Comparing inter-specific competition for continuous corn grown in a living mulch with stover removal

Chapter 3: Agronomic Response of Living Mulches in Continuous Corn with Stover Removal A paper to be submitted to Agronomy Journal Dustin R. Wiggans, Jeremy W. Singer, Kenneth J. Moore, and Kendall R. Lamkey Corn stover provides producers a potential additional market for selling biomass for biomass production. However, corn stover returns nutrients to the soil, decreases soil erosion, and helps maintain soil properties. Long term stover removal has been determined to cause detrimental environmental effects (Wilhelm et al., 1986; Mann et al., 2002; Nelson, 2002). Perennial groundcovers or living mulches grow simultaneously with the main row crop and are maintained as living groundcover throughout the growing season. Groundcovers grown in the interrow of row crops may provide beneficial functions such as weed suppression, water infiltration, nutrient cycling, and carbon inputs, but should not disrupt corn development and productivity. The objective of this research was to evaluate management systems including living mulches grown in continuous corn with stover removal. Corn was planted into three perennial groundcovers: creeping red fescue (CF) (Festuca rubra L.), Kentucky bluegrass (KB) (Poa pratensis L.), and a mixture of creeping red fescue and white clover (MX) (Trifolium repens L.) in 2008 and 2009 near Ames, IA. Management treatments were fall strip tillage (ST) and no-tillage (NT), accompanied with either a pre-planting paraquat burn-down followed by two post-planting glyphosate applications (PQ), or a pre-planting glyphosate band followed by two post-planting glyphosate applications (RU). Grain yields ranged from 5620 (MX RU ST) to 11339 (KB PQ ST) kg ha-1 in 2008, and 7611 (CF RU NT) to 12768 (KB PQ NT) kg ha-1 in 2009. Kentucky bluegrass PQ ST produced similar yields compared to the control in 2008, and all treatments were similar to the control in 2009, except CF RU NT. Kentucky bluegrass PQ ST produced the greatest stover dry matter (DM) (6883 kg ha-1) in 2008, and KB PQ NT produced the most in 2009 (10862 kg ha-1), excluding the control. In both years the herbicide significantly affected grain yield and stover DM with PQ producing better yields than RU (except in the MX stover DM treatments in 2008). Tillage did not have similar effects. Kentucky bluegrass, paraquat herbicide, and either no-tillage or strip-tillage provide the most consistent response across these growing seasons and showed the greatest potential to implementing living mulches in corn bioenergy cropping systems. Chapter 4: Corn Water Use in Living Mulch Systems with Stover Removal A paper to be submitted to Agronomy Journal Dustin R. Wiggans, Jeremy W. Singer, Kenneth J. Moore, and Kendall R. Lamkey Corn stover returns nutrients to the soil, decreases soil erosion, and helps maintain overall soil properties. Additionally, corn stover may provide producers an additional market for selling biomass, but long term stover removal has been determined to cause detrimental environmental effects (Wilhelm et al., 1986; Mann et al., 2002; Nelson, 2002). Living mulches, or perennial groundcovers, grow simultaneously with the main row crop and are maintained as living groundcover throughout the growing season. Groundcovers grown in the interrow of row crops can provide beneficial functions such as weed suppression, nutrient cycling, and increase water infiltration, but should not disrupt corn development and productivity. The objectives of this research were to quantify soil and plant water use in continuous corn with and without a living mulch with stover removal. Corn was planted into living mulch groundcovers of creeping red fescue (CF) (Festuca rubra L.), and Kentucky bluegrass (KB) (Poa pratensis L.) in 2008 and 2009 near Ames, IA. Management was no-tillage (NT) with a pre-planting paraquat burn-down followed by two post-planting glyphosate applications (PQ) during the season. Kentucky bluegrass (P = 0.3743) was less competitive than CF (P = 0.0482) compared to a no living mulch control for soil water content (SWC) at the 15 cm soil depth during the vegetative growth period in 2008. Additionally in 2008, both KB (0.3681 m3 m-3) and CF (0.3696 m3 m-3) were significant compared to a no living mulch control (0.3473 m3 m-3) for SWC at the 15 cm soil depth during the post-maturity period. There were no significant affects on SWC at the 15 cm level among treatments in 2009. Soil water content at the 45 cm soil depth and soil temperature (ST) at the 15 cm soil depth were non-significant among treatments both years. Living mulch did affect leaf area index (LAI) at V6, V12, and R1 in 2008, and only at V6 in 2009. Carbon dioxide exchange rate (CER) and corn transpiration rate (TR) were not affected by groundcover either year. Reproductive water use efficiency (RWUE) for KB (50 and 41 g grain cm water-1) was greater compared to the control (41 and 36 g grain cm water-1) by 22 and 14% in 2008 and 2009, respectively. Kentucky bluegrass was less competitive than CF both years, and used water more efficiently during reproductive growth compared to a no-living mulch control. Therefore, KB demonstrates the greatest potential to implementing living mulches in a corn bioenergy cropping systems

Response of Continuous Maize with Stover Removal to Living Mulches

Constraints to maize (Zea mays L.) stover biomass harvest may be mitigated by using a living mulch (LM) to offset C exports and control soil erosion. Living mulches can compete with the main crop for resources. The objective of this research was to quantify competitive effects of LM management systems grown in continuous maize with stover removal. Maize was planted into creeping red fescue (CF) (Festuca rubra L.), Kentucky bluegrass (KB) (Poa pratensis L.), and a mixture of CF and white clover (Trifolium repens L.) (MX) LMs in 2008, 2009, and 2010 near Ames, IA. Management treatments were fall strip-tillage (ST) and no-tillage (NT), with either a pre-planting paraquat burn-down followed by two glyphosate bands (PQ) or glyphosate bands only (GLY). Kentucky bluegrass PQ ST produced similar grain yields (11,230 kg ha−1) all 3 yr as the no LM control (11,810 kg ha−1) with a harvest index (HI) of 0.55 compared to 0.52 in the control, averaged across years. The control produced greater stover dry matter (SDM) (10,110 kg ha−1) 2 of the 3 yr compared to KB PQ ST (8600 kg ha−1). Total groundcover averaged 80% in KB PQ ST compared to only 45% in the no LM control. These results indicate that a combination of herbicide suppression and ST suppresses LMs adequately to maintain competitive maize grain yields. Additional research under varying climatic conditions will further quantify the risk of LM management systems to increase the sustainable stover harvest of maize biomass feedstocks

Embolized Stems Recover Overnight in Zea mays: The Role of Soil Water, Root Pressure, and Nighttime Transpiration

It is not currently well-understood how much xylem conductance is lost in maize plants during the day, if conductance is recovered during the night, or what soil water conditions are required for recovery to take place. To answer these questions we designed a greenhouse experiment whereby two genetically dissimilar maize genotypes were subjected to a level of water stress commonly experienced in the field (Ψxylem ∼-2 MPa). We then measured the loss of stem-specific conductivity associated with this level of stress, as well as the overnight recovery following three re-watering treatments: Ψsoil ∼ 0 MPa, Ψsoil ∼-0.40 MPa, and Ψsoil ∼-1.70 MPa. Mid-day leaf water potentials of -1.98 MPa resulted in stem-specific conductivity (KS) values that were 31.5% of maximal (i.e., 68% loss). Returning soils to field capacity (Ψsoil ∼ 0 MPa) overnight allowed for the significant recovery of KS (76% of maximal), whereas partial watering (Ψsoil ∼-0.40 MPa) resulted KS values that were 51.7% of maximal values, whereas not watering resulted in no recovery (35.4% of maximal; Ψsoil ∼-1.7 MPa). Recovery of KS was facilitated by the generation of root pressure and low rates of nighttime transpiration