A system for identifying and quantifying the stages of growth and development of perennial forage grasses was developed. The system consists of a universal set of morphological descriptors for forage and range grasses and a continuous numerical index. The life cycle of individual grass tillers is divided into five primary growth stages (i) germination, (ii) vegetative, (iii) elongation, (iv) reproductive, and (v) seed ripening. Substages corresponding to specific morphological events are defined within each primary stage. Each growth stage consists of a primary and secondary stage and has both a mnemonic code and numerical index associated with it. The codes were designed to be easily memorized and are useful for applying the system in the field. The numerical index is included so that the stages can be expressed quantitatively.

A literature survey was made for the occurrence of C, and C, photosynthetic pathways in the United States Gramineae. Distinctive characteristics of the two photosynthetic pathways are discussed. Leaf anatomy, CO, compensation point, net enhancement of photosynthesis in oxygen-deficient atmosphere, QC discrimination, and initial product labeling were criteria selected to evaluate data for 6 subfamilies including 25 tribes, 138 genera, and 632 species. The Arundinoideae, Bambusoideae, Oryzoideae, and Pooideae (Festucoideae) are composed of species with C, pathways. All tribes within the Eragrostoideae have C, pathways with the exception of Unioleae. Within the Panicoideae, the Andropogoneae and all of the Paniceae, excepting the genera Sacciolepus, Isachne, Oplismenus, Amphicatpum, and Panicum, have C, pathways. The subgenus Dichanthelium within Panicum is C, while the Bupanicum subgenus contains plants with both C, and C, photosynthetic pathways. Plant productivity is dependent on several environmental and biological factors. The most important single factor is photosynthesis. A pathway for carbon dioxide (CO;?) fixation was described by Calvin and Bassham (1962) in which CO2 was incorporated into a 6-carbon compound and rapidly converted to a 3-carbon compound, 3-phosphoglyceric acid (3PGA). Previous to discoveries of Kortschalk et al. (1965) and Hatch and Slack (1966), the Calvin cycle (C,, reductive pentose pathway) was considered the major photosynthetic mechanism for carbon (C) fixation. However, Hatch and Slack (1966) described CO;! fixation in which labeled CO;! was first incorporated in 4-carbon compounds (malic, aspartic , or oxaloacetic acid) prior to transfer to sugars by way of 3-phosphoglycerate. The proposed mechanism involved the operation of two interconnected metabolic cycles. Downton (1970) described carbon fixation into Cd-dicarboxylic acids in mesophyll cells and subsequent incorporation into the Calvin cycle located in the bundle sheath cells. Plants (Cd plants) possessing the 4-carbon pathway (also called Cd, dicarboxylic acid, Kranz type, low CO;! compensation, tropical, Hatch and Slack, or p carboxylation pathway) were of tropical ongm and more efficient. They produced two-to threefold more dry matter than plants possessing the 3-carbon pathway (C, plants), especially in relatively sunny, warm, dry climates (Black 197 1). Distinctive characteristics associated with the Ca pathway prompted intensive research in photosynthetic processes of flowering plants. The most important photosynthetic pathways

Two herbicide treatments were initiated in southeastern Nebraska on a Wymore silty clay loam (clayey range site) during the spring of 1979, to change species composition of overgrazed, native range from cool-to warm-season grasses. Treatments consisted of late spring applications of atrazine [2-chloro-4-(ethylamino)&(isopropylamino)-s-triazione] at 2.24 kg/ha, and glyphosrte [N-(phosphonomethyl)lycine] at 1.12 kg/ha. Both herbicide treatments significantly (P<.O5) reduced smooth brome (Bromus inermis Leyss.) and Kentucky bluegrass (Poa pratensis L.) production and relative species composition while increasing big bluestem (Andropogongerardii Vitman) in 1979 and the effects were maintained during the second growing season. Warm-season herbage yield, primarily big bluestem, was greater following herbicide treatments (5345 kg/ha) compared to control (1610 kg/ha). Herbage yields of cool-season grasses from herbicide treated plots were reduced. However, total herbage yield was higher on herbicide treated plots during the first and second year after treatment. Total, warm-season and cool-season herbage yields for both years were not different between atrazine and glyphosate treated plots. Both herbicide treatments have potential for rapid recovery of overgrazed, native tallgrass prairies in eastern Nebraska when sufficient warm-season tallgrass remnants are present. The eastern one-third of Nebraska was described as the True Prairie (Weaver 1954) and the native plant community was a tallgrass bluestem prairie, composed of warm-season vegetation. Currently, much of the area is incropland. Remaining native range occurs as small scattered tracts of land which are generally unsuited for cultivation due to rocky or shallow soils or erosion hazards. Over I million acres of native range are located in this area (Bose 1977). Over 60% of the native pasture in eastern Nebraska is in low range condition (Bose 1977). The availability of high producing cool-season species for hay and pasture and accessibility of crop residues encourage high stocking rates, often above the available summer forage supply. This imbalance in seasonal forage supply often contributes to range deterioration. High stocking rates and season-long grazing characteristic of this area contributed to a shift in species composition from the warm-season native community, to cool-season species, primarily Kentucky bluegrass (Poaprurensis L.) and smooth brome (Bromus inermis Leyss.). Although forage is readily available in the spring, fall and winter with improved cool-season species and crop residues, a void of high quality summer forage exists which could be minimized by shifting species composition ofthe native pastures to native warm-season dominants. Atrazine [Z-chloro-4-(ethylamino)-6-(isopropylamino)-striazine], a soil active herbicide, has been reported to be phytotoxic

Seed dormancy and slow seedling development often limit establishment of warm‐season grass stands. Establishment of seedlings with two solid matrix seed priming (SMP) treatments [2‐d moistened (17°C) and 14‐d wet‐chill (4°C)] was compared with untreated seed of ‘Kaw’ and ‘Pawnee’ big bluestem (Andropogon gerardii Vitman) and ‘Path‐finder’ and ‘Cave‐in‐Rock’ switchgrass (Panicum virgatum L.) in greehouse and field experiments. In two greenhouse studies, seedling emergence was monitored from 7 to 26 d after planting and number of adventitious roots were monitored from 2 to 5 wk after planting. Field experiments were initiated on 19 Apr. 1988, 3 June 1988, and 23 May 1989, on a Sharpsburg silty clay loam (fine montmorillonitic, mesic, Typic Argiudolls). In the greenhouse, SMP treatments increased big bluestem emergency by 18%. In the field, final seedling emergency from dry untreated big bluestem seed was equal to or higher than that of SMP‐treated seed. The SMP treatments had no effect on adventitious root formation for big bluestem in either greenhouse or field experiments. In the greenhouse, the moistened and wetchill treatments increased seedling emergency of switchgrass 35 and 150%, respectively. In the greenhouse, SMP treatments slightly increased the percentage of switchgrass plants with adventitious root development 5 wk after planting but not in the field studies. Number of adventitious roots per plant were unaffected by treatment. In the field, the SMP‐treated seed produced the highest seedling emergence for switchgrass under moist planting conditions and had the potential to improve stands when seed was planted without drying. However, final seedling emergence from dry untreated seed was greater than that for SMP‐treated seed under dry soil conditions.

Response of key warm-season grasses to time, frequency, and duration of defoliation is needed to develop grazing systems for the Nebraska Sandhills. A 3year (1986 to 1988) study was conducted on a Valentine fine sand (mixed, mesic Typic Ustipsamments) at the Gudmundsen Sandhills Laboratory near Whitman, Nebraska, to determine the effect of defoliation on little bluestem [Sch&uchyrium scopurium (Michx.) Nash]. Treatments were: 1 defoliation (to 7 cm)