Effect of 2,4-D on Carbohydrate and Nutrient-Element Content and on Rapidity of Kill of Soybean Plants Growing at Different Nitrogen Levels

Abstract

1. Soybeans were grown in sand culture with nutrient solutions containing 14, 56, or 336 p.p.m. of nitrogen. After 3 weeks of differential nitrogen applications, a solution containing 20 p.p.m. 2,4-D was applied to the sand for 14 days. The plants were then harvested and analyzed. 2. The 2,4-D-treated plants receiving high-nitrogen solutions were dead 14 days after the 2,4-D treatment was begun. At this time the medium-nitrogen plants showed severe chlorosis of leaves and stems and splitting of the stems, whereas the low-nitrogen plants showed only mild chlorosis. 3. Roots of 2,4-D-treated plants receiving high-nitrogen were badly decomposed at harvest. Roots of 2,4-D-treated, medium-nitrogen plants showed some decomposition, whereas roots of treated, low-nitrogen plants were nearly normal. 4. The hemicellulose content was higher and the starch content lower in 2,4-D-treated plants than in untreated plants. 5. Total sugars were higher in 2,4-D treated, low- and high-nitrogen plants and lower in the 2,4-D-treated, medium-nitrogen plants than in their respective controls. 6. Reducing sugars were consistently higher at each nitrogen level in 2,4-D-treated plants than in control plants. 7. At each nitrogen level both the size of the plants and the proportion of leaves to leaves-plus-stems were lower in 2,4-D-treated plants than in controls. 8. Similar cation-anion ratios were noted for untreated plants, for all nitrogen levels, for leaves, for stems, and also for leaves and stems combined. On 2,4-D-treated plants this ratio in leaves was directly related to nitrogen concentrations in the nutrient solution but was inversely related in the stems. When leaves and stems were combined, the ratios for treated plants were higher than for control plants but nearly constant among themselves. These differences in ratios were due mainly to difference in the nitrogen and phosphorus anions. 9. Potassium was considerably lower and calcium was higher in leaves of 2,4-D-treated plants than in controls, but, when results of leaves were combined with stems, these differences largely disappeared. 10. Phosphorus, sulfur, and chlorine contents in the untreated plants were inversely related to nitrogen concentration in the nutrient solution. This was also true of the treated and untreated plants if considered as separate series. At each nitrogen level chlorine and sulfur were higher in treated plants than in controls, while phosphorus was lower in treated plants than in controls of low- and medium-nitrogen level.