Leafy and Floury Leafy Corn Silage Hybrids have a different plant architecture and the key to realizing all of their silage-specific benefits is a lower plant population of 28,000 to 30,000 plants per acre or 70,000-75,000 plants per hectare.
plant population video
HOW DOES LEAF AREA TRANSLATE INTO YIELD?
A corn plant’s leaves are the factories that convert sunlight to yield. The chloroplasts within leaf cells produce glucose sugars during photosynthesis. This sugar energy is used for plant growth and development while the plant is young. After the plant reaches flowering, these sugars are transported to the developing kernels on the ear to become starch. Starch accumulation is fueled primarily by the above ear leaves, which receive the most sunlight once the plant is grown to full height, while the early growth of the plant was achieved by the below ear leaves, which become shaded as the plant grows.
The yield potential of a corn crop is related to its leaf area index, which is the one-sided green leaf area per unit of ground surface area. The leaf area index of a corn crop can be maximized by increasing plant population or by increasing leaf area on a per plant basis. Grain corn hybrids produce a maximum of 5-7 leaves above the ear, so these hybrids are planted at a high population of 33-36,000 plants per acre (ppa) or 82,500-90,000 plants per hectare (pph) to maximize their leaf area index. Leafy Corn Silage Hybrid plants have 8-13 leaves above the top ear, so they have an increased leaf area on a per plant basis. Because Leafies are larger plants, they need more room to produce their intended crop. To achieve this, they must be planted at a lower population of 28,000-30,000 ppa or 70,000-75,000 pph. Leafy Corn Silage Hybrids have an increased potential over non-Leafy hybrids to produce high starch yields on a per plant basis because of their high leaf area combined with their flex ear type.
Figure 1 shows the typical stature of a grain hybrid and a Leafy Corn Silage Hybrid. Note the number of leaves above the ear (LAE), the size of these leaves and the position of the ear. The Leafy Corn Silage Hybrid has 10 LAE compared to 6 LAE on the grain plant.
Figure 2 shows the difference in leaf area between the two plants. The four leaves highlighted in red just above the ear are the extra leaves on the Leafy Corn Silage Hybrid. This Leafy plant has 70% more leaf area above the ear than the grain hybrid. The ear position on the Leafy is lower than the grain hybrid, so the Leafy has about 40% more total leaf area than the grain hybrid.
COMPARING APPLES TO APPLES
The dominant industry message is to plant all corn hybrids at high populations in order to maximize silage yield. While this advice is well-taken for grain hybrids, it is detrimental to a Leafy Corn Silage crop to plant it at the high populations recommended for grain. Table 1 below takes into account the higher leaf area of a Leafy Corn Silage Hybrid and compares that to the population density of a grain hybrid.
When leaf area is accounted for, you can see that planting a Leafy Corn Silage Hybrid at 35,000 ppa (87,500 pph) gives a comparable canopy to the grain hybrid at 49,000 ppa (122,500 pph). Planting the Leafy at 28,000 ppa (70,000 pph) gives the same leaf canopy as the grain hybrid at 39,000 ppa (97,500 pph). To achieve the equal leaf area canopy as a grain hybrid that is planted at its recommended population of 35,000 ppa (87,500 pph), the Leafy would be planted at 25,000 ppa (62,500 pph).
POPULATION AFFECTS YIELD
Leafy Corn Silage Hybrids have been bred and tested for the market since the 1980's. In that time, numerous population studies have been conducted on the best hybrids. They have suffered hot dry seasons and experienced major weather events with high winds and heavy rains. What has been discovered is that plants with 8-9 LAE achieve maximum yields at 30,000 ppa (75,000 pph). For plants with 10-11 LAE, maximum yields result when they are planted at 28,000 ppa (70,000 pph). At 28,000 to 30,000 ppa (70,000-75,000 pph), Leafy Corn Silage Hybrids have strong roots and good drought response. They also produce a crop with excellent feed qualities – high starch and a good proportion of digestible fiber. At these populations Leafies are higher-yielding than grain hybrids that are planted at 35,000 ppa (87,500 pph) by about 10%.
Plant at 30,000 ppa (75,000 pph) for Leafies with 8 to 9 leaves above the ear and at 28,000 ppa (70,000 pph) for 10 to 11 leaves above the ear.
BALANCING YIELD WITH QUALITY
When we plant a Leafy Corn Silage Hybrid, we are growing FEED that must be digested to produce MILK, so we aim to grow this crop at the population that will produce the highest quantity of dry matter with the highest grain yield and best fiber digestibility, while achieving the best crop security. In our population studies, we have seen that in average conditions, the YIELD of a 10-11 LAE Leafy will not be different between 28,000 and 32,000 ppa (70,000 and 80,000 pph), and will often be less at 36,000 ppa (90,000 pph). But when we look at the difference in the QUALITY of the feed that is produced at different populations, we see that maximum grain yield and digestible fiber is achieved at the lower 28,000 ppa (70,000 pph). For 8-9 LAE Leafy hybrids, this number is 30,000 ppa (75,000 pph). Feed quality affects milk production potential.
Figure 3 illustrates the differences between the same Leafy Corn Silage Hybrid planted at 28,000 ppa and 35,000 ppa (70,000 and 87,500 pph) at the same location. At 28,000 ppa (70,000 pph), the hybrid produced large ears and thick stalks. At 35,000 ppa (87,500 pph) the ear and stalk size declined. As the stalk size declines, so too does its digestibility.
It is essential to grow Leafies at their intended populations. Increasing density can alter flowering dates and maturity, drought response, standability and overall plant composition, all of which affect the feeding value of the silage product.
SELECT THE BEST CORN SILAGE FOR YOUR DAIRY
Selecting a corn silage hybrid based on its performance in State Trials should be a no-brainer. Unfortunately, these trials are planted at a population that is much too high for Leafy Corn Silage Hybrids. All states publish their comparative yield data based on trials that were planted at 33-35,000 ppa (82,500-87,500 pph). As we know, when the Leafy is planted at this population, it is comparable to planting a grain hybrid at 49,000 ppa (122,500 pph). How would a grain hybrid do at 49,000 ppa (12,500 pph)? You have seen higher populations when the rows on headlands come closer together. Plants are thinner, ears are smaller, they mature more rapidly and if you look at the amount of grain in the whole plant community, it is much lower than where the rows are regularly spaced. The high population community has a low grain to stover ratio and the plants are very susceptible to drought stress, fertility stress, and root lodging. You would NEVER grow that grain hybrid at 49,000 ppa (122,500 pph). In State Trials, the data that is produced on Leafy Corn Silage Hybrids grown at 33,000-35,000 ppa (82,500-87,500 pph) does not reflect performance at their intended population.
In State Trials where the Milk 2006 formula is used to calculate milk per ton, the Leafy Corn Silage Hybrids show less starch and milk per ton, though they generally still have competitive yield per acre. In our trials we grow dual-purpose hybrids at their recommended population of 35,000 ppa (87,500 pph) and Leafy Corn Silage Hybrids at their population of 28,000 ppa (70,000 pph), in three row plots. We harvest only the center row to get the best comparable data. In these population-sensitive trials, the Leafies show their undeniable advantage in milk per ton and milk per acre.