Bill Cox, School of Integrative Plant Science, Soil and Crop Sciences Section, Cornell University
It is generally recognized that the 2.0 planting depth is optimum for corn stand establishment and yield. Too shallow a planting depth (<1.5 inches) may result in drying out of the seed, if extended dry conditions occur before and after planting (especially in tilled seed beds), and increased lodging because of poor brace root development. Too deep a planting depth may delay emergence under cool soil conditions (especially in heavy clay soils), leading to increased pest incidence, soil crusting, and potentially poor stands.
We conducted field-scale (10 to 20 acres) studies in 2013 and 2014 with growers in Cayuga, Livingston, Orleans, and Seneca County to evaluate early plant populations and yield of corn planted at 1.0, 1.5, 2.0, and 2.5 inch depths. Planting dates differed across locations and growing seasons (May 14 and June 1 at Cayuga Co.; May 6 and May 29 at Livingston Co.; May 14 in both years at Orleans Co.; and May 7 and June 2 at Seneca Co. in 2013 and 2014, respectively). Because wet conditions delayed corn planting in2014, growers at three locations had to shorten the maturity of their hybrids (P0533X at four sites in 2013; but P0216 at Orleans Co.; DKC50-84 at Seneca Co.; and P9690 at Cayuga Co. and Livingston Co. in 2014). Seeding rates also differed across locations (~38,000 kernels/acre in 2013 and 32,000 kernels/acre in 2014 at Cayuga Co.; ~37,000 kernels/acre at Livingston Co. in both years; ~34,000 kernels/acre at Orleans Co. in both years, and ~33,000 kernels/acre at Seneca Co.in both years). Silt loam soils predominated at the Cayuga Co. site, clay loam soils at the Livingston Co. and Orleans Co. sites, and silty clay loam soils at the Seneca Co. site. The Cayuga Co. site (20-inch rows) was chisel-tilled, the Livingston Co. site (30-inch rows) was moldboard- plowed, the Orleans Co, site (30-inch rows) was disk-tilled, and the Seneca Co. site (15-inch rows) was no-tilled. Soybean was the preceding crop at all locations in 2013 and at Cayuga and Seneca Co. sites in 2014, but corn was the preceding crop at Livingston (same field) and Orleans Co. in 2014.
Corn plant populations responded to seeding depths at all locations in both years but the optimum depth varied across locations and years, including across years within locations (Table 1). Likewise, corn yields responded to seeding depths at all locations in both years (except for Cayuga Co. in 2013), but as with populations, the optimum depth varied across locations and years, including across years within locations (Table 2).
Plant populations did not have a year x seeding depth interaction at Cayuga County and showed quadratic responses to seeding depths in both years with maximum populations at the 1.5 to 2.0 inch seeding depths (Table 1). Yield, however, did show a year x seeding depth interaction. Yield did not show linear nor quadratic responses to seeding depth in 2013 at Cayuga Co. (although the 1.5 inch depth yielded significantly greater than the 2.0 inch depth), but did show a quadratic response in 2014 with maximum yield occurring at the 1.5 inch seeding depth. The 1.5 inch seeding depth resulted in close to maximum plant populations and yielded more than the 2.0 inch seeding depth (but similar to the 1.0 and 2.5 inch seeding depths) when planting in mid-May in 2013 or early June in 2014 on silt loam soils at this site.
Corn plant populations and grain yields had year x seeding depth interactions at Livingston Co. (mostly because of damage to corn at the 1.0 inch seeding depth in 2013). Corn plant populations showed a quadratic response to seeding depth in 2013 but a linear response in 2014. (Table 1). Plant populations and resulting yields were exceptionally low at the 1.0 inch seeding depth in 2013, presumably because heavy rains shortly after planting resulted in herbicide and/or fertilizer damage to corn planted at the 1.0 inch depth. Plant populations and grain yield showed linear responses to seeding depths in 2014 as the 2.5 inch depth had the greatest plant populations and grain yield. Extended dry conditions ensued shortly after planting at this site in 2014, which delayed and reduced emergence at the 1.0 inch and 1.5 inch depths. Clearly, the 2.5 inch seeding depth was optimum at this moldboard-plowed clay loam site when planting in early May of 2013 or late May of 2014.
Corn plant populations and grain yield had strong year x seeding depth interactions at Orleans Co. (Table 1), presumably because of very different weather conditions after planting. In 2013, an extended dry period occurred for a few days before planting and for 15 days after planting. This probably contributed to the quadratic plant population response to seeding depths (higher populations at the 2.0 and 2.5 inch depths compared to the shallower depths, which apparently dried out). Yield, however, showed a linear response to seeding depth with maximum yield occurring at the 2.5 inch depth in 2013. In 2014, a severe thunderstorm dropped almost 2 inches of rain immediately after the grower finished planting the study. The clay loam soil crusted significantly before and during corn emergence. Consequently, a negative linear response of plant populations to seeding depth was observed with low plant populations at the 2.0 and 2.5 inch seeding depths. Despite, the negative linear response of plant populations to seeding depths in 2014, yields did not differ among seeding depths. It is hard to determine what the optimum seeding depth should be when planting on this disk-tilled clay-loam soil in mid-May because disk-tilling contributed to drying and reduced emergence at the 1.0 and1.5 inch planting depths in 2013, and heavy rains resulted in severe crusting and reduced emergence at the 2.0 and 2.5 inch seeding depths in 2014.
Corn plant populations had significant year x seeding depth interactions but grain yield did not have a year x seeding depth interaction at the Seneca Co. site (Table 1). Heavy rains shortly after planting resulted in soil crusting on this silty clay soil in 2013, which resulted in a negative linear response of plant populations to seeding depths in 2013. Grain yields, however, showed a quadratic response to seeding depth with maximum yield observed between the 1.5 and 2.0 inch depth. In 2014, an extended dry period was observed at this location after the late planting, but plant populations showed a quadratic response to seeding depth with maximum populations at the 1.5 inch depth. Regression equations indicated that maximum yield occurred between the 1.5 and 2.0 inch seeding depth in 2014. The 1.0 and 1.5 inch seeding depths on this no-tilled silty clay site resulted in maximum plant populations, but regression equations indicated that the 1.5 inch to 2.0 inch seeding depth resulted in maximum yield when planting in early May of 2013 or early June of 2014.
Corn plant populations and grain yields had strong year x location x seeding depth interactions indicating that the “one size fits all” 2.0 inch seeding depth was not optimum across all years and sites. When torrential rains occurred shortly after planting, the 1.0 inch seeding depth had maximum plant populations on a no-till silty clay soil planted in early May of 2013, and on disk-tilled clay loam soil planted in mid-May of 2014. The 1.0 inch seeding depth, however, did not have maximum yield at these sites nor any sites in the study. Consequently, the 1.0 inch seeding depth is probably too shallow a planting depth for corn in almost all situations.
The 2.5 inch seeding depth had the lowest plant populations at the two sites mentioned above but had among the highest plant populations and the highest grain yields at the moldboard-plowed clay loam site in both years and at the disk-tilled clay loam site in 2013. Clearly, there is a place for the 2.5 inch seeding depth on some soils in some years.
The 1.5 inch and 2.0 inch seeding depths resulted in maximum grain yields on the no-tilled silty clay site planted in early May of 2013 or early June of 2014. At the chisel-tilled silt loam soil, however, the 1.5 inch seeding depth yielded higher than the 2.0 inch seeding depth when planted in mid-May of 2013 and early June of 2014. Consequently, the 2.0 inch seeding depth never solely resulted in the highest yield in any of our 8 site/year comparisons.
Although yield differences among seeding depths were usually small, increasing the seeding depth from 2.0 to 2.5 inches at the no-tilled silty clay site decreased yield an average ~6%. In contrast, a decrease in the seeding depth from the 2.5 inch to 2.0 inch seeding depth at the moldboard-plowed clay loam site decreased yield an average ~9%. The significant year x location x seeding depth interaction for grain yield indicates that corn growers in NY should adjust seeding depth to soil conditions (although it is difficult to predict ensuing soil conditions after planting, which can greatly influence the optimum seeding depth for plant populations and yields).