Crop Residues

Crop residues (e.g., corn stover and small grain straw) are sometimes excluded when discussing cellulosic energy crops per se, but because of the vast area upon which they are grown and their current role in the development of cellulosic energy systems, this chapter will review several important attributes of this “herbaceous” feedstock. Crop residues are potential feedstock sources for second-generation biofuel production. These materials, along with dedicated energy crops (e.g., switchgrass [Panicum virgatum L.], Miscanthus [Miscanthus × giganteus]), are considered to have greater potential for biofuel production than current first-generation feedstock (i.e., corn grain) [1–3]. Production of ethanol and other fuel sources from these lignocellulosic materials is receiving increased financial support for research and development [4–6]. Furthermore, biofuel production from crop residues provides a multipurpose land use opportunity where grain can be harvested to meet food and feed demands, while a sustainable portion of the residues provide a potentially available biofuel feedstock. Corn stover, the aboveground plant material left in fields after grain harvest,was identified as an important biomass source in the Billion-Ton Study (2005 BTS) [7]. The vast area from which this feedstock could potentially be harvested was confirmed by USDA National Agricultural Statistics Service (NASS) data showing that between 2005 and 2011, corn was harvested in the U.S.A. from an average of 32 460 000 ha each year [8]. Wheat straw was the other dominant residue identified in the 2005 BTS, and from 2005 through 2011, wheat was harvested in the U.S.A. from an average of 20 037 000 ha each year. Based on thesevast harvest areas, the 2005 BTS projected total annual corn and wheat residue production to be approximately 250 and 90 million Mg, respectively, with a sustainable removal of 82 and 12 million Mg after accounting for that needed to mitigate wind and water erosion. The 2005 BTS projections of available crop residue immediately raised concern among many soil scientists because harvesting residues as a biofuel feedstock or for any other purpose (e.g. animal feed) will decrease annual carbon input and may gradually diminish soil organic carbon (SOC) to a level that threatens the soil’s production capacity [9]. Concerns within the U.S. Corn/Soybean Belt were accentuated knowing that for many soils artificial drainage, intensive annual tillage, and less diverse plant communities have already reduced SOC by 30–50% when compared to pre-cultivation levels [10]. Returning a portion of crop residues to replenish SOC was deemed essential for sustainability [11–16] because crop residues influence many vital soil, water, and air functions. Many scientists stated that caution must be used to ensure that harvesting residue for any use does not compromise ecosystem services or decrease overall soil productivity. Furthermore, others argued that for several current cropping systems, soil erosion and organic matter depletion indicate that crop residue returns to the soil are already insufficient [17, 18]. As a result of soil resource sustainability concerns raised by the 2005 BTS, a follow-up report (2011 BT2) was developed by the U.S. Department of Energy (DOE) to include (1) a spatial, county-by-county inventory of potentially available primary feedstocks, (2) price and available quantities (i.e. supply curves) for individual feedstocks, and (3) a more rigorous treatment and modeling of resource sustainability [19]. The 2011 BT2 recognizes the importance of crop yield variation and the need to balance the economic drivers with ecologically limiting factors [20]. Table 8.1 presents some of the estimated feedstock supplies for various crop residues at selected price levels. These values are also consistent with several other estimates including those used for the U.S. National Academy of Science (NAS) study on Liquid Transportation Fuels from Coal and Biomass [21]. The 2011 BT2 also provides a more realistic overview of total crop residue availability and sets some achievable research and development goals for available feedstock supplies by creating various production scenarios that strive for higher crop yields and integrate multiple cellulosic energy crops into potential production systems. Several assessments examining the multiple roles that crop residues have for maintaining multiple ecological functions have been published since the 2005 BTS [22–30]. Therefore, this chapter focuses on current corn stover and wheat straw research designed to address concerns raised by those previous reviews and to help ensure that commercial bioenergy develops in an economically, environmentally, and socially acceptable manner

Soil quality, yield stability and economic attributes of alternative crop rotations

Three long-term rotational crop studies in Iowa and one in Wisconsin were examined for conclusive evidence of rotational effects on soil quality. Long-term yield data also were evaluated to determine if there was a quantifiable relationship between soil quality and yield or yield stability

Ridge, Moldboard, Chisel, and No-Till Effects on Tile Water Quality beneath Two Cropping Systems

Soil conservation tillage systems, including ridge-tillage, often reduce surface water contamination by pesticides because soil erosion and surface runoff are reduced. However, the effects on losses through subsurface drainage tile are somewhat uncertain. Our field study quantified the effects of four tillage practices in continuous corn (Zea mays L.) and corn-soybean [Glycine max (L.) Merr] rotations on herbicide and nitrate N losses in tile drainage water. Fertilizer and pesticide application methods were uniform for ridge, moldboard, chisel, and no-till systems. Pesticide and nitrate N leaching losses were significantly affected by crop rotation. Tillage practice had little influence on nitrate N and pesticide losses to the subsurface drainage water within a corn-soybean rotation. However, ridge-till and no-till resulted in larger losses of atrazine than the moldboard plow and chisel based systems under continuous corn. Tillage system did not affect the timings of peak tile flow occurrences, although peak tile flow volume was affected by tillage, presumably because each system bad its own macropore system related to preservation or annual destruction of biopores by tillage. Corn yields were significantly higher under corn-soybean rotation than with continuous-corn for all tillage practices. These results indicate that continuous corn production is not an environmentally sustainable practice for this area because it resulted in higher nitrate N leaching losses to groundwater, received higher N-applications, and resulted in lower corn yields than the corn-soybean rotation. The results also reinforce the need for studies on chemical placement, rate, and timing for various tillage practices to reduce tile drainage losses of agricultural chemicals

RZWQM simulation of long-term crop production, water and nitrogen balances in Northeast Iowa

Agricultural system models are tools to represent and understand major processes and their interactions in agricultural systems. We used the Root Zone Water Quality Model (RZWQM) with 26 years of data from a study near Nashua, IA to evaluate year to year crop yield, water, and N balances. The model was calibrated using data from one 0.4 ha plot and evaluated by comparing simulated values with data from 29 of the 36 plots at the same research site (six were excluded). The dataset contains measured tile flow that varied considerably from plot to plot so we calibrated total tile flow amount by adjusting a lateral hydraulic gradient term for subsurface lateral flow below tiles for each plot. Keeping all other soil and plant parameters constant, RZWQM correctly simulated year to year variations in tile flow (r2 = 0.74) and N loading in tile flow (r2 = 0.71). Yearly crop yield variation was simulated with less satisfaction (r2 = 0.52 for corn and r2 = 0.37 for soybean) although the average yields were reasonably simulated. Root mean square errors (RMSE) for simulated soil water storage, water table, and annual tile flow were 3.0, 22.1, and 5.6 cm, respectively. These values were close to the average RMSE for the measured data between replicates (3.0, 22.4, and 5.7 cm, respectively). RMSE values for simulated annual N loading and residual soil N were 16.8 and 47.0 kg N ha−1, respectively, which were much higher than the average RMSE for measurements among replicates (7.8 and 38.8 kg N ha−1, respectively). The high RMSE for N simulation might be caused by high simulation errors in plant N uptake. Simulated corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] yields had high RMSE (1386 and 674 kg ha−1) with coefficient of variations (CV) of 0.19 and 0.25, respectively. Further improvements were needed for better simulating plant N uptake and yield, but overall, results for annual tile flow and annual N loading in tile flow were acceptable

Effects of Corn Crop Residue Grazing on Soil Physical Properties and Subsequent Soybean Production in a Corn-Soybean Crop Rotation (A Progress Report)

The highest cost to beef cow-calf producers is the feeding of stored feeds in winter months. To lower feed costs, many producers will try to extend the grazing season into the winter. The primary resource for winter grazing in the Midwest is corn crop residues. On the average, corn crop residue grazing will reduce the amount of hay needed to maintain cows by approximately one-half ton per acre grazed over the winter. Although crop residue grazing is quite effective in reducing feed costs, some producers are concerned that corn residue grazing will have an adverse effect on soybean yields the following year resulting from soil compaction. It has already been proven that the use of large machinery will cause soil compaction in wet conditions and that it reduces corn grain yields from 6 to 10%

Winter grazing of corn residues: Effects on soil properties and subsequent crop yields from a corn-soybean crop rotation

Corn residues could be a good resource for winter cattle grazing. The study investigates whether winter grazing causes soil compaction and yield reduction in crops that are planted following grazing

CHARACTERIZING THE STATISTICAL DISTRIBUTION OF ORGANIC CARBON AND EXTRACTABLE PHOSPHORUS AT A REGIONAL SCALE

Greater awareness of potential environmental problems has created the need to monitor total organic carbon (TOC) and extractable phosphorus (P) concentrations at a regional scale. The probability distribution of these soil properties can have a significant effect on the power of statistical tests and the quality of inferences applied to these properties. The objectives of this study were to: (1) evaluate the probability distribution of TOC and extractable P at the regional scale in three Major Land Resource Areas (MLRA), and (2) identify appropriate transformations that will result in a normal distribution. Both TOC and extractable P were non-normally distributed in all three MLRAs. Suggested power transformations did not result in normality, but a natural log and negative binomial transformation did produce distributions that met the assumptions of normality in most cases. Statistical analysis of TOC and extractable P data at the regional scale will need to take into account the non-normal distribution of these properties for accurate and precise estimates

Crop Residue Harvest Economics: An Iowa and North Dakota Case Study

Rigorous economic analyses are crucial for the successful launch of lignocellulosic bioenergy facilities in 2014 and beyond. Our objectives are to (1) introduce readers to a query tool developed to use data downloaded from the Agricultural Research Service (ARS) REAPnet for constructing enterprise budgets and (2) demonstrate the use of the query tool with REAPnet data from two field research sites (Ames, IA, and Mandan, ND) for evaluating short-term economic performance of various biofuel feedstock production strategies. Our results for both sites showed that short-term (\u3c3 years) impacts on grain profitability were lower at lower average annual crop residue removal rates. However, it will be important to monitor longer term changes to see if grain profitability declines over time and if biomass harvest degrades soil resources. Analyses for Iowa showed short-term breakeven field-edge biomass prices of $26–$42Mg−1 among the most efficient strategies, while results for North Dakota showed breakeven prices of $54–$73 Mg−1. We suggest that development of the data query tool is important because it helps illustrate several different soil and crop management strategies that could be used to provide sustainable feedstock supplies