Leaf elongation rate (LER) in grasses is dependent on epidermal cell supply (number) and on rate and duration of epidermal cell elongation. Nitrogen (N) fertilization increases LER. Longitudinal sections from two genotypes of tall fescue (Festuca arundinacea Schreb.), which differ by 50% in LER, were used to quantify the effects of N on the components of epidermal cell elongation and on mesophyll cell division. Rate and duration of epidermal cell elongation were determined by using a relationship between cell length and displacement velocity derived from the continuity equation. Rate of epidermal cell elongation was exponential. Relative rates of epidermal cell elongation increased by 9% with high N, even though high N increased LER by 89%. Duration of cell elongation was approximately 20 h longer in the high-than in the low-LER genotype regardless of N treatment. The percentage of mesophyll cells in division was greater in the high-than in the low-LER genotype. This increased with high N in both genotypes, indicating that LER increased with cell supply. Division of mesophyll cells adjacent to abaxial epidermal cells continued after epidermal cell division stopped, until epidermal cells had elongated to a mean length of 40 micrometers in the high-LER and a mean length of 50 micrometers in the low-LER genotype. The cell cycle length for mesophyll cells was calculated to be 12 to 13 hours. Nitrogen increased mesophyll cell number more than epidermal cell number: in both genotypes, the final number of mesophyll cells adjacent to each abaxial epidermal cell was 10 with low N and 14 with high N. A spatial model is used to describe three cell development processes relevant to leaf growth. It illustrates the overlap of mesophyll cell division and epidermal cell elongation, and the transition from epidermal cell elongation to secondary cell wall deposition.Leaf growth in grasses is predominantly unidirectional, parallel with the longitudinal axis of the leaf. A 3 Abbreviations: SLW, specific leaf weight; LER, leaf elongation rate; PPFD, photosynthetic photon flux density. 549Volenec and Nelson (29) used high and low rates of N fertilization to further alter LER of two genotypes of tall fescue selected for contrasting leaf growth rates. Mean LER of these genotypes was 89% higher with high N, but length of fully elongated epidermal cells was unaffected by N treatment. The number of epidermal cells produced per file per day increased 90% with high N, suggesting that much of the increase in LER following N fertilization was due to increased cell division.Our long-term goal is to understand carbohydrate metabolism during the growth of grass leaves. Our objectives in the present study were to evaluate the effect of N on mesophyll cell division and rate and duration of epidermal cell elongation in leaf blades of two genotypes of tall fescue. Data for epidermal cell lengths utilized here have been reported previously (28, 29).Mesophyll cell division data reported here, and data for leaf elongation rate and structural ...

1996, A role for nitrogen reser\es in forage regrowth and stress tolerance. -Physiol. Plant, 97;[185][186][187][188][189][190][191][192][193] Carbohydrate accumulation and utilization during shoot regrowth after defoliation and winter has been studied extensively in most species used as forage. However, recent woik suggests that N reserves found in vegetative tissues also are important for defoliation tolerance and winter hardiness. Results suggest that these N reserves constitute an altemative N source used when N; fixation and/or mineral N uptake are reduced. "N labelling experiments indicate that a large proportion of herbage N is derived from N reserves mobilized from stem bases or roots to developing leaves and shoots. Amino acids and specific proteins (i,e, vegetative storage proteins, VSPs) are deposited in roots and stem bases and, in the case of VSPs, are degraded rapidly after defoliation. Identification and characterization of VSPs will increase our understanding of the role N reserves play in stress toierance and may lead to innovative approaches for improving forage persistence and productivity.

A trend toward early planting of soybean [Glycine max (L.) Merr.] in Indiana results in higher yield, but the limit to which a positive response to early planting occurs has not been evaluated. Our objective was to determine how early planting aff ects yield components and seed composition of indeterminate soybean planted in late March through early June in Indiana. Th ree cultivars (Pioneer brand 92M61, Becks brand 321NRR, and Becks brand 367NRR) were sown at six planting dates (late March through early June) in West Lafayette, IN, in 2006 and 2007. Across cultivars, yield in 2006 ranged between 4.24 to 4.43 Mg ha −1 at the planting dates from late March to mid-May, and decreased to 3.36 and 3.56 Mg ha −1 at later planting dates. In 2007, yield ranged from 4.21 to 4.44 Mg ha −1 for the 10 April, 30 April, and 9 May planting dates. Yield was reduced at the late March and early June plantings and ranged from 3.85 to 3.99 Mg ha −1 . Path analysis revealed that pods m −2 had the greatest impact on yield, but seed mass was also an important constituent. Mean oil concentration decreased approximately 12 g kg −1 as planting was delayed in both years. In 2006, average seed protein concentration varied by planting date. In 2007, mean protein concentration increased 14 g kg −1 as planting was delayed. Delaying planting until late May or early June altered seed composition slightly, but significantly reduced yield. Planting in April or early May is an eff ective management strategy to increase soybean yield in Indiana.

Understanding differences in herbage yield of alfalfa (Medicago sativa L.) can be simplified by using yield components: plants per area; shoots per plant; and yield per shoot (YPS). Our objective was to examine the influence of plant population on yield components, plant morphology, and forage quality of ‘Vernal’, ‘Hi‐Phy’, and Beltsville International Composite 5‐WH alfalfa. Ten‐week‐old seedlings were transplanted in 0.9‐m2 plots at populations of 11, 22, 43,97, and 172 plants m−2 in early May 1984 and 1985. Plants were clipped in late June of both years, and plants were harvested at first flower, twice in 1984, and three times in 1985. Yield per area increased with plant population up to 172 plants m−2, while yield per plant, shoots per plant, and YPS decreased with increasing plant populations. Path coefficient analysis indicated that YPS was always an important component of yield per plant, but especially so at high plant populations. Stem diameter and nodes per stem decreased as plant population increased. Stems from plants grown at 172 plant m−2 populations contained 10 g kg−1 less lignin and were 30 g kg−1 more digestible than were stems from plants grown at 11 plant m−2 populations. Vernal produced more and finer stems per plant, and these stems were lower in lignin and higher in digestibility when compared to the other cultivars. Selection of genotypes with high YPS may be an effective means of increasing yield, but may result in larger diameter, less digestible stems.

Phosphorus and K fertilization increases alfalfa (Medicago sativa L.) yield and stand persistence, but the changes in yield components as affected by P and K fertility level are not known. Our hypothesis is that P and (or) K fertilization will increase one or more alfalfa yield components, and those component responses may change with stand age. The objectives of this field study were to determine the impact of P and K fertilization on alfalfa forage yield and yield components during the initial 3 yr after establishment. Treatments were the factorial combinations of four P rates (0, 25, 50, and 75 kg P ha−1) and five K rates (0, 100, 200, 300, and 400 kg K ha−1) arranged in a randomized complete block design with four replications. Forage harvests occurred four times annually, and yield, mass shoot−1, and shoots area−1 were determined. Plant populations were determined in early December and late May each year. Incremental additions of P and K increased alfalfa yield in each year. Potassium fertilization did not influence plant population, while robust P‐responsive alfalfa plants apparently crowded out smaller, less vigorous plants thus decreasing plants m−2 Stand assessments based on shoot counts, or aboveground plant counts may not accurately indicate alfalfa yield potential. Shoots plant−1 was not affected by application of either nutrient, while shoots m−2 generally declined with increased P and K fertilization. Improved forage yield of P‐ and K‐fertilized plots was consistently associated with greater mass shoot−1 Because fertilizer‐responsiveness is closely associated with greater mass shoot−1, cultivars possessing this trait may be relatively more productive under well‐fertilized conditions.

Cold hardiness among zoysiagrass (Zoysia spp.) genotypes varies, but the physiological basis for cold hardiness is not completely understood. The objective of this study was to determine the relationship of carbohydrate (starch, total soluble sugars, total reducing sugars, sucrose, glucose, and raffinose family oligosaccharides) and proline concentrations with the cold acclimation of zoysiagrass and the lethal temperature killing 50% of the plants (LT50). Thirteen genotypes of zoysiagrass were selected with contrasting levels of winter hardiness. Plants were grown for 4 wk of 8/2°C day/night cycles and a 10‐h photoperiod of 300 μmol m−2 s−1 to induce cold acclimation. Rhizomes and stolons were sampled from nonacclimated and cold‐acclimated plants and used for carbohydrate and proline analysis. Concentrations of soluble sugars and proline increased during cold acclimation, while starch concentrations decreased. Starch, sugar/starch ratio, glucose, total reducing sugars, and proline in cold‐acclimated plants were correlated (r = 0.61, −0.67, −0.73, −0.62, and −0.62, respectively) with LT50 These correlations indicate that higher concentrations of total reducing sugars, glucose, and proline are positively associated with zoysiagrass freeze tolerance, whereas higher concentrations of starch appeared detrimental to freeze tolerance.

The Soil and Water Assessment Tool (SWAT) is increasingly used to quantify hydrologic and water quality impacts of bioenergy production, but crop-growth parameters for candidate perennial rhizomatous grasses (PRG) Miscanthus 9 giganteus and upland ecotypes of Panicum virgatum (switchgrass) are limited by the availability of field data. Crop-growth parameter ranges and suggested values were developed in this study using agronomic and weather data collected at the Purdue University Water Quality Field Station in northwestern Indiana. During the process of parameterization, the comparison of measured data with conceptual representation of PRG growth in the model led to three changes in the SWAT 2009 code: the harvest algorithm was modified to maintain belowground biomass over winter, plant respiration was extended via modified-DLAI to better reflect maturity and leaf senescence, and nutrient uptake algorithms were revised to respond to temperature, water, and nutrient stress. Parameter values and changes to the model resulted in simulated biomass yield and leaf area index consistent with reported values for the region. Code changes in the SWAT model improved nutrient storage during dormancy period and nitrogen and phosphorus uptake by both switchgrass and Miscanthus.Abbreviations ACRE = agronomy center for research and education BIO_E = radiation use efficiency 9 10 BLAI = maximum leaf area index CMN = rate of humus mineralization CYLD = nutrient fraction at harvest DLAI = point of the growing season when senescence begins HEFF = harvest efficiency HI = harvest index HU = heat unit LAI = leaf area index OAT = one-at-a-time method PAR = photosynthetically active radiation PLTFR = plant nutrient fraction PLTNFR = plant nitrogen fraction PLTPFR = plant phosphorus fraction PRG = perennial rhizomatous grasses RUE = radiation use efficiency SWAT = soil and water assessment tool T_BASE = base temperature WQFS = water quality field station.

Carbohydrate accumulation and utilization during shoot regrowth after defoliation and winter has been studied extensively in most species used as forage. However, recent work suggests that N reserves found in vegetative tissues also are important for defoliation tolerance and winter hardiness. Results suggest that these N reserves constitute an alternative N source used when N2 fixation and/or mineral N uptake are reduced. 15N labelling experiments indicate that a large proportion of herbage N is derived from N reserves mobilized from stem bases or roots to developing leaves and shoots. Amino acids and specific proteins (i.e. vegetative storage proteins, VSPs) are deposited in roots and stem bases and, in the case of VSPs, are degraded rapidly after defoliation. Identification and characterization of VSPs will increase our understanding of the role N reserves play in stress tolerance and may lead to innovative approaches for improving forage persistence and productivity.