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Research Bulletin (Iowa Agriculture and Home Economics Experiment Station)

Abstract

A study, extending over a 4-year period, has been made to determine the effect of environmental factors on the response of corn plants grown under field conditions. The principal factors of the environment which were measured were available soil moisture, air temperature, evaporation and relative humidity. Factors of the environment, during each growing season, were further modified by varying the rate of planting from one to five plants per hill.

Height of plants, increase in leaf area, size of stalks, dry weight of vegetative and reproductive parts, rate of photosynthesis, carbohydrate fractions of leaf samples, and nitrogen content of the ears were measured at regular intervals throughout the growing season. The relation between the plant responses and environmental factors, particularly as modified by rate of planting, was studied.

The rainfall of the growing season, May, June, July and August, is a better criterion for predicting corn yield than the rainfall of the entire year.

Where corn was planted one to five plants per hill there was usually less available soil moisture in the thicker rates of planting than in the thinner rates. The difference was greater in July and August during periods without rain.

During the day relative humidity was 3 to 5 percent lower where plants were planted one plant per hill than where planted five plants per hill. At night the relative humidity was higher in the thinner rates of planting.

The rate of evaporation from porous porcelain atmometer cups in cubic centimeters was 22 percent greater during July and August where there was one plant per hill than where there were five plants.

Height of the corn plants was not appreciably influenced by rate of planting.

There was considerable difference in the leaf area per plant from different rates of planting. In 1932 the maximum leaf area, per plant, was 8,900, 7,908 and 6,573 square centimeters respectively where there were one, three and five plants per hill. Loss of effective leaf area due to firing began earlier and proceeded at a more rapid rate in the thicker rates of planting.

At maturity the average cross-sectional area, at the level of the ground, of stalks, where there were three plants per hill, was 60 percent as large as where there was one plant. Stalks planted, five plants per hill, were only 40 percent as large as where there was one plant.

One hundred hills with one, three and five plants per hill produced a total of 141, 265 and 359 ears, respectively, in 1932. The same year 42 percent of the ears were less than 15 centimeters long-"nubbins"-where there were five plants per hill, while -only 12 percent of the ears were "nubbins" where there was one plant per hill.

Rate of planting does not significantly influence the rate of food making per unit of leaf area as determined by increase in dry weight of leaf samples collected at 4 :30 a. m. and 4 p. m. Data from these experiments show that rate of food making is proportional to area and not to dry weight of leaf samples.

The quantity of alcohol-soluble carbohydrate fractions separated as diastase extract, dextrins and acid hydrolyzable were determined for leaf samples collected at 4 :30 a. m. and 4 p. m. the same day from different rates of planting. There was a statistically significant difference in the non-reducing sugars and diastase extract between samples from different rates of planting and in the reducing and non-reducing sugars, and acid hydrolyzable between samples collected at 4 :30 a. m. and 4 p. m.

An analysis of variance showed that there was a significant difference in the quantity of nitrogen in kernel and cob samples attributable to date of collection. There was no significant difference in the quantity of nitrogen in the kernels attributable to rate of planting, while the quantity in the cob samples was slightly significant.

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