Sustainable aboveground crop biomass harvest estimates for cellulosic ethanol production, to date, have been limited by the need for residue to control erosion. Recently, estimates of the amount of corn (Zea mays L.) stover needed to maintain soil carbon, which is responsible for favorable soil properties, were reported (5.25-12.50 Mg ha 21 ). These estimates indicate stover needed to maintain soil organic carbon, and thus productivity, are a greater constraint to environmentally sustainable cellulosic feedstock harvest than that needed to control water and wind erosion. An extensive effort is needed to develop advanced cropping systems that greatly expand biomass production to sustainably supply cellulosic feedstock without undermining crop and soil productivity.

of greenhouse gases in the atmosphere (IPCC, 2001), and ability of our agricultural systems to sustain produc-Society is facing three related issues: overreliance on imported fuel, tion at rates needed to feed a growing world population increasing levels of greenhouse gases in the atmosphere, and producing sufficient food for a growing world population. The U.S. De-

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Remote sensing—the process of acquiring information about objects from remote platforms such as ground‐based booms, aircraft, or satellites—is a potentially important source of data for site‐specific crop management, providing both spatial and temporal information. Our objective was to use remotely sensed imagery to compare different vegetation indices as a means of assessing canopy variation and its resultant impact on corn (Zea mays L.) grain yield. Treatments consisted of five N rates and four hybrids, which were grown under irrigation near Shelton, NE on a Hord silt loam in 1997 and 1998. Imagery data with 0.5‐m spatial resolution were collected from aircraft on several dates during both seasons using a multispectral, four‐band [blue, green, red, and near‐infrared reflectance] digital camera system. Imagery was imported into a geographical information system (GIS) and then georegistered, converted into reflectance, and used to compute three vegetation indices. Grain yield for each plot was determined at maturity. Results showed that green normalized difference vegetation index (GNDVI) values derived from images acquired during midgrain filling were the most highly correlated with grain yield; maximum correlations were 0.7 and 0.92 in 1997 and 1998, respectively. Normalizing GNDVI and grain yield variability within hybrids improved the correlations in both years, but more dramatic increases were observed in 1997 (0.7 to 0.82) than in 1998 (0.92 to 0.95). This suggested GNDVI acquired during midgrain filling could be used to produce relative yield maps depicting spatial variability in fields, offering a potentially attractive alternative to use of a combine yield monitor.

Crop residue has been identified as a near-term source of biomass for renewable fuel, heat, power, chemicals and other bio-materials. A prototype one-pass harvest system was used to collect residue samples from a corn (Zea mays L.) field near Ames, IA. Four harvest scenarios (low cut, high-cut top, high-cut bottom, and normal cut) were evaluated and are expressed as collected stover harvest indices (CSHI). High-cut top and high-cut bottom samples were obtained from the same plot in separate operations. Chemical composition, dilute acid pretreatment response, ethanol conversion yield and efficiency, and thermochemical conversion for each scenario were determined. Mean grain yield in this study (10.1 Mg ha −1 dry weight) was representative of the average yield (10.0 Mg ha −1 ) for the area (Story County, IA) and year (2005). The four harvest scenarios removed 6.7, 4.9, 1.7, and 5.1 Mg ha −1 of dry matter, respectively, or 0.60 for low cut, 0.66 for normal cut, and 0.61 for the total high-cut (top+bottom) scenarios when expressed as CSHI values. The macro-nutrient replacement value for the normal harvest scenario was $57.36 ha −1 or $11.27 Mg −1 . Harvesting stalk bottoms increased stover water content, risk of combine damage, estimated transportation costs, and left insufficient soil cover, while also producing a problematic feedstock. These preliminary results indicate harvesting stover (including the cobs) at a height of approximately 40 cm would be best for farmers and ethanol producers because of faster harvest speed and higher quality ethanol feedstock. RightsWorks produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted. AbstractCrop residue has been identified as a near-term source of biomass for renewable fuel, heat, power, chemicals and other bio-materials. A prototype one-pass harvest system was used to collect residue samples from a corn (Zea mays L.) field near Ames, IA. Four harvest scenarios (low cut, high-cut top, high-cut bottom, and normal cut) were evaluated and are expressed as collected stover harvest indices (CSHI). High-cut top and high-cut bottom samples were obtained from the same plot in separate operations. Chemical composition, dilute acid pretreatment response, ethanol conversion yield and efficiency, and thermochemical conversion for each scenario were determined. Mean grain yield in this study (10.1 Mg ha À1 dry weight) was representative of the average yield (10.0 Mg ha À1 ) for the area (Story County, IA) and year (2005). The four harvest scenarios removed 6.7, 4.9, 1.7, and 5.1 Mg ha À1 of dry matter, respectively, or 0.60 for low cut, 0.66 for normal cut, and 0.61 for the total high-cut (top+bottom) scenarios when expressed as CSHI values. The macronutrient replacement value for the normal harvest scenario was $57.36 ha À1 or $11.27 Mg À1 . Harvesting stalk bottoms increased stover water content, risk of combine damage, estimated transportation costs, and left insuffi...

The phyilochron, which is defined as the interval between similar growth stages of successive leaves on the same calm, has been used extensively to describe and understand development of grasses. The purpose of this paper is to introduce seven papers presented as part of the symposium Understanding Development and Growth in Grasses: Role of the Phyllochron Concept. Environmental (temperature, water, and day length) factors and genetics affect the duration of the phyllochron. The following seven papers broaden the discussion of these topics and present new concepts about how the environment and genetics impact the relationship between leaf appearance and whole plant development.

Crop residues (stover) have many potential uses by society: food, feed, shelter, fuel, and soil amendment. Use of residues for purposes other than as a soil amendment may have serious negative consequences on crop productivity. This study was conducted to investigate the yield response of continuous corn (Zea maysL.) and continuous soybean [Glycine max(L.) Merr.] to removal or addition of crop residues under no‐tillage management. The study was conducted near Lincoln, NE, on a Crete‐Butler silty clay loam (fine, montmorillonitic, mesic Pachic Arguistoll‐Abruptic Argiaquoll) with 1 to 2% slope. Crop residue was collected and weighed immediately after harvest in autumn. Quantity of residue to be returned to each treatment (0, 50, 100, or 150% of that produced) was calculated and uniformly spread over the plot area (12.2 by 12.2 m) by hand. Corn and soybean were planted into the established residue levels with no tillage the following spring. Data were collected on soil water, soil temperature, and grain and residue yield. A positive linear response was found between grain and stover yield and amount of residue applied to the soil surface. Each Mg ha−1of residue removed resulted in about a 0.10 Mg ha−1reduction in grain yield and a 0.30 Mg ha−1reduction in residue yield. Quantity of applied residue accounted for 81 and 84% of the variation in grain yield of corn and soybean, respectively, and 88 and 92% of the variation in residue yield. Amounts of stored soil water at planting were closely associated with quantity of residue applied the previous year. Differences in total available water (soil storage at planting plus rainfall) accounted for approximately 70% of the yield variation associated with the residue treatments. Soil temperature (50‐mm depth) and total available water accounted for nearly the same amount of variation in yield (80 to 90%) as quantity of residue, emphasizing the importance of these factors in evaluating response of crops to residue‐management practices. Residue removal reduced grain and residue yields by amounts equal to 10 and 30%, respectively, of the quantity of residue removed. Residue effects on crop yield were induced mainly through changes in soil water and soil temperature.

Comparisons of growth analysis functions within and among experiments are often confounded by sources of variation other than those imposed by treatment. We suggest use of a temperature index, such as modified growing degree days, as the divisor in growth functions to facilitate treatment comparisons within certain experiments and to reduce the effects of differing temperature regimes among experiments on these comparisons. Three experiments were identified to provide data to analyze this new approach. Mean absolute growth rate () and mean relative growth rate () were compared in two experiments with maize (Zea mays L.) conducted in eastern Nebraska. Previously published values of and mean net assimilation rate () of barley (Hordeura vulgare L.) grown under controlled environments in a soil temperature and P fertility study were also evaluated. Use of modified growing degree days, rather than days, as the divisor in these growth functions led to the recognition of physiological differences due to or associated with treatment, which were previously masked by normal crop response to temperature, and clarified other treatment differences by reducing the effect of temperature.