Soil Science 3(4): 393-398 (1917)

THE INFLUENCE OF SOIL TEMPERATURE UPON SEEDLING CORN1
BYRON D. HALSTED, Botanist, New Jersey Agricultural Experiment Station, and
SELMAN A. WAKSMAN,2 Fellow in Physiology, University of California

1Received for publication December 7, 1916.
2This paper was prepared when the junior author was Research
Assistant at the New Jersey Agricultural Experiment Station.

INTRODUCTION

Two fully comparable lots of corn were subjected to different temperatures in a greenhouse, namely, (1) the warmth of the bed in mid-summer, from July 30 to August 26, and (2) the comparatively cool condition of the same bed from October 29 to November 29 before the furnace fire was started.

3These daily records yield averages that are somewhat below the absolute.

The temperature of the soil was taken twice daily, 6 a.m. and 6 p.m.,3 during the two series of tests, with the results in averages for each series as shown below.

  6 a.m. 6 p.m. Daily Averages Range
Summer Series 21.85°C. 29.52°C. 25.68°C. 17.34°C.
Autumn Series 10.35°C. 15.32°C. 12.83°C. 5.5-21°C.
Differences 11.50°C. 14.20°C. 12.85°C. 12.5-13°C.

It is seen that the thermometrical records for the summer series averaged nearly twice as far above the freezing point as those for the autumn tests.

It is, of course, true that the length of day was a varying environmental factor, but the daily loss of light for the autumn series was compensated for by the greater length of time allowed for this test.

THE SUBJECTS

The tests involved the factors of (1) texture, and (2) size of grain, and these were obtained by the selection of the crosses that carried upon the same ears both starchy and sugary grains, as follows:

1. Golden Nugget upon Adams Crosby F2; a large starchy upon a medium-sized sugary kind.

2. Voorhees Red upon Eight-rowed Pop F2; a medium sugary upon a large pop (starchy) kind.

3. Voorhees Red Stowell upon Golden Queen F2; a large sugary upon a small pop (starchy) kind.

Only enough ears were taken, to yield the required number of sugary grains of each cross, thus limiting, as nearly as possible, an otherwise wide range of parentage.

The shelled corn was next assorted into the: (1) starchy, and (2) sugary grains, and these again separated into the (3) larger and (4) smaller kernels, all defective kernels having been discarded.

When ready for planting, there were in duplicate the following sets of the grains, all units having 250 kernels: (1) starchy larger, (2) starchy smaller, (3) sugary larger, (4) sugary smaller, making a total of 3000 grains each for the summer and the autumn tests.

PLANTING, CARE AND HARVESTING

The soil of the greenhouse bed was of good quality, and the grains were planted uniformly 2 inches deep, in drills, with 8 square inches of surface for each grain.

The beds were cared for alike, in the usual manner as to watering, ventilation, protection, etc.

Records of emergence of seedlings from the soil were taken twice a day, at 6 a. m. and 6 p. m., and the harvest consisted of the careful removal of the plants from the soil, the measuring of the mesotyl and the whole length of each plant not including the roots. The weights were taken of (1) the grains of each of the several groups, and (2) their seedlings.

From these records the viability of the seed and vigor and variability have been computed, as shown in the following series of tables.

TABLE I
WEIGHT OF SEED, AS RELATED TO TEXTURE AND SIZE OF GRAIN

  Averages
gm.
Starchy
gm.
Sugary
gm.
Larger
gm.
Smaller
gm.
1. Gold Nugget—Crosby .331 .380 .280 .375 .285
2. Voorhees Red—Eight-rowed Pop .211 .230 .190 .237 .185
3. Voorhees Stowell—Golden Queen .224 .245 .200 .247 .197
Averages .256 .285 .223 .286 .222

In Table I it is shown that the Gold Nugget—Crosby was over 60 per cent larger than the other two kinds and here the difference between the starchy and sugary grains was the greatest, being nearly 25 per cent. The same wide difference between the large and small is seen here, while the two crosses with pop corn show far less range.

From the averages it is seen that accidentally the group of starchy grains weighs practically the same as that of the larger grains used in the test. Likewise, the sugary and smaller groups agree closely in weights. The two sets of the lighter weights differ from their heavier associates by nearly 22 per cent.

It is noted in Table II that the difference in viability is very great between the summer and autumn-grown crops (63.44 per cent) and in favor of the warm temperature.

It is seen, that there are decided differences in viability among the crosses, and that the rank is maintained throughout the table, excepting in the column for summer grown, where the second and third rank change places.

TABLE II
VIABILITY, AS RELATED TO SOIL TEMPERATURE AND TEXTURE AND SIZE OF GRAIN

  Summer
per cent
Autumn
per cent
Averages
per cent
Starchy
per cent
Sugary
per cent
Larger
per cent
Smaller
per cent
1. Gold Nugget—Crosby 85.30 56.30 70.82 89.50 52.50 70.35 71.39
2. Voorhees Red—Eight-rowed Pop 95.80 73.70 84.75 94.00 75.05 87.10 82.40
3. Voorhees Stowell—Golden Queen 89.00 41.30 65.15 81.60 48.70 61.90 89.00
Averages 90.03 57.10 73.57 88.50 58.60 73.11 80.90

The line of averages shows that the starchy is far ahead of the sugary grain in viability, and the larger grains are less viable than the smaller grains.

Table III gives the differences in other respects.

TABLE III
MESOCOTYL LENGTH, AS RELATED TO SOIL TEMPERATURE AND TEXTURE AND SIZE OF GRAIN

  Summer
mm.
Autumn
mm.
Averages
mm.
Starchy
mm.
Sugary
mm.
Larger
mm.
Smaller
mm.
1. Gold Nugget—Crosby 30.65 27.26 28.95 28.62 29.29 29.11 28.79
2. Voorhees Red—Eight-rowed Pop 34.15 31.11 32.63 33.27 32.00 33.26 31.99
3. Voorhees Stowell—Golden Queen 33.47 31.87  32.67 32.70 32.65 31.87 33.47
Averages 32.85 30.08 31.41 31.53 31.30 31.41 31.41

The mesocotyl (that is, the first internode formed in the corn seedling, the stem portion that separates the grain from the first joint, where a set of roots soon forms) is remarkably uniform in the three subjects, being practically the same for the two pop corns, and somewhat less for the other. There is somewhat less development in the autumn set, and here it is possible that the full length had not been attained when the harvest was made.

No differences are found associated with the texture or size of the seed.

The mesocotyl is a structure that varies with the amount of light and moisture, and may elongate greatly when the seedling is in a moist, dark place, as when deeply planted, and serves to bring the first node near to the surface, where secondary or anchor roots are developed. It is not a suitable subject for the study of variability.

In Table IV there is shown, of course, a striking difference of 10 days between the average emergence of the summer and autumn series, but when the two results are averaged, the range among the three crosses is but slight, there being a half-day only between the two extremes. In all instances the starchy are quicker in "coming up" than the sugary, the difference being 14 hours. In like measure the smaller seeds are quicker than the larger, but the difference is only 4 hours.

TABLE IV
EMERGENCE, IN DAYS, AS RELATED TO SOIL TEMPERATURE AND TEXTURE AND SIZE OF GRAIN

  Summer
days
Autumn
days
Averages
days
Starchy
days
Sugary
days
Larger
days
Smaller
days
1. Gold Nugget—Crosby 4.46 14.27 9.37 9.74 9.74 9.64 9.11
2. Voorhees Red—Eight-rowed Pop 3.89 14.33 9.11 8.80 9.42 9.25 8.9
3. Voorhees Stowell—Golden Queen 3.84 15.30 9.57 9.01 10.13 9.42 9.72
Averages 4.06 14.63 9.35 9.18 9.76 9.43 9.24

Under the same conditions in a special test the starchy smaller grains gave an emergence record of 3.81 days, while the sugary larger kernels required 5.04 days, a difference of 25 per cent in time.

TABLE V
LENGTH OF PLANT, AS RELATED TO SOIL TEMPERATURE AND TEXTURE AND SIZE OF GRAIN

  Summer
mm.
Autumn
mm.
Averages
mm.
Starchy
mm.
Sugary
mm.
Larger
mm.
Smaller
mm.
1. Gold Nugget—Crosby 44.5 12.6 28.6 30.0 27.0 28.4 28.7
2. Voorhees Red—Eight-rowed Pop 41.0 11.9 26.5 27.7 25.2 26.4 26.4
3. Voorhees Stowell—Golden Queen 39.3 10.8 25.1 26.1 23.9 26.2 23.8
Averages 41.6 11.7 26.7 27.9 25.3 27.0 26.3

The summer-grown plants are nearly four times the length of those grown in the autumn as shown in Table V. The variety with the largest grains grew the largest plants, and the starchy out-grew the sugary, possibly because the latter are slow in starting. There was but little difference in length of plants between those from the larger and smaller grains. Here again it is recalled that the small grains start more quickly and the results at the end of this test may not represent the differences that might obtain a month or more later.

In Table VI the great difference is associated with temperature, the weight being 3.4 times as much for the summer as for the autumn series.

The general averages were the same for the pop corn crosses, and were much exceeded by the large-grained cross Gold Nugget—Crosby. The starchy and larger seeds both gave larger plants than the sugary and small-seeded groups.

TABLE VI
WEIGHT OF SEEDLINGS; AS RELATED TO SOIL TEMPERATURE AND TEXTURE AND SIZE OF GRAIN

  Summer
gm.
Autumn
gm.
Averages
gm.
Starchy
gm.
Sugary
gm.
Larger
gm.
Smaller
gm.
1. Gold Nugget—Crosby 4.96 1.54 3.25 3.67 2.85 3.34 3.16
3. Voorhees Red—Eight-rowed Pop 3.83 1.22 2.53 2.71 2.35 2.58 2.47
3. Voorhees Stowell—Golden Queen 4.04 1.04 2.54 2.87 2.22 2.74 2.35
Averages 4.27 1.27 2.77 3.08 2.47 2.88 2.66

TABLE VII
VIGOR OF SEEDLING, AS RELATED TO SOIL TEMPERATURE AND TEXTURE AND SIZE OF GRAIN

  Summer
gm.
Autumn
gm.
Averages
gm.
Starchy
gm.
Sugary
gm.
Larger
gm.
Smaller
gm.
1. Gold Nugget—Crosby 4.64 1.21 2.93 3.29 2.57 2.97 2.88
2. Voorhres Red—Eight-rowed Pop 3.61 1.01 2.32 2.48 2.16 2.34 2.28
3. Voorhees Stowell—Golden Queen 3.82 0.83 2.33 2.63 2.03 2.50 2.15
Averages 4.02 1.02 2.53 2.80 2.25 2.60 2.44

TABLE VIII
VARIABILITY IN LENGTH OF SEEDLINGS, AS RELATED TO SOIL TEMPERATURE AND SIZE OF GRAIN

  Summer
per cent
Autumn
per cent
Averages
per cent
Starchy
per cent
Sugary
per cent
Larger
per cent
Smaller
per cent
1. Gold Nugget—Crosby 1.11 1.85 1.48 1.28 1.69 1.69 1.29
2. Voorhees Red—Eight-rowed Pop 1.04 2.00 1.52 1.32 1.73 1.41 1.63
3. Voorhees Stowell—Golden Queen 1.09 3.10 2.10 1.92 2.28 2.13 2.07
Averages 1.08 2.32 1.70 1.50 1.90 1.73 1.66

As given in Table VII the vigor is expressed in terms of live substance, that is, the weight of the crops less that of the seeds planted. Soil temperature was the chief modifying factor. The results seem to be quite parallel with those for weights of seedlings. The Gold Nugget—Crosby, with its large grains, showed much the greatest growth, the other two crosses being nearly alike. Starchy grains uniformly lead the sugary ones, and the larger ranked above the smaller grains, but less strikingly.

Table VIII indicates that, first of all, variability is somewhat inborn, as may be seen by making a comparison of the second and third cross, the former being less variable than the latter in each of the six tests. From the average it is found that the autumn-grown crop is over twice as variable as the summer one, which had the more favorable temperature and made the larger development. In like manner, the plants from the sugary are more variable than those from the starchy grains.

As an extreme instance, not shown in the tables, the average variability in length for the summer-grown plants from starchy large grains is only 0.89 per cent, while the sugary smaller grains grown in autumn gave a range of 2.85 per cent, showing, in other words, three times as much variability.

SUMMARY

It goes without writing, that the environmental factor of soil temperature is a controlling one in the growth of seedling corn.

Starchy grains of the same ears are much larger (27 per cent) than sugary grains; and more viable (51 per cent), and emerge from a depth of 2 inches nearly a day sooner, showing 25 per cent more vigor and 26 per cent less variability.

The larger grains of the same ears weigh 29 per cent more than the selected smaller, and are only 4 per cent more viable, emerge more slowly by 4 hours, show 7 per cent more vigor and have nearly the same viability as the smaller kernels of the same texture.

One of the features of the present tests is the suggestion, that in somewhat favorable conditions for seedlings there may be a practical method of eliminating the weaker members, thus leaving only those that may yield better final results than when all plants developed from the same lot of seeds, under highly stimulating conditions, are grown. It is a method of selection and an application to crop-growing of the general law of the survival of the fittest—an early sifting out of weaker individuals.

Any conditions of a seed-bed, that tend to bring to light the degree of vigor of the seedlings are essential in the vital test. It is possible, that a lack in any of the three leading physical environmental factors, namely heat, moisture or light, may give the results sought.

With small seeds, like those of tomatoes, eggplants, peppers, etc., it may be that a lack of high soil fertility might suffice in this sifting process.

In an exhaustive study of the kind here begun, all the associated inherited characters carried by the different varieties of seeds need to be fully considered.