Agronomy Journal 92:967-973 (2000)
© 2000 American Society of Agronomy
FORAGES
Codified Morphological Stage for Predicting Digestibility of Italian Ryegrass during the Spring Cycle
Maria Eugenia Valentea,
Giorgio Borreanib,
Pier Giorgio Peirettia and
Ernesto Tabaccob
a Centro di Studio per l'Alimentazione degli Animali in Produzione Zootecnica, CNR, Torino, Italy
b Dep. Agronomia, Selvicoltura e Gestione del Territorio, Univ. of Turin, via Leonardo da Vinci 44, 10095 Grugliasco, Turin, Italy. The work is attributable in equal part to the authors
borreani{at}agraria.unito.it
 |
ABSTRACT
|
|---|
A precise prediction of changes in digestibility of grasses during the growth cycle would allow targeting of harvests to desired levels of nutritive composition to meet specific animal requirements. In this study, regression analysis was used to formulate and test prediction equations for organic matter digestibility (OMD) of standing crops of Italian ryegrass (Lolium multiflorum Lam.) with codified morphological stage, canopy age, growing degree days (GDD), and N fertilization as independent variables. The field study was conducted for 7 yr with six Italian ryegrass cultivars, diversified for ploidy and earliness, grown in the western Po Valley (Italy). Nitrogen fertilizer was applied at various rates as top dressing. Sequential harvesting from early vegetative to full flowering provided herbage samples
varying in age and stage of development. The 0–400 classification system that was used to evaluate the morphological stage included four primary stages: vegetative, elongation, inflorescence emergence, and flowering. The OMD decreased from 928 to 576 g kg-1 OM, as the herbage aged. All cultivars responded in the same way during the whole growth cycle. Morphological stage was a better predictor of OMD than GDD or age in days, with a higher r2 (0.88) and a lower root mean square error (28.0 g kg-1 OM). Nitrogen fertilization slightly decreased digestibility. The developed equation tested on an independent set of farm scale data
showed that this codified morphological stage system can provide a rapid and easy estimate of Italian ryegrass digestibility in the field.
Abbreviations: GDD, growing degree days • GE, gross energy • JDAYS, age in days from 1 January • NF, nitrogen top dressing fertilization • NP, organic nitrogen fertilization on the preceding maize crop • OM, organic matter • OMD, organic matter digestibility • RMSE, root mean square error • STAGE, codified morphological stage • TLIT, total hours of above-horizon sunlight
|
INTRODUCTION
|
|---|
ITALIAN RYEGRASS
(Lolium multiflorum Lam.) is native to the Po Valley of northern Italy where it represents the main grass component of irrigated permanent meadows since the 13th century (Tyler and Chorlton, 1978). Today it is grown during winter as double crop followed by maize (Zea mays L.) silage or soybean [Glycine max (L.) Merr.]. The chief users of Italian ryegrass are livestock farmers who use it for silage and as supplemental pasture, because of its high dry matter (DM) yield and good potential nutritive value. Italian ryegrass included in rotation with maize increases soil organic matter, improves soil structure, reduces soil erosion in winter, and utilizes residual soil N after maize harvest (Shipley et al., 1992).
Prediction of the nutritive value of forages is important for several reasons. Accurate prediction of forage quality during the spring growth cycle would allow targeting of harvests or grazing to desired levels of nutritive composition to meet specific animal requirements. It is also necessary for optimization of ration composition with respect to maximal production, minimal excretion of undigested material, and minimal cost (Hvelplund et al., 1995).
Although intake is more important than digestibility in assessing forage quality, extensive research has been devoted to measuring digestibility and relating it to feed characteristics because digestibility can be accurately measured with relative ease compared to intake (Mertens, 1994).
In temperate grasses, digestibility depends mainly on the growth stage, the growth cycle, and the species (Van Soest, 1994). Digestibility generally decreases with advancing age, especially during the first growth cycle. This decline results from the interaction of factors such as increased fiber concentration in plant tissues (Wilson et al., 1991), increased lignification during plant development (Morrison, 1980), and the different leaf/stem ratio (Hides et al., 1983). Terry and Tilley (1964) reported that at early stages of growth, all parts of the grass plant are highly digestible, but that during stem elongation and flowering there is a more rapid decline in the digestibility of stem than of leaf.
In the field, the environment is constantly changing, and crops show a corresponding, genetically programed response to environmental signals (Fick et al., 1988). High temperatures decrease digestibility by increasing cell wall contents and lignification, and promoting a more rapid metabolic activity (Van Soest, 1994). In temperate species, N input and the resulting level of yield do not appear to influence the maturational processes affecting digestibility during the growing cycle (Demarquilly, 1970).
Stage of growth in terms of plant development has been frequently associated with forage quality. Several methods of classifying morphological stages have been proposed for grasses (Hedlund and Höglund, 1983; Moore et al., 1991; Simon and Park, 1983), legumes (Kalu and Fick, 1981; Ohlsson and Wedin, 1989), and cereals (Feekes, 1941; Haun, 1973; Zadoks et al., 1974). Phenological staging schemes take into account both climate and age of the crop and have proven to be effective in predicting digestibility in the field with good accuracy and more quickly than expensive labor and time-consuming laboratory analyses (Fick et al., 1988).
In previous investigations of Italian ryegrass, the relationships between the codified stage and the nutritional value of the forage were investigated (Borreani et al., 1998a; Valente et al., 1998). To improve and generalize those prediction equations, additional studies were needed with different cultivars and environmental conditions and with different stress factors (Sanderson, 1992).
The objective of this study was to determine the relationships between organic matter digestibility (OMD) and stage of development for different Italian ryegrass cultivars during the first growing cycle under different weather and management conditions. It is based on 7 yr of data with evaluation from an independent set of farm-scale data.
|
Materials and methods
|
|---|
Several sets of field data, collected in different studies from 1991 to 1997, were used to develop and evaluate a prediction equation for organic matter digestibility of Italian ryegrass herbage. The trials were carried out in the western Po Valley near Turin, Italy (44°50'N, 7°40'E, altitude 232 m above sea level, annual mean temperature 11.3°C, and annual average rainfall 751 mm) on recent alluvium soil (Typic Udifluvents; USDA, 1997) with a sandy loam texture and pH (in water) of 7.6. Climatic patterns of North Italy are characterized by high precipitation in April, May, and October (96–110 mm month-1) with little rainfall in summer and winter. Mean daily temperatures increase from 0.5°C in January to 22°C at the end of July. Daily class A pan evaporation increases from about 2.5 mm d-1 in April to about 6 mm d-1 in July.
All the stands were seeded in the autumn before 10 October after maize was harvested for silage. The cultivars were diversified for ploidy and earliness with a maximum difference of about 15 d in inflorescence emergence, as shown in Table 1
. Nitrogen fertilizer was applied at various rates, ranging from 0 to 110 kg N ha-1, as top dressing before 20 March (NF). Specific sampling dates, rate of fertilization, and cultivars used each year are presented in Table 2
.
Organic N fertilization (manure) applied on the preceding maize crop was also taken into account (NP) because 10 to 25% of N may be released in the succeeding year (Beauchamp, 1986; Jensen et al., 1999). Manure decomposition rate and nutrient losses are difficult to determine; therefore, the value used in the regression equations was the whole amount of organic N applied (0, 180, 200, and 300 kg N ha-1).
Herbage samples were collected at progressive morphological stages from early vegetative to full flowering, within a 1-m2 randomly located quadrat in stands of about 1000 m2 with two replicates cut to a 4-cm stubble height. The sampling period ranged between 26 March and 2 June.
The morphological stage was evaluated on a sample of about 50 tillers clipped at ground level and classified following the equations proposed for Italian ryegrass, cv. Barmultra, by Borreani et al. (1998a). The mean stage code of the canopy was defined in the following four primary stages:
Vegetative. Code 0 to 100, as the mean height (cm) of the crop measured with weighted disc (Castle, 1976).
- Code = 6.67 (Mean height)
- Elongation. Code 100 to 200, as the mean of the inflorescence height (cm) inside each sample tiller.
- Code = 100 + 2.77 (Inflorescence height) – 0.0251 (Inflorescence height)2
- Inflorescence Emergence. Code 200 to 300, as the percentage of the tillers with an emerging inflorescence (at least one-third emerged) in the sample.
- Code = 200 + 140 (Fraction of tillers with emerged inflorescence)
- Flowering. Code 300 to 400, as the percentage of flowering tillers in the sample.
- Code = 300 + 200 (Flowering tillers/Total tillers)
Some representative stages are reported in Table 3
.
Model evaluation samples were collected (with the same criteria as described above) in 1996 from five different dairy farms chosen to be representative of the western Po Valley and from field data designed for a different study (Borreani et al., 1998b) (cf. Table 2).
Chemical Analysis
The herbage samples were immediately dried in a forced-draft oven to constant weight at 65°C (Deinum and Maassen, 1994), air equilibrated, weighed, ground in a Cyclotec mill (Tecator, Herndon, VA, USA)1
to pass a 1 mm screen, and stored for later analyses.
The dried samples were analyzed to determine GE with an adiabatic calorimeter bomb (IKA C7000, Staufen, Germany), and OMD according to the two-stage rumen fluid technique (Tilley and Terry, 1963). The OMD values were expressed in vivo by the regression equation of Goldman et al. (1987).
Statistical Analysis
The data were analyzed across years, cultivars, rate of fertilization, and harvest maturity for regression analysis. The data were averaged across field replicates before statistical analysis; therefore, a data set of 153 OMD values were used to evaluate regression relationships. The data were regressed on the codified morphological stage (STAGE), GDD > 0°C cumulated from 1 January [(Daily high temperature + Daily low temperature)/2; negative values were not included in the summation], the total hours of above-horizon sunlight for the growth (TLIT) computed for the same time interval as GDD, and age in days from 1 January (JDAY) as independent variables. Linear and quadratic regressions were compared using the Draper and Smith (1981) stepwise selection procedure to select the best regression model at the 0.05 probability level. All the determination coefficients (r2 or R2) reported in this paper were adjusted for degrees of freedom. The MANOVA analysis of covariance was used to verify the equivalence of the equations for all years. The best equation was selected using criteria of simplicity, coefficient of determination, and root mean square error (RMSE). The equation selected was tested by regressing the pooled 34 observations from the farm and Borreani et al. (1998b) data sets on the predictions made with the equations.
|
Results
|
|---|
Weather Data
Years were very similar in mean temperature with a maximum difference of 1.4°C from the 25-yr mean (Table 4)
. Differences in monthly mean temperature were found only in March. It was colder in April and May of 1991 than in other years. Annual precipitation was similar or higher than the mean, except for 1997, which was a droughty year.
Gross Energy and Organic Matter Digestibility
The GE of the herbage did not show any significant relationship with the stage and was almost constant over the years and cultivars with a mean value of 17.4 ± 0.25 MJ kg-1 DM.
Digestibility decreased greatly as herbage increased in age and ranged from 928 to 576 g kg-1 OM as maximum and minimum values observed for the period from April to the beginning of June. When OMD in different years was regressed on GDD (Fig. 1) or age in days (Fig. 2)
, different trends among years were found, all with a high coefficient of determination (Table 5)
. When OMD was regressed on the codified morphological stage of growth, regression equations with high adjusted r2 and very similar patterns among years were found (Fig. 3
and Table 5). Since equations on JDAY had linear and quadratic trends, the test for homogeneity of slopes was made only on equations based on GDD and STAGE. It was significant for GDD
and not significant for the STAGE variable
.
View larger version (28K):
[in this window]
[in a new window]
|
Fig. 2 Organic matter digestibility (OMD) in Italian ryegrass as a function of age in days from 1 January
|
|
All cultivars responded in the same way over the whole growth cycle. When cultivars were compared at the same age in days (Fig. 4a)
, there were differences in digestibility higher than 100 g kg-1 OM. These differences were greatly reduced using codified morphological stage (Fig. 4b).
View larger version (17K):
[in this window]
[in a new window]
|
Fig. 4 Organic matter digestibility (OMD) in Italian ryegrass cultivars as a function of (a) age in days, and (b) codified morphological stage of 2-yr data set (1994–1995),
|
|
The regression equations of the pooled data of digestibility
on growing degree days (Eq. [1]), age in days (Eq. [2]), and morphological stage (Eq. [3]) are reported in Table 6
. Morphological stage was a better predictor of OMD than GDD or JDAY with a higher r2 and lower RMSE. Introducing a variable for applied N improved the STAGE equation. Fertilization with N slightly decreased digestibility by 3.4 and 1.0 g kg-1 OM for each 10 kg N ha-1 applied as NF and NP, respectively.
Validation
The four developed equations were tested with data
not used in the models development. In Table 7
are reported r2 and RMSE of the regression equations between observed and predicted values. For all equations the y intercept was not significantly different from zero, and the slope was not significantly different from unity. Equation [4], based on stage, had the best fitting line between observed and predicted values (Fig. 5)
.
View this table:
[in this window]
[in a new window]
|
Table 7 Parameters of the regression of observations of Italian ryegrass digestibility on predictions of those observations made with the equations developed (n = 34)
|
|
View larger version (25K):
[in this window]
[in a new window]
|
Fig. 5 Evaluation of the model to predict organic matter digestibility (OMD) from codified stage by regressing field observations on predictions
|
|
|
Discussion
|
|---|
The GE of Italian ryegrass did not show any significant difference with the variation of weather, N fertilization, and crop factors; therefore, OMD may be considered the most important determinant of the metabolizable energy of the forage (Hvelplund et al., 1995). Focusing on factors influencing digestibility allows us to closely predict, in the field, the nutritive value of the forage that will be harvested. Moreover, many experiments have shown that, with efficient conservation methods, the digestibility of conserved feed is very close to that of the standing crop (McDonald et al., 1992).
The results indicate that plant morphological development is the major factor affecting digestibility. The great decline of OMD of about 40% is known to be due to the interactive effects of the increase of fiber and lignin in tissues, which is more marked in stem tissue than in leaf tissue and to the different ratio between plant tissue components (Nelson and Moser, 1995).
To predict quality, the first step was to find a variable suitable for describing the changes in digestibility throughout the growing season. Growing degree days used in predicting OMD (Eq. [1], Table 6) was inaccurate and only partially explained the variance of the data set. The sum of temperature, found by others to be effective in predicting single fiber fractions (Sanderson, 1992; Valente et al., 1998), did not adequately predict OMD, because the decline of digestibility seems to be somewhat insensitive to fluctuations in temperature and more closely related to photoperiod. At the latitude of this research site, inflorescence emergence and reproductive development occurred for individual cultivars on approximately the same day of the year, regardless of temperature or rainfall, suggesting a strong influence of day-length in determining morphological development.
Age in days (Eq. [2], Table 6) was a better predictor than GDD, because it was more related to photoperiod, but it did not account for earliness or lateness of the cultivars. When cultivars were compared at the same date of cutting, large differences in OMD were observed, mainly because of the earliness (about 15 d of difference in our data set) and not any real genetic variability. Furthermore, at the same stage of development there were no differences between diploid and tetraploid strains, even though such differences have been observed in perennial ryegrass (Lolium perenne L.) (Morrison, 1980).
The codified morphological stage (Eq. [3], Table 6) proved to be the most accurate independent variable for describing the decline of digestibility of different cultivars of Italian ryegrass, because phenology and environmental factors were well integrated in the codified schemes. The same results were found for other grasses (Sanderson and Wolf, 1995) and legumes (Fick and Onstad, 1988).
During the growing season, temperature, N fertilization, and water stress, have large effects on the chemical components of herbage (Wilson et al., 1991), but only small effects on OMD, principally because of the compensatory effects of variations of individual components (Buxton and Fales, 1994; Van Soest, 1994). These environmental factors influence chemical composition of forages directly and indirectly through their influence on morphological development and growth.
The similar temperature patterns during the studied years and the small differences in mean daily temperature during growing seasons (Table 4) do not allow us to estimate the effect of temperature pattern on digestibility observed by others (e.g., Thorvaldsson, 1992; Wilson and Ford, 1971). In the absence of large differences in mean daily growth temperature, the primary effect of temperature on forage quality is to determine the rate of plant development rather than to depress digestibility by increasing lignification of cell wall. These small changes in forage growth rate are well expressed by codified stage.
Positive, negative, and insignificant changes in digestibility have been reported in response to N fertilization by various authors (Illius, 1985; Van Soest, 1994). In our experiment, N fertilization applied both as top dressing and as organic fertilization on the preceding crop reduced digestibility. Probably N fertilization slightly depressed digestibility because increased N compounds are compensated for by a reduction in water-soluble carbohydrate and increased lignification (Van Soest et al., 1978).
Equation [4] (Table 6), developed with the pooled data and used to predict Italian ryegrass digestibility on a farm scale, showed the practical applicability of the codified morphological stage for predicting the herbage quality changes in the field. The RMSE of the predicted data was similar to the RMSE of the calibrated model, which indicates a good fit between field observation and model prediction in these studies. Equation [3] also performed well, indicating that the codified stage alone can be used to predict digestibility with good accuracy.
|
Conclusions
|
|---|
The codified stage effectively predicted changes in the OMD of Italian ryegrass in the field during the first spring cycle. It provides an easy way to obtain a rapid assessment of the nutritive value, when more expensive and time-consuming laboratory analyses are not available. Because the data represent a narrow range in latitudes (all about 45°N), a greater geographical range is needed to refine and generalize the proposed prediction equations.
|
ACKNOWLEDGMENTS
|
|---|
The authors thank Professor Angelo Ciotti for his useful comments on the manuscript, Sara Antoniazzi (C.S. Alimentazione degli Animali in Produzione Zootecnica, CNR, Torino) for the excellent laboratory analysis, and Mario Gilardi for the technical assistance in the field. This paper was greatly improved by the critical readings and comments of Dr. Matt A. Sanderson and two anonymous reviewers. Work supported by the Italian "Ministero per le Politiche Agricole," "Foraggicoltura prativa" project.
|
NOTES
|
|---|
1 Mention of trade names is for the benefit of the reader and does not constitute endorsement by the CNR and the University of Italy over other products not mentioned. 
Received for publication September 13, 1999.
|
REFERENCES
|
|---|
- Beauchamp E.G. Availability of nitrogen from three manures to corn in the field. Can. J. Soil Sci. 1986;66:713-720.
- Borreani G., Ciotti A., Valente M.E., Peiretti P.G., Canale A. Forage quality and quantified morphological stage relationships in Italian ryegrass during the spring growth cycle: I. Stage codification, yield and ensilability characteristics. Ital. J. Agron. 1998;2:39-46 a.
- Borreani G., Gaspari N., Tabacco E., Rossi-Pisa P. Evaluation of the morphological stage as a predictor of Italian ryegrass forage quality in two environments. In: Nagy G., Peto K., eds. Ecological aspects of grassland management. Reading, UK: Brit. Grassl. Soc, 1998:23-27 b Proc. 17th Gen. Meet. Eur. Grassl. Fed., Debrecen, Hungary. 18–21 May 1998..
- Buxton D.R., Fales S.L. Plant environment and quality. In: Fahey G.C., et al. , ed. Forage quality, evaluation and utilization. Madison, WI: ASA, CSSA, and SSSA, 1994:155-199.
- Castle M.E. A simple disc instrument for estimating herbage yield. J. Br. Grassl. Soc. 1976;31:37-40.
- Deinum B., Maassen A. Effects of drying temperature on chemical composition and in vitro digestibility of forages. Anim. Feed Sci. Technol. 1994;46:75-86.
- Demarquilly C. Feeding value of green forages as influenced by nitrogen fertilization. Ann. Zootech. 1970;19:423-437.
- Draper N.R., Smith H. Applied regression analysis, 2nd ed New York: John Wiley & Sons, 1981.
- Feekes, W. 1941. De tarwe en haar milieu. p. 560–561. In Versl. XVII Techn. Tarwe Comm., Groningen.
- Fick G.W., Holt D.A., Lugg D.G. Environmental physiology and crop growth. In: Hanson A.A., et al. , ed. Alfalfa and alfalfa improvement. Madison, WI: ASA, CSSA, and SSSA, 1988:163-194 Agron. Monogr. 29..
- Fick G.W., Onstad D.W. Statistical models for predicting alfalfa herbage quality from morphological or weather data. J. Prod. Agric. 1988;1:160-166.
- Goldman A., Genizi A., Yulzari A., Seligman N.G. Improving the reliability of the two-stage in vitro assay for ruminant feed digestibility by calibration against in vivo data from wide range of sources. Anim. Feed Sci. Technol. 1987;18:233-245.
- Haun J.R. Visual quantification of wheat development. Agron. J. 1973;65:116-119.[Abstract/Free Full Text]
- Hedlund K., Höglund S. Scheme for stages of development in timothy, red clover and lucerne. Uppsala, Sweden: M.S. thesis. Swedish Univ. of Agricultural Sciences, 1983.
- Hides D.H., Lovatt J.A., Hayward M.V. Influence of stage of maturity on the nutritive value of Italian ryegrasses. Grass Forage Sci. 1983;38:33-38.
- Hvelplund, T., J. Andrieu, M.R. Weisbjerg, and M. Vermorel. 1995. Prediction of the energy and protein value of forages for ruminants. p. 205–227. In M. Journet, et al. (ed.) Recent developments in the nutrition of herbivores. Proc. 4th Int. Symp. Nutr. Herb., Clermont-Ferrand, France. 11–15 Sept. 1995. INRA, Paris, France.
- Illius A.W. A predictive model of seasonal changes in herbage digestibility. J. Agric. Sci. (Cambridge) 1985;105:505-512.
- Jensen B., Sørensen P., Thomsen J.K., Jensen E.S., Christensen B.T. Availability of 15N-labeled ruminant manure components to successively grown crops. Soil Sci. Soc. Am. J. 1999;63:416-423.[Abstract/Free Full Text]
- Kalu B.A., Fick G.W. Quantifying morphological development of alfalfa for studies of herbage quality. Crop Sci. 1981;21:267-271.
- McDonald P., Henderson A.R., Heron S.J.E. The biochemistry of silage, 2nd ed Marlow, Bucks, UK: Chalcombe Publ, 1992.
- Mertens D.R. Regulation of forage intake. In: Fahey G.C., ed. Forage quality, evaluation and utilization. Madison, WI: ASA, CSSA, and SSSA, 1994:450-493.
- Moore K.J., Moser L.E., Vogel K.P., Waller S.S., Johnson B.E., Pedersen J.F. Describing and quantifying growth stages of perennial forage grasses. Agron. J. 1991;83:1073-1077.[Abstract/Free Full Text]
- Morrison I.M. Changes in the lignin and hemicellulose concentrations of ten varieties of temperate grasses with increasing maturity. Grass Forage Sci. 1980;35:287-293.
- Nelson C.J., Moser L.E. Plant factors affecting forage quality. In: Fahey G.C., ed. Forage quality, evaluation and utilization. Madison, WI: ASA, CSSA, and SSSA, 1995:115-154.
- Ohlsson C., Wedin W.F. Phenological staging schemes for predicting red clover quality. Crop Sci. 1989;29:416-420.[Abstract/Free Full Text]
- Sanderson M.A. Predictors of alfalfa forage quality: Validation with field data. Crop Sci. 1992;32:245-250.
- Sanderson M.A., Wolf D.D. Morphological development of switchgrass in diverse environments. Agron. J. 1995;87:908-915.[Abstract/Free Full Text]
- Shipley P.R., Meisinger J.J., Decker A.M. Conserving residual corn fertilizer nitrogen with winter cover crops. Agron. J. 1992;84:869-876.[Abstract/Free Full Text]
- Simon, U., and B.H. Park. 1983. A descriptive scheme for stages of development in perennial forage grasses. p. 416–418. In J.A. Smith and V.W. Hays (ed.) Proc. 14th Int. Grassl. Congr., Lexington, KY. 15–24 June 1981. Westview Press, Boulder, CO.
- Terry R.A., Tilley J.M.A. The digestibility of the leaves and stems of perennial ryegrass, cocksfoot, tymothy, tall fescue, lucerne and sainfoin, as measured by an in vitro procedure. J. Br. Grassl. Soc. 1964;19:363-372.
- Thorvaldsson G. The effects of temperature on digestibility of timothy (Phleum pratense L.), tested in growth chambers. Grass Forage Sci. 1992;47:306-308.
- Tilley J.M.A., Terry R.A. A two-stage technique for the in vitro digestion of forage crops. J. Br. Grassl. Soc. 1963;18:104-111.
- Tyler B.F., Chorlton K.H. A Lolium and Festuca plant collecting expedition to northern Italy. Riv. Agron. 1978;12:181-190.
- U.S. Department of Agriculture. Keys to soil taxonomy, 7th ed Pocahontas, VA: Pocahontas Press, 1997 Soil Survey Staff, USDA-SCS..
- Valente M.E., Peiretti P.G., Canale A., Borreani G., Ciotti A. Forage quality and quantified morphological stage relationships in Italian ryegrass during the spring growth cycle: II. Chemical composition and nutritive value. Ital. J. Agron. 1998;2:47-55.
- Van Soest P.J. Nutritional ecology of the ruminant, 2nd ed Ithaca, NY: Cornell Univ. Press, 1994.
- Van Soest P.J., Mertens D.R., Deinum B. Preharvest factors influencing quality of conserved forage. J. Anim. Sci. 1978;47:712-720.[Abstract/Free Full Text]
- Wilson J.R., Deinum B., Engels F.M. Temperature effects on anatomy and digestibility of leaf and stem of tropical and temperate forage species. Neth. J. Agric. Sci. 1991;39:31-48.
- Wilson J.R., Ford C.W. Temperature influences on the growth, digestibility, and carbohydrate composition of two tropical grasses, Panicum maximum var. trichoglume and Setaria sphacelata, and two cultivars of the temperate grass Lolium perenne. Aust. J. Agric. Res. 1971;22:563-571.
- Zadoks J.C., Chang T.T., Konzak C.F. A decimal code for the growth stages of cereals. Weed Res. 1974;14:415-421.
This article has been cited by other articles:
|
|
|
|
 
G. Borreani, P. P. Roggero, L. Sulas, and M. E. Valente
Quantifying Morphological Stage to Predict the Nutritive Value in Sulla (Hedysarum coronarium L.)
Agron. J.,
November 1, 2003;
95(6):
1608 - 1617.
[Abstract]
[Full Text]
[PDF]
|
|
|
TOP
ABSTRACT
INTRODUCTION
