Search

Crop and livestock production are rarely integrated together in modern farming systems. Reintegrating crops with livestock production has been shown to produce many agronomic and environmental benefits. The objective of this study was to evaluate how an integrated crop-livestock system would influence weed biomass and weed species composition compared with a conventional, continuous corn (Zea mays L.) cropping system. The experimental farming system used in this study was established on a 90-ha site near Pana, IL, in 2002. The integrated system included two phases: (i) a corn and oat (Avena sativa L) cash crop rotation, grown in summer, and (ii) post-harvest grazing of corn stover with annual cover crops. Over a 4-yr period (2004-2007), weed biomass was approximately 4.5 times higher in the conventional system (8.4 g [m.sup.-2]) compared with the integrated system (1.8 g [m.sup.-2]). Weed species composition was affected by the integrated system and showed a temporal disjunction between the time of year and weed life history. Surprisingly, cattle grazing on cropland had little effect on weed biomass or species composition. The primary drivers that suppress weed biomass and change species composition appear to be use of crop rotation and annual cover crops within the integrated system. Wider adoption of integrated crop-livestock systems, such as the one used in this study, should reduce reliance on herbicides compared with more conventional cropping systems.

The [C.sub.4] perennial grasses have many potential virtues as bioenergy crops--high productivity and water use efficiency, multiyear crop cycle that minimizes replanting costs, and wide environmental adaptation. In the productive San Joaquin Valley (SJV) of California, these species also confront high levels of ozone ([O.sub.3]) air pollution. It is often assumed that [C.sub.4] species will exhibit tolerance to [O.sub.3], relative to [C.sub.3] species, based on limited crop yield-loss data and on responses to a contrasting gaseous air pollutant, sulfur dioxide (S[O.sub.2]). Tolerance to [O.sub.3] of high-biomass [C.sub.4] crops such as sugarcane (Saccharum spp.) has not been demonstrated. Here we tested the hypothesis that a clone of sugarcane currently grown on a small commercial scale in the [O.sub.3]-impacted SJV will exhibit tolerance to [O.sub.3]. The hypothesis was disproven. Biomass production declined by over one-third and allocation to roots declined by over two-thirds, over a range of [O.sub.3] exposures (4, 58, and 114 ppb, 12-h means). These responses are comparable to responses previously reported for [O.sub.3]-sensitive [C.sub.3] crop species. Greater [O.sub.3] tolerance may be required to maximize the potential viability of bioethanol production using tall tropical grasses such as sugarcane (for sucrose) or energy canes (for cellulose) in [O.sub.3]-impacted western valleys. In the case of the locally successful sugarcane clone examined here, the [C.sub.4] photosynthetic pathway did not confer resistance to [O.sub.3] exposure.

Improving the biomass yield of switchgrass (Panicum virgatum L.) will improve its utility as a dedicated energy crop by increasing both its net and total energy yield per hectare. In a previous space-transplanted study, midparent heterosis for biomass yield was reported for population and specific [F.sub.1] hybrids of the Lowland-tetraploid cultivar Kanlow and the upland-tetraploid cultivar Summer. These two cultivars were proposed to be two different heterotic groups. The objective of this study was to determine the extent of heterosis for biomass yield in reciprocal Kanlow (K) and Summer (S) [F.sub.1] population hybrids grown in simulated swards and to determine the effect of advance in generation on biomass yield. Parent populations and their [F.sub.1], [F.sub.2], and [F.sub.3] population hybrids were grown in transplanted sward plots located near Mead, NE, for a three-year period. Plant density in the simulated swards was equivalent to acceptable stands in seeded plots. Plots were not harvested the establishment year to enable them to become fully established. Biomass yields were determined for the following two years. There was significant high-parent heterosis of 30 to 38% (P [less than or equal to] 0.01) for biomass yield for both the K x S [F.sub.1] and S x K [F.sub.1] hybrid populations. Heterosis for biomass yield declined with advance in generation. Heterosis for biomass yield in switchgrass may need the competitive conditions of swards to be fully expressed. Additional trials of specific hybrids established from seed are needed to further verify these conclusions. These results do provide ample justification for additional research to develop switchgrass population and specific hybrids.

Politica and environmental concerns have resulted in a growing interest in renewable energy, especially transportation fuels. In the United States the majority of fuel etnanol s currently produced from corn (Zea mays L.) starcn but grain supplies will be insufficient to meet anticipated demands. Enzymatic hydrolysis of lignocellulosic biomass such as corn and sorghum [Sorghum bicolor [L.) Moench] stover can provide an abundant alternative source of fermentable sugars. While production of cellulosic ethanol from stover is feasible from an energy-balance perspective, its production is currently not economically competitive Along with improvements n bioprocessing, enhancing the yield and composition of the biomass has the potential to make ethanol production considerably more cost effective. This requires (i) a petter understanding of now cell wall composition and structure affect the efficiency of enzymatic hydrolysis. (ii) the development of traits that enhance biomass conversion efficiency and increase biomass yield, and (iii) the development of rapid screening protocols to evaluate biomass conversion efficiency. Several genetic resources are available to improve maize and soronum as sources of lignocellulosic biomass. This includes the use of existing mutants, forward and reverse genetics to obtain novel mutants, and transgenic approaches in which the expression of genes of interest is modified. Plant breeding can be implemented to improve biomass yield, biomass quality, and biomass conversion efficiency, either through selection among progeny obtained by crossing parents with desirable traits, or as a way to enhance the agronomic performance of promising mutants and transgenics. Examples from current research will be used to illustrate progress in these different areas.

Current technologies for measuring plant water status are limited, while recently remote sensing techniques for estimating N status have increased with limited research on the interaction between the two stresses. Because plant water status methods are time-consuming and require numerous observations to characterize a field, managers could benefit from remote sensing techniques to assist in irrigation and N management decisions. A 2-yr experiment was initiated to determine specific wavelengths and/or combinations of wavelengths indicative of water stress and N deficiencies, and to evaluate these wavelengths for estimating in-season biomass and corn (Zea mays L.) grain yield. The experiment was a split-plot design with three replications. The treatment structure had five N rates (0, 45, 90, 134, and 269 kg N [ha.sup.-1]) and three water treatments [dryland, 0.5 evapotranspiration (ET), and full ET]. Canopy spectral radiance measurements (350-2500 nm) were taken at various growth stages (V6-V7, V13-V16, and V14-R1). Specific wavelengths for estimating crop biomass, N concentration, grain yield, and chlorophyll meter readings changed with growth stage and sampling date. Changes in total N and biomass in the presence of a water stress were estimated using near-infrared (NIR) reflectance and the water absorption bands. Reflectance in the green and NIR regions were used to estimate total N and biomass without water stress. Reflectance at 510, 705, and 1135 nm were found for estimating chlorophyll meter readings regardless of year or sampling date., AVAILABLE WATER is one of the most limiting factors in crop production; while in non-leguminous crops, low available soil N can be an additional yield reduction factor. Denmead and Shaw [...]

Production of herbaceous biomass for biofuel seeks to maximize lignocellulose yields and minimize N and mineral (especially K) concentrations in the biomass. Our objective was to relate changes in biomass composition of switchgrass (Panicum virgatum L.) to thermal time [degree days (DD), base = 10 [degrees] C] in several environments. 'Alamo' switchgrass at Stephenville, TX, was sampled weekly or every 2 wk from April to June in 1989 and April to September in 1990, 1991, and 1992. Field plots of Alamo and 'Cave-in-Rock' at Stephenville were sampled 17 times during 1993, and at Blacksburg, VA, were sampled on 11 dates in 1992 and nine dates in 1993 from May to September. Biomass samples were analyzed for lignocellulose, crude protein, total ash, K, and Ca concentrations. Linear and nonlinear regressions were used to relate concentrations of constituents to cumulative DD after burning in spring. Concentrations of each constituent were closely related to cumulative DD and a single equation was able to describe the relationship across several years. At Stephenville, lignocellulose concentrations increased linearly up to 800 to 1000 DD. At Blacksburg, lignocellulose concentrations increased linearly up to 400 to 800 DD after burning. At both locations, the time at which the rapid increase in lignocellulose concentration ended coincided with internode elongation. Crude protein, ash, and K concentrations decreased curvilinearly with accumulated DD. There were no differences in composition between Alamo or Cave-in-Rock at Blacksburg. At Stephenville, Alamo had a greater concentration of lignocellulose than did Cave-in-Rock, but similar concentrations of crude protein, ash, and K. The close relation between DD and composition of switchgrass could be used for predictive purposes.

In maize (Zea mays L.), a strong reproductive (grain) sink has been associated with increased stalk and root lodging. A weak reproductive sink may result in reduced production of photosynthate. Endosperm mutants sugary1 (su1) and shrunken2 (sh2) reduce the strength of the reproductive sink. Our objective was to examine stalk and root quality, biomass production, and reproductive sink size using su1 and sh2 in near-isogenic backgrounds. In 1989 and 1990, seed of two half-diallels made from six inbreds was planted. The same inbreds were used; however, one diallel used su1 versions of the inbreds and the other, sh2 versions. Each diallel was planted twice; in one planting the su1 and sh2 diallels were pollinated with su1 pollen and in the other, they were pollinated with sh2 pollen. This resulted in four sets of hybrids that varied only for endosperm type. Stalk and root quality and biomass and partitioning traits were measured. Percentage root lodging, root pull resistance, stalk diameter, stalk section weight, and grain yield differed significantly between starchy and sh2 endosperm types. Hybrids with sh2 had less grain yield and root lodging, higher root pull resistance and stalk section weight. Starchy types had a slightly higher harvest index than the su1 endosperm types. There were no significant differences in biomass among the four groups. The significant reduction in reproductive sink caused by the sh2 endosperm was not associated with decreased biomass.

Tall genotypes of elephantgrass (Pennisetum purpureum Schum.) and energycane (Saccharum spp.) are potential biomass energy plants in subtropical areas because annual dry matter (DM) yields often exceed 40 Mg ha to the -1. A field study was conducted to characterize crop performance of these C4 bunchgrasses during the 35- to 40-wk warm season in north-central Florida. Entries included two tall elephantgrasses (PI 300086 and N51), a tall energycane (L79-1002), and an intermediate pearlmillet (Pennisetum glaucum (L.) R. Br.) X elephantgrass hybrid (S41). In 1989 at Gainesville and in 1990 at another location 20 km away, the grasses were mowed on 28 March and fertilized 1 wk later with 200 kg N, 22 kg P, and 83 kg K ha to the -1. One-time harvests of above-ground biomass were made at 28-d intervals from 16 May through 28 November. Final harvest DM yields (2-yr means) were 46 Mg ha to the -1 yr to the -1 for PI 300086, 47 for N51, 49 for L79-1002, and 37 for S41. Near-linear DM accumulation continued for 140 to 196 d at mean crop growth rates ranging from 18 to 27 g m to the -2 d to the -1. For the tall bunchgrasses, DM production at any point during the season was accurately predicted from canopy height, since height was linearly related to the square root of DM yield (0.87 less than or equal to r squared less than or equal to 0.96). Gross energy yields (2-yr means) in barrels of crude oil equivalent (158.8 L barrel to the -1) were 135 ha to the -1 yr to the -1 for PI 300086, 139 for N51, 141 for L79-1002, and 106 for S41. The high-yielding abilities of the grasses were related to the long linear DM accumulation period.

Elephantgrass (Pennisetum purpureum Schum.) and energycane (Saccharum spp.) have been identified as biomass plants for renewable energy. A field study was conducted at Gainesville, FL, in 1989 and 1990 to identify plant attributes that allowed these C4 bunchgrasses to accumulate high annual dry matter (DM) yields and to compute the efficiency by which solar energy is collected and stored in plant biomass. Entries were PI 300086 (PI3) and N51 elephantgrasses, L79-1002 (L79) energycane, and S41 elephantmillet (Pennisetum glaucum (L.) R. Br. X P. purpureum Schum.). Plots were mowed to 10-cm height on 28 March to begin the season. For PI3, light interception by the top green portion of the canopy was greater than 90% from 49 to 217 d after mowing. For L79, interception increased from 83% on 49 d after mowing to 90% on 91 d and remained above 90% to 245 d after mowing. Two-year means for radiation-use efficiency (RUE), computed for near-linear DM accumulation phase, were 1.25 g DM MJ to the -1 of total solar radiation (TSR) for PI3, 1.26 for N51, 1.24 for L79, and 1.11 for S41. Mean energy concentrations of mature growth ranged from 17.1 to 18.2 kJ g to the -1 DM. Two-year average percentages of TSR converted to chemical DM energy, were 2.3 for PI3, 2.3 for N51, 2.2 for L79, and 1.9 for S41. These bunchgrasses produced greater annual DM yields than other C4 plants because tillers grew vegetatively for 30 to 35 wk. During this period, a green canopy top was maintained and light interception and RUE continued at levels generally expected for actively growing C4 grasses.