SOIL VOLUME AND FERTILIZER EFFECTS ON GROWTH AND NUTRIENT CONTENTS OF SUNFLOWER PLANTS

Abstract

Growth of sunflowers in clay loam soil was increased approximately six times with an eightfold increase in soil volume. Added nitrogen and phosphorus increased growth only 30 to 60%. The interaction between soil volumes and fertilizers indicated a greater effect from fertilizers in larger soil volumes than in smaller ones, a result which is opposite to expectation. In sandy loam soil the volume effect was smaller than in the clay, and increases from fertilizers were not evident. The larger the soil volume the lower the root densities, and the higher the fertilizer rate the higher the root densities. Nutrient contents of the plants were increased as much by increased soil volume as by added fertilizers. Higher nutrient contents were generally associated with lower root densities. Additions of N and P fertilizers to these two soils compensated slightly or not at all for small soil volumes that reduced the growth of sunflowers.