Physiological and Ecological Studies on Corn Growth and Yield : III. Influence of plant population on growth and yield of corn in relation to variety and soil fertility

Abstract

Relationships of corn plant population rates, soil fertility levels and varieties with grain yield, total dry matter and composition of corn leaves were examined in 1967. The results are as follows. 1. The logarithm of grain yields per plant decreased linearly as plant population was increased. By using the linear relationships between the logarithm of the grain yields per plant and the number of plants per land area of one are, the maximum grain yields and optimum plant populations on each soil fertility level were determined after Duncan's example. The highest value of the calculated maximum grain yield was 87.1 kg per are at 749 plants per are on the high fertility soil for Tomorokoshi Ko No. 7 (variety cross), and 67.7 kg per are at 562 plants per are on the high fertility soil for Yellow Dent corn (openpollinated variety). 2. There were also the linear relationships between the logarithm of total dry matter yields per plant and the number of plants per are for Tomorokoshi Ko No. 7. The logarithm of total dry matter of a plant decreased linearly as plant population increased. The highest total dry matter yield was 202kg per are at 932 plants per are on the high fertility soil. The optimum plant populations for the highest total dry matter production were higher than those for the highest grain production on each soil fertility level. 3. Tomorokoshi Ko No. 7 required higher populations than Yellow Dent corn to reach the point of maximum yields on each soil fertility level. It is suggested that Tomorokoshi Ko No. 7 possess an inherent capacity to perform better than Yellow Dent corn under the stress of high population rates. 4. As the soil fertility increased, the number of plants per are required for maximum grain yields and maximum total dry matter yields increased. The higher maximum grain yields and maximum total dry matter yields were obtained on the higher soil fertility level than on the lower. It is suggested that increase of plant population for higher grain yields and total dry matter yields should keep pace with increase of soil fetility. 5. Chemical analysis of the leaves on the nodes just below the primary ear for total N, P and K at silking stage showed that the yields of Yellow Dent corn increased with increase of N and P contents when N and P were below 2.4% and 0.26%, respectively. But little or no yields increased when they exceeded 2.4% N and 0.26% P. The yields of Tomorokoshi Ko No. 7 increased with increase of N and P contents within the limits of observation in these experiments. There was little change in K contents with difference of plant population and soil fertility. 6. The conclusions drawn from these experiments are that for Tomorokoshi Ko No. 7 high yields above 850 kg per are may be obtained at plant populations above 650 plants per are when N and P contents of the leaf are above 2.5% and 0.34%, respectively, and that for Yellow Dent corn, likewise, higer yields above 650 kg per are, at plant populations above 450 plants per are when N and P contents, above 2.4% and 0.26%, respectively.