Category: Field Crop Production

Bill Cox, School of Integrative Plant Science, Soil and Crop Sciences Section, Cornell University

Correct soybean planting depth is considered essential for maximum soybean yields. Too shallow a seeding depth (<1.0 inch) may result in poor early stand establishment. Soybean must imibibe half of its weight in water before it germinates. Tilled soils may dry out in the top inch after planting, resulting in the initiation of the emergence process but not completion. Consequently, poor stand establishment can occur at a shallow planting depth because of seed desiccation under extended dry periods after planting. On the other hand, planting deeper than 2.0 inches may also result in poor stand establishment. The soybean hypocotyl, the plant part that breaks through the soil surface during soybean emergence, is somewhat fragile. Heavy rains after planting may result in soil crusting, resulting in hypocotyl damage and unsuccessful emergence, especially for deep-planted soybeans struggling to break through a thick soil crust.

We conducted field-scale (5 to 10 acre) studies in 2013 and 2014 with growers in Cayuga, Livingston, and Tompkins County to evaluate early plant populations and yield of soybeans planted at 1.0, 1.5, 2.0, and 2.5 inch depths. Group II varieties were used at all sites but varieties differed as did planting dates (May 8 and May 24 at Cayuga Co.; May 27 and June 6 at Livingston Co.; and May 18 and June 2 at Tompkins Co. in 2013 and 2014, respectively), and seeding rates (~140,000 seeds/acre at Cayuga and Livingston Co. and ~175,000 seeds/acre at Tompkins Co.). Silt loam soils predominated at the Cayuga Co. site, clay loam soils at the Livingston Co. site, and gravelly loam soils at the Tompkins Co. The Cayuga Co. site (30-inch rows) was no-tilled, and the Livingston and Tompkins Co. sites (15-inch rows) were chisel-tilled. Corn was the preceding crop at all sites.

Negative linear responses of plant populations to seeding depths were observed at Livingston and Tompkins Co. sites in both years, indicating a decrease in early plant populations as seeding depth increased from 1.0 to 2.5 inches (Table 1). In contrast, seeding depth did not affect early soybean plant populations at the Cayuga Co. site in 2013, and showed a positive quadratic response to seeding depth in 2014 (no significant increase in early plant populations beyond the 1.5 inch depth). It is not clear if soil type (silt loam soil), row spacing (30-inch rows), land preparation (no-till), or planting date (earliest planting date among three locations in both years) influenced the different response at the Cayuga Co. site, or if the response was unique to this particular farm. Visual observation during plant population estimates in 2014, however, indicated poor penetration of the planter unit in one of the rows at the 1.0 inch depth, resulting in low plant populations in that row, suggesting that the response was unique to this farm in Cayuga Co.

Early plant populations at all sites in both years exceeded ~114,000 plants/acre, except at the 2.5 inch depth at Livingston Co. in 2013, the threshold below which soybeans yields decreased in previous studies in NY (Cox and Atkins, What’s Cropping Up, Vol.21, No.2, p. 5-6). Consequently, it was not clear until harvest if plant population decreases with deeper seeding depths were of sufficient magnitude to result in yield differences. Soybean yields at the Cayuga Co. site showed a positive quadratic response to seeding depth with maximum yield occurring at the 1.0 depth in 2013, despite no differences in early plant populations (Fig.1). In 2014, the 1.5 inch depth yielded the greatest (least at the 1.0 depth with early plant populations of ~111,000 plants/acre) , similar to the early plant population response (Fig.1). Despite negative linear responses of early plant populations to seeding depth at the Livingston Co. site, yields did not respond to seeding depth in either year of the study (Fig.2). Evidently, early plant populations of ~112,000 plants/acre in 2013  was sufficient to attain maximum soybean yield at this site. Soybean yields showed a positive quadratic response to seeding depth at the Tompkins C. site in 2013 with maximum yields occurring at the 1.5 inch depth, but yield did not respond to seeding depth in 2014 (Fig.3). It is not clear why the early plant population response to seeding depth was consistent across years, but the yield response to seeding depth was inconsistent across years at this location.

Conclusion

Late May and early June conditions were generally wet and warm at all locations in both years so weather conditions were not conducive to drying of the seed at the 1.0 inch seeding depth, nor soil crust development and subsequent hypocotyl damage to deep-planted soybeans. Consequently, soil and weather conditions were close to ideal for soybean emergence. Nevertheless, deeper seeding depths (2.0 to 2.5 inch range) consistently decreased early plant populations at two sites in both years, indicating that deeper planted soybeans, especially beyond the 1.5 inch depth, can result in poorer stand establishment even under ideal emergence conditions. At the third site, however, where soybeans were no-tilled in 30-inch rows, seeding depth had minimum effect on early plant populations, except at the 1.0 inch depth in 2014, when one planter unit had trouble penetrating the soil. It is not clear if 30-inch row spacing (~8 seeds/foot of row combining to break through the soil compared to 4-5 seeds/foot of row in 15-inch rows) allowed for better emergence from the deeper seeding depths at this location.

Yield did not respond to seeding depth in 3 site/years and showed quadratic responses in 3 site/years.  Yield differences, however, were generally small at responsive sites with only 4.5 to 6.0% differences between the highest and lowest yields at the 30-inch row, no-tilled site, and 7.0% at the gravelly loam site. Despite the somewhat muted yield responses in this study, in part because of ideal conditions for emergence (>72% for all seeding depths at all sites in both years), soybean growers should be mindful that the 1.0 inch seeding depth can be too shallow in some instances (Cayuga Co. in 2014) and the 2.5 inch seeding depth can be too deep in some instances (Tompkins Co. site in 2013). The 1.5 inch seeding depth generally resulted in excellent early stand establishment (>85% emergence for all site/years except for 77% at Tompkins Co. site in 2013) and maximum yield in two of the three instances where yields responded to seeding depth. Growers should probably strive to be ~1.5-2.0 inch seeding depth range to avoid potential desiccation of the seed at depths < 1.5 inch and potential soil crusting problems at depths >2.0 inches.

Corn and soybeans are typically planted sometime in May and mature from mid-to late September. Consequently, their growing seasons in NY are considered to occur from May 1 through September 30, with the understanding that an additional ~100 growing degree days (GDD) can be accumulated in October before the first fall frost; offsetting the loss of ~100 GDD from May 1 until either crop is planted. The 2014 growing season started slowly for both crops because of wet conditions during the first 20 days of May in most grain corn and soybean growing regions. Consequently, only 15% of corn and less than 1% of soybeans had been planted in NY by May 15^th. The second half of May was dry in most regions so 58% of corn and 31% of soybean had been planted by June 1. By June 8^th, 79% of corn and 46% of soybean had been planted by June 8^th. Consequently, almost half of the NY corn crop (probably 75% of the grain corn crop) did not accumulate the typical 300 GDD that most grain corn and soybean regions receive in May. In addition, growing conditions were cool from mid-July though most of September and there were reports of isolated frost in some parts of the state on the morning of September 19^th. So what is the outlook for grain corn and soybeans in NY in 2014?

In many respects, the 2014 growing season was similar to the 2013 growing season; mostly wet soil conditions in the spring and summer, followed by cool August and September conditions, and even a light frost in isolated pockets of the State in mid-September, although not in the major grain corn and soybean growing regions. So let’s examine both growing seasons and see if the 2014 crops will be similar to the 138 bushel/acre corn crop (3^rd highest state average on record) and the 48 bushel/acre soybean crop (tied for the highest state average on record) in 2013. About 70% of the grain corn and 85% of NY soybeans are grown in western NY and the Finger Lakes regions so my discussion will mostly be in the context of the growing season in those regions.

The second half of May and the month of June were exceedingly wet in 2013 (Table 1), resulting in drowned out grain corn in poorly drained areas of many fields. In addition, the somewhat poorly drained areas of most fields had stunted corn that was yellow during grain-filling because most of the pre-plant or at planting N fertilizer denitrified. Despite ideal growing conditions for the remainder of the 2013 growing season (more than adequate precipitation in July and August and below normal growing degree days from July 20 through September, Table 2), the damage had been done. So instead of the projected 150 bushel/acre grain corn yield ,based on grower surveys in October and November (who apparently were just looking at the high-yielding corn in the drained areas), the final crop came in at 138 bushels/ acre because of the early-season damage to the crop. Soybeans, on the other hand, are not quite as sensitive to wet soils in June and can fill in somewhat if gaps occur due to drainage problems. Consequently, soybean yields came in 1 bushel/acre higher than the projected 47 bushel/acre crop, based soybean grower surveys in October and November.

What about the 2014 crops?  Well, the late planting of corn in 2014 may have been been a blessing in disguise (because both crops avoided the wet May conditions and most of the ensuing problems that the 2013 crops suffered from). Despite somewhat wet June soil conditions, only the poorly drained areas (and not the somewhat poorly drained areas of each field) suffered some stunting of growth and much less denitrification of pre-plant or at planting fertilizer N compared to the 2013 growing season. In addition, July was wet as was the first half of August in most regions so corn was essentially stress-free through the early grain-filling period. Some grain corn fields did encounter dry conditions during September but temperatures were cool so minimal stress would have been incurred. Likewise, soybeans never experienced any real drought stress in August and September because of the cool conditions. Consequently, based on soil and growing conditions in 2014, the September projected 2014 corn yield of 150 bushels/acre and a record soybean crop of 49 bushels/acre in NY might be right on.  

But what about the late planting date for both crops, coupled with the perceived cool growing season?  Will that hurt the 2014 corn crop and reduce the projected yield from 150 bushels/acre to 138 bushels/acre as in 2013? Believe it or not, western, eastern and northern regions of NY had above average growing degree days from June 1 through September 30 so delayed planting in those regions are not much of a concern (Table 2). In the Finger Lakes region, however, total GDD from June 1 until September 30 were about 100 below normal (Table 2), raising concerns about crop maturity. Most grain corn and soybean fields in Western NY and the Finger Lakes fortunately have not had a frost event and no frost is in the forecast through mid-October for those regions. In addition, both regions have already accumulated an additional 50-60 GDD through the first 5 days of October. Consequently, if the growers scaled back their hybrid maturity and the crop silked out by early August, enough GDD should have accumulated before a frost so grain corn should mature, albeit with delayed harvest well into November. If growers did not scale back their hybrid maturity when planting grain corn during the first week of June in the Finger Lakes, maturity could be an issue. Soybeans, on the other hand, respond more to photoperiod when planted in June so even if soybean growers did not scale back maturity, soybeans should make it (a 2.4 Maturity Group that we planted in a planting date study at Aurora on May 29 was at maturity or the R8 growth stage on October 1 and planted on June 11 was at the R8 growth stage on October 7th). So I am not concerned with maturity for most of the soybean crop.

In conclusion, despite another very challenging and yes stressful year from a grower perspective (delayed planting in the spring and fear of potential frost in the fall), yields, according to the grower surveys in September, should come to fruition. The next report is due on October 10^th , based on growers surveys in late September, and I hope that the isolated frost reports in the non-major grain corn and soybean growing regions don’t bias the yields down. In fact, light frosts occurred in isolated pockets of these regions on the morning of September 17^th in 2013 (31 in Ithaca and Watertown), which escaped the September 19^th frost of 2014 (32 in Ithaca and Watertown). So in many respects the 2013 and 2014 growing seasons, including the light September frosts in isolated pockets, were similar, which should bode well for soybean yields. For grain corn, the blessing in disguise of the delayed planting date probably reduced crop damage during vegetative growth compared to 2013,, resulting in 5-6% higher State yields or about 150 bushels/acre. We won’t really know until the crops are in the bin so let’s hope for a great harvest season for both crops.

Bill Cox, Section of Crop and Soil Sciences, Cornell University

Corn acreage for grain in NY, as of June 1, is expected to total 660,000 acres in 2014, a decrease of about 4% from 2013 (690,000 acres). Corn acreage for silage production in NY, as of June 1, is expected to total 500,000 acres in 2014, down about 2% from 2013 (510,000 acres). Only 58% of the corn in NY was planted by June 1, however, so grain acreage could decrease further because of maturity concerns for June-planted corn, especially on dairy farms. Likewise, the price of grain corn has dropped significantly since June 1, providing more incentive for dairy farmers to switch from grain to silage. Overall, total corn acreage in NY is projected to be 1,160,000 acres in 2014, down by 3.3% (1,200,000 acres in 2013. A further update on the corn acreage will be provided on August 11^th by USDA, based on the August 1 survey. Total corn acreage in NY could decrease further because the first half of June was wet in the Southern Tier region of NY, which may have prevented planting some of the remaining 42%, intended acreage.

Wheat acreage in NY in 2014 declined by 20,000 acres or 17% (95,000 acres) compared to 2013 (115,000 acres). This was somewhat surprising because about 40,000 soybean acres were declared as Prevented Planting in NY in 2013, and it was assumed that a significant number of those acres would be planted to wheat. The projected wheat yield in NY as of July 1 was projected to be 66 bushels/acre, down 2 bushels/acre from the record yields in 2013 (68 bushels/acre). Preliminary testimonies by NY wheat producers indicate average yields so far in 2014 as of July 24th so final yield estimates may decrease a bit.

The 2013 June report estimated 320,000 acres of soybeans were expected to be planted in NY but the wet June conditions prevented many acres from being planted; thereby reducing harvested soybean acreage to 278,000 acres. Soybean acreage in NY in 2014, as of June 1, was expected to increase to 397,000 acres, a stunning 43% increase from the previous year. Only 66% of the intended soybean acreage was planted as of June 15, however, so wet conditions in some regions of NY during the first half of June may have prevented some of these intended acres from being planted in 2014. Soybeans can be successfully planted in NY until about June 25^th in the Finger Lakes Region and western NY, and 93% of the crop was reported to be planted as of June 29th. Consequently, it is expected that at least 370,000 of these intended acres were planted, thereby eclipsing the previous soybean acreage record in NY of 315,000 acres in 2012. A further update on soybean acreage will be provided on August 11^th by USDA, based on the August 1 survey. If 370,000 acres of soybeans were planted in NY in 2014, this would represent an 8.25 fold increase in soybean acreage over the last 25 years (40,000 acres planted in 1990). Truly, soybean expansion in NY is an unheralded success story of NY agriculture.