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Theses and Dissertations

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Browsing Theses and Dissertations by Subject "agronomy"

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    ItemOpen Access
    Ground based active remote sensors for precision nitrogen management in irrigated maize production
    (Colorado State University. Libraries, 2009) Shaver, Timothy Michael, author; Westfall, Dwayne G., advisor; Khosla, Rajiv, advisor
    Precision agriculture can increase farm input efficiency by accurately quantifying variability within a field. Remotely sensed normalized difference vegetation index (NDVI) has been shown to quantify maize (Zea mays) N variability. Ground-based active remote sensors that can determine NDVI are commercially available and have been shown to accurately distinguish N variability in maize. There are several active sensors available but no studies directly comparing active sensors have been reported. Therefore, a study was conducted to evaluate active sensor performance and develop an in-season maize N recommendation algorithm for use in Colorado using NDVI. Previous studies have demonstrated an association of active sensor NDVI with maize N content and height. However, the NDVI from a GreenSeeker™ green NDVI prototype active sensor had not yet been tested when our study began. Therefore, the green sensor was evaluated to determine if differences in plant growth across MZ could be determined by the active sensor. Results show that the prototype active sensor did not record NDVI values that were associated with MZ. The NDVI from two different sensors (Crop Circle™ amber NDVI and GreenSeeker™ red NDVI) were then examined under greenhouse and field conditions. Results show that NDVI from the amber and red sensors equally distinguished applied N differences in maize. Each active sensor's NDVI values had high R2 values with applied N rate and plant N concentration. Results also show that each sensor's NDVI readings had high R2 values with applied N rate and yield at the V12 and V14 maize growth stages. An N recommendation algorithm was then created for use at the V12 maize growth stage for both the amber and red sensors using NDVI. These algorithms yielded N recommendations that were not significantly different across sensor type suggesting that the amber and red NDVI sensors performed equally. Also, each N recommendation algorithm yielded unbiased N recommendations suggesting that each was a valid estimator of required N at maize growth stage V12. Overall results show that the amber and red sensors equally determine N variability in irrigated maize and could be very important tools for managing in-season application of N fertilizer.
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    ItemOpen Access
    Precision manure management across site-specific management zones
    (Colorado State University. Libraries, 2009) Moshia, Matshwene Edwin, author; Khosla, Rajiv, advisor
    In the western Great Plains of the USA, animal agriculture is an important contributor to the agricultural economy, and many livestock farms are close to water bodies where manure can potentially contaminate the environment. The objectives of the study were to (i) assess the influence of variable rate applications of animal manure on grain yield in continuous maize production fields across management zones (MZs) in dryland and limited irrigation cropping systems, (ii) to study the effects of variable rate application of animal manure on selected surface soil quality parameters across MZs, (iii) to evaluate the variable rate application of manure using environmental risk assessment tools of N leaching and P runoff indices and to understand its impact on environmental quality, and (iv) to evaluate and compare the nitrogen (N) mineralization of variable rates of dairy cattle manure applied on low, medium and high MZs in a controlled environment. To accomplish objectives (i) through (iii), the study was conducted under a continuous maize cropping system on dryland and limited furrow-irrigated fields in northeastern Colorado, USA. For objective (iv), a 120 day laboratory incubation study was conducted. The results of this project indicated that using animal manure alone for maize grain yield production was economically inefficient using enterprise budget analysis. The study suggests that manure can, therefore, be used in conjunction with synthetic N fertilizer to meet crop N requirements at early growth of maize, while animal manure improve soil quality of low productivity soils over time. This can potentially help to limit the amount of N and P lost into the environment. For N mineralization, the study showed a significant difference (P≤0.05) in mineralized N across zones when dairy animal manure treatments were compared. However, N from animal manure does not mineralize differently between low, medium and high management zones. The key in precision manure management was to find a balance between economically, agronomically and environmentally sound manure management strategies across spatially variable soils.