Academic literature on the topic 'Agronomic measurements'

<p> Among all nutrients that are important for crop production, nitrogen (N) is one of the least efficiently utilized, mainly due to its high mobility in soil. The possibility of using crop sensing in real-time to detect variability in N deficiency within a field has the potential to enhance N efficiency, increase crop yield, and reduce potential environmental risks and crop production costs. Potassium (K), another important crop nutrient, can also lead to higher yield when applied in the right amount and manner. Real-time fluoro-sensing is a new technology for crop sensing and studies have shown that it could enable variable rate nutrient management for precision agriculture practices. The objective of this study was (1) to evaluate if fluorescence sensing can detect variability of N and K in crop canopy at early growth stages of maize (prior to V6 crop growth stage) under controlled condition (greenhouse), (2) to evaluate the effect of different fertilization dosages of N over the plant growth, and (3) to verify if induced fluorescence can detect <i>in situ </i> N variability at early growth stages of maize. Research was conducted in two stages, first in a greenhouse condition and later in field spread over three site-years. The greenhouse research was conduct in year 2011 and plants were grown in plant-pots with silica sand and supplied with modified Hoagland solution with different rates of N and K. Field trials were conducted in year 2012 and 2013 in northern Colorado. For the greenhouse study, data collected via fluorescence sensor (Multiplex^&reg;3) were analyzed using ANOVA and Tukey&rsquo;s HSD to test significant differences among treatments in each experiment. For the N experiment, regression analysis between the seven fluorescence indices and N uptake was performed for the 12 days of data acquisition at five different growth stages (i.e. 2-leaf to 6-leaf growth stages) and coefficient of determination was used to identify the best fluorescence indices to detect N status. Also, root mean square error (RMSE) was used to test the precision of the estimates for each index. Results of this study indicated that all fluorescence indices were able to detect N variability in maize canopy prior to V2 growth stage. However, the fluorescence indices failed to identify K deficiency as the maize plants with K treatments showed small variability at early crop growth stages. For the field study, two site-years had 5 N rate treatments applied as UAN 32% (urea ammonium nitrate; 32-0-0), while one site-year had 6 N treatments applied pre-planting. Sensors used in this study were the Multiplex^&reg;3 for fluorescence sensing and the GreenSeeker^&reg; for reflectance sensing (NDVI). Sensor measurements were correlated with aboveground biomass, N content, and N uptake measured at two growth stages (V6 and V9 maize growth stage). The aboveground biomass, N content, N uptake, yield, and sensors readings were analyzed using ANOVA and Tukey&rsquo;s HSD to test significant differences among the N treatments. Also, a regression tree between N uptake and the fluorescence indices was fitted along with the coefficient of determination (R²). The N rates had no effect on aboveground biomass, N content and N uptake (for both sampled growth stages). Under field conditions, fluorescence indices failed to detect N variability in maize at early growth stages for all three site-years. This finding may require further investigation, as for most of the N treatment plots, maize plants had sufficient N levels and another biotic or abiotic stress may be responsible for unexplained differences in N variability as measured by fluorescence sensor. Contrasting findings under greenhouse conditions versus field conditions limit the application of fluorosensing sensor. Further field studies are needed to evaluate the potential of this sensor for detecting N variability <i>in situ.</i></p>

This work investigates the application of new sensors to enable agronomists and farm managers to make decisions for variable treatment strategies at key crop growth stages. This is needed to improve the efficiency of crop production in the context of precision farming. Two non-invasive sensors were selected for investigation. These were: 1) The MGD-1 ion mobility gas detector made by Environics OY, Finland. 2) The EM38 electromagnetic induction (EMI) sensor made by Geonics Inc., Canada. The gas detector was used to determine residual nitrogen and to measure carbon dioxide gas as a surrogate indicator of soil quality. In the latter, increased microbial carbon dioxide production was expected on soils with high organic matter content. Overall, the results of gas detection were disappointing. The main problems inherent in the system were; lack of control of the gas sampling, insufficient machine resolution and cross contamination. This led to the decision to discontinue the gas detection research. Instead, the application of electromagnetic induction (EMI) to measure soil variation was investigated. There were two principle advances in the research. Firstly the application of EMI to the rapid assessment of soil textural class. Secondly the mapping of available water content in the soil profile. These were achieved through the development of a new calibration procedure based on EMI survey of the sites at field capacity, working with field experiments from five sites over two years. Maps of total available water holding capacity were produced. These were correlated with yield maps from wet and dry seasons and used to explain some of the seasonal influences on the spatial variation in yield. A product development strategy for a new EMI sensor was considered which produced a recommendation to design a new EMI sensor specifically for available water content and soil texture mapping, that could be mounted on a tractor. For the first time, this procedure enables routine monitoring of the spatial variation in available water content. This enables the effects of seasonal and spatial variation to be included in crop models, targeted irrigation and to aid decisions for the variable application of inputs.

A two year study was conducted to determine the optimum timing of the initial post-plant irrigation for cotton (Gossypium hirsutum L.). A short-season Upland variety, DPL 20, was planted on 19 April 1993 and 15 April 1994 at the Marana Agricultural Center. Daily midday leaf water potential measurements were taken using the pressure chamber technique. Treatments, designated T1, T2, and T3, received the initial post-plant irrigation when the midday LWP measured -1.5, -1.9, and -2.3 MPa, respectively. Soil-water data was collected at 25 cm depth increments using neutron attentuation. Yields were 1263, 1244, and 1110 kg lint/ha in 1993 and 1229, 1176, and 1095 kg lint/ha in 1994 for T1, T2, and T3, respectively. When treatments were initiated, approximately 84 (T1), 62 (T2), and 32% (T3) of the total plant-available water was present in the upper 150 cm of the soil profile.

A data acquisition system to collect soil moisture readings at 60 field locations was developed. The system predicted a resistance value from a measured counts per time. An error was associated with the measured counts and time, however, this error was minimized by increasing the time for resistance measurement. The effect of temperature was minimized by an automatic calibration of the system before collecting readings. The Watermark electrical resistance moisture sensor was used to sense water content. The system, including eight sensors, was tested in the field. The data collected was difficult to explain. An evaluation of the Watermark sensors indicated a large variation from sensor to sensor, and also indicated a marked influence of soil texture on sensor resistance.

A comparative study was performed to investigate the tolerance levels of beet armyworm to three insecticides, cyfluthrin, profenofos, and methomyl. The field strains were collected from Yuma and Marana, AZ whereas the susceptible laboratory strain was obtained from California. Dosage-mortality data were obtained by topical application on third instar larvae. Compared to the susceptible strain, both Yuma and Marana strains exhibited an increase in the LD50 to cyfluthrin by 15.65 and 5.45-fold, respectively. Both strains also exhibited an increase in the LD50 to profenofos and methomyl by 14.10, 17.77 and 2.95, 8.07-fold, respectively. The cyfluthrin-selected strain (Marana strain) tested for cross resistance to profenofos and methomyl and exhibited an increase in LD50 by 24.68 and 3.32-fold,respectively.