Year of Publication

2020

Degree Name

Master of Science (MS)

Document Type

Master's Thesis

College

Agriculture, Food and Environment

Department

Plant and Soil Sciences

First Advisor

Dr. Montserrat Salmeron

Abstract

Corn (Zea Mays L.) is a grain crop with large productivity, but also elevated evapotranspiration demand, making it highly susceptible to periods of water stress occurring during critical reproductive stages. Environmental conditions in Kentucky make it possible to grow corn under rainfed conditions, but the crop is still likely to experience water stress during some times of the growing season depending on the year and location. There is limited information on the size of the yield gap due to water stress in Kentucky, and the timing and intensity of water deficit.

In addition, evaluating the interactive effects of hybrid maturity and planting Population may allow management recommendations that increase corn yield productivity and stability for irrigated and rainfed conditions in Kentucky. This thesis is structured in three chapters that analyze different aspects of this interaction. In Chapter 1 we analyzed data from corn performance tests (2005-2017) in three states with variable number of sites under irrigation (KY, 0% irrigated sites; NE, 62% of irrigated sites; and AR, 100% irrigated sites), to study the yield stability of different hybrid maturities. Results from this analysis showed that later maturities maximized yield under irrigated conditions, but reduced yield stability, meanwhile in rainfed conditions, early hybrids increased stability, with small yield penalties. Thereafter, field experiments were conducted in 2017 and 2018 to quantify the yield response of early and late maturities to irrigation (Chapter 2), and the interactive effect of hybrid maturity and plant population on corn yield and yield components under irrigation (Chapter 3). A preliminary analysis of the expected water deficit during the growing season based on historical water data indicated that 85 to 103 days with cumulative water deficit above 50 mm are expected during the months of May to September in Kentucky. Field experiments showed a 6 to 28 % yield increase under irrigation in 2017, but no effect in 2018 due to higher precipitation. Overall, yield increased with later maturities by 67 to 205 kg ha-1 per unit increase in CRM. Results from Chapter 3 showed that increasing plant population from 7.8 to 10 pl m-2 increased kernel number in early maturities, and kernel weight in later ones. However, there was a compensation of yield components and no effect of plant population on yield. Most of the yield variability was explained by hybrid maturity. Interestingly, higher yields in late maturities was explained by a higher kernel weight in 2017, but by a higher number of kernels in 2018. No differences found in KGR among hybrids in 2018, suggesting that higher KW for later hybrids was associated with an extension in three days of the EFP. Further research should focus on water use of contrasting maturities and populations to develop management recommendations in irrigated cornfields across Kentucky.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.056

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