suggesting that vacuum infiltration conditions can be tailored to achieve optimal transient transgene expression levels after agroinfiltration.

Tractive characteristics of radial ply and bias ply tyres in a California soil

Abstract Four tyres (18.4-38, 18.4R38, 14.9-28, 14.9R28) were tested using the UCD single wheel traction tester. Each tyre was tested at two different inflation pressures and three different vertical loads at each inflation pressure. All tests were conducted in a well tilled Yolo loam soil. A dimensional analysis procedure was used to design and analyse the experiment. Two models were considered: (A) using inflation pressure as a variable, and (B) using tyre deflection as a variable. The effect of tyre type, tyre size, tyre inflation pressure and dynamic load on (1) net traction ratio at 20% slip and (2) average tractive efficiency in the 0–30% slip range were investigated using an ANOVA technique. An estimate of the possible energy savings due to the use of radial ply tyres instead of bias ply tyres in California agriculture was made.

Sources of variability in traction data

Abstract A 18.4R38 tyre was tested at 124 kPa inflation pressure, approximately 24 kN axle load in a firm and in a tilled Yolo-loam soil using (i) constant slip, (ii) constant draught, (iii) varying slip and (iv) varying draught tyre testing procedures. The results indicated that the constant slip test procedure leads to repeatable and consistent results whereas a variable slip test procedure leads to considerable scatter in the data. The constant draught test procedure yielded acceptable results. Varying slip appeared to influence the system dynamics much more than varying draught during tyre testing. An accurate method of predicting “true rolling radius” and “true slip” for an assumed zero condition is presented. The concept of motion resistance, its variability due to assumed zero conditions, and possible interpretations are discussed. The traction test data indicates that the motion resistance is not constant but varies with slip.