The relation of photosynthesis by phytometers in the profiles of kale crops to leaf area index above them.
To estimate the effect of the foliage at different positions in the profiles of kale crops on the rate of photosynthesis below it, the leaf area index (L) of the crops was varied either by removing some of the plants or by cutting off all the leaves above specified heights from the ground. The net assimilation rates (E) of phytometers (sugar-beet seedlings supplied with nutrient solution) placed at different depths in the profiles were then measured. Phytometer F at a given height in the profile increased as the plant population was decreased by thinning, or as the height of the crop above the phytometers was decreased by topping to lower levels. The changes in F were almost completely explained by the changes in L above the phytometers. However, leaves near the bottom of crop canopies decreased phytometer F slightly less than equal areas of leaves higher in the crop, although they did not intercept less light. Phytometer E was zero when crop L above the phytometer was approximately 4, -Rothamsted exp, Stat., Harpenden.