Published in Agron J 98:922-929 (2006)
DOI: 10.2134/agronj2005.0299
© 2006 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
Production Papers
Dry Matter Accumulation and Silage Moisture Changes after Silking in Leafy and Dual-Purpose Corn Hybrids
B. L. Ma*,
K. D. Subedi,
D. W. Stewart and
L. M. Dwyer
Agriculture and Agri-Food Canada, Eastern Cereal and Oilseed Research Centre (ECORC), Central Experimental Farm, 960 Carling Avenue, Ottawa, ON, Canada K1A 0C6
* Corresponding author (mab{at}agr.gc.ca)
Received for publication October 27, 2005.
 |
ABSTRACT
|
|---|
The increasing use of new silage-specific corn (Zea mays L.) hybrids, including Leafy types, has created a need for more information on the decision of hybrid choice and time of harvest. A field experiment including dual-purpose and Leafy silage-specific hybrids was conducted for 4 yr (1999–2002) at Ottawa, ON, Canada. Specific objectives were to determine (i) differences in whole plant moisture and dry matter (DM) accumulation after silking, and (ii) the optimum harvest windows of the contrasting corn types. Samples of whole plant moisture and DM accumulation were taken and analyzed at 3- to 7-d intervals from approximately 3 wk after silking to physiological maturity. Our results showed that the rate of decline in silage moisture content varied among the years and hybrid types. On average, 85% of total DM accumulation was achieved when the whole plant moisture was about 65% for all hybrids. Compared to dual-purpose hybrids, the whole plant moisture of Leafy silage-specific hybrids declined more slowly, especially for hybrid ‘Mycogen TMF94’. We concluded that 65% whole plant moisture normally corresponded to the 50% kernel milk line (ML), and occurred between 50 and 60 d after silking under the northeast climate conditions. Silage-specific hybrids had larger windows for harvest than dual-purpose hybrids. However, ML progression was irregular for Leafy hybrids and changed more rapidly for dual-purpose hybrids. Under extreme weather conditions, kernel ML does not correspond to silage moisture content in the same way as under normal conditions, therefore, silage harvest should be based on actual moisture content.
Abbreviations: ADF, acid detergent fiber • CHU, crop heat unit • DM, dry matter • ML, milk line • NDF, neutral detergent fiber
|
INTRODUCTION
|
|---|
WHOLE plant corn silage continues to be a major forage in the North American dairy industry (Johnson et al., 1999). In Canada, silage hybrids make up approximately 20% of corn acreage with concentrated production in Ontario and Quebec, supporting the dairy industry (Dwyer et al., 1998). As eastern Ontario and western Quebec account for approximately half the silage corn production in Canada, improvement in silage corn hybrids adapted to this region would enhance economic returns (Dwyer et al., 1998). Until recently, it was generally accepted that the characteristics of a good silage hybrid were those of a good grain hybrid, based on the assumption that silage nutritive value was dominated by the grain component (Andrews et al., 2000; Bagg, 2001). Introduction of single purpose silage hybrids in the recent decade has raised questions about this assumption and about selection criteria and management practices that will optimize silage production. Selection criteria such as hard, high density kernels, strong stalks, and rapid kernel dry-down, which favor grain production, may be undesirable for silage harvest, fermentation, and digestibility. Silage varieties are expected to mature slowly with gradual decline in whole plant moisture (slower dry-down rate), and have softer kernels and low neutral detergent fiber (NDF) with high NDF digestibility (Dwyer et al., 1998). These distinct characteristics of the two types of corn hybrids may be reflected in the changes in DM accumulation and kernel ML progression during the grain-filling stage. Consequently, the traditional benchmark of 50% ML stage for silage harvest may also vary between corn types.
Many of the single purpose silage corn hybrids increasingly available to date are Leafy (Lfy) types. The Leafy genotypes are those with an extra number of leaves above the ear (Shaver, 1983) compared to conventional hybrids of the same maturity. Earlier studies focused on determining the degree of leafiness (number of leaves above the ear) best suited for the 85 to 95 d region, which is with 2700 to 2900 crop heat unit (CHU) (Brown and Bootsma, 1993). Additional concerns were optimum ear position and the significance of stay-green, or a longer duration of green leaf area (Dwyer et al., 1995), with different plant architecture and population densities (Begna et al., 1997a, 1997b; Costa et al., 2001). There have been ongoing assessments of yield (grain and whole plant) responses to population density (Begna et al., 1997a, 1997b; Dwyer et al., 1998; Subedi and Ma, 2005b) and fertilizer N rates (Costa et al., 2001; Subedi and Ma, 2005a, 2005c). More detailed chemical analysis has compared carbohydrate (soluble sugar and starch) concentrations at different levels in the canopy (Dwyer et al., 1995; Andrews et al., 2000). As the most noticeable difference between Leafy and conventional genotypes is above-ear leaf number, a common focus of these studies has been leaf area distribution, both vertically in the canopy and horizontally across the row, and its effect on light interception and photosynthetic production through the day (Stewart et al., 2003). Compared to the conventional dual-purpose hybrids, Leafy silage-specific varieties appeared to have lower ear placement, greater total leaf area and areas above the ear node (Subedi and Ma, 2005b), which contributed to a large amount of the silage dry matter with greater total digestibility (Dwyer et al., 1998).
The Leafy hybrids have been gaining popularity as a silage-specific corn in recent years (Roth, 2003). Constraints faced by silage producers are determining the optimum time to harvest and the length of the harvest window. Determining the proper timing of harvest for corn silage is critical because it influences the overall quality of the product that is preserved and stored in silo (Sulc, 2004; Herrmann et al., 2005). Silage moisture content at harvest is a major factor in determining the nutritive value of silage since this value decreases as crop maturity advances (Johnson et al., 1999) and silage moisture drops below 62% (Bagg, 2001). Harvesting at a whole plant moisture above 70% will not only reduce silage yield, but also lead to seepage and very undesirable clostridia (Clostrium spp.) formation (Bagg, 2001). On the other hand, harvesting at a moisture content that is too low (<62%) will result in poor silage packing, inadequate air exclusion, poor fermentation and heating. This will lead to higher DM losses, greater spoilage, and poor bunk life. Delaying harvesting can reduce both the fiber and starch digestibility as the stover gets more lignified, and the overmature kernels become harder and less digestible if left unbroken after ensiling (Roth and Heinrichs, 2001). The digestibility of the fiber in the stover decreases as the crop matures and the acid detergent fiber (ADF) and NDF increase. The time for silage harvest is usually determined by the kernel ML dropping from the tip toward the cob. The challenge is to achieve a maximum total silage DM with whole plant moisture at about 65%.
The optimum time for silage harvest has been demonstrated to be at about 50% ML stage of the kernels in dual-purpose corn hybrids (Crookston and Kurle, 1988; Cox, 1994). The relationship between kernel DM accumulation and ML progression in relation to kernel moisture changes has been studied in grain corn hybrids (Ma and Dwyer, 2001). It was suggested that corn silage is better harvested at a DM content of 310 instead of 295 g kg–1 in the U.S. Northeast (Cox and Cherney, 2005). In Ohio, it was reported that variation in plant DM content within a stage was sufficient to raise concern over the reliability of the kernel ML method for determining time of silage harvest (Sulc et al., 1996). An examination of silage DM accumulation vs. whole plant moisture content would identify hybrids which can be harvested at a wider harvest window.
The objectives of this study were, first, to examine the decline in silage moisture content of hybrids from above 80% through the ideal harvest window to <60%, second, to establish quantitative relationships between silage dry matter, silage moisture, and number of days after silking (DAS) in Leafy, dual-purpose, and non-Leafy silage-specific corn hybrids, and, third, to determine the optimum harvest window for these contrasting corn types.
|
MATERIALS AND METHODS
|
|---|
Experimental Design and Crop Management
A field experiment was conducted at the Greenbelt Research Farm, Ottawa, ON, Canada (45°17' N, 75°45' W) for four consecutive years (1999–2002) on a Dalhousie clay loam, classified as the Gleyed Melanic Brunisol in the Canadian system and Eutrocryept Cryept Inceptisol in the USDA system. In 1999, 2001, and 2002, the experiment was planted in a field (different sections each year), previously cropped to corn, while the section for the 2000 experiment had spring wheat (Triticum aestivum L.) as the preceding crop. The experiment was a 2 x 4 factorial, arranged in a split plot design with four replications in each year. Two densities (66 000, 81 000 plants ha–1) were assigned to the main plots and four hybrids were randomly assigned to the subplots. The hybrids were two Leafy silage-specific types (‘Maizex Leafy 4’ and Mycogen TMF 94) and two non-Leafy dual-purpose hybrids (‘Max 86’, ‘Pioneer 37M81’). In 2001 and 2002, Max 86 was substituted with a newly registered non-Leafy hybrid, ‘N.K. Enerfeast I’, which was developed mainly for silage use. Both TMF94 and Maizex Leafy 4 require 2700 CHU (Brown and Bootsma, 1993) to reach silage harvest (65% silage moisture). The dual-purpose hybrids require 2850 to 2950 CHU to reach physiological maturity and are considered late hybrids for grain production for this region. The subplot dimensions were 13.7 by 6.1 m consisting of eight rows spaced 76.2 cm. The experiment was planted between 14 and 22 May in each year.
Before corn planting, the field was broadcast with P and K fertilizers according to soil test recommendations. Specifically, 50 kg P ha–1 as 11–52–0 in 1999, and 20 kg P ha–1 as 11–52–0 in 2000 and 2001, and 100 kg P ha–1 as 0–34–15 in 2002 were applied. In all years, ammonium nitrate (NH4NO3) fertilizer at 200 kg N ha–1 was applied and incorporated into the soil shortly before planting. Different herbicides were applied at recommended rates for weed control: Primextra II Magnum (s-metolachlor/benoxacor/atrazine [2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine])) in 1999, 2001, and 2002; and tank mix of Primextra Light (metolachlor/atrazine) and Fieldstar (flumetsulam/clopyralid) in 2000. Additional mechanical weeding was performed to control escaped weeds in all years.
Daily maximum (Tmax) and minimum (Tmin) air temperatures, and rainfall were collected from an automated weather station near the experiment site. Crop heat units required to reach maturity are calculated according to Brown and Bootsma (1993):
 | [1] |
where Ymax representing daytime temperature relationships
 | [2] |
and Ymin representing night time temperature relationships
 | [3] |
Silage Sampling
Phenological data were collected throughout the growing season based on observations taken on a minimum of three replications three times per week in each year. Silage DM and moisture content were monitored from approximately 3 wk after silking to R6 or 0 ML (physiological maturity) from each subplot on an area basis. The sample areas were predetermined from rows 2 to 7 to make sure uniformity within the area and proper borders between samples. At each sampling, 13 to 16 plants from the designated area (1.3 by 1.52 m; two rows) were harvested and recorded for total fresh weight. Ears were dehusked for fresh weight measurement. After recording the fresh weight, ears were broken lengthwise into two halves, and percentage ML and black layer if appropriate, of each ear were recorded, with progression of ML rated from 100 to 0% (Afuakwa and Crookston, 1984). A numerical value of ML for each subplot was calculated based on the average stages of the ears. After chopping (4–5 cm pieces) of the whole plants, a subsample of silage was taken and oven-dried at 80°C until a constant weight to determine the DM. The harvest windows for each hybrid in each growing season were estimated to be the period when the whole-plant moisture dropped from 70 to 62% with total silage dry matter reaching 85% or greater.
Data Analysis and Model Fit
Within a year, data of silage dry matter and moisture from each sampling date were analyzed for normality using the UNIVARIATE procedure of SAS (SAS Institute, 1997) before a pooled analysis of variance where sampling dates were treated as a split factor. Similarly, separate analysis was done for each year followed by a pooled analysis of variance across years if all the error variances were homogenous. In each case, year, replications, and sampling dates were considered random effects, and hybrid and population density were fixed factors. When hybrid-by-population density interaction was not significant (P > 0.05), hybrid means were separated with an F-protected least significant difference (LSD0.05).
The dry matter accumulation (Y) as a function of the number of days after silking (X) was fitted to a quadratic-plateau model:
 | [4] |
where Ymax is the plateau of silage dry matter (kg ha–1), X0 is the initial number of days after silking when Ymax is reached. Sometimes a plateau was not evident. In these cases a simple quadratic equation was used. Similarly, the decline in whole plant moisture (M) was fitted to an exponential decay model:
 | [5] |
where M0 represents the initial value of whole plant moisture at the first sampling. Model fitting to individual hybrid was performed each year. For visual clarity, only a common fitting across all hybrids is presented in the figure. However, results were presented and discussed when differences among hybrids were significant.
|
RESULTS AND DISCUSSION
|
|---|
Weather Patterns
Rainfall and accumulated CHU both varied considerably in the 4 yr (Fig. 1
). In 1999, total rainfall from April to October was similar to the long-term average, but distributed unevenly. Shortage of rainfall in May and early June did not prevent vegetative growth while above average rainfall in late July with sufficient heat accumulation benefited flowering, and may have partially compensated for the drought effect during the early grain-filling period (August). Accumulated CHU in 1999 was >3400, the highest across the 4 yr and the long-term average (Fig. 1). As a result, the great silage DM, especially for TMF94 was produced in that year.
View larger version (46K):
[in this window]
[in a new window]
|
Fig. 1. Monthly total precipitation and accumulated crop heat units (CHU) during the growing seasons of 1999, 2000, 2001, 2002, and 43-yr average (1960–2002).
|
|
The spring of 2000 was unusually wet. April and May had a rainfall of approximately 50% above the average of the last 43 yr, while June had slightly more than double the average precipitation. An earlier than normal frost occurred on 29 Sept. 2000 (–2.7°C). Excess rainfall coupled with periods of low temperatures during the growing season resulted in an immature crop of some late maturing hybrids (e.g., Maizex Leafy 4) at the initial fall killing frost (Fig. 2
). In contrast, the summer of 2001 was very dry with prolonged periods of drought in June, July, and August with only 70% of total rainfall, and air temperature was 2 to 3°C above the normal of the last 43 yr (Fig. 1). The crop suffered from severe drought and had lower total silage DM production (Table 1). Year 2002 had above average rainfall during the early part of the growing season (May and June), but the crop experienced periods of drought stress from late July to early August. In 2001 and 2002, the total CHU values were >2850 during the growing season (May–September). Unlike the weather in 1999, the cool temperatures in May and early June, and warm weather from late June to September plus sufficient rainfall during the early grain-filling period in 2002 favored silage DM accumulation, which explained, at least in part, why silage DM accumulation during the grain filling did not plateau in 2002 (Fig. 3
).
View larger version (28K):
[in this window]
[in a new window]
|
Fig. 2. Time taken to progress from 100% milk line to physiological maturity (0% milk line) in four corn hybrids in 4 yr (1999–2002). The horizontal line in each figure indicates the 50% milk line (i.e., the ideal stage for silage harvest). Hybrids Pioneer 37M81, Maizex Leafy 4, and TMF94 were grown in all years while Max 86 used in 1999 and 2000 was replaced with N.K. Enerfeast I (non-Leafy silage corn) in 2001 and 2002.
|
|
View this table:
[in this window]
[in a new window]
|
Table 1. The size of the ideal harvest window ( 85% of maximum dry matter [DM] with 62–70% of whole plant moisture) and the silage DM yield averaged for two densities and sampling dates through the ideal harvest window of each hybrid in 4 yr (1999–2002).
|
|
View larger version (22K):
[in this window]
[in a new window]
|
Fig. 3. Silage dry matter (DM) (Y) accumulation as a function of number of days after silking (DAS; X). Each data point is the average of two densities and four replications. The overall curve was fitted to a quadratic-plus-plateau model: Y = a + bX – cX2 when X < X0, and Y = Ymax when X X0. Hybrids Pioneer 37M81, Maizex Leafy 4, and TMF94 were in common in all years while Max 86 used in 1999 and 2000 was replaced with N.K. Enerfeast I (non-Leafy silage corn) in 2001 and 2002.
|
|
Phenology
Across the 4 yr, for all five hybrids, plant density had a negligible effect on phenological stage and ML development. Time taken to 50% silking ranged from 73 to 80 d after planting among the hybrids in different years. Pioneer 37M81 was the earliest hybrid to reach silking while Maizex Leafy 4 took the longest time, followed by Mycogen TMF94, in all years (data not shown). Trends of decline in ML from 100% to physiological maturity (0% ML) for different hybrids in 4 yr are presented in Fig. 2. It was evident that the ML developed earlier and the rate of progress toward 0% ML was faster in the dual-purpose hybrids than in the Leafy hybrids. The kernel ML for Maizex Leafy 4 and TMF 94 declined more slowly than the other two hybrids, and time taken to 50% ML (silage harvest) stage was also delayed by 4 to 12 d, especially for Maizex Leafy 4 (Fig. 2). Because of the early killing frost in September, this hybrid did not reach 50% ML in year 2000. In general, all hybrids reached 0% ML after 60 to 80 d after silking, with the exception of Maizex Leafy 4 in 2001. Unlike other years, the time differences among the hybrids reaching 50% ML were small in 2002. Cool temperatures in late May and early June 2002, compared to those in 1999 (Fig. 1), may have caused the delay in early crop development in 2002. As a result, silking date differed by 9 d between the two years whereas there was only 2 d difference in planting. Consequently, grain filling in 2002 was slowed because of cool night temperatures in late September. In general, unlike grain corn (Afuakwa and Crookston, 1984; Ma and Dwyer, 2001), our field observations showed that kernel ML progression from the tip (early dent; 100%) toward the cob (0 ML) in Leafy silage-specific hybrids was irregular, fainter (more difficult to see) and nonlinear (i.e., ML progression from rare change to sudden decline), and especially sensitive to environment conditions. For example, there was very little change in kernel ML for Maizex Leafy 4 from 44 to 56 d after silking in 2000, and from 33 to 54 d after silking in 2001 (Fig. 2).
Silage Dry Matter Accumulation
Hybrids differed significantly for total silage DM over the 4 yr (Table 1). For example, TMF 94 produced the largest silage yield (plateau yield of 24.2 Mg ha–1 compared to 18.5 Mg ha–1 or less for the dual purpose hybrids) in 1999 and slightly greater yield in the other years (Fig. 3). Environmental factors, especially heat and rainfall accumulation and seasonal distribution greatly affected the silage yields. In general, the highest yield was achieved in 1999 and lowest yield in 2001. Stage of crop at harvest (i.e., ML) had also direct effect on total and ear DM accumulation. The ear/silage ratio ranged from 0.43 to 0.62 (on a fresh weight basis), and the Leafy hybrids usually had smaller ear/silage ratios (data not shown). In general, the high population density produced slightly greater total silage DM with slightly higher silage moisture each year (data not shown). However, hybrid-by-population density interaction effect was not significant in any year. While the relationship between the DM and time taken to harvest after silking followed a quadratic-plateau model in 1999 and 2000, under drought-prone conditions such as 2001 and 2002, silage DM increased linearly with the progression in the number of days after silking with R2 > 0.80 (Fig. 3). In 1999, the plateau yield and the slope of the model were significantly larger (b = 0.95; P < 0.01) for TMF94 than those (b = 0.43 or 0.54) for Max 86 or Pioneer 37M81. In 2000, the estimated plateau yield and the slope of the model were slightly greater (plateau yield of 17.9 Mg ha–1 and b = 0.67; P = 0.10) for TMF94 than those (plateau yield 
17 Mg ha–1 and b 0.59) of the rest hybrids. In all cases, silage DM (85%) with the suitable silage moisture (from <70 to >62%) was attained around 60 to 70 d after silking. Our results support the recommendation for timing of silage harvest (Bagg, 2001) and are also in good agreement with findings reported elsewhere (Sulc et al., 1996; Fransen, 2004; Cox and Cherney, 2005; Herrmann et al., 2005).
Changes in Silage Moisture
The silage moisture was >80% at 3 wk after silking, then continuously declined to <55% (Fig. 4
). There were large differences in silage moisture content changes between hybrids in 1999. The moisture content of Max 86 dropped more rapidly (with the decay slope coefficient k = 0.0142) while TMF 94 had consistently greater whole plant moisture (k = 0.0067; P < 0.01) for a longer period with the other two hybrids followed intermediate patterns (Fig. 4). The kernel ML in Maizex Leafy 4 was less obvious (more difficult to see) and its progression with time was irregular (from rare change for a long time to reaching one-half ML suddenly), compared with other hybrids (Table 2), suggesting that kernel ML was not a reliable indicator for silage harvest. In 2000, the ML vs. silage moisture correspondence was poor due to the rapid decline in ML after the early fall frost. In 2001, the drop in whole plant moisture of the dual-purpose hybrid Pioneer 37M81 was clearly faster (k = 0.0077 ± 0.0004) than the Leafy hybrids (k 0.0063 ± 0.0005). At 75% ML, average silage moisture was 68%, but ranged from 66% for Maizex Leafy 4 to 70% for TMF94 (Table 2). In 2002, the difference among hybrids in silage moisture at different sampling dates was not obvious; all hybrids reached 60% moisture by about 60 d after silking (Table 2).
View larger version (21K):
[in this window]
[in a new window]
|
Fig. 4. Silage moisture changes as a function of number days after silking (DAS; X). Each data point is the average of two densities and four replications. The overall curve was fitted to a negative exponential decay model: M = M0 e(–kX). Hybrids Pioneer 37M81, Maizex Leafy 4, and TMF94 were in common in all years while Max 86 used in 1999 and 2000 was replaced with N.K. Enerfeast I (non-Leafy silage corn) in 2001 and 2002.
|
|
View this table:
[in this window]
[in a new window]
|
Table 2. Silage moisture content (Moisture; % fresh weight) and number of days after silking (DAS) at the observed initial critical stages of kernel milk line (ML) of each hybrid in Ottawa, ON, Canada in 4 yr (1999–2002).
|
|
The negative exponential decay model fitted well to the mean silage moisture data with R2 > 0.8 and P < 0.01 in all years (Fig. 4). Based on this relationship and measured silage moisture content (Table 2), the ideal silage moisture content of 62 to 70% was achieved between 50 and 60 d after silking, with the exception of 1999, where these moisture levels were achieved between 40 and 50 d, depending on the hybrids and growing season (Fig. 4). For all hybrids, 50% ML was found to correspond approximately to 65% silage moisture. At 25% ML, average silage moisture was 59% (Table 2).
Window for Silage Harvest
The time-span during which the silage moisture is between 70 and 62% and the silage DM is 85% of its final value is defined as the ideal harvest window (Bagg, 2001). Despite different weather conditions in the 4 yr, Maizex Leafy 4, Max 86, and Pioneer 37M81 had a very similar harvest windows (approximately 8 d), while the harvest window for TMF94 was much wider and varied greatly with the year (Table 1). TMF 94 had the widest harvest window, approximately 14 d in 1999 and 16 d in 2000, twice as long as that of Maizex Leafy 4, Max 86, and Pioneer 37M81 (Table 1). The recently-registered, N.K. Enerfeast I, a non-Leafy hybrid, had also the widest window for harvest in 2001 (Table 1). The ideal silage moisture (around 65%) was reached between 75 and 50% ML stages (Table 2) with 85% of maximum silage DM accumulation within the ideal silage moisture range (Fig. 3). The corresponding ideal harvest windows in 2001 were 8 d for Pioneer 37M81, 9 d for TMF94 and Maizex Leafy 4 and approximately 15 d for NK Enerfeast I. There was a smaller window in 2002 because all hybrids had a narrow range of 50% ML (Fig. 2) due to slow development early in the growing season caused by cool temperature, but fast dry-down from mid- to late September associated with shortage of rainfall (Fig. 1).
Harvesting at the right stage of maturity has a significant effect on the amount and quality of corn silage. The stage of maturity at harvest is a major factor in determining the nutritive value of silage (Johnson et al., 1999). This study clearly showed the differences between different corn types in silage DM production and whole plant moisture dynamics. The Leafy silage-specific hybrids appeared to have a slower moisture decline (smaller decay slopes), which led to a wider harvest window. The slower dry down of Leafy silage-specific hybrids may be an advantage for chopping for silage, because it provides a wider window of opportunity to harvest at the right moisture content (Squire, 2002). It should also be noted that in all cases, % ML was only an approximation of maturity and large variations existed within plots, among replications, hybrids, and seasons. Furthermore, it was often difficult to determine the ML stages for the Leafy hybrids. Similarly, in Ohio, it was reported that kernel ML was a less reliable method for determining silage harvest (Sulc et al., 1996). The variation in kernel ML exists largely because of extreme environmental conditions and differences in specific hybrids related to their ability to lose whole plant moisture at the same rate as grain maturity (Rankin, 2004). Therefore, a decision on silage harvest time should be based on the actual measurement of silage moisture, while kernel ML can give an indication for whole plant moisture test.
There existed a large variation among the hybrids for silking and subsequent ML development, and not all the hybrids had similar moisture content at 50% ML. Moreover, not all the hybrids tested reached 50% ML on the same date. Therefore, the study demanded a large number of samples. The silage DM reported was from various dates for different hybrids in each year. The common observation from this study was that for all hybrids, the maximum DM was attained about 60 to 70 d after silking, during which time, the kernel ML in most hybrids was <50% and whole plant silage moisture content dropped to 65%. The window for these parameters was smaller for the dual-purpose hybrids than the Leafy silage types, especially for TMF94.
Our study did not evaluate feeding quality of the silage from the two types of hybrids. As the Leafy type had more foliage and thus a smaller ear/silage ratio, and because of the softer kernels (Ma et al., unpublished data, 2006), the digestibility of the silage may have been greater. A recent report by Nennich et al. (2003) demonstrated that inclusion of Leafy hybrids (TMF 2404 and TMF 2450) in cow (Bos taurus) diets at 40% of the dietary DM did not have a significant impact on the performance of dairy cattle. Similarly, Ballard et al. (2001) reported that the hybrid Mycogen TMF 94 was high yielding but less digestible and gave lower milk production than a hybrid with the brown mid-rib trait. However, there were no studies to compare Leafy silage-specific hybrids with dual-purpose hybrids and dual-purpose hybrids do not have the brown mid-rib trait. The feeding value of the silage from the Leafy maize requires further investigation.
|
CONCLUDING REMARKS AND SUMMARY
|
|---|
It is evident that the relationship between kernel ML and silage moisture content is affected by growing conditions and hybrid types. The results from this 4-yr study consistently showed that compared to dual-purpose hybrids, the whole plant moisture of Leafy silage-specific hybrids with extra number of leaves and smaller cob/stover ratios, declined more slowly, especially for Mycogen TMF94, thus providing producers with a larger window of opportunity to harvest. In general, kernel ML progression in Leafy silage-specific hybrids was more difficult to observe and changed nonlinearly with time; it did not follow the same pattern with moisture change as grain corn did. Accordingly, 50% ML benchmark used for silage harvest of dual-purpose hybrids may not be suitable for Leafy silage-specific hybrids. Under severe drought conditions, kernel ML did not correspond to silage moisture content in the same way as under normal weather conditions; whole plant moisture at 50% ML, used for silage harvest timing, also varied with hybrid type. This study has established quantitative relationships between silage moisture content and growing stage in Leafy and dual-purpose corn. This information can be useful in determining silage harvest time for different types of hybrids based on the relationship between silage moisture content and stage of crop development after silking.
|
ACKNOWLEDGMENTS
|
|---|
This project was funded in part by the Glenn Seed Ltd. through a Matching Investment Initiative program agreement of Agriculture and Agri-Food Canada. We wish to thank Dr. Judith Fregeau-Reid, who helped us with kernel hardness tests and D. Balchin, L. Evenson, and Karen Conty for excellent technical assistance in the field. Critical review by Dr. L.M. Reid and Dr. M.J. Morrison is greatly appreciated. ECORC contribution 05-522.
|
REFERENCES
|
|---|
- Afuakwa, J.J., and R.K. Crookston. 1984. Using the kernel milk line to visually monitor grain maturity in maize. Crop Sci. 24:687–691.[Abstract/Free Full Text]
- Andrews, C.J., L.M. Dwyer, D.W. Stewart, J.A. Dugas, and P. Bonn. 2000. Distribution of carbohydrate during grain fill in Leafy and normal maize hybrids. Can. J. Plant Sci. 80:87–95.
- Bagg, J. 2001. Harvesting corn silage at the right moisture. Available at www.omafra.gov.on.ca/english/crops/facts/harvesting_corn.htm (verified 4 Apr. 2006). Ontario Ministry of Agriculture, Food, and Rural Affairs, Queen's Park, ON, Canada.
- Ballard, C.S., E.D. Thomas, D.S. Tsang, P. Mandebvu, C.J. Sniffen, M.I. Endres, and M.P. Carter. 2001. Effect of corn silage hybrid on dry matter yield, nutrient composition, in vitro digestion, intake by dairy heifers, and milk production in dairy cows. J. Dairy Sci. 84:442–452.[Abstract]
- Begna, S.H., R.I. Hamilton, L.M. Dwyer, D.W. Stewart, and D.L. Smith. 1997a. Effects of population density and planting pattern on the yield and yield components of leafy reduced-stature maize in a short-season area. J. Agron. Crop Sci. 179:9–17.
- Begna, S.H., R.I. Hamilton, L.M. Dwyer, D.W. Stewart, and D.L. Smith. 1997b. Effects of population density on the yield and yield components of leafy reduced–stature maize in short-season areas. J. Agron. Crop Sci. 178:103–110.
- Brown, D.M., and A. Bootsma. 1993. Crop heat units for corn and other warm-season crops in Ontario. Factsheet, Agdex 111/31. Ontario Ministry of Agriculture, Food, and Rural Affairs, Queen's Park, ON, Canada.
- Costa, C., L.M. Dwyer, P. Dutilleul, R.I. Hamilton, D.W. Stewart, B.L. Ma, and D.L. Smith. 2001. Inter-relationships of applied nitrogen, SPAD and yield of Leafy and non-Leafy maize genotypes. J. Plant Nutr. 24:1173–1194.
- Cox, W.J. 1994. Kernel milk line stage and corn harvest. Agfocus. Cornell Coop. Ext. Cornell Univ., Ithaca, NY.
- Cox, W.J., and J.H. Cherney. 2005. Timing corn forage harvest for bunker silos. Agron. J. 97:142–146.[Abstract/Free Full Text]
- Crookston, R.K., and J.E. Kurle. 1988. Using the kernel milk line to determine when to harvest corn for silage. J. Prod. Agric. 1:293–295.
- Dwyer, L.M., C.J. Andrews, D.W. Stewart, B.L. Ma, and J.A. Dugas. 1995. Carbohydrate levels in field-grown leafy and normal maize genotypes. Crop Sci. 35:1020–1027.[Abstract/Free Full Text]
- Dwyer, L.M., D.W. Stewart, and F. Glenn. 1998. Silage yields of Leafy and normal hybrids. p. 193–216. In Proc. 53rd Annu. Corn and Sorghum Res. Conf. 1998. Am. Seed. Trade Assoc., Washington, DC.
- Fransen, S.C. 2004. Yield components and quality of silage corn in the Pacific Northwest. p. 123. In S. Bittman and C.G. Kowalenko (ed.) Advanced silage corn management. Pacific Field Corn Assoc., Agassiz, BC, Canada.
- Herrmann, A., A. Kornher, and F. Taube. 2005. A new harvest time prognosis tool for forage maize production in Germany. Agric. For. Meteorol. 130:95–111.
- Johnson, L., J.H. Harrison, C. Hunt, K. Shinners, C.G. Doggett, and D. Sapienza. 1999. Nutritive value of corn silage as affected by maturity and mechanical processing: A contemporary review. J. Dairy Sci. 82:2813–2825.[Abstract]
- Ma, B.L., and L.M. Dwyer. 2001. Maize kernel moisture, carbon and nitrogen concentrations from silking to physiological maturity. Can. J. Plant Sci. 81:225–232.
- Nennich, T.D., J.G. Linn, D.G. Johnson, M.I. Endres, and H.G. Jung. 2003. Comparison of feeding corn silages from leafy and conventional corn hybrids to lactating dairy cows. J. Dairy Sci. 86:2932–2939.[Abstract/Free Full Text]
- Rankin, M. 2004. Limitations to kernel milk-line for predicting silage moisture. Available at www.uwex.edu/ces/crops/milkline.htm (verified 4 Apr. 2006). Univ. of Wisconsin Coop. Ext., Madison, WI.
- Roth, G.W. 2003. Experience with Leafy hybrids in Pennsylvania for silage production. p. 49–54. In Proc. of the Northeast Corn Improvement Conf. Agriculture and Agri-Food Canada, Ottawa, ON, Canada.
- Roth, G.W., and A.J. Heinrichs. 2001. Corn silage production and management. Agron. Facts 18. The Pennsylvania State Univ., University Park.
- SAS Institute. 1997. SAS/Stat user's guide. Version 7. SAS Inst., Cary, NC.
- Shaver, D.L. 1983. Genetics and breeding of maize with extra leaves above the ear. Proc. of the 38th Annual Corn and Sorghum Research Conf. Am. Seed Trade Assoc., Washington, DC.
- Squire, J. 2002. Why select "dual purpose" silage hybrids from LG Seeds? Available at www.lgseeds.com/lg_Tech2/Tech_58.asp (verified 4 Apr. 2006). Technical Resources, LG Seeds, Issue 58, Aug. 2002.
- Stewart, D.W., C. Costa, L.M. Dwyer, D.L. Smith, R.I. Hamilton, and B.L. Ma. 2003. Canopy structure, light interception, and photosynthesis in maize. Agron. J. 95:1465–1474.[Abstract/Free Full Text]
- Subedi, K.D., and B.L. Ma. 2005a. Nitrogen uptake and partitioning in stay-green and Leafy maize hybrids. Crop Sci. 45:740–747.[Abstract/Free Full Text]
- Subedi, K.D., and B.L. Ma. 2005b. Ear position, leaf area, and contribution of individual leaves to grain yield in conventional and leafy maize hybrids. Crop Sci. 45:2246–2257.[Abstract/Free Full Text]
- Subedi, K.D., and B.L. Ma. 2005c. Effects of N-deficiency and timing of N supply on the recovery and distribution of labeled 15N in contrasting maize hybrids. Plant Soil 273:189–202.[CrossRef]
- Sulc, R.M. 2004. Timing harvest of silage corn. p. 118–120. In S. Bittman and C.G. Kowalenko (ed.) Advanced silage corn management. Pacific Field Corn Assoc., Agassiz, BC, Canada.
- Sulc, R.M., P.R. Thomison, and W.P. Weiss. 1996. Reliability of the milk line method for timing corn silage harvest in Ohio. J. Prod. Agric. 9:376–381.
TOP
ABSTRACT
INTRODUCTION
