Kernel Milkline Stage and Corn Forage Yield, Quality, and Dry Matter Content

Abstract

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 milkline (1/2 ML) (milkline positioned half‐way between the tip and base of the kernel); 3/4 milkline (3/4 ML) (milkline positioned 3/4 of the way from tip to base); and no milkline (No ML) (milkline 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 40%) 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. Research Question In the North Central states, a high proportion of corn ( Zea mays L.) harvested for silage is planted in the extreme northern part of the region, where adapted hybrids range from 70 to 90 d relative maturity (RM). When growing corn intended for silage use, critical factors which influence optimum harvest timing include whole plant dry matter (DM) content, total yield, and nutritional quality. Determining the proper maturity to harvest corn for whole plant silage is difficult for growers. The objective of this study was to determine the relationship between kernel milkline position and whole plant yield, quality, and dry matter content. Our goal was to develop a means to predict the optimum stage for harvesting corn silage. Literature Summary Estimates of whole plant DM content in corn frequently are based on grain maturity. Researchers in Minnesota demonstrated that kernel milk‐line position was a reliable and useful visual indicator of grain maturity and whole plant DM content. Several investigations have evaluated corn whole plant DM accumulation and nutritive value at various stages of crop maturity. Maximum whole plant yield is generally reported to occur at whole plant DM contents between 30 and 35%. Previous studies did not evaluate relationships between kernel maturity stage and all three critical factors: corn forage yield, nutritive value, and DM content. Study Description Four early maturity hybrids (85d RM) were evaluated for yield, forage quality, and DM content at five stages of kernel maturity over 3 yr (1988–1990) in north central Wisconsin. Kernel maturity stages Soft dough — dents first visible Early dent — dents visible on 95% of kernels 1/2 Milkline (ML) — milkline positioned halfway between the tip and base of the kernel 3/4 ML — milkline positioned 3/4 of the way between the tip and base of the kernel No ML — milkline no longer present in the kernel; physiological maturity. Applied Questions Can the kernel milkline method reliably predict whole plant DM content? We have verified that the kernel milkline method is a valid indicator of kernel and whole plant DM content for corn grown in a short season region. Although DM contents vary by up to 7 percentage units at particular stages across years and among hybrids, this is not large enough to discourage use of the kernel milkline method in northern corn silage production regions. The method offers farmers a simple, field‐based tool to assist in judging corn maturity and DM content of whole plant and grain. When is the optimum stage to harvest corn for silage? The optimum stage to harvest corn for silage depends primarily on whole plant DM content, yield, and forage quality (Table ). Our results indicate that whole plant DM content is within the acceptable ensiling range (30 to 40% DM content) beginning at 1/2 ML. Whole plant yield appears to reach a peak at 1/2 ML. Concentrations of crude protein decline with increasing maturity, indicating that harvest delays to No ML stage result in lower forage quality. Whole plant acid detergent fiber, neutral detergent fiber, and in vitro dry matter disappearance appear to be at an optimum between the early dent and 3/4 ML stages of maturity. Based on these criteria, corn silage harvest should begin at 1/2 ML and should conclude by 3/4 ML. Three year average of whole plant DM, yield, CP, ADF, NDF, and digestibility at five stages of kernel maturity. Whole plant Maturity DM Yield CP ADF NDF Digestibility stage % ton/acre % % % units, % Soft dough 24 5.4 10.3 27.2 52.7 77.1 Early dent 27 5.6 9.9 24.3 48.0 79.0 1/2 milkline 34 6.3 9.2 22.8 45.1 80.0 3/4 milkline 37 6.4 8.9 23.8 47.3 79.6 No milkline 40 6.3 8.4 24.0 47.3 78.6 Means across four 85d RM corn hybrids and 3 yr (1988–1990). DM = dry matter, CP = crude protein, ADF = acid detergent fiber, NDF = neutral detergent fiber. Digestibility = in vitro dry matter disappearance.