Internal N efficiency (IE) is defined as the amount of grain dry matter (GDM) produced per unit of N in the above ground plant at physiological maturity (PMN). Currently, a static value of IE (48 kg GDM kg^-1N) is used to define the optimal PMN in yield goal-based N recommendations used in 30 U.S. states and several N recommendation models. To evaluate the accuracy and variability of this value of IE at the economic optimum N rate (IE_E), experiments were conducted at 47 sites located in eight states over a three year period (2014-2016). To establish IE_E, N treatments ranged from 0 to 315 kg N ha^-1 in 45 kg N ha^-1 increments, applied either at-planting or split with 45 kg N ha^-1 at-planting and the remainder at the V9±1 V-stage. Average IE_E across all site-years was 53 kg GDM kg^-1 N with 79% of the observations between 46 and 60 kg GDM kg^-1 N, higher than the currently accepted value of IE. Half of the time the timing of N application affected IE_E, with greater IE_E with split N in 70% of these instances due to lower PMN arising from reduced stover dry matter. In most cases the timing of N did not affect IE_E. Across all site-years, GDM at the EONR or EONR were unrelated to IE_E. Plant N content at VT of the non-fertilized and 45 kg N ha^-1 at planting treatments were single variables most highly correlated with IE_E (<i>p</i> ≤ 0.10, r = -0.42 and -0.50, respectively). These variables reflected the amount of residual or available N retained in the plant and/or SDM at the optimal N rate. Other factors such as plant available water content at various depths and crop reflectance at the V9 leaf stage (sufficiency and simple ratio indices for both NDVI and NDRE at 0 and 45 kg N ha^-1) were negatively related to IE_E across all site-years, but only weakly. Predictive models for IE_E at planting and prior to sidedressing accounted for < 50% of the variation in IE_E. Internal N efficiency varied considerably, but was difficult to predict, thus contributing to the inaccuracy of the yield-goal based N recommendations.

Presently there are two forms of biological fibre extraction, water retting or dew retting, which use bacteria or fungi, respectively. Microbial action results in release of the cellulose fibres due to modification of the pectin, hemicellulose and lignin content from parenchyma cells and the middle lamellae. Water retting results in pollution, high costs associated with labour and drying, as well as significant waste water production, while disadvantages to dew retting include the need for appropriate climates, variable and inferior fibre quality, risks of over-retting as well as health effects due to dust and fungal contaminants. The overall objective of this research was to explore silage retting as a new pre-processing technique allowing use of available farm infrastructure and contained retting conditions to produce plant-derived fibres with improved physical and chemical characteristics suitable for application in biocomposites. The corn processing ability of the hemp retting agents Clostridium felsineum and Bacillus subtilis was also investigated. Pleiotropic and/or crop management practices were assessed by comparing the physico-mechanical properties and the microbial populations during silage fermentation of genetically equivalent conventional, Roundup Ready® (RR) and Bt-Roundup Ready® (Bt-RR) corn isolines. Potential recovery of volatile organic acids in silage retting effluent as value-added chemicals was also explored. The results indicated that C. felsineum is an effective corn retting agent given the effective release of the fibre bundles from the corn pith, with B. subtilis contributing to the retting process by reducing the oxygen content and providing the required anaerobic conditions for clostridial growth. The native microflora present in the plant phyllosphere also showed some retting ability. Composition, thermostability and mechanical properties of the biocomposites produced using the fibres from the retted corn were all found to vary depending on the variety of corn. Specifically, retted Bt-RR cornstalk showed a 15°C increase in onset of degradation. Divergences between corn silage microbial communities analyzed by community-level physiological and enzyme activity profiling indicated that metabolic shifts were time-, region-, and contaminant-sensitive. Acetic and butyric acid production in silage retting effluent was found to be highest under anaerobic conditions and was also influenced by corn hybrid variety, although a specific variety was not identified as most or least favourable for organic acid production due to high variability. Bt-RR cornstalk material was found to have higher cellulose content and better thermostability with an onset of degradation of up to 45°C higher than its genetic RR and conventional counterparts. However, fibres from the RR corn isoline produced biocomposites with the highest flexural strength and modulus. RR cornstalk-reinforced polypropylene showed a 37 and 94% increase in flexural strength and modulus, respectively when compared to the mechanical properties of the pure polypropylene. The Bt-RR and conventional varieties produced biocomposites with an average increase of 26.5% in flexural strength and 83.5% in flexural modulus. The thermostability of ensiled corn biomass was found to be influenced by region, use of inoculants and silage treatment, while the silage treatment accounted for most of the variability in corn biomass composition. Polypropylene matrix biocomposites produced with (30 wt%) pre- and post-silage corn did not show significant differences in mechanical properties. However, ensiled corn resulted in an increase in fibres and potential microbial biomass of smaller particle sizes with more optimal thermostability and purity, producing biocomposites with higher flexural strength and modulus especially at higher extrusion temperatures. Cornstalk is an effective reinforcement material, producing biocomposites with higher flexural strength, flexural modulus and impact strength. Whole corn biomass presents a potential alternative to other plant fibres, especially as filler material. Silage retting resulted in fibres with a higher thermostability and smaller particle size distribution that, given their already smaller aspect ratio, could result in better mechanical properties in thermoplastics with a higher melting temperature or biocomposites requiring higher shear for mixing.

Presently there are two forms of biological fibre extraction, water retting or dew retting, which use bacteria or fungi, respectively. Microbial action results in release of the cellulose fibres due to modification of the pectin, hemicellulose and lignin content from parenchyma cells and the middle lamellae. Water retting results in pollution, high costs associated with labour and drying, as well as significant waste water production, while disadvantages to dew retting include the need for appropriate climates, variable and inferior fibre quality, risks of over-retting as well as health effects due to dust and fungal contaminants. The overall objective of this research was to explore silage retting as a new pre-processing technique allowing use of available farm infrastructure and contained retting conditions to produce plant-derived fibres with improved physical and chemical characteristics suitable for application in biocomposites. The corn processing ability of the hemp retting agents Clostridium felsineum and Bacillus subtilis was also investigated. Pleiotropic and/or crop management practices were assessed by comparing the physico-mechanical properties and the microbial populations during silage fermentation of genetically equivalent conventional, Roundup Ready® (RR) and Bt-Roundup Ready® (Bt-RR) corn isolines. Potential recovery of volatile organic acids in silage retting effluent as value-added chemicals was also explored. The results indicated that C. felsineum is an effective corn retting agent given the effective release of the fibre bundles from the corn pith, with B. subtilis contributing to the retting process by reducing the oxygen content and providing the required anaerobic conditions for clostridial growth. The native microflora present in the plant phyllosphere also showed some retting ability. Composition, thermostability and mechanical properties of the biocomposites produced using the fibres from the retted corn were all found to vary depending on the variety of corn. Specifically, retted Bt-RR cornstalk showed a 15°C increase in onset of degradation. Divergences between corn silage microbial communities analyzed by community-level physiological and enzyme activity profiling indicated that metabolic shifts were time-, region-, and contaminant-sensitive. Acetic and butyric acid production in silage retting effluent was found to be highest under anaerobic conditions and was also influenced by corn hybrid variety, although a specific variety was not identified as most or least favourable for organic acid production due to high variability. Bt-RR cornstalk material was found to have higher cellulose content and better thermostability with an onset of degradation of up to 45°C higher than its genetic RR and conventional counterparts. However, fibres from the RR corn isoline produced biocomposites with the highest flexural strength and modulus. RR cornstalk-reinforced polypropylene showed a 37 and 94% increase in flexural strength and modulus, respectively when compared to the mechanical properties of the pure polypropylene. The Bt-RR and conventional varieties produced biocomposites with an average increase of 26.5% in flexural strength and 83.5% in flexural modulus. The thermostability of ensiled corn biomass was found to be influenced by region, use of inoculants and silage treatment, while the silage treatment accounted for most of the variability in corn biomass composition. Polypropylene matrix biocomposites produced with (30 wt%) pre- and post-silage corn did not show significant differences in mechanical properties. However, ensiled corn resulted in an increase in fibres and potential microbial biomass of smaller particle sizes with more optimal thermostability and purity, producing biocomposites with higher flexural strength and modulus especially at higher extrusion temperatures. Cornstalk is an effective reinforcement material, producing biocomposites with higher flexural strength, flexural modulus and impact strength. Whole corn biomass presents a potential alternative to other plant fibres, especially as filler material. Silage retting resulted in fibres with a higher thermostability and smaller particle size distribution that, given their already smaller aspect ratio, could result in better mechanical properties in thermoplastics with a higher melting temperature or biocomposites requiring higher shear for mixing.

The aim of the thesis was to evaluate and to compare the rate of corn borer and the production capability of 4 hybrids of corn (Zeamays L.) of different earliness. For the comparison a variety test was layed out in the land of my father in Klimětice (Central Bohemia). Before the harvest a sampling for detection of dry matter content in the biomass has been made to determinate the date of harvest. The number of samplings depended on the attainment of required dry matter content in the biomass. By the harvest the yield and dry matter content of the biomass, yield and percentage of corn ears, dry matter yield and the starch yield were determined. In the experiments the differences in infestation of corn borer were determined. Further differences in observed parameters were found out, which were dependent on the different utility trends and earliness of the given hybrids. The result was the appreciation of the given hybrids and determining of their suitability for their growing in conditions of my fathers lands.

Cereal rye (CR), the most common and effective nitrogen (N) scavenging cover crop option in the Midwest, is often utilized in cropping systems to reduce nitrate loss for environmental benefits. To increase environmental efficiency in Midwest corn cropping systems, we must increase the overall adoption of CR. However, due to the yield reduction potential (6%) for corn planted after CR termination, CR is primarily recommended before soybean. To increase CR adoption, we must develop adaptive fertilizer management practices that achieve competitive grain yields relative to cropping systems where CR is not adopted. Therefore, the objectives of this study are to determine (1) the effect of CR and starter nitrogen rate on corn growth and nitrogen content. (2) the optimum starter nitrogen rate to achieve agronomic optimum corn yield following CR. (3) the impact of phosphorus (P) at starter on plant growth, nitrogen content, and yield with the inclusion of CR. For our study, five starter N rates were applied in a 5x5 cm band to both CR and non-CR plots, concentrations ranged from 0-84 kg N ha^-1in 28 kg N ha^-1 intervals. Total N applied was the same for each treatment, relative to its location, and was split between starter N at planting and sidedress applied at growth stage V6 relatively. Although CR termination took place at least two weeks before planting, CR decreased corn grain yield at one of three locations by an average of 8%, nitrogen recovery efficiency (NRE) by 27%, and R6 total N content by 23%, relative to the conventional control (non-CR 0N), when no starter N was applied. At one of three locations, starter N rates of 56 kg N ha^-1, 56 kg N ha^-1plus 17 kg P ha^-1, and 84 kg N ha^-1 increased corn grain yield, in CR plots, and 56 kg N ha^-1 plus 17 kg P ha^-1 increased corn grain yield in non-CR plots. Phosphorus increased corn grain N content at growth stage R6 in one of three locations and did not impact corn grain yield at all locations. We conclude that the inclusion of starter N at planting has the potential to increase agronomic productivity in CR corn cropping systems in soil environments with a high capacity to mineralize soil N. However, further research is required to refine our starter N results to find an optimum starter N rate to apply before planting corn following CR.