Crop Science 42:248-254 (2002)
© 2002 Crop Science Society of America
FORAGE & GRAZING LANDS
Effect of Dairy Compost Application and Plant Maturity on Forage Kenaf Cultivar Fiber Concentration and In Sacco Disappearance
James P. Muir*
Texas Agricultural Experiment Station, 1229 North U.S. Hwy. 281, Stephenville, TX 76401-9698
* Corresponding author (j-muir{at}tamu.edu)
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ABSTRACT
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The forage potential of kenaf (Hibiscus cannabinus L.) grown for silage has not been fully realized, in part, because of lack of understanding of its quality dynamics. This study was conducted for 2 yr to compare fiber components and in sacco dry matter (DM) disappearance (ISD) differences among cultivars, dairy manure compost application rates, and plant maturity. The application of compost increased (P = 0.05) neutral detergent fiber (NDF) values only. Fiber components were affected by cultivar x plant maturity x year interactions [P < 0.05 for NDF, acid detergent fiber (ADF) and acid detergent lignin (ADL)] with cultivar EV41, late-season rainfall, and low maturity combining for the lowest values. Cultivar India, however, had as high or higher ISD values compared with the other two cultivars at any given plant maturity both years (cultivar x plant maturity x year ISD interaction, P < 0.05). Cultivar ISD residue fiber concentrations differed (P < 0.05) independently of year or plant maturity; ISD residue ADL and P concentrations also changed (P < 0.05) with plant maturity independently of year and cultivar. Changes in ISD residue NDF and ADF depended on both plant maturity and yearly rainfall patterns (NDF and ADF plant maturity x year interaction, P < 0.05). The proportion of N and P that disappeared in sacco was over 90% for all cultivars, maturities, and years. The proportions of NDF, ADF and ADL that disappeared in sacco, however, decreased with plant maturity and were generally higher for India. In this study, kenaf showed promise as a forage silage in semiarid regions. Differences in fiber concentrations and ISD among cultivars and plant maturity can be manipulated to increase kenaf's feed value to herbivores.
Abbreviations: ADF, acid detergent fiber • ADL, acid detergent lignin • DAP, days after planting • DM, dry matter • ISD, in sacco disappearance • NDF, neutral detergent fiber
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INTRODUCTION
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DESPITE KENAF'S fiber crop origins (Taylor and Kugler, 1992), its potential as a ruminant animal feed has been recognized (Swingle et al., 1978; Wildeus et al., 1995), especially as a silage (Wing, 1967). As an alternative forage crop, it tolerates drought and integrates well with dryland winter-wheat stocker cattle production systems (Dicks et al., 1992). Kenaf appears to have the potential to maintain high forage quality under conditions of limited moisture (Nielsen, 1998). Low palatability to cattle, however, has often been cited as limiting its future as a forage, although favorable consumption rates relative to alfalfa (Medicago sativa L.) belie this impression (Hancock et al., 1993) and may reflect initial rather than long-term palatability problems. Its utility as a feed for browsers such as goats is particularly promising (Wildeus et al., 1995).
Webber (1993) has shown that kenaf leaf percentage of yield decreases with age. In another study, leaf digestibility, notably immature growth, was high (Swingle et al., 1978). Quality of stems, by contrast, can be low and ruminants may refuse to consume this portion of green-chop (Phillips et al., 1990). Overall plant digestibility, however, compares favorably with traditional forages in the southeastern USA when harvested at 30 to 45 d (Hollowell, 1997; Vinson et al., 1979). The ideal maturity for harvest at which production and nutritive value are balanced needs to be determined.
A better understanding of kenaf quality as it relates to cultivar growing conditions, and maturity may shed light on why ruminants do well on this crop. Tissue component disintegration in the rumen may partially explain what this forage can contribute to animal nutrition. Agronomic practices such as soil amendments may also change fiber concentrations. This study was conducted to determine differences in in sacco DM disappearance and fiber concentrations in three kenaf cultivars as affected by cultivation with dairy manure compost and maturity of the crop. A second objective was to determine ISD of kenaf fiber components and minerals.
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MATERIALS AND METHODS
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In April of 1998 and 1999, ‘Everglades 41’ (EV41), ‘Guatemala 4’ (G4) and India kenaf were seeded in the same 9- by 12-m plots each year at the Stephenville, Texas Agricultural Research Station. The soil was a Windthorst fine sandy loam (fine, mixed thermic Udic Paleustalf), pH was 7.6 and Texas A&M extract P and K were 13 and 126 mg kg-1, respectively. Seeding rate was 9.6 kg ha-1 in 50-cm row spacing at 1.5–2.5-cm seed depth. Metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-l-methylethyl)acetamide] was applied at 1.12 kg ai/ha before seeding the first year and clethodim [(E,E)(+/-)-2-[1[[3chloro-2-propenyl)oxy]imino]propyl]-5-[2-ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one] was applied at 0.15 kg a.i. ha-1 post-emergence the second year to control weeds. The plots were hand-weeded each year at 30 d after planting (DAP).
The factors studied in this experiment consisted of three kenaf cultivars, three dairy compost rates, and three harvest regimes. Dairy manure compost (5.6 g P DM kg-1, 11.2 g N DM kg-1, 42.0 g organic matter DM kg-1) was incorporated in March of each year to the same 9- by 4-m sub-subplots at 0, 10 (56 kg P ha-1), and 20 (112 kg P ha-1) Mg DM ha-1. Nitrogen (NH4NO3) was added to all plots to adjust every plot up to a 150 kg N ha-1 rate. The inner 2 by 2 m of all sub-subplots were harvested at a 12-cm stubble height at either 60, 90, and 120 DAP from the same sub-subplots each year.
This experiment was not irrigated and rainfall was not uniform over years or months within years. Total rainfall for the 1998 growing season, including about 1 mo prior to seeding (March through August), was 353.1 mm compared with a total 253.7 mm (38% less) for the 1999 growing season. Soil moisture was very low at seeding in 1998, resulting in variable initial germination. Precipitation was zero in the last 45 d of the 1999 trial, essentially stopping growth for the last 30 d of the 120 DAP harvest treatment (Muir, 2001).
Sub-subplots were harvested with a sickle bar harvester; subsamples were dried at 55°C for 48 h and ground through a 2-mm screen in a shear mill. Variables measured for each sub-subplot included NDF, ADF, and ADL concentrations in the plant tissue (Van Soest and Robertson, 1980). To determine P and N in the in sacco residue, samples were digested using a modification of the aluminum block digestion procedure of Gallaher et al. (1975). Pre-ISD concentrations of N and P were derived by the same methodology and were reported in Muir (2001). Sample weight was 1.0 g, digested in 5 g of 33:1:1 K2SO4:CuSO4:TiO2 and digestion was conducted for 2 h at 400°C in 17 mL of H2SO4. Phosphorus and N in the digestate were determined by semiautomated colorimetry (Hambleton, 1977) with a Technicon Autoanalyzer II (Technicon Industrial Systems, Tarrytown, NY).
In sacco disappearance after 48 h was measured utilizing 2.5-g samples in 8- by 8-cm polyester cloth bags held in 381- by 483-mm polyester 10-mm mesh bags, a procedure adapted from Lowrey (1970). Triplicate samples were weighed and placed in rumen-fistulated steers fed a 100% sorghum-sudan [Sorghum bicolor (L.) Moench] diet containing 135 g CP kg-1 DM. Following disappearance, bags were washed and dried for 48 h at 55C, and the remaining material was weighed to measure ISD percentage. Residue was then analyzed for NDF, ADF, ADL, N and, in 1999, P concentrations following previously discussed procedures. The percentage of each of these components that disappeared during the 48 h in the rumen was estimated by the following formula: [1 - (component fraction of ISD residue x ISD residue fraction)/component fraction of pre-ISD plant material] x 100 = % component disappeared in sacco.
The experimental design used was a randomized complete block with a split-strip plot (harvest regimes in strips; Gomez and Gomez, 1984) arrangement of treatments in four blocks. Whole plant fiber components, ISD and ISD residue fiber components, N, and P concentrations were submitted to analysis of variance. In sacco disappearance of fiber components, N, and P were not submitted to analysis of variance since these were derived data. Least significant differences (LSD0.05) were determined for mean separation for interactions or, if interactions among factors were not significant, for main effects. Cultivar, plant maturity, and year were treated as independent variables in the model.
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RESULTS AND DISCUSSION
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Fiber and Acid Detergent Lignin Concentrations
The application of compost raised NDF values from 386 g kg-1 DM in the control plots to 402 g kg-1 DM and 405 g kg-1 DM for the 10 and 20 Mg compost yr-1, respectively, when averaged over years, plant maturity and kenaf cultivars (P = 0.05; LSD0.05 = 25 g kg-1). Compost application did not affect (P > 0.05) ADF or ADL concentrations.
Kenaf cultivars, plant maturity, and year interacted (P < 0.05) to affect NDF, ADF, and ADL concentrations. EV41 had the lowest NDF and ADF values at 60 DAP both years and at 90 and 120 DAP in 1999 (Fig. 1, 2, 3, and 4)
. India and G4 NDF and ADF values were undifferentiated both years at all plant maturities except at 120 DAP in 1998 when India had lower NDF values as a result of greater EV41 plant growth response to late season-rainfall (Muir, 2001). Both NDF and ADF values increased with plant maturity but were dependent on rainfall-driven yield increases. Differences for both fiber components were more marked between 90 and 120 DAP (except for India) in 1998 and between 60 and 90 DAP in 1999.
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Fig. 1. Neutral detergent fiber (NDF) of three kenaf cultivars in 1998 at 60, 90, and 120 d after planting (DAP) averaged for plots with varying amounts of dairy compost (cultivar x plant maturity x year interaction, P < 0.05; LSD0.05 = 39).
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Fig. 2. Neutral detergent fiber (NDF) of three kenaf cultivars in 1999 at 60, 90, and 120 d after planting (DAP) averaged for plots with varying amounts of dairy compost (cultivar x plant maturity x year interaction, P < 0.05; LSD0.05 = 39).
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Fig. 3. Acid detergent fiber (ADF) of three kenaf cultivars in 1998 at 60, 90, and 120 d after planting (DAP) averaged for plots with varying amounts of dairy compost (cultivar x plant maturity x year interaction, P < 0.05; LSD0.05 = 31).
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Fig. 4. Acid detergent fiber (ADF) of three kenaf cultivars in 1999 at 60, 90, and 120 d after planting (DAP) averaged for plots with varying amounts of dairy compost (cultivar x plant maturity x year interaction, P < 0.05; LSD0.05 = 31).
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Acid detergent lignin patterns were very similar to those seen in NDF and ADF concentrations (Fig. 5 and 6)
. Acid detergent lignin concentrations in 1998 were undifferentiated among cultivars and 60 or 90 DAP but, except for India, rose with increased yield as a response to rains after the 90 DAP harvest (Muir, 2001). India ADL concentrations were higher in 1999 than in 1998 at all plant maturities despite lower yields in 1999. This indicates that India, in contrast to other cultivars, accumulates greater ADL when adequate rainfall results in earlier season growth.
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Fig. 5. Acid detergent lignin (ADL) of three kenaf cultivars in 1998 at 60, 90, and 120 d after planting (DAP) averaged for plots with varying amounts of dairy compost (cultivar x plant maturity x year interaction, P < 0.05; LSD0.05 = 3.6).
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Fig. 6. Acid detergent lignin (ADL) of three kenaf cultivars in 1999 at 60, 90, and 120 d after planting (DAP) averaged for plots with varying amounts of dairy compost (cultivar x plant maturity x year interaction, P < 0.05; LSD0.05 = 3.6).
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In Sacco Disappearance
Compost application did not change (P > 0.05) ISD in the rumen. In sacco disappearance differed, however, among cultivars at different plant maturities for each year (cultivar x plant maturity x year interaction P = 0.05; Fig. 7 and 8)
. Except for EV41 in 1998, ISD decreased for all cultivars both years from 60 to 90 DAP. That trend continued from 90 to 120 DAP in 1998, with good soil moisture and subsequent plant growth (Muir, 2001), except for G4. In contrast, ISD did not decrease from 90 to 120 DAP for any cultivar in 1999 when no plant growth occurred. India was consistently higher or as high in ISD compared with the other two cultivars at any given plant maturity both years.
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Fig. 7. In sacco disappearance of three kenaf cultivars in 1998 at 60, 90, and 120 d after planting (DAP) averaged for plots with varying amounts of dairy compost (cultivar x plant maturity x year interaction, P < 0.05; LSD0.05 = 36.4).
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Fig. 8. In sacco disappearance of three kenaf cultivars in 1998 following application of three levels of compost averaged for plots harvested at different maturities (cultivar x plant maturity x year interaction, P = 0.05; LSD0.05 = 36.4).
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In Sacco Disappearance Residue
In sacco disappearance residue NDF, ADF, and ADL concentrations differed among cultivars (P < 0.05; Table 1). EV41 NDF was highest while both EV41 and G4 ADF values were higher than that of India. EV41, however, had the lowest ADL while there were no differences (P > 0.05; Table 1) in P concentration.
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Table 1. In sacco disappearance residue neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), P and N concentrations in three kenaf varieties averaged over three plant maturities and 2 yr.
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In sacco disappearance residue NDF and ADF concentrations were also affected differently each year by plant maturity (plant maturity x year interaction, P < 0.05; Table 2). Concentrations of ADF concentrations were generally higher in 1999 compared with 1998 as a result of greater plant development during the 60-DAP period the second year (Muir, 2001). In contrast to ADF values, 1999 and 1998 NDF concentrations increased from 60 to 90 DAP, but not from 90 to 120 DAP.
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Table 2. In sacco disappearance residue neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), P and N concentrations for kenaf harvested at 60, 90 and 120 d after planting (DAP) and averaged over three kenaf varieties and three compost application rates.
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In sacco disappearance residue ADL concentration decreased with plant maturity independent of year (P = 0.001; Table 2). Phosphorus concentration in ISD residue also tended to decrease (P = 0.06; Table 2) in 1999 from the 60 to 90 DAP maturity but was undifferentiated between 90 and 120 DAP.
In sacco disappearance residue N concentrations were affected by an interaction among plant maturity x cultivar x year (P = 0.03; Table 3). Values decreased for India in 1999 and G4 in 1998 from 60 to 90 DAP, but changed little for any cultivar from 90 to 120 DAP. India ISD residue N was higher at 60 DAP in 1999 than at any other time, indicating a high rate of rumen degradation resistance of N in that cultivar when early-season growth is high.
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Table 3. In sacco disappearance residue N concentrations in three kenaf varieties harvested at three plant maturities (variety x plant maturity x year, P = 0.02; LSD0.05 = 12.4).
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For both years, the percent of total N and P that disappeared in sacco was higher for India but above 90% for all cultivars (Fig. 9 and 10)
. Absolute values in vivo cannot be implied from the ISD procedure, however. For example, Xiccato et al. (1998) found that in vivo crude protein digestibility coefficients of an unidentified kenaf cultivar silage were only 0.35. The corresponding lower ADL in India that disappeared in sacco relative to the other cultivars would indicate that a lower portion of India N was held in the lignin, possibly accounting for its higher ISD. According to most studies (Weiss, 1994), these figures should confer on India a corresponding in vivo digestibility ranking superior to both EV41 and G4.
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Fig. 9. In sacco disappearance of neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), and N in 1998 in three kenaf cultivars.
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Fig. 10. In sacco disappearance of neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), N, and P in 1999 in three kenaf cultivars.
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Precipitation patterns, by influencing plant development (Muir, 2001), influenced kenaf fiber concentrations and ISD in conjunction with plant age. Adequate rainfall for kenaf growth early in the first growing season and late in the second growing season resulted in increases in NDF, ADF, and lignin concentrations after those rains. Conversely, during periods in which lack of rainfall precluded plant development, fiber components did not change with plant maturity. Disappearance of NDF and ADF in sacco, but not ADL, followed this same pattern (Fig. 11 and 12)
. These data indicate that increased plant maturity affects forage fiber concentration and ISD but only when plant growth occurs. Kenaf appeared to shut down plant development when moisture stressed and, after 90 DAP in 1999, suffered leaf loss (Muir, 2001). Despite this phenomenon, however, ISD of N and P did not decrease as much as NDF, ADF, and ADL.
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Fig. 11. In sacco disappearance of neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), and N in 1998 in kenaf harvested at 60, 90, and 120 d after planting (DAP).
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Fig. 12. In sacco disappearance of neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), N, and P in 1999 in kenaf harvested at 60, 90, and 120 d after planting (DAP).
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The proportion of N and P that disappeared in sacco decreased only slightly with plant maturity (Fig. 11 and 12). Even at 120 DAP the values were still close to 90%. The proportion of all fiber components that disappeared at 60 DAP in 1999 (a year with high forage production between 60 and 90 DAP; Muir, 2001) was considerably higher than what disappeared at 90 DAP, indicating that ADL accumulation during this period may be at least partially responsible for a decrease in ISD.
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CONCLUSIONS
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All variables studied in this experiment had some effect on kenaf forage fiber concentrations and ISD. The application of compost increased kenaf forage NDF concentrations but not ADF or ADL, likely an artifact of increased yield (Muir, 2001). Among the three cultivars studied, EV41 showed the greatest promise for producing high-quality forage. Its NDF, ADF, and ADL concentrations were as low or lower than the other two cultivars at all plant maturities. In contrast, India's ISD was higher than the other two cultivars at 120 DAP in 1998 and at any plant maturity in 1999. Subsequent ISD residue analyses indicated that all the measured components (NDF, ADF, ADL, N, and P) tended to disappear at a higher rate in India compared with the other cultivars.
In this study, kenaf had sufficiently low fiber concentrations and high ISD to be of some promise as an alternative, dry-land forage for regions with a climate similar to north-central Texas. India, in particular, compared favorably with other drought-tolerant silage crops such as sorghum. In a north-central Texas study, Prostko et al. (1998) measured sorghum NDF averages of 606 g kg-1 DM and ADF averages of 330 g kg-1 DM, 70 and 20% higher than the respective averages for India in this trial. India's ISD concentrations were especially high and declined only slowly from 60 (868 and 859 g kg-1 DM in 1998 and 1999, respectively) to 120 (788 and 794 g kg-1 DM in 1998 and 1999, respectively) DAP. If feeding trials confirm this data and show that palatability problems can be overcome, use of this forage in semiarid dry-land cropping is promising.
Received for publication October 6, 2000.
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REFERENCES
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TOP
ABSTRACT
INTRODUCTION
