Corn Silage and Grain Yield Responses to Plant Densities

Many corn (Zea mays L.) producers in New York harvest fields for either silage or grain, depending upon growing conditions, storage space, and grain prices. Corn producers, who plant corn for dual purposes require more information on silage and grain yield responses of modern hybrids to plant density. Silage and grain yield responses of seven commercial hybrids were evaluated at harvest densities from 12 000 to 36 000 plants/acre on a well‐drained soil in a wet (1992) and dry (1993) year to compare optimum plant densities among hybrids with recommendations by seed companies and Cornell Cooperative Extension. When averaged across hybrids, optimum densities for corn silage exceeded 36 000 plants/acre in 1992 and averaged 35 231 in 1993. When averaged across hybrids, optimum densities for grain exceeded 36 000 plants/acre in 1992 and averaged 30 452 in 1993. Apparently, plant densities should average about 7.5% higher for silage than for grain on well‐drained soils in New York. Hybrid responses to plant density varied most in the dry year when optimum silage and grain densities ranged from about 27 500 to above 36 000 plants/acre. Optimum silage and grain yield densities did not vary much among hybrids with fixed, flex, and semi‐prolific ear types. Optimum grain densities in this study exceeded the 1992 recommendations of seed companies and Cornell Cooperative Extension by more than 6000 plants/acre. Seed companies and Cooperative Extension should periodically evaluate plant density responses of newly released hybrids in specific growing regions to accurately adjust plant density recommendations. Research Question Modern corn hybrids, which tolerate more stress than older hybrids did, have higher optimum plant densities for grain. Nevertheless, seed companies and Cornell Cooperative Extension recommended densities of about 25 000 plants/acre in 1992 on well‐drained soils in New York. In the northeastern USA, where climatic conditions are relatively cool, corn producers often harvest fields for either grain or silage. The objectives of this study were (i) to compare silage and grain yield responses of modern commercial hybrids to plant density, (ii) to compare silage and grain yield responses among hybrids with different ear types, and (iii) to compare optimum plant densities in this study with recommendations by seed companies and Cornell Cooperative Extension. Literature Summary Research from the 1950s suggested that maximum corn grain yields occurred at the plant density at which dry matter yields began to level off. Consequently, seed companies and Cooperative Extension have recommended corn silage densities about 10% higher than grain corn densities. Grain yields of older hybrids decreased rapidly at densities above the optimum because of increased lodging and barrenness. Studies in Canada, however, suggested that modern hybrids tolerate high density stress because of decreased lodging and barrenness. Consequently, hybrids released in the late (1980s had similar silage and grain yield responses in a study in Ontario, Canada. Study Description Seven commercial hybrids were evaluated at plant densities of 12 000 to 36 000 plants/acre at increments of (3000 plants/acre on a well‐drained Honeoye silt loam soil in central New York in 1992 and 1993. The experimental design was a randomized complete block in a split‐plot arrangement with hybrids as main plots (120 by 60 ft) and densities as subplots (40 by 20 ft). Rows 2 and 3 of each subplot were harvested for silage at 60 to 65% whole plant moisture and rows 6 and 7 were harvested for grain a month later at about 25% grain moisture. At silage harvest, a six‐plant subsample was used to estimate ears per plant and harvest index values. Before grain harvest, lodged plants in the harvest rows were counted. Regression analyses and price data were used to estimate the optimum plant density for silage and grain yields of each hybrid in both years of the study. Applied Questions Do corn silage and grain have different responses to plant density? When averaged across hybrids, corn silage and grain had optimum densities above 36 000 plants/acre in the cool wet growing season. This suggests that, under favorable growing conditions, plant density recommendations for silage and grain should not differ on well‐drained soils in New York. When averaged across hybrids, corn silage had an optimum density at about 35 000 plants/acre and grain corn had an optimum density at about 30 500 plants/acre in a warm dry growing season. Because dry and wet growing seasons occur about equally, plant density recommendations for silage should average about 7.5% higher than that of grain on well‐drained soils in New York. Do individual hybrids differ in silage or grain yield responses to plant density? Optimum silage densities among hybrids ranged from about 32 000 to above 36 000 plants/acre in the cool wet growing season. In the warm dry growing season, optimum densities ranged from about 27 000 to above 36 000 plants/ acre. Nevertheless, all but two of the hybrids required densities of 32 500 plants/acre or higher for optimum yields in the dry year. Ear type did not influence the silage yield responses of individual hybrids at the low or high densities in either year of the study. Hybrids showed more variability in grain yield responses than silage yield responses to plant density. In the cool wet year, optimum grain densities among hybrids ranged from about 32 000 to above 36 000 plants/acre. In the warm dry year, optimum densities ranged from about 28 000 to above 36 000 plants/acre. Hybrid ear type did not contribute much to the variability in yield responses among hybrids. How did optimum grain densities in this study compare with recommendations by seed companies and Cooperative Extension? Optimum plant densities in this study exceeded recommendations by seed companies for individual hybrids by 6000 to 12 000 plants/acre. Apparently, seed companies and Cornel1 Cooperative Extension recommended too 1ow a plant density in the early 1990s for grain and silage corn on well‐drained soils in New York. Seed companies and Cooperative Extension should periodically evaluate the response of newly released hybrids to plant density in specific growing regions to adjust density recommendations.