Corn Row Spacing and Plant Population

by Lyle Paul

• Introduction
• Procedure
• Findings
• Key Points
• Table 1
• Table 4

Introduction:

Farmers are looking for methods to increase the profitability of corn production, which can include increased corn yields. A couple of suggested methods for increasing yields have been higher plant population and narrower rows. Neither of these are new ideas, but with changing hybrids, the potential yield outcome of any cultural practice changes are of continuing interest. This study was designed to provide current answers for the question of the yield response to narrower rows. The comparison was with 22" rows compared to 30" rows, and different plant populations in each of these row widths.

Procedure:

Six hybrids were chosen for this study to give a range of plant types and ear flexing characteristics. The six hybrids were Pioneer Hybrid brand 3417; Garst 8481IT, 8541IT and 8550; and DeKalb Genetics DK 580 and DK 604. The row spacing selected were 30", which is currently the most used row width, and 22" which is the same row width as is used for sugar beets and for corn in the sugar beet areas. There is commercially manufactured equipment available for both planting and harvest for this row spacing. The study was conducted in 1996, 1997 and 1998. Each year of the study, the corn was planted in as timely a manner as weather would allow. The planter used for the 22" rows was a commercial unit made for that row width. Each variety was planted at a population of 45,000 plants per acre and then thinned to the desired final harvest plant population before the corn was knee high. The harvest stands used were: 20, 24, 28, 32, and 36,000 plants per acre. The same population levels were established in each of the row spacings. The plots were machine harvested with a specially designed plot combine and corn heads that were manufactured or modified to fit both row widths.

Findings:

The growing conditions in the study years were good and the yields averaged near or over 200 bushel for each of the years. The use of the narrower row spacing (22") gave a statistically significant slight yield increase (1.8%) over the 30" rows. The yield increase with the narrower rows occurred with all hybrids, but was not consistent as to the percentage of increase nor was it the same for all populations of all hybrids.

The yields also statistically significantly increased with increasing populations. The yield response for increasing harvest populations from 20,000 to 24,000 was 7 to 22 bushels per acre with an average increase of 15 bushels per acre. The change from 24,000 to 28,000 was good for yield increases from 6 to 18 bushels per acre with an average of 9 bushels per acre. The rate of change decreased as populations reached the upper levels of the study, but almost all hybrids had higher yields at the highest populations in both row spacings. The final two increments of 4000 plants per acre gave average increases of 3 and 2 bushels per acres . The plant characteristics (Table 1) of the hybrids as to height, response to population and ear flex did not seem to make the differences in row and population responses that were expected.

Using population study data, the computer can predict the best population for maximum yield in any given year at that location. Harvest populations for maximum yield were calculated from the changing response to population of each hybrid and in each row spacings (Table 2). Since this was done by the computer, it might not work well in the field for hybrids with maximum yielding populations above the 36,000 plants per acre harvest level as this was beyond the range of the study.

The economics of changing population and changing row spacing must be considered before changes in operations are made. Changing populations only needs a change of gears on the corn planter and the purchase of additional seed. The population change more than paid for the additional seed costs up to a harvest population of 28,000 plants per acre for all varieties. Above that harvest population level, the yield increases for most of the hybrids continued, but the value of the increasing yields were often offset by the cost of the additional seed. The higher harvest populations and yield results from those populations must be evaluated more closely for each hybrid to decide if the higher populations would be profitable.

Changing row spacings is a larger financial investment. The economics of the possible return to the investment must be carefully evaluated. Some of the additional equipment costs would be offset by possible improved soybean yields due to the narrower row spacing if that crop had previously been planted in wider rows. Factors other than the cost of different equipment are also a consideration. These would include the cost of additional insecticide if the corn is continuous or if the crop is grown in the area where the corn rootworms are laying eggs into the soybean crop. Another factor that could play a part in the decision is whether the crop would need to be cultivated and could be cultivated in the narrower rows.

Key Points:

• There was a slight advantage for 22" rows over 30" rows (1.8%).
• Corn yields increased with increasing population at levels within this study.
• The rate of yield response to higher populations decreased as populations increased.
• Economic considerations must be evaluated before making cultural practice changes.

Table 1: Characteristics* of the corn hybrids used in the study.

Variety	Plant Height	Population	Ear Flex
Pioneer 3417	Average -	Low - high	----
DeKalb DK580	M-T	M-H	Moderate
DeKalb DK604	M-T	MH-H	Limited
Garst 8481IT	Short	MH	Limited
Garst 8541IT	M-T	M-MH	Good
Garst 8550	M-S	M-H	Limited

Table 4: Average yields, 1996-1998