TECHNICAL NOTES
U.S. DEPARTMENT OF AGRICULTURE
SOIL CONSERVA TION SERVICE
UTAH
APR 02 1993
ECS AGRONOMY TECHNICAL NOTE UT190-3-4 190-VI
SUBJECT:
ECS - AGRONOMY - CROPLAND - STAGE OF HARVEST FOR OPTIMUM CORN SILAGE YIELD, QUALITY, AND DRY MATTER CONTENT
Purpose. To transmit information on the stage at which corn silage should be harvested for optimum yield, quality, and dry matter content.
Effective Date.
When received.
In the past, many Utah farmers have waited until after a killing frost or until formation of the black layer to harvest corn silage. Latest studies, as enclosed, have determined that the optimum stage of harvest is between 1/2 milk and the black layer. We need to encourage Utah farmers to harvest a few days earlier than they may be accustomed to.
Filing Instructions. Please make copies for appropriate personnel before filing. File in the Technical Notes notebook under Agronomy - Cropland.
Contact. Kerry I. Goodrich, Conservation Agronomist, (801) 524-5054.
FRANCIS T. HOLT
State Conservationist
Enclosure
Using the Kernel Milk Line to Determine When to Harvest Corn for Silage
R. Kent Crookston* and James E. Kurle
The position of the kernel milk line can be used to visually monitor grain maturation in corn (Zea mays L.). The objective of this study was to determine if the kernel milk line could be used to determine when to harvest corn for silage. Four hybrids (two full seasons, and two short seasons) were grown in the field during each of three years. As plants approached maturity, ears were removed and the position of the kernel milk line was noted. Ears and stover were then chopped together and moisture content of the fodder was determined. Measurements were taken at: full-dent (every kernel on the ear dented), 1/2-milk (milk line positioned half way between the tip and base of the kernel), 1/4-milk (milk line positioned 3/4 of the way from tip to base), and no-milk (milk no longer present in the kernel). The kernel milk line was determined to be a reliable indicator of fodder moisture status. Fodder moisture values at the four selected stages were: full-dent, 74%; ½-milk, 69%; 1/4–milk, 65%; and no-milk, 61%. The ideal fodder moisture for corn silage stored in upright, unsealed silos is considered to be 65%. This fodder moisture occurred very near the 1/4-milk stage. The recommended range in fodder moisture for silage harvest is usually between 68 and 61%. This range was found to be coincident with the interval between the ½-milk and no-milk stages. Under the conditions of the present study, this interval lasted an average of 13 d.
T
HE "KERNEL milk line" (Fig. 1) appears on the endosperm side of corn (Zea mays L.) kernels soon after denting (1). The milk line is a transitional zone, or boundary, between the solid and liquid matrices of the maturing endosperm. As the starch, or endosperm, farthest from the cob solidifies, it turns yellow. The endosperm nearest the cob remains liquid and milky, or white. As more of the kernel solidifies, the milk line moves away from the dent and inward toward the cob. The moving boundary between the solid yellow endosperm and the liquid white endosperm is easy to see, and can be monitored over a period of 3 to 4 wk. Its relative position can thus be used as an indication of time until maturity (1). When all the kernel milk disappears, the kernel is mature, or has reached its final dry weight (1, 2). At this time, the placental region also turns black (1, 3, 6).
Afuakwa and Crookston (1) reported that, in addition to being a useful indicator of corn kernel maturity, the position of the milk line was a fairly reliable indicator of grain moisture content. They found, for example, that when the milk line was positioned halfway between the tip and the base of the kernel, the grain moisture content was
Dep. of Agronomy and Plant Genetics, Univ. of Minnesota, S1. Paul, MN 55108. Paper no. 15596 of the Scientific Journal Series, Minn. Agric. Exp. Stn. Received 16 Sept. 1987. *Corresponding author.
Published in J. Prod. Agric. 1:293-295 (1988).
!
consistently near 40%. We wanted to know if the position of the kernel milk line might also be a reliable indicator of above-ground fodder (whole-plant) moisture content. Our specific objective was to evaluate the position of the milk line as an indicator of when to harvest corn for silage.
MATERIALS AND METHODS
Field plots were established at St. Paul MN, in 1984, 1985, and 1986 on a well-drained Waukegan silt loam soil (fine-silty over sandy or sandy-skeletal, mixed, mesic, Typic Hapludoll). Soil preparation consisted of fall plowing and spring disking. Ammonium nitrate was broadcast prior to spring disking at a rate of 150 (1984), 100 (1985), and 150 (1986) lb N/acre. Soil tests indicated extractable P levels of 172 and exchangeable K levels of 334 lb/acre. The herbicide alachlor (Lasso) was preplant incorporated at a rate of 2.0 lb a.i./acre, and cyanazine (Bladex) was applied post emergence at a rate of 2.5 lb a.i./acre. Plots were cultivated approximately 30 dafter emergence of the corn.
The study included four corn hybrids (two full season, and two short season) during each of the 3 yr. These were: 'Minhybrid 4202', and 'Minhybrid 4203' [110 d relative maturity (RM)) and 'Minhybrid 7301' and 'Pioneer Brand 3950' (90 RM). Planting occurred in early May of each year. Rows were 25 ft long. Row spacing was 30 in. There were three rows/plot. Plants were thinned at the 5- to 6-leaf stage to a stand density of 24,000 plants/acre. The study was arranged as a randomized complete block, with each hybrid replicated four times.
Sampling occurred at four stages of kernel development (Fig. 2). The earliest, or least mature stage was “full dent.”
Fig. 1. When an ear of corn is broken in half, the tip haIf (left) contains kernels with their smooth or endosperm sides exposed. If the kernels are approaching maturity, a "line," or change of color, can be seen on this smooth kernel face (see arrow). This line is called the milk line.
J. Prod. Agric., Vol. 1, no. 4, 1988
293.
Table 1. Three years of average coin fodder moisture at four visible stages of kernel maturity. Each value is the average of four hybrids.
Year
Stage / 1984 / 1985 / 1986 / Mean% Fodder moisture
Full dent / 73 / 73 / 76 / 74a'
Half milk / 68 / 68 / 69 / 69b
1;.1 milk / 63 / 63 / 67 / 65c
No milk / 61 / 64 / 58 / 61d
, Mean values followed by a different letter are significantly different at the 0.05 level of probability according to Duncan's new multiple range test. LSD (0.05) for comparison of mean values = 1.5. (Coefficient of
variability = 4.9.
At this stage, every kernel on the ear was fully dented. The next stage was the" 1/2-milk" stage, and it occurred when the milk line was positioned halfway between the tip and base of the kernel. The "1/4-milk" stage occurred when the milk line had moved 3/4 of the way from the tip to the base of the kernel. The final stage was "no-milk," and occurred when milk or liquid endosperm could no longer be expressed from the kernel. At the no-milk stage, the kernel is physiologically mature (1).
Sampling consisted of removing ears from five randomly selected plants that were at the predetermined stage of development. Ten kernels were removed from the center portion of each ear and bulked for gravimetric kernel moisture determinations. The five ears, along with their accompanying above-ground stover, were then chopped together, weighed, and sub-sampled for gravimetric fodder moisture content determination. Data were subjected to analysis of variance, using the 5OJo probability level for tests of significance.
RESULTS
The position of the kernel milk line was determined to be a reliable indicator of corn fodder moisture content. Values at a given developmental stage were fairly consistent across years and hybrids (Tables 1 and 2). The frequently suggested ideal fodder moisture content for
Sampling
Stages
- kernels at-
◊◊◊◊
Full dent
□= endosperm
"milky";
white color
1 /2 milk
1 /4 milk
▒= endosperm
solid; yellow color
No milk
Fig. 2. Diagram of com kernels at each of the four developmental stages
during which plants were sampled for fodder moisture.
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J. Prod. Agric., Vol. 1, no. 4, 1988
Table 2. Average corn fodder moisture of four hybrids at four visible stages of kernel maturity. Each value is the average of three years.
Hybrids
Full season
Short season
Stage / M4202 / M4203 / M7301 / P3950 / Mean% fodder moisture
Full dent / 73 / 73 / 74 / 74 / 74a'
Half milk / 69 / 68 / 69 / 69 / 69b
1;.1 milk / 65 / 62 / 67 / 64 / 65c
No milk / 55 / -- / 61 / 62 / 61d
, Mean values followed by a different letter are significantly different at the 0.05 level of probability according to Duncan's new multiple range test. LSD (0.05) for comparison of mean values = 1.5. Coefficient of
variability =4.9.
corn silage harvest is 65% (4, 5). In this study, a fodder moisture content of 65% occurred after the 1/2-milk stage, but before the no-milk stage. In other words, the 1/4-milk stage was close to the stage recommended by extension specialists as ideal for ensiling corn.
There was some variability in fodder moisture from year to year (Table 1). The greatest variability was at the no-milk stage. The low value in 1986 was due to failure to harvest on the exact day that milk disappeared. Although kernels were free of milk on the day sampled, they appeared to have been that way for a few days. The high value for 1985 resulted from rain that preceded the sampling of some hybrids by only a few hours.
Although there was some variability between individual hybrids, full-season and short-season hybrid groups did not differ (Table 2). The majority of the variability again occurred at the no-milk stage. In 1986, M4202 was not sampled until some time after kernel milk had disappeared. M4203 failed to reach the no-milk stage by the time the first killing frost occurred (2 yr) and was rain-soaked the third year. Data for the no-milk stage was therefore not included for M4203.
INTERPRETIVE SUMMARY
The position of the kernel milk line was determined to be a reliable and useful field indicator of when to harvest corn for silage (reliable because at any given milkline position, essentially all of the variability in fodder moisture appeared to be the result of sampling errors or rain contamination; and useful because the milk line is easy to see, and neither instruments nor record keeping are required for its implementation). The frequentlyrecommended range for best silage harvest is from 68 to 61 % fodder moisture (4, 5). This interval corresponded with the movement of the kernel milk line from the half-milk to the no-milk position, which under our conditions took an average of 13 d.
l. Afuakwa, 1.1., and R.K. Crookston. 1984. Using the kernel milk
line to visually monitor grain maturity in maize. Crop Sci. 687-691.
2. Aldrich, S.R. 1943. Maturity measurements in corn and an indication that grain development continues after premature cutting. 1.
Am. Soc. Agron. 35:667-680.
3. Daynard, T.B., and W.G. Duncan. 1969. The black layer and grain
maturity in cron. Crop Sci. 9:473-476.
Kernel Milk-line Stage and Corn Forage Yield, Quality, and Dry Matter Content
D. W. Wiersma, * P. R. Carter, K. A. Albrecht, and J. G. Coors
Determining the proper time to harvest corn (Zea mays L.) for whole plant silage is difficult for growers. The objective of this study was to determine the relationship between kernel milk-line position and whole plant yield, quality, and dry matter (DM) content. Our goal was to develop a means to predict the optimum stage for harvesting corn for silage. Four early maturity(85 d) hybrids were evaluated for yield, forage quality, and DM content at five stages of kernel maturity, including: soft dough (SD) (dents first visible); early dent (ED) (dents visible on 95% of kernels); 1/2 milk-line (1/2 ML) (milk-line positioned halfway between the tip and base of the kernel); 3/4 milk-line (3/4 ML) (milk-line positioned 3/4 of the way from tip to base); and no milk-line (No ML) (milk-line no longer present in kernel) over 3 yr (1988-1990) in north central Wisconsin. Whole plants, stover, and ears were harvested before killing frosts, except in 1989 when plants were frozen shortly after 1/2 ML. Whole plant DM content was within the optimum range for silage harvest (30 to 40070) when corn plants were between the 1/2 and 3/4 ML stages. Maximum whole plant yield was reached by 1/2 ML, while grain yield reached maximum levels by 3/4 ML. Whole plant neutral detergent fiber (NDF) and acid detergent fiber (ADF) decreased an average of 7.6 and 4.4 percentage units from SD to 1/2 ML and then increased at the No ML stage. Whole plant in vitro dry matter disappearance (IVDMD) was greatest between ED and 3/4 ML. Whole plant and stover crude protein (CP) concentration declined at each successive harvest stage from SD to No ML. Early season hybrids can be harvested for silage between 1/2 and 3/4 ML for maximum whole plant yield and optimum quality and DM content. Kernel milkline position was a good indicator of optimum harvest stage for this range of kernel maturities.
A
HIGH PROPORTION of corn harvested for silage is planted in the extreme northern part of the North
Central states, where adapted hybrids range from 70 to 90 d relative maturity (RM) (Carter et al., 1992). When growing corn for silage use, critical factors which influence optimum harvest timing include whole plant DM content, total DM yield, and nutritional quality.
Harvesting silage at the correct DM content is important since ensiling forages that are too wet « 30% DM content) results in losses due to poor fermentation patterns and excessive seepage, while ensiling forages that are too dry (> 50070 DM) increases the potential for heat damage and mold problems (Vetter and VonGlan, 1978). Silage preserved between 30 and 40% DM content provides acceptable fermentation, preservation, and animal performance (Lusk, 1978).
D.W. Wiersma, Marshfield Agric. Res. Stn., 8396 Yellowstone Dr., Marshfield, WI 54449; P.R. Carter, K.A. Albrecht, and J .G. Coors, Dep. of Agronomy, Univ. of Wisconsin, Madison, WI 53706. Received 3 Apr. 1992. .Corresponding author.
Published in J. Prod. Agric. 6:94-99 (1993).
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J. Prod. Agric., Vol. 6, no. 1, 1993
Estimates of whole plant DM content in corn are frequently based on grain maturity. Work by Daynard and Hunter (1975) showed that grain DM content varied with whole plant DM content in a predictable manner, therefore, grain DM content was suggested as an indicator of the proper stages of ensiling. Daynard and Duncan (1969) and Rench and Shaw (1971) found that black layer development in the placental region of the kernel indicated that grain had reached maximum DM accumulation. Since the early 1970s, a common recommendation was to harvest corn for silage when the black layer appears. Daynard (1972) reported, however, that grain DM content varied from 58 to 70% at black layer appearance and that premature appearance of the black layer might occur due to cool weather. This large variation of whole plant DM content often means harvesting silage with a DM content that is not optimal for proper ensiling. Afuakwa and Crookston (1984) and Crookston and Kurle (1988) demonstrated that kernel ML position was a more reliable and useful visual indicator of grain maturity and proper DM content for ensiling.
Several investigations have evaluated corn whole plant DM accumulation and nutritive value at various stages of crop maturity or DM content (Caldwell and Perry, 1971; Daynard and Hunter, 1975; Weaver et al., 1978). Maximum whole plant yield is generally reported to occur at whole plant DM contents between 30 and 35%. Cummins (1970) reported that whole plant digestibility increased with advancing plant maturity until DM content levels reached 35 to 40070, but Daynard and Hunter (1975) found whole plant digestibility to be constant from 24 to 44% DM content.
Previous studies did not evaluate relationships between kernel maturity stage and all three critical factors: corn forage yield, nutritive value, and DM content. Nevertheless, based on Minnesota work by Crookston and Kurle (1988), many dairy producers in the northern USA now harvest corn for silage when the kernel ML is between 1/2 ML and No ML stages. Hunt et al. (1989), in Idaho and California, recommended harvesting between 1/2 ML and 2/3 ML to optimize yield and quality. In Pennsylvania, however, Ganoe and Roth (1993) found that corn plants were often drier than optimum for silage fermentation when corn reached the 1/2 ML stage. They also stated that the ML method was inconsistent.
Therefore, this study was conducted to determine relationships among kernel ML position, yield, nutritional
Abbreviations: ADF, acid detergent fiber; CP, crude protein; DM, dry matter; ED, early dent stage; IVDMD, in vitro dry matter disappearance; KMS, kernel maturity stage or stages; ML, milkline; NDF, neutral detergent fiber; No ML, milkline no longer present in kernel; RM, relative maturity; SD, soft dough stage; 1/2 ML, milkline halfway between tip and base of kernel; 3/4 ML, milkline 3/4 of way between tip and base of kernel.
Table 1. Dry matter (DM) content of four hybrids averaged acrosskernel maturity stages from 1988 to 1990.
Whole plant / Stover
Hybrid / 1988 / 1989t / 1990 / 1988 / 1989t / 1990
- DM content (%)
CMI05 x W182BN / 31.6 / 34.1 / 29.0 / 24.9 / 25.8 / 21.3
A554xCMI05 / 32.0 / 35.4 / 30.2 / 24.9 / 27.0 / 22.0
LH82 x LH145 / 32.2 / 36.4 / 31.6 / 26.5 / 27.1 / 23.5
Pioneer 3790 / 33.3 / 37.0 / 31.6 / 25.9 / 28.5 / 24.5
LSD (0.10) / NS / 1.5 / 1.0 / NS / 1.3 / 0.9
t 1989 averages include plots harvested post-frost.