Cultural Methods for Early Production of Sweet Corn

Research report from OSU's North Willamette Agricultural Research and Extension Center

Delbert Hemphill
OSU Dept of Horticulture, NWREC

N. Mansour
OSU Dept of Horticulture

The purpose of this experiment was to investigate methods for establishing earlier and more complete stands and more vigorous corn seedling growth during periods of suboptimal air and soil temperatures. Phosphoric acid (PA) was applied alone and in combination with banded treble superphosphate (banded P) and clear plastic mulch in an attempt to enhance early seedling growth. These techniques might allow production of sweet corn at earlier than normal harvest dates, taking advantage of possible premium prices, and increase yields at relatively little expense.

Methods

The experiment was designed as a 2x2x2 factorial (plastic, PA, f banded P) in a randomized block design with four replications of each of the eight combinations of factors. PA was applied to the appropriate plots immediately after seeding as a 3-inch band of 15 percent acid, 16 ounces of dilute acid per 25 feet of row. Banded P was applied two inches to the side and two inches below the seed at a rate of 270 pounds P 0 /acre. Plastic mulch was 12 mil clear polyethylene covering single rows of the appropriate plots. Plot size was three rows wide with 30-inch row spacing and 25-foot length. The middle row of each plot was used for all stand counts, seedling weights, and yield.

After plowing, two hundred pounds/acre of 0-0-52.5 and 400 pounds/acre of treble superphosphate were broadcast and incorporated. On May 4, the plots were seeded, banded P applied, 1.25 pounds/acre atrazine and 2.0 pounds/acre alachlor were applied, and PA sprays applied. Seeding was at a rate which would give nearly 40,000 plants/acre assuming 100 percent stand. Plastic mulch was applied on May 5. On May 19, the plastic was slit to allow emergence of the seedlings. On June 6 all record rows were thinned to eliminate multiple seedlings per hole and fresh weights were obtained. Nitrogen, as 450 pounds/acre of 34-0-0,was applied to all plots on May 30.

Results

During the three weeks after seeding, the average daily air temperature was 52.5°F and soil temperature at 2-inch depth was 58°, clearly less than optimal for corn germination and growth. Plastic mulch increased average air temperature at ground level by 9° and 2-inch soil temperature by 6°. The other treatments had little or no effect on air or soil temperature except that PA without plastic appeared to raise soil temperature within the band by 0.5°. Fifty percent emergence occurred on May 10 for all combinations of plastic-covered seed and on May 16 for all treatments without plastic.

A stand count was taken on June 6 after all treatments showed maximum emergence (Table 13). No single treatment alone had a significant effect on stand. However, statistical analysis of the multifactor interactions revealed that the check plots had a significantly lower stand than the average of all other treatments (95 percent confidence level), the combination of plastic, PA, and banded P resulted in higher stand than the average of all other treatments (90 percent level), and that there was a significant PA x plastic interaction. The latter interaction is manifested in the fact that plots with PA alone had the best stand in the absence of plastic mulch while PA alone resulted in the poorest stand in the presence of plastic. None of these effects on stand has any practical significance for a corn crop with the plant density obtained in this experiment.

The main effects of the treatments on seedling growth are best reflected in seedling weight at thinning (Table 14). Seedlings from plastic covered plots weigh more than four times as much as non-covered seedlings. PA treatment resulted in a slight increase in seedling weight and banded P resulted in a slight decrease in seedling weight on plastic-covered plots.

The yield of Grade 1 ears was affected primarily by the plastic mulch (Table 15), with a nearly 6-fold yield difference. However, all plots were harvested on the same day. Non-mulched treatments would have yielded much higher if allowed to stand an additional one or two weeks since maturity was the primary factor in assigning a No. 1 grade. Phosphoric acid also produced a small increase in yield of Grade 1 ears and, considering non-mulched plots only, there was a significant increase in yield because of the combination of PA and banded P. The plastic effect on total ear weight (Grade 1 and 2, Table 16) was much less striking and is probably much closer to the true effect of the mulch on corn yield potential. PA-treated plots again had a slightly higher yield and the three-way interaction of PA, banded P, and plastic also was significant.

The results for total ear weight confirm that the primary effect of plastic mulch is to promote early maturity while the PA and banded P may more directly affect total yield potential. The number, as opposed to-weight, of Grade 1 ears was increased 6-fold by plastic and to a far lesser degree by banded P (Table 17). Again, this was primarily due to earliness. Table 18 presents results for the total number of ears, which includes all ears showing any kernel development. Plastic mulch significantly increased the number of ears produced, but the effect is small compared to the increase in weight or number of Grade 1 ears. PA also had a small effect. Plastic mulch significantly increased the average size of individual Grade 1 ears (Table 19), but the size increases were small compared to the plastic effects on earliness. No treatment or combination had any significant effect on corn silage fresh weight (Table 20).

Effects of plastic, PA, and banded P treatments in 1977 were similar except that the plastic treatment effect on weight of Grade 1 ears was much larger in 1978 than in 1977, probably because of an earlier 1978 harvest which accentuated maturity differences. The results can be summarized as follows: Clear plastic mulch will produce a small increase in sweet corn yield, but, more importantly, will increase earliness by as much as two weeks for early plantings. Banded P and PA effects are much smaller and less consistent in these experiments, but the banded P and PA combination, particularly in the presence of plastic, produces a significant increase in yield and earlier maturity.

  Table 13. Effect of Plastic Mulch, PA, and Banded P on Stand of Sweet Corn   Treatments             Check    Banded P  PA   Banded P + PA  Mean, plastic                          ------------Number of seedlings/25 feet-------------  With plastic           56.5       53.3    51.3      57.5          54.6  No plastic             48.0       54.0    54.8      51.8          52.1  Mean, + or - PA:       -PA        53.0    +PA       53.9  Mean, + or - Banded P: -Banded P  52.7    +Banded P 54.2                         Table 14. Effect of Plastic Mulch, PA, and Banded P on Sweet Corn   Seedling Weights One Month after Seeding                                     Treatments             Check    Banded P  PA   Banded P + PA  Mean, plastic   With plastic            6.3        5.0    6.7        6.1           6.0Z  No plastic              1.3        1.3    1.4        1.6           1.4  Mean, + or - PA:        -PA        3.5    +PA        4.0Y  Mean, + or - Banded P: -Banded P   3.9    +Banded P  3.5Y  ____________________________________________________________________________________________________   ZMeans for plastic treatments significantly different at 99.9 percent    confidence level.  YMeans for PA treatments and Banded P treatments significantly different    only at 90 percent level.      Table 15. Effect of Plastic Mulch, PA, and Banded P on Fresh Weight of Grade 1   Ears of Sweet Corn                                                              Treatments             Check   Banded P  PA   PA+Banded P  Mean, plastic                               -Grade 1 earsZ, tons/acre fr. wt., including husks-  With plastic            8.1       8.4    8.3       9.3         8.5Y  No plastic              1.1       1.0    1.3       2.4         1.5  Mean, + or - PA:        -PA       4.7    +PA       5.3X  Mean, + or - Banded P:  -Banded P 4.7    +Banded P 5.3                          ZGrade 1 ears are completely filled ears having at least 80 percent mature kernels.  YMeans for plastic treatments significantly different at 99.9 percent confidence level.  XMeans for PA treatments significantly different at 90 but not 95 percent level.      Table 16. Effect of Plastic Mulch, PA, and Banded P on Fresh Weight of   Total Ears (Grade 1 plus Grade 2) of Sweet Corn                            Treatments             Check   Banded P  PA   Banded P+PA  Mean, plastic 	                         -Total ears, tons/acre fr. wt., including husks-  With plastic           10.9      10.3   10.4      11.6        10.8Z  No plastic              6.8       7.6    8.6       8.8         8.0  Mean, + or - PA:        -PA       8.9    +PA       9.9Z  Mean, + or - Banded P:  -Banded P 9.2    +Banded P 9.6                     ZMeans for plastic treatments and PA treatments significantly different at    99 percent confidence level.      Table 17. Effect of Plastic Mulch, PA, and Banded P on Number of Grade   Number 1 Ears of Sweet Corn Produced                                        Treatments              Check   Banded P   PA   Banded P+PA  Mean, plastic                          -------Number of Grade 1 ears/25 feet--------  With plastic            33.8      35.3    32.0       40.3       35.4Z  No plastic               4.8       4.5     5.5       10.8        6.4  Mean, + or - PA          -PA      19.6     +PA       22.2  Mean, + or - Banded P   -Banded P 19.0    +Banded P  22.7Y  ___________________________________________________________________________________________________  ZMeans for plastic treatments significantly different at 99.9 percent    confidence level.  yMeans for banded P significantly different at 95 percent level.      Table 18. Effect of Plastic Mulch, PA, and banded P on Total Number  of Ears of Sweet Corn Produced                                                Treatments               Check   Banded P   PA   Banded P+PA   Mean, plastic                                --------Total number of ears/25 feet--------  With plastic             52.0      44.0    46.0      56.0        49.5Z  No plastic               34.5      37.0    42.3      41.3        38.8  Mean, + or - PA:          -PA      41.9    +PA       46.4Y  Mean, + or - Banded P:   -Banded P 43.7    +Banded P 44.6                     ZMeans for plastic treatments significantly different at 99 percent    confidence level.  YMeans for PA treatments significantly different at 95 percent    confidence level.      Table 19. Effect of Plastic Mulch, PA, and Banded P on Average Weight of   Grade 1 Ears of Sweet Corn                                                  Treatments              Check   Banded P   PA    BandedP+PA  Mean, plastic	                          -Mean fresh wt. of Grade 1 ears (lb), incl. husks-  With plastic            0.69      0.69     0.77      0.67      0.71Z  No plastic              0.64      0.59     0.64      0.64      0.63  Mean, + or - PA:        -PA       0.65     +PA       0.68  Mean, + or - Banded P:  -Banded P 0.69     +Banded P 0.65                   ZMeans for plastic treatments significantly different at 99 percent    confidence level.      Table 20. Effect of Plastic Mulch, PA, and Banded P on Silage   Weight of Sweet Corn                                                       Treatments             Check   Banded P   PA   BandedP+PA   Mean, plastic	                         --------Silage fresht weight, tons/acre------  With plastic           25.2      22.7    23.3      24.6         24.0  No plastic             21.5      23.8    22.0      24.0         22.8  Mean, + or - PA:       -PA       23.3    +PA       23.5  Mean, + or - Banded P: -Banded P 23.0    +Banded P 23.8                    

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