Degree Type

Thesis

Date of Award

2014

Degree Name

Master of Science

Department

Agronomy

First Advisor

Mahdi Al-Kaisi

Abstract

Companies in the U.S have started using corn (Zea mays L.) residue as feedstock for cellulosic ethanol production. However, concerns including field storage and removal methods effects on crop growth and development, soil health, and environmental quality have been raised requiring the investigation of management and strategies to mitigate such effects. In the Mid-west corn cob have being utilized as feedstock material for cellulosic ethanol production in addition to corn residue. Nevertheless, there are many management issues that need to be addressed in order to efficiently store and remove corn cob from the field with minimum damage to subsequent crops and soil health. The current practices include the storage of loose corn cob mixed with corn residue as piles and bales at the edge of harvested fields over winter for later use in ethanol production. The corn cob residue refers to the mixture of corn cob and corn stover in the loose and baled corn cob treatments used in this experiment. Unfavorable plant growth responses have been observed after storing corn cob residue in the field. The objectives of this study were 1) to investigate the effects of loose and baled corn cob residue storage methods and management practices on plant development and crop yield, 2) evaluate and understand the effects of both methods on soil health, and 3) determine the effects of different amounts of loose corn cob residue left after removal and management practices on greenhouse gas (CO2 and N2O) emission and management practices to mitigate such effects.

The study investigated two storage methods at two different sites that were established in fall of 2010. Trials ran through the fall 2012. The loose corn cob residue study was conducted at the Agronomy Research Farm at Iowa State University located near Ames, Iowa (AC site). The soil type is Canisteo silty clay loam (Fine-loamy, mixed, superactive, calcareous, mesic Typic Endoaquolls) and Harps loam (Loam, mixed, superactive, mesic Typic Calciaquolls). The treatments for the loose corn cob residue method consisted of two randomized tillage systems conventional tillage (CT) and no-tillage (NT), which represented the main treatment. Each tillage system was split into five corn cob residue treatments as Control, Removed Residue (7.5 cm applied in the fall and completely removed early spring), 2.5, 5.0, and 7.5 cm corn cob residue depths randomly assigned at each tillage treatment and replication. Then each corn cob residue treatment was split to receive four N fertilizer rates of 0, 90, 180, and 270 kg N ha-1 randomly assigned at each corn cob residue treatment and replication. The N fertilizer was 32% liquid UAN (NH4NO3), which was side-dressed and injected in May after planting using a spoke point injector. The AC site was planted on 6th May, 2011 and 14th May, 2012 using a 111 day maturity corn variety (P33W84) with a seeding density of 79,000 seeds ha-1.

The second study was established at a Northwest Iowa farmer's field near Emmetsburg and near the POET, Biorefinery plant (ENW site). The soil type is Clarion loam (Fine-loamy, mixed, superactive, mesic Typic Hapludolls). The ENW site used a square corn cob residue bale as a storage method, in which bales were placed in the field after harvest and stored over winter, but removed in the spring before planting. The main treatment consisted of corn cob residue left after bales removal: 1) Corn cob residue left after bales removal as a result of breakdown of bales if any, 2) corn cob residue completely cleaned or removed from each plot, and 3) the control treatment, where no bales were placed on plots. Each of the corn cob residue treatments were split into four N fertilizer rates of 0, 90, 180, and 270 kg N ha-1 and randomly assigned at each corn cob residue treatments. The different N fertilizer rates were hand applied using granular urea in May after planting. The ENW site was planted on 5th May, 2011 and 25th April, 2012 using a 111 day maturity corn variety (P0448AM1), with a seeding density of 89,000 seeds ha-1.

Field data collection and measurements for plant, soil, and other parameters were conducted at both sites on weekly, monthly, and seasonal basis. These measurements included plant growth and development parameters, soil physical, chemical, and biological properties such as, soil organic carbon (SOC), soil total nitrogen (STN), microbial biomass (MBC), soil pH, organic acids (only at the AC site), soil penetration resistance (SPR), water stable aggregates (WSA), soil bulk density (ρb), and soil water infiltration rate (Ir only at the AC site only). Also, measurements of greenhouse gas emission (CO2 and N2O) were monitored along with soil mineral N (NO3-N and NH4-N), soil temperature, and moisture at the AC site only.

The findings of the loose corn cob residue study suggest that plant growth and development were negatively affected by the presence of loose corn cob residue. In general, the emergence rate index (ERI), extended plant leaf heights, above-ground biomass and grain yield are negatively affected when corn cob residue is left on the soil surface after pile removal. Tillage systems show no difference in preventing the effects of corn cob residue, but it was observed that NT showed a slight advantage over CT, for plant growth and development. As expected N fertilizer at the agronomic rate (180 kg/ha) helped plant development and growth. Above-ground biomass and grain organic C and N concentrations were affected by the increase of N fertilizer rates, but not by other management practices such as tillage or corn cob residue treatments.

Additionally, soil biological and chemical properties such as, SOC, STN, soil pH, and organic acids were not affected by different management practices. Changes in MBC values were affected at different times in the growing season by corn cob residue treatments. The highest soil MBC concentration was observed at the 2.5 cm and 7.5 cm corn cob residue treatments, especially in June and July (mid-summer) compared to the control and removed corn cob residue treatments. Also, soil organic acids concentrations of oxalic and butyric were the most detectable in the soil with all residue treatments in 2011 only.

However, the findings suggest that soil physical properties such as, WSA, ρb, SPR, and Ir were affected by the amounts of corn cob residue left on the soil surface. The results showed a decrease in soil macro-aggregates percentage across all corn cob residue treatments due to seasonal variability as moisture condition changed. The SPR was affected by the amount of corn cob residue left on the soil surface and the degree of residue removal, where machinery and human traffic led to increase in soil compaction. Soil ρb was lower at the 0-7.5 cm soil depth in general compared with lower soil depths, and Ir was also affected by corn cob residue under the CT tillage system, where 2.5 cm and 7.5 cm corn cob residue showed higher Ir than that under control and removed at all N fertilizer rates.

At the AC site soil CO2 and N2O were monitored along with soil mineral N (NO3-N and NH4-N), soil moisture, and soil temperature. The findings from the study suggested that soil CO2 and N2O emission were higher under the 2.5 cm and 7.5 cm corn cob residue treatments than the control and removed treatments. Soil moisture and soil temperature were also affected by the level of corn cob residue treatments covering the soil surface, which subsequently affected soil CO2 and N2O emission. Also, soil N2O emission was affected by N fertilizer rates, where higher N fertilizer rates caused higher soil N2O emission. It was also observed that dry conditions in 2012 decreased soil CO2 and N2O emission across all management practices, due to lower soil moisture and high soil temperatures. The soil CO2 and N2O emission were affected by corn cob residue left after removal, where areas with excessive amounts of corn cob residue on soil surface showed greater CO2 and N2O emission rates than clean areas.

In the corn cob residue bale study, findings suggest that plant growth and development are not greatly impacted by the presence of corn cob residue left after bale removal from the site. It was observed that a minimum amount of corn cob residue was left on the soil surface after bales removal. In general, ERI, extended plant leaf heights, plant population, vegetative growth stages, above-ground biomass, and grain yield for clean and left corn cob residue treatments were slightly lower than control where no corn cob residue bales were placed. Over the study period no changes were observed in organic C and N concentrations of the above-ground biomass and grain.

Nonetheless, corn cob residue bale storage on the field showed some changes in the SOC and STN contents at different soil depths. In general, changes in SOC and STN contents were similar across all corn cob residue treatments within each soil depth. However, at the top 7.5 cm soil depth greater SOC and STN content were observed compared to lower soil depths across all corn cob residue treatments. Also, soil pH at the top 7.5 cm soil depth was lower than that at lower soil depths across all corn cob residue treatments. Soil MBC concentration was also monitored during the corn cob residue bales study, where in general no corn cob residue treatment effect on MBC was observed within each soil sampling period for both years. However, greater MBC values were observed in the fall for both years across all corn cob residue treatments than early spring. The increase in MBC concentrations can be due to increase in organic matter and its decomposition when left on the soil surface after harvest and removal of corn cob residue bales.

At the ENW site physical properties were affected by the storage of corn cob residue bales, where soil macro-aggregates stability and associated C content across all corn cob residue treatments showed a decline by the end of the experiment. While an increase for those parameters associated with micro-aggregates was observed, changes in ρb were mostly found at the top 7.5 cm soil depth across all corn cob residue treatments which are consistent with the increase in SPR values at the same depth. The greatest SPR values are observed in areas where corn cob residue bales were stored.

The most effective practices in mitigating corn cob residue effects on plant growth and development, soil physical and chemical properties, and soil CO2 and N2O emission are adequate control of field machinery traffic for corn cob residue removal and corn cob residue cleaning. Field machinery for removal of loose and baled corn cob residue should be conducted under suitable conditions (i.e. dry soil condition) to minimize soil compaction during the removal of corn cob residue left on the soil surface. Such management practices can reduce corn cob residue effects on corn productivity and soil health (physical, biological, and chemical optimum functions). Also, an adequate application of N fertilizer rates will help reduce corn cob residue effect of N-immobilization and subsequent effects on plant development.

Copyright Owner

Carlos Gilberto Tenesaca

Language

en

File Format

application/pdf

File Size

167 pages

Share

COinS