1996 EFFECT OF STAGE OF GROWTH AND CULTIVARS ON CHEMICAL COMPOSITION OF WHOLE MAIZE PLANT AND ITS MORPHOLOGICAL FRACTIONS

Samples of whole plant, leaf and stem of Akbar, Neelum, U. M -XI and I. Z31 cultivars of maize fodder harvested at weekly intervals/growth stages were drawn and analysed for dry matter contents and various cell wall constituents such as neutral detergent fibre (NDF), acid detergent fibre (ADF), hemicellulose. cellulose, lignin, cutin and silica. The dry matter contents of whole maize plant, leaf and stem increased significantly with advancing plant age. Maximum dry matter was found in the leaf fraction of the plant. The cell wall components continued to increase significantly in whole maize plant and its morphological fractions as the age advanced. Maximum values for NDF, ADF, cellulose and lignin were observed in stem followed by whole plant and leaf, whereas hemicellulose .. cutin and silica contents were higher in leaf fraction of the plant. The cultivars were observed to have some effects on chemical composition of all plant fractions. The results indicated that maturity had a much greater effect on the concentration of all the structural components than did the cultivars, It was concluded that maize fodder should be cut preferably between 8th to 9th week of age (flowering stage) to obtain more nutritious and digestible feed for livestock. Among the maize cultivars, Neelum proved to be the best, due to its higher digestibility and dry matter contents and lower lignin concentration. ..•.•.


INTRODUCTION
ln recent years the plant breeders have paid much attention to varietal development to increase the production of good quality fodders since this is a key to increase livestock production.
The value of green fodder for animal production depends upon its nutrient concentration as well as intake by an animal.
Generally.the chemical composition of fodders varies between regions due to variation in soil.plant species.climatic conditions and agronomic practices.The fibre level in the forages is not constant rather it varies widely according to the stage of maturity of the plant when harvested and the environmental conditions (Singh and Pradhan, 1981).Poor digestibility and lower intake are usually associated with high lignin contents which increase with advancing stage of maturity.As the plant matures, dry matter and cell wall constituents increase and erude protein and cell contents decrease (Gupta et al., 1976).
Maize (Zea mavs) has for centuries been used as a forage crop in the ludo -Pak subcontinent.
Generally.the whole plant, when cobs are at the milking stage is cut and fed to animals.
Maize fodder provides adequate energy and protein for physical growth and milk production of buffaloes and cattle (Choudhry. 1983).Maize is an important summer (Kharif) crop grown basically for grain and at the same time is a popular fodder for livestock.The yield per hectare of maize fodder is [4.80 tonnes (Bhatti , 1996).Commonly three crops of maize per year are grown in Pakistan.Maize is also a major crop of the northern areas and a part of the Punjab province.The information on local maize fodder is scanty, particularly with reference to plant parts, effects of harvesting stages and varietal differences.
The study under report was therefore conducted to determine the changes in chemical composition of different varieties and morphological fractions of maize plant at various growth stages.Urea (125 kg / hectare) was applied as fertilizer.TIle experimental fields were irrigated six times during the experimental period.

MATERIALS AND METHODS
The representative samples of maize fodder were harvested from different parts of the experimental fields at weekly intervals (1st to 14th week).The morphological fractions such as leaves and stem were also collected at various harvest stages.The leaves (blade + sheath) were separated manually from stem and saved for further analysis.All fodder samples were chaffed into 2 -3 cm pieces and dried at 60"C to constant weight (AOAC, 1984).The dried fodder samples were ground in a laboratory mill and passed through lrnm screen (Harris, 1970).Various structural components such as neutral detergent fibre (NDF), acid detergent fibre (ADF), hemicellulose, cellulose, lignin, cutin and silica were determined by the method of Van Soest and Robertson ( 1985).A brief description of the methods is as under:

Neutral
Detergent Fibre (NDF): One gram of fodder sample was refluxed with 100 ml neutral detergent solution (pH 7) for 60 minutes.The insoluble residue so obtained was filtered.dried at 105 "C and weighed.The loss in weight was recorded as NDF.

Acid Detergent
Fibre (ADF) and Silica: One gram of fodder sample was refluxed for 60 minutes in 1 N sulphuric acid containing 2 % cetyl trimethyl ammonium bromide (CTAB) as the detergent.
The residue was filtered.dried at !O5 "C and weighed.The loss in weight was taken as ADF.The residue left after ADF extraction was ashcd at 600 "C in a muffle furnace and silica so obtained was measured.

Hemicellulose:
The hemicellulose contents of the fodders were determined by difference between the NDF and ADF.

Cellulose,
Lignin and Cutin: The fodder samples were first digested with neutral detergent and then with acid detergent to dissolve all detergent soluble fractions.The residue was further digested by 72 % sulphuric acid.The loss in weight was considered as cellulose.The remaining residue after elimination of cellulose was oxidized by potassium permanganate (KM nO .•)solution to separate the plant cuticle which was resistant to KMnO .•.The loss in weight was taken as lignin.The residue left after KMnO .•treatment was cutin and acid insoluble ash (silica).The residue was ashed and loss in weight was determined as cutin.
Statistical Analysis: The data were subjected to statistical analysis by using analysis of variance technique.Duncari's new multiple range test was used to compare treatment means (Steel and Torrie , 1984).

.. ~RESUL TS AND DISCUSSION
A verage dry matter (DM) contents and various cell wall constituents such as NDF.ADF.hemicellulose.cellulose.lignin.cutin.and silica of different fractions of maize plant at various growth stages have been presented in Table I.A verage dry matter contents and structural components of different cultivars of maize plant are given in Table 2.

Dry Matter:
A significant increase in DM contents of maize fodder and its morphological fractions was observed with advancing stage of maturity.The highest OM contents were found in leaf fraction (l3.60± 0.23 to 3699±0.66%)followed by whole plant (l2.26±0.18 to 33.80±0.63%).whereas the lowest DM contents (9.87±0.09 to 26.93±1.37%)were observed in stem fraction.This was probably due to increased photo-synthetic activity in leaves than in stem leading to higher DM production.
Azim et al. (1989) reported that dry matter contents of whole maize plant.leaf and portions of stem increased significantly with the stage of maturity.They further reported that the maximum dry matter content was found in top portion of stem followed by leaves.However, their values were comparable with values obtained in the present study.The variations due to cultivars were found to be non -significant in whole plant and its fractions.

NDF:
The Gupta and Sagar (1987) also reported an increase in NDF contents of some non -legume fodders, harvested at pre-flowering, flowering and post-flowering stages.Azim et al. (1989) reported that maximum values for NDF were found in the bottom portion of the stem followed by those of whole maize plant.The results reported by these workers are quite comparable with those of the present study.
The changes due to cultivars were also significant in whole maize plant.however.the effect of cultivars was nonsignificant in case of leaf and stem fractions.U. M -81 cuItivar had significantly higher NDF contents than other cultivars.The differences in NDF between Akbar and I .Z -3 I were non -significanr.Significantly lower NDF content was recorded in Neelum cultivar.Hunt et al.
(1993) also reported some varietal differences in maize hybrid.They observed that whole plant samples of maize hybrid pioneer 3377 had a lower (P < 0.01) NDF than 3389 hybrid.
ADF: The values for ADF also showed similar trend as by NDF.A significant increase in ADF content was observed in whole plant.leaf and stem fractions 'with advancing stages of maturity.ADF concentration was higher (24.79±0.15 to 43.75 ±0.45 %) in stem than that of whole plant (22.71 ±0.25 to 38.52±0.36%).
whereas the leaf fraction of the plant had lower (20.74 ±O.17 to 36.20±0.22%)ADF contents.Azim et at.(1989) reported that the values for ADF also showed similar trend as NDF and were maximum in bottom portion of stem followed by whole maize plant.Variations due to cultivars were non _ significant in whole plant and its morphological fractions.
Hemicellulose: A significant increase in hemicellulose
Cellulose: A significant increase in cellulose contents was ,- Tahk 2, Awrage chemical composition of various cultivars of maize fodder and its mOlphological fractions Cultivars whereas the values for whole plant and stem are slightly higher than those of this study.The effect of cultivars on cellulose contents was found to he non-significant in whole plant as well as its leaf and stem fractions.
with advancing age in whole maize plant and its leaf and stem fractions.Lignin contents of stem fraction were higher (2.41 ±0,07 to 6,98±O, 17%) than that of whole plant (l,95±O.19 to 5.27±O,23%) and were minimum (1,47 ±(Ul5 10 4.66±O.11%) in leaf fraction of the maize plant.Gupta and Sugar (1987)  Cutin contents of whole maize plant and its morphological fractions such as leaf and stem continued to increase signiticantly with advancing stage of growth.Cutin contents in leaf fraction of the plant ranged from (042±O.OI to 1.50±O.02%1.being higher than those of whole maize plant (O.37±O.02 to I 44±0.02%) and stem fraction (O.29±O.OI to I 35±(H)1 %).Cultivar effects on cutin content were found to be SIgnificant only in case of whole maize plant.Akbar and U .M-81 cultivars had significantl~higher cutin contents than those of Neclum and 17-1 I Silica: Silica contents of whole maize plant and its leaf and stern tractions were significantly affected by .ulv.mccmcut in stage of growth.Higher silica concentration (I.S5±:O.03 to 3.13 ± .O.03'Yt) was observed in leaf fraction followed by whole maize plant (149±O.073.0S±O.04';{).whereas these values were minimum in case of stem fraction of the planu 1.54±O.06 to 2.76ttU)2'1t).
This may be due to the reason that whatever silica is absorbed from the soil.gets deposited in leaves after being transported to that site.Rakkiyappan and Krisunaruoorthy (19!Q) also reported a higher silica content in leaf than whole plant and stem.Variations in silica contents due to cultivars were found to be sigriilic.uuonly in case of stem fraction of the maize plant.Stem fractions of Akbar and U. M -81 cultivars had signilicantly higher silica contents than those of Ncelum and 1.7-31.

Table 1 .
Average chemical composition of whole maize plant and its morphological fractions at different stages of growth Growth stages (age in weeks)